Developing and testing plant health management
options against the maize cob borer, Mussidia
nigrivenella Ragonot (Lepidoptera: Pyralidae) in West
Africa
Dissertation
To obtain the Ph.D. degree
in the Faculty of Agricultural Sciences,
Georg-August-University Göttingen, Germany
Presented by
AGBOKA Komi
Born in Gati-Soun, Rep. Togo
Göttingen, October 2009
ii
D7
Referee:
Prof. Dr. Stefan Vidal
Department of Crop Sciences,
Agricultural Entomology,
Georg-August University, Goettingen, Germany
Co-Referee:
Prof. Dr. Teja Tscharntke
Department of Crop Sciences,
Agroecology
Georg-August University, Goettingen, Germany
Examiner:
Prof. Dr. Stefan Schütz
Department of Forest zoology and Forest Conservation
Georg-August University, Goettingen, Germany
Place and date of Disputation: Goettingen, 11th November 2009…
iii
Dedicated to my late Mother
TOUGLO Dadakoedji
iv
Summary
SUMMARY
The present research project aimed at developing and testing different IPM components
focusing on i) habitat management particularly maize-legume intercropping and trap
crops, ii) botanical formulations with special emphasis on neem and Jatropha curcas and
iii) biological control using redistribution or new association approach for sustainably
controlling the maize cob borer Mussidia nigrivenella Ragonot (Lepidoptera: Pyralidae)
in field and in storage systems. To this end, field and lab experiments were conducted
mainly in different locations in Benin.
Field experiments conducted in four different locations in Benin using four by two
pattern of maize-legumes or cassava planting indicated that intercrops could reduce the
number of eggs (>25%) and larvae (17.9-53%) of M. nigrivenella compared to the
monocrop. Maize-Canavalia ensiformis and maize-Tephrosia vogelii proved to be the
most effective combinations for reducing M. nigrivenella populations in the different
locations.
The effect of two leguminous cover crops, C. ensiformis and Sesbania rostrata
(which varied in the onset and duration of their fruiting period, and cowpea planted as
border rows on infestations of maize by the pyralid M. nigrivenella and of other cobboring lepidopteran pests was studied in two field trials. Towards harvest of both the
main and minor season trials, M. nigrivenella densities were higher in the maize alone
than the legume treatments, though the effect depended on the timing of planting of the
cover crop in relation to that of maize. However, pest loads expressed as cumulative
number of feeding-days varied with treatment during the minor season only, and they
were lower on maize with C. ensiformis planted 4 weeks before maize and maize
surrounded by S. rostrata than in the maize alone treatment. There were no discernable
trends for other borers such as the noctuid Sesamia calamistis Hampson (Lepidoptera:
Noctuidae), the pyralid Eldana saccharina Walker (Lepidoptera: Pyralidae), and the
tortricid Thaumatotibia leuctotreta Meyrick (Lepidoptera: Tortricidae). Furthermore, M.
nigrivenella pest loads were considerably higher on C. ensiformis than maize. Thus, the
lack of significant differences between or the lower pest loads in some of the treatments
as compared to maize alone suggests that there was no movement of M. nigrivenella from
Summary
v
the legumes to maize. Thus, the presence of alternative host plant species in the vicinity
of maize fields does not increase M. nigrivenella attack on maize.
The results of laboratory and field experiments using two concentrations of aqueous
extracts of Tephrosia vogelii and Hyptis suaveolens, and of oils of Azadirachta indica
and Jatropha curcas, as well as the pesticide Furadan 5G showed that oil emulsions of A.
indica and J. curcas oils act not only as oviposition deterrent but also as ovicides.
Overall, treated plants had a strong deterrent effect on ovipositing M nigrivenella. In
addition, egg hatch was adversely affected by neem and Jatropha oils; it decreased with
an increase in concentrations of oil emulsions and varied from 3-25.5% for neem and
from 6-16% for J. curcas. By contrast, larval survival was not affected by the treatment.
In the field, Furadan, neem and J. curcas oils significantly reduced the number of M.
nigrivenella larvae by 16-49.2%, while aqueous extracts of T. vogelii and H. suaveolens
were similar to the control consisting of emulsified water.
Although M. nigrivenella is mostly described as a field pest, it can be found feeding
on stored maize up to the 4th month. Survey conducted in Benin in 2006 to assess M.
nigrivenella infestations in different maize storage systems in the Southern (SGS) and
Northern Guinea Savanna (SGS) showed that in SGS and NGS the percentage of infested
stores decreased from 86.7% to 26.7% and from 51.4% to 14.3%, respectively, during the
first 28 weeks of storage. During the same time, mean numbers of M. nigrivenella per
cob decreased from 0.36 to 0.04 across both zones. All larval stages, but mostly 3rd to 5th
instars, were frequently found even after more than 12 weeks, showing that M.
nigrivenella could reproduce in storage. Highest M. nigrivenella incidence of 16.8% and
14.4% were found in the “Ava” and crib stores, respectively. Infestations were highest in
“Ava” and lowest in maize grain stored in polyethylene bags or in mud silos. In a
laboratory experiment, presence of post-harvest beetles negatively affected the bionomics
of the cob borer indicating strong interspecific competition.
Surveys for natural conducted in Malaysia pointed out the presence of three genera
parasitizing Parkia speciosa pod borer: Bracon spp. (Hymenoptera: Braconidae)
accounted for 64%, Eurytoma sp. (Hymenoptera: Eurytomidae) (32%) and Sphaeripalpus
sp. (Hymenoptera: Pteromalidae) (4%). Overall, mortality caused by parasitoids could
Summary
vi
reach <40% hence they were considered a key mortality factor in the population
dynamics of the Mussidia spp./or pyralid species in Malaysia. These results coupled with
parasitoids found in Kenya on Mussidia spp. open the ways for the redistribution and new
association in M. nigrivenella bio-control in West Africa.
vii
Contents
SUMMARY................................................................................................................................................. IV
ABBREVIATIONS ..................................................................................................................................VIII
CHAPTER 1:GENERAL INTRODUCTION............................................................................................... 1
CHAPTER 2: THE ROLE OF MAIZE-LEGUMES-CASSAVA INTERCROPPING IN THE
MANAGEMENT OF MAIZE EAR BORERS WITH SPECIAL REFERENCE TO MUSSIDIA
NIGRIVENELLA RAGONOT (LEPIDOPTERA: PYRALIDAE) ............................................................... 16
CHAPTER 3: THE EFFECT OF LEGUMINOUS COVER CROPS AND COWPEA PLANTED AS
BORDER ROWS ON MAIZE EAR BORERS WITH SPECIAL REFERENCE TO MUSSIDIA
NIGRIVENELLA RAGONOT (LEPIDOPTERA: PYRALIDAE) ............................................................... 36
CHAPTER 4: EFFECTS OF PLANT EXTRACTS AND OIL EMULSIONS ON THE MAIZE EARBORER MUSSIDIA NIGRIVENELLA RAGONOT (LEPIDOPTERA: PYRALIDAE) IN LABORATORY
AND FIELD EXPERIMENTS..................................................................................................................... 57
CHAPTER 5: THE IMPORTANCE OF MUSSIDIA NIGRIVENELLA RAGONOT (LEPIDOPTERA:
PYRALIDAE) AS A POST-HARVEST PEST IN DIFFERENT STORAGE STRUCTURES IN BENIN 79
CAHPTER 6: SURVEYS FOR NATURAL ENEMIES OF MUSSIDIA SPP AND OTHER PYRALIDS
IN MALAYSIA: PERSPECTIVES OF BIO-CONTROL OF THE MAIZE COB BORER MUSSIDIA
NIGRIVENELLA IN WEST AFRICA ........................................................................................................ 100
CHAPTER 7: GENERAL DISCUSSION ................................................................................................ 108
ACKNOWLEDGEMENTS ..................................................................................................................... 115
LIST OF PUBLICATIONS ..................................................................................................................... 116
CURRICULUM VITAE .......................................................................................................................... 118
DECLARATION ...................................................................................................................................... 119
viii
Abbreviations
ANOVA
Analysis of Variance
BC
Biological Control
CID
Cumulative Insect Day
DAP
Day After Planting
DAS
Day After Sowing
DF
Degree of Freedom
DMR
Downy Mildew Resistant
F
Statistical F-value
FRIM
Forest Research Institute Malaysia
GLM
General Linear Model
HM
Habitat Management
HPR
Host Plant Resistance
ID
Insect Day
IITA
International Institute of Tropical Agriculture
IPM
Integrated Pest Management
LSM
Least Square Mean
m.c
Moisture content
NGS
Northern Guinea Savannah
P
P-value (statistical significance level)
QPM
Quality Protein Maize
R2
Coefficient of determination in regression
r.h
Relative Humidity
SAS
Statistical Analysis System
SD
Standard Deviation
SE
Standard Error of the mean
SGS
Southern Guinea Savannah
SNK
Student Newman Keuls
SSA
Sub-Saharan Africa
CHAPTER 1
General Introduction
Maize is of increasing importance in western Africa, where around 7.5 million ha of the
crop are grown (CIMMYT, 2001). It is grown in all major ecologies from the humid
forest to the Sudan savannah, and from sea level to over 2000m altitude. Maize has
diversified uses, including food, animal feed and industrial uses, but over 70% of the crop
is grown for human consumption, and in some regions, maize is also becoming a cash
crop; in such areas, farmers may keep maize for extended period in store in order to sell
the commodity when market prices are at their peak (Compton et al., 1998). In Benin,
maize constitutes the principal staple for the majority of the population (Miracle, 1966;
CIMMYT, 1988) and it is grown both as subsistence and as a commercial crop. Food
security and human nutritional status of small-scale and resource-poor farmers are
directly impacted by losses in quantity and quality of the harvested crop. Average yields
are around 1.2 t ha-1 which is far below the 4.3 t ha-1 world average or the 6.1 t ha-1
obtained in trials in Ghana (CIMMYT, 2001). The low productivity is attributed to
various factors such as climate, poor soil fertility, inadequate farming practices, pests and
diseases, and varieties susceptible to those biotic constraints, and socio-economic factors
such as availability of labour, lack of access to credit facilities to purchase inputs, poor
road infrastructure etc. (Mokwunye & Vlek, 1985; Stoorvogel et al., 1993; Smaling et al.,
1993; McHugh & Kikafunda-Twine, 1995; Weber et al., 1996). Africa-wide, the most
cited biotic constraints to yield and stability of maize production are lepidopterous stemand cob-borers (van Rensburg 1988, Bosque-Pérez and Mareck, 1991, Gounou et al.
1994, Polaszek 1998). The problem is particularly acute in the small-scale, resource-poor
systems under which maize is typically produced, and in areas with two cropping
seasons. In some cases, losses due to both pre- and post-harvest pests and diseases far
outweigh any reasonable hope for increases in productivity through improved germplasm
and pre-harvest management. The most damaging field pests of maize in sub-Saharan
Africa (SSA) are lepidopterous stem and cob borers belonging to the families Noctuidae,
Pyralidae and Crambidae (see overview by Polaszek 1998). Stem borers such as Sesamia
calamistis Hampson, Busseola fusca (Fuller) (Lepidoptera: Noctuidae), Eldana
General Introduction
2
saccharina (Walker), are indigenous to Africa and have moved on to maize after having
evolved with native grasses and sedges or cereals such as sorghum and millet, and other
host plant species (Bowden, 1976; Conlong, 1990; Schulthess et al., 1997; Polaszek,
1998). The only exception is the cob-boring Mussidia nigrivenella Ragonot (Lepidoptera:
Pyralidae) for which maize is the only gramineous host; it is both a field and storage pest
and only important in western Africa (Sétamou et al., 2000).
Mussidia nigrivenella distribution and host plants
The distribution of the genus Mussidia is mostly limited to Africa. Of eight known
species, five are native to Africa, two to Réunion and Madagascar Island in the Indian
Ocean, and one to the Himalayan region (Janse, 1941). Although described for the first
time in 1888 by Ragonot (Moyal, 1988) from “Baie de Lagoa”, M. nigrivenella is a
poorly known species. Recent taxonomic studies on Mussidia spp. undertaken in Kenya
indicated that this genus is complex and that several Mussidia spp. exist in eastern Africa;
however they can not ascertain the presence of M. nigrivenella in eastern and southern
Africa (Muli et al., 2009). Most of the earlier reports on M. nigrivenella are based on
scattered observations of the borer in stored commodities and mainly cacao. Mussidia
nigrivenella has been reported from different parts of the African continent (Janse, 1941;
Le Pelley, 1959; Whitney, 1970; Staeubli, 1977; Bordat and Renand, 1987; Moyal, 1988)
(Fig. 1.1.), but the borer is particularly abundant in West Africa, where it has been
recognized as an economically important pest of maize (Whitney, 1970; Atachi, 1985;
Bosque-Pérez and Mareck, 1990; Moyal and Tran 1991; Shanower et al., 1991; Silvie,
1993).
Mussidia nigrivenella appears to be highly polyphagous (Moyal, 1988; Silvie, 1993;
Sétamou, 1996) feeding on various cultivated and wild plants. In addition to maize, the
borer attacks the maturing structures (cobs, seed pods and fruits) of a great variety of
plants, including cotton (Gossypium hirsutum L. (Malvacae)), cocoa (Theobroma cacao
L.), lima bean (Phaseolus lunatus L.), jackbean (Canavalia ensiformis (L.) DC.),
velvetbeans (Mucuna pruriens DC.), the néré-tree (Parkia biglobosa (Jacq.) Benth.), and
the shea butter-tree (Butyrospermum parkii (G. Don) Kotschy) (Moyal, 1988; Silvie,
1993; Sétamou, 1996). Surveys in agro-ecological zones of Benin, conducted between
3
General Introduction
1993 and 1997, revealed about 20 plant species from11 plant families hosting the borer,
but only 13 host plants enable the borer to develop to the pupal stage (Sétamou et al.,
2000). Whereas a maize crop usually supports one generation per season, several
generations of M. nigrivenella were recorded on P. biglobosa and Gardenia spp.
(Sétamou et al., 2000). Incidence of the borer in maize varied between the different agroecological zones, with a higher prevalence of M. nigrivenella in the Savanna zones of
West Africa (Moyal, 1988; Gounou et al., 1994; Sétamou, 1996). The high agroecological variation in the availability and abundance of wild host plants coupled with
their overlapping fruiting periods explained the high M. nigrivenella densities on maize.
B
A
Fig 1.1. Damage caused by larvae to maize ear (A) and adult of Mussidia nigrivenella (B)
Biology and damages
On maize, M. nigrivenella lays its eggs on the silks and the husk of the cob (Moyal, 1988;
Moyal and Tran, 1989; Bosque-Pérez and Mareck, 1990). In the field, egg laying starts
60 days after the emergence of the maize plants. Soon after emergence, neonate larvae
enter the cob and feed cryptically in the grains, often causing extensive damage in maize
(Fig 1.1). Prior to pupation, the last instar larvae leave the grains and pupae are formed in
a tough cocoon near the exit holes. The pupae develop in 10-12 days. No diapause has
been observed (Moyal and Tran, 1991). Adults (Fig 1.1) mate the same day of
emergence, and no preoviposition period have been observed (Bolaji and Bosque-Pérez,
General Introduction
4
1998; Sétamou et al., 1999b). Oviposition lasts for 5-7 days. On maize, the life cycle is
roughly 38 days (Bordat and Renand, 1987; Moyal and Tran, 1991b; Bolaji and BosquePérez, 1998; Sétamou et al., 1999b).
Mussidia nigrivenella damage is identified according to its characteristic feeding
damage as described by Sétamou et al. (1998). M. nigrivenella starts feeding from the tip
of the cob and its larvae produce conspicuous amounts of silky frass, which is easily
detected as the larvae bore into the grains (Sétamou, 1996). The cob borer, Mussidia
nigrivenella Ragonot (Lepidoptera: Pyralidae) is one of the key borers attacking maize in
West Africa (Bosque-Pérez and Mareck, 1990; Shanower et al., 1991, Moyal & Tran,
1991a). Because of its feeding behaviour, i.e., attacking the maize grain, M. nigrivenella
constitutes a major limiting factor for maize production. Typically, more than half of the
cobs in the field are infested by the borer (Whitney, 1970; Sétamou, 1996). Yield loss
estimates in field grown maize are 5-15% (Moyal and Tran, 1991b; Sétamou et al.,
1999a) but M. nigrivenella also persists in the store, where it may cause an additional 1015% loss of grain (Sétamou, 1996; Sétamou et al., 2000a). Moreover the percentage of
grains attacked per cob and therefore worthless for sowing is high (15-20%) at five
insects per cob (Moyal and Tran, 1991). Furthermore, grain damage by lepidopterous
borers also predisposes maize to pre- and post-harvest infestations by storage beetles,
infections by Aspergillus flavus and Fusarium verticillioides and subsequent
contamination with mycotoxins such as aflatoxin and fumonisin (Sétamou et al., 1998;
Cardwell et al., 2000; Hell et al., 2000; Schulthess et al., 2002; Ngoko et al., 2002).
Hence, both the quantity and the quality of the maize are affected by M. nigrivenella.
Control strategies
The search for control of stem- and cob-borers has been a prime concern of agricultural
researchers in Africa since the 1950s (see overview by Polaszek, 1998; Kfir et al., 2001).
Currently, no technologies are available to provide a satisfactory control of M.
nigrivenella.
Chemical control, using contact insecticides is particular difficult probably because
of the cryptic feeding behaviour of the larvae (Moyal, 1988; Sétamou et al., 1995;
Ndemah and Schulthess, 2002). Pesticides have to be directed against the ovipositing
General Introduction
5
females and the earlier instars before they penetrate the cob, which requires monitoring
by the farmers. Thus, the use of oviposition-deterrent pesticides or ovicides timely
applied can play an important role in the borer control. Furthermore timely applied fast
acting insecticides can be a convenient solution but such ingredients should meet basic
prerequisites: complete environmental degradability, low human toxicity, easy and cheap
to produce as well as partial selectivity to various beneficial organisms and low risk of
selecting pest biotypes. Given these attributes the so-called “green” insecticides or biopesticides are suitable candidates for sound IPM tactics. Therefore, bio-pesticides such as
neem products extracted from seeds of the neem tree, Azadirachta indica Juss (Meliacae)
are of special interest. In Africa, apart from neem products, other indigenous plants
derived extracts such as the ones from Hyptis suaveolens L. (Lamiacae), Tephrosia
vogelii (Fish bean) Hook F. (Leguminosae) and Jatropha curcas (physic nut) L.
(Euphorbiacae) recently gained more attention with regard to their insect pests control
potential.
Maize varieties resistant to borers have been suggested as one of the most promising
means of control (Bowden, 1976; Girling, 1980; Ajala et al. 2002). Thus, the first
approach to borer problems was host plant resistance (HPR). However, no resistant
varieties were developed against M. nigrivenella. Moreover, strong antibiosis is often
achieved at the cost of yield. Thus a holistic breeding strategy that aimed at developing
varieties with acceptable agronomic characteristics and yield, and resistance to the major
diseases yielded moderate resistance to borers only (Bosque-Pérez et al., 1997;
Schulthess and Ajala, 1999, 2002). It was recognized that HPR alone would not solve the
problem, thus in the 90ies, alternative solutions such as habitat management (HM)
techniques and forms of biological control (BC) were sought, which would complement
HPR.
Habitat management, i.e. the manipulation of the cultivated and natural environment
to preserve the floral and faunal biodiversity is also another promising technique for the
management of stem and cob borers in SSA. This approach includes the use of trap
plants, mixed cropping and management of soil nutrients (Sétamou et al., 1995,
Schulthess et al., 2004, Chabi-Olaye et al. 2005a&b, Agboka et al., 2006).
General Introduction
6
Small-scale farmers traditionally intercrop maize with vegetables, legumes, cassava
or other cereals in order to obtain a greater total land productivity and insurance against
the failure or unsure market value of a single crop, and in many cases pest densities are
decreased in diversified systems (see overview by Risch et al., 1983; Vandermeer, 1989;
van den Berg et al., 1998; Thies and Tscharntke, 1999; Kruess and Tscharntke, 2000).
Consequently, any attempt to control those pests must take into consideration the close
link between the ecology and biology of the pest and that of its natural habitats which
include alternate hosts and associated crops in the cropping system, which can be hosts or
non-hosts, as well as soil physical and chemical properties, which affect the bionomics of
pests and thereby also that of their natural enemies (Bowden 1976; Schulthess et al.,
1997; Khan et al., 1997a, b; Ndemah, 1999; Ndemah et al., 2001a&b, 2002, 2003). There
are number of studies that showed a reduction in stem and cob borer densities when
intercropped with legumes or other non-host plants (Adesiyun, 1983; Dissemond and
Hindorf, 1990). This may be due to various mechanisms such as the non-host acting as
trap plants (Ampong-Nyarko, 1995), increased parasitism (Sokovgard and Pats, 1996) as
a result of volatiles produced by non host (Khan et al., 1997), or increased mortality due
to starvation and/or predation (e.g. by ground beetles or other predators) of migrating
borer larvae from non- hosts (Ndemah et al. 2003; Schulthess et al. 2004; Chabi-Olaye et
al. 2005b; Wale et al. 2007; Songa et al. 2007). Many studies in tropical as well as
temperate zones reported low pest densities in diversified systems (Altieri and
Letourneau, 1982; Risch et al., 1983; Thies and Tscharntke, 1999; Kruess and
Tscharntke, 2000). In Africa, such techniques include pest diversion or trap cropping
(Khan et al., 1997; Ndemah et al., 2002) and mixed cropping (Litsinger and Moody,
1976; Okigbo and Greenland, 1976; Baliddawa, 1985; Schulthess et al., 2004). There are
a number of studies in Africa that have shown a reduction in stem borer densities when
maize was intercropped with non-hosts such as cassava or legumes. However, most of
them were carried out in eastern Africa and dealt with the invasive crambid stem borer
Chilo partellus (Swinhoe) (van den Berg et al., 1998; Songa et al., 2007; Wale et al.,
2007). Recent work in western and central Africa showed that maize intercropped with
cassava or grain legumes considerably reduced the amount of eggs of the noctuids
General Introduction
7
Sesamia calamistis Hampson (Schulthess et al., 2004) and B. fusca (Chabi-Olaye et al.,
2005a), as a result of reduced host finding by the ovipositing adult moths.
Biological control is an important component of IPM. At present, however, efficient
bio-control strategies for M. nigrivenella are not available. Surveys on wild and
cultivated host plants of M. nigrivenella in West Africa, yielded a paucity of natural
enemy species and low parasitism; from most host plants no parasitoids were obtained
and they appear to play no role in the population dynamics of the pest (Sétamou et al.
2002). M. nigrivenella is only known as a crop pest from western Africa and it was
hypothesized that in eastern Africa it is under natural control on wild host plants, which
opens possibilities for the redistribution or new association approach (Sétamou et al,
2001; Ndemah et al., 2001c). Tritrophic level studies were proposed in regions where M.
nigrivenella is not a crop pest such as East Africa and in Asian regions where other
Mussidia species or sympatric species may occur, in order to identify promising biocontrol candidates to be introduced. However, recent studies by Muli et al. (2009)
showed that in Kenya parasitoids of Mussidia spp., were even scarcer than in West
Africa.
Major objectives of the study
i) Establish whether intercropping maize with grain legumes, cover crops, and cassava
would reduce the infestation of M. nigrivenella and its damages in the maize cropping
system in different ecological zones in Benin (Chapter 2)
ii) Evaluate the potential of cover crops such as Canavalia ensiformis L. and Sesbania
rostrata Brem. & Oberm, and cowpea planted as border rows in affecting the infestations
of cob borers and their damage in maize field (Chapter 3).
iii) Evaluate the effectiveness of extracts of four indigenous plants to control M.
nigrivenella infestation, their effects on the borer oviposition behavior as well as their
ovicide properties (Chapter 4).
iv) Understand the population dynamic of M. nigrivenella in stored maize and study the
influence of different storage structures on the borer infestation (Chapter 5).
General Introduction
8
v) Conduct thorough surveys of Mussidia or sympatric species and their parasitoids in
Malaysia to identify potential new association parasitoids for introduction into West
Africa (Chapter 6).
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General Introduction
15
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CHAPTER 2
The role of maize-legumes-cassava intercropping in the management of
maize ear borers with special reference to Mussidia nigrivenella Ragonot
(Lepidoptera: Pyralidae)
Agboka K.1,2, Gounou S.1, Tamo M.1
1
International Institute of Tropical Agriculture 08 BP 0932 Tripostal, Cotonou Republic of Benin 08 BP 0932
Tripostal, Cotonou Republic of Benin. 2 Georg-August University, Goettingen, Agricultural Entomology,
Grisebachstrasse 6, 37077 Goettingen Germany Email: k.agboka@cgiar.org
(Accepted for publication in Annales de la Société Entomologique de France)
Abstract:
Effects of intercropping maize with cowpea, lima bean, soybean, three leguminous cover
crops (Tephrosia vogelii, Canavalia ensiformis, Sesbania rostrata) and cassava on the
infestation of Mussidia nigrivenella and other lepidopteran ear borers were studied. Field
experiments were conducted in four different locations in Benin using four by two pattern
of maize-legumes or cassava planting. Intercrops reduced the number of eggs (>25%) and
larvae (17.9-53%) of M. nigrivenella compared with the monocrop. Maize-C. ensiformis
and maize-T. vogelii proved to be the most effective combinations for reducing M.
nigrivenella populations in the different locations. Grain loss and ear damage, which were
significantly correlated with number of insects in the ear, were significantly affected by the
intercrops, with losses abated by < 46.8%. No parasitized larvae were found in any of the
locations.
Key words: Maize, intercropping, Canavalia ensiformis, Tephrosia vogelii, Mussidia
nigrivenella.
Role of intercropping in the management of Mussidia nigrivenella
17
Introduction
Mussidia nigrivenella Ragonot 1888 (Lepidoptera: Pyralidae) is one of the key pests
attacking maize ears in West Africa (Bosque-Perez and Mareck, 1990; Shanower et al.,
1991; Moyal and Tran, 1991a&b). It is a commonly occurring pest, which causes serious
damage to maize grain in the field and store (Moyal, 1988; Moyal and Tran, 1991ab; Silvie,
1993).
Management practices have relied on early harvesting (Sétamou, personal
communication), drying of the ears after harvest. Trials on the use of chemicals such as
deltamethrine did not give any significant effect on the ear borer (Moyal, 1988). Research
on the natural enemies of M. nigrivenella in West Africa indicated that they are very rare
and not efficient (Sétamou et al., 2002).
In Benin maize is traditionally intercropped with other crops, some of them are nonhosts of M. nigrivenella, which may reduce pest incidence on the crops (Dissemond and
Hindorf 1990, Ayisi et al., 2001). The only available information on the use of
intercropping maize to reduce the infestation by M. nigrivenella was the work done with
peanut by Moyal (1993 a &b) without any measurable effect, although cases of success
have been reported on maize stem borers (Omolo, 1986; Oloo and Ogeda, 1990; Skovgard
and Paets, 1996; Paets et al., 1997; Schulthess et al. 2004).
The contribution of cover crops to the sustainability of agriculture is becoming
increasingly evident in many regions of the world. Because of great interest of West
African farmers in cover crops such as Canavalia ensiformis L., Tephrosia vogelii Hook. F.
and Sesbania rostrata Brem. & Oberm., it is expected that they will become key
components of farming systems. However the selection of a cover crop should be based not
only on its efficiency in restoring soil fertility but also on its reactions vis-à-vis pests and
natural enemies.
This study is to establish whether intercropping maize with grain legumes, cover crops
and cassava would reduce the infestation of M. nigrivenella and its damages in the maize
cropping system in different ecological zones in Benin.
Role of intercropping in the management of Mussidia nigrivenella
18
Materials and Methods
The trials were set up during the long rainy season of 2004 in collaboration with farmers, in
four locations representing three different ecological zones: the International Institute of
Tropical Agriculture (IITA)-Benin located in Abomey-Calavi (latitude 6o24’ N longitude
2o24’E in Costal Savanna with 210 days rainfall distributed over two cropping seasons;
Cana (latitude 7o13’N longitude 2o07’E) and Djidja (latitude 7o33’N, longitude 1o93’E) in
the Southern Guinea Savanna with 181 days rainfall and two cropping seasons; Bantè
(latitude 8o42’N, longitude 1o83’E), in the Northern Guinea Savanna with <150 days of
rainfall and one cropping season. The following treatments were considered in each
location: sole maize, maize-cowpea (Vigna unguiculata L. var. KVx erected variety),
maize- lima bean (Phaseolus lunatus L.), maize-soybeans (Glycine max L.), maize-cassava
(Manihot exculenta Krantz), a common practice in Benin, maize-jackbean (Canavalia
ensiformis L.), maize-fish bean (Tephrosia vogelii Hook. F.) and maize-Sesbania rostata
Brem. & Oberm. (Leguminosae). All leguminous plants were recorded as host plants of
Mussidia nigrivenella (Sétamou et al, 2000a). Canavalia, Tephrosia and Sesbania are also
used as cover crops in Benin (Carsky et al. 2003). Planting pattern in the intercrops was 4
rows of maize and 2 rows of legumes or cassava with 0.4 m within row and 0.75m between
rows. Maize, legumes and cassava were sown simultaneously in a complete randomized
block design with plots size of 10m x 12.75m; 1m between plots and 2m between blocks.
The eight treatments were repeated three times. No insecticide was applied throughout the
study period. Fertilizer 15-15-15 (NPK) was applied two weeks after sowing and urea 45
days after sowing. The maize variety QPM (Quality Protein Maize, 110-120 days) was
used.
Data collection
From soft dough stage (approximately 70 days after sowing) to harvest, three destructive
samples of ten plants per plot were randomly taken at two week interval. Ears were
thoroughly examined, dissected and the numbers of Mussidia eggs, different stages of
larvae and pupae as well as ear damage were assessed. Other insects found in the maize ear
Role of intercropping in the management of Mussidia nigrivenella
19
such as Eldana saccharina Walker 1865 (Lepidoptera: Pyralidae), Sesamia Calamistis
Hampson 1910 (Lepidoptera: Noctuidae) and Thaumatotibia (Cryptophlebia) leucotreta
Meyrick 1913 (Lepidoptera: Tortricidae) were also recorded. The damages caused by the
ear borers were calculated as the percentage of grains consumed and contaminated by
fungi. At harvest, the percent grain loss was estimated by the following formula: grain loss
(%) = 100*(Pi – Pf)/Pi, where Pi is the initial weight of the cob and Pf is the weight of the
cob after the damaged grains were removed. The loss (g) per cob is the difference between
Pi and Pf. The damage by the ear borers predisposes the ears to pre- and post-harvest
infestations by storage beetles, infections by fungi such as Aspergillus flavus and Fusarium
verticillioides and subsequent contamination with mycotoxins. Therefore, both quality and
quantity of the grains are seriously affected and the damaged cobs cannot be sold nor used
as food. Thus, these damaged grains were removed and considered as actual ear weight
loss.
Mussidia nigrivenella larvae or pupae collected were maintained on Canavalia pods to
record larval or pupal parasitism. Moreover ten ears were also selected randomly from each
plot and weighted to determine the effects of each treatment on the ear weight. Additionally
fifty pods of cowpea and Canavalia were also randomly harvested for Mussidia eggs and
larvae; the other leguminous were not yet at the fruiting stage.
Statistical analysis
Analysis of variance in the mixed model in repeated measures over sampling dates (SAS,
1997) was used to compare counts of immature pest stages according to borer species, plant
damage and grain losses. Variables were compared between cropping systems with
location, cropping system and their interaction as fixed effects. The random effects were
sampling date, block (or replication), and plant. Plants were nested within treatments,
treatments within block, block within location and location within sampling dates. Counts
were log (x+1) and percentages arcsine transformed before analyses in order to stabilize
variances. However, non-transformed means are reported. Means were separated with
Student-Newman-Keuls (SNK) at P =0.05.
Role of intercropping in the management of Mussidia nigrivenella
20
Pearson correlation analysis was used to examine whether pest numbers and damage
affected crop yield and yield losses. Simple regression analyses were used to assess to
which extent numbers of each pest species accounted to ear damage and ear losses.
Results
Ear borers’ population densities in different intercrops
The results showed that intercropping maize with legumes or cassava has a significant
effect on the infestation of M. nigrivenella (F = 3.4, d.f. = (7; 712) P ≤ 0.015) and other ear
borers included T. leucotreta (F = 2.5, d.f. = (7; 712) P < 0.05) but the performance of each
treatment differed from one location to another. Significant interactions between cropping
system and locations (P ≤ 0.02) showed that these factors jointly influenced Mussidia
population. In Bantè, the intercrops reduced significantly the number of M. nigrivenella
eggs and larvae and E. saccharina immature compared to the monocrop (Table 2.1) while
only soybean, Canavalia and Tephrosia as companion crops showed significant effects on
Sesamia. Overall, ear borers recorded, numbers of larvae on maize cropped with Sesbania
were similar to those in sole maize, and they were both significantly different from the rest
of the treatments. In Cana similar trend was observed on the number of M. nigrivenella
eggs. The treatments were not as effective as in Bantè in reducing M. nigrivenella larvae,
except for maize intercropped with soybean and Tephrosia (Table 2.2). The treatments
reducing M. nigrivenella infestation were not always effective against other insects found
in the ear; e.g., numbers of E. saccharina on maize intercropped with cowpea and
Phaseolus were similar to those of the control. Overall, only maize intercropped with
cassava, soybean, Canavalia and Tephrosia gave a significant reduction in pest
populations. In Djidja eggs were rarely found in any of the treatments. The numbers of M.
nigrivenella larvae in the maize-Canavalia and Tephrosia intercropping were significantly
different from maize intercropped with cowpea, Phaseolus, and Sesbania, which were
similar to those in the monocrop (Table 2.3). No difference was found in the infestation of
Eldana, Sesamia and other insects found in the ear between mono- and intercrops (P ≥
0.05). Overall, insect numbers in the ear were significantly affected by the intercrops (P =
0.05). At IITA, eggs of Mussidia were found in the mono- but rarely in the intercrops.
Maize intercropped with soybean, Canavalia and Tephrosia reduced significantly the
21
Role of intercropping in the management of Mussidia nigrivenella
Table 2.1. Effect of cropping systems on per ear number of M. nigrivenella and other maize ear borers’ infestations, ear
weight, ear damages in Bantè
Intercrops
No of M.
No of M.
No of E.
No of S.
No of Other
Total ear
nigrivenella
nigrivenella
saccharina
calamistis
insects*
borers
eggs
larvae+pupae
Ear weight (g)
% Ear
Ear loss (g)
% Loss
damage
Maize mono
0.08±0.06b
1.09±0.20b
0.29±0.14c
0.08±0.03b
0.49±0.12b
1.54±0.23b
92.7±7.8a
17.3±3.1b
10.2±2.0b
12.1±1.8b
Maize-Cass.
0.01±0.01a
0.56±0.11a
0.02±0.02a
0.06±0.02ab
0.31±0.07a
0.95±0.15a
114.8±6.5a
7.0±2.2a
6.7±1.0ab
6.4±1.6a
Maize-Cowp
0.01±0.01a
0.61±0.14a
0.04±0.03a
0.07±0.03b
0.40±0.09b
1.12±0.16a
103.6±8.4a
9.6±2.1a
7.5±1.9ab
7.7±1.7a
Maize-Phaseo.
0.03±0.03a
0.75±0.15a
0.08±0.05b
0.08±0.03b
0.48±0.11b
1.17±0.18a
102.6±9.6a
10.4±2.0a
8.2±1.5ab
9.1±1.8ab
Maize-Soyb.
0.01±0.01a
0.57±0.12a
0.02±0.02a
0.04±0.02a
0.37±0.10b
1.00±0.21a
109.8±9.6a
9.3±2.0a
7.1±1.9ab
7.7±1.6a
Maize-Canav.
0.01±0.01a
0.52±0.09a
0.01±0.01a
0.03±0.02a
0.30±0.06a
0.86±0.16a
113.0±7.0a
7.7±1.8a
6.7±1.4ab
5.9±0.9a
Maize-Sesb.
0.06±0.03b
0.68±0.13a
0.08±0.03b
0.07±0.03b
0.47±0.09b
1.30±0.20b
98.8±7.6a
11.4±2.5ab
10.0±1.1b
9.4±1.9ab
Maize-Tephr.
0.01±0.01a
0.51±0.10a
0.00±0.00a
0.02±0.02a
0.27±0.06a
0.80±0.12a
118.86±7.00a
6.73±0.97a
4.6±1.2a
5.4±1.7a
(7; 712)
(7; 712)
(7; 712)
(7; 712)
(7; 712)
(7; 712)
(7; 230)
(7; 232)
(7; 230)
(7; 230)
0.020
0.048
0.006
0.004
0.028
0.049
0.290
0.006
0.016
0.024
DF**
P
Means within columns followed by the same letter are not signifi cantly different (SNK, P=0.05). *Other insects are Thaumatotibia leucotreta, beetles (Sitophilus zeamais,
Carpophilus sp. and Cathartus quadricollis). Cass: cassava; Cowp: cowpea; Phaseo: Phaseolus lunatus; Soyb: soybean; Canav: Canavalia ensiformis; Sesb: Sesbania rostrata;
Tephr: Tephrosia vogelii. DF** indicates degree of freedom for both treatment and the experimental error.
22
Role of intercropping in the management of Mussidia nigrivenella
Table 2.2: Effect of cropping systems on M. nigrivenella and other maize ear borers’ infestations, ear weight, ear damages in
Cana
Intercrops
No of M.
No of M.
No of E.
No of S.
No of Other
Total ear
Ear weight
% Ear
nigrivenella
nigrivenella
saccharina
calamistis
insects*
borers
(g)
damage
eggs
larvae+pupae
Ear loss (g)
% Loss
Maize mono
0.21±0.21b
0.28±0.07b
0.24±0.06b
0.32±0.07 b
1.60±0.61 b
2.45±0.53b
33.4±2.5a
26.7±6.5b
4.3±1.1b
14.0±4.8b
Maize-Cass.
0.00±0.00a
0.21±0.05b
0.12±0.04a
0.23±0.07ab
0.92±0.27ab
1.47±0.29a
40.9±6.2a
17.6±4.8ab
3.1±0.7ab
8.7±1.6ab
Maize-Cowp
0.00±0.00a
0.22±0.06b
0.19±0.05b
0.28±0.07 b
1.36±0.43 b
2.01±0.48b
35.3±3.5a
19.2±5.2ab
3.6±1.6a
10.2±3.8a
Maize-Phaseo.
0.01±0.01a
0.23±0.05b
0.22±0.04b
0.32±0.18 b
1.55±0.58 b
2.17±0.65b
31.7±2.5a
20.5±5.7ab
3.7±1.7ab
11.1±3.7ab
Maize-Soyb.
0.00±0.00a
0.15±0.04a
0.11±0.04a
0.18±0.04 a
0.90±0.23ab
1.33±0.28a
37.3±4.1a
16.7±3.1a
2.4±0.6a
8.6±2.0a
Maize-Canav.
0.00±0.00a
0.19±0.04ab
0.09±0.04a
0.17±0.04 a
0.68±0.19 a
1.13±0.16a
37.6±5.0a
15.5±4.6a
2.2±0.5a
8.3±2.9a
Maize-Sesb.
0.00±0.00a
0.21±0.05b
0.12±0.04a
0.23±0.05ab
1.54±0.47 b
2.06±0.62b
39.5±2.5a
21.6±5.5ab
3.72±1.3ab
13.9±3.4ab
Maize-Tephr.
0.00±0.00a
0.17±0.04a
0.08±0.03a
0.16±0.04 a
0.32±0.07 a
0.73±0.12a
43.9±7.7a
13.3±4.1a
1.4±0.5a
2.7±2.0a
DF**
(7; 712)
(7; 712)
(7; 712)
(7; 712)
(7; 712)
(7; 712)
(7; 222)
(7; 229)
(7; 222)
(7; 220)
P
0.0440
0.0042
0.0450
0.0050
0.0048
0.0362
0.059
0.018
0.034
0.024
Means within columns followed by the same letter are not signifi cantly different (SNK, P=0.05). *Other insects are Thaumatotibia leucotreta, beetles (Sitophilus zeamais,
Carpophilus sp. and Cathartus quadricollis). Cass: cassava; Cowp: cowpea; Phaseo: Phaseolus lunatus; Soyb: soybean; Canav: Canavalia ensiformis; Sesb: Sesbania rostrata;
Tephr: Tephrosia vogelii. DF** indicates degree of freedom for both treatment and the experimental error.
23
Role of intercropping in the management of Mussidia nigrivenella
Table 2.3: Effect of cropping systems on M. nigrivenella and other maize ear borers’ infestations, ear weight, ear damages in
Djidja
Intercrops
No of M.
No of M.
No of E.
No of S.
No of Other
Total ear
Ear weight
% Ear
nigrivenella
nigrivenella
saccharina
calamistis
insects*
borers
(g)
damage
eggs
larvae+pupae
Ear loss (g)
% Loss
Maize mono
0.00±0.00
0.27±0.08c
0.01±0.01
0.04±0.02
0.87±0.21
0.98±0.22c
119.1±8.7
7.6±2.13c
7.8±3.0c
6.6±1.9
Maize-Cass.
0.00±0.00
0.10±0.04a
0.00±0.00
0.01±0.01
0.37±0.08
0.48±0.15a
133.1±10.4
2.6±0.8ab
2.8±1.0ab
2.3±0.7
Maize-Cowp
0.00±0.00
0.19±0.08bc
0.01±0.01
0.03±0.02
0.48±0.07
0.71±0.11b
126.8±8.0
3.3±1.5ab
3.3±1.1ab
2.9±1.4
Maize-Phaseo.
0.00±0.00
0.19±0.09bc
0.01±0.01
0.04±0.02
0.50±0.11
0.74±0.15b
125.8±5.8
4.4±1.8ab
3.9±1.8ab
3.5±1.3
Maize-Soyb.
0.00±0.00
0.12±0.05ab
0.01±0.01
0.02±0.02
0.47±0.10
0.62±0.13ab
130.4±11.6
3.2±0.9ab
3.2±0.8ab
2.7\±0.7
Maize-Canav.
0.00±0.00
0.11±0.05a
0.00±0.00
0.02±0.02
0.45±0.12
0.58±0.12ab
135.9±7.5
2.21±0.7ab
2.6±0.8ab
1.9±0.6
Maize-Sesb.
0.00±0.00
0.20±0.09bc
0.01±0.01
0.04±0.02
0.68±0.17
0.84±0.20bc
122.4±9.6
6.7±3.8bc
6.4±3.2bc
5.6±3.1
Maize-Tephr.
0.00±0.00
0.08±0.03a
0.00±0.00
0.00±0.00
0.33±0.08
0.41±0.12a
138.5±9.3
1.2±0.5a
1.4±0.7a
1.0±0.5
(7; 712)
(7; 712)
(7; 712)
(7; 712)
(7; 712)
(7; 712)
(7; 232)
(7; 232)
(7; 232)
(7; 232)
1.00
0.031
0.885
0.470
0.064
0.05
0.087
0.050
0.050
0.027
DF**
P
Means within columns followed by the same letter are not signifi cantly different (SNK, P=0.05). *Other insects are Thaumatotibia leucotreta, beetles (Sitophilus zeamais,
Carpophilus sp. and Cathartus quadricollis). Cass: cassava; Cowp: cowpea; Phaseo: Phaseolus lunatus; Soyb: soybean; Canav: Canavalia ensiformis; Sesb: Sesbania rostrata;
Tephr: Tephrosia vogelii. DF** indicates degree of freedom for both treatment and the experimental error.
Role of intercropping in the management of Mussidia nigrivenella
24
number of Mussidia larvae compared to maize intercropped with Phaseolus, which was
similar to that of the monocrop (Table 2.4). Cassava and cowpea had intermediate effects.
Eldana infestations were also significantly reduced by the intercrops. The total ear borers
were significantly reduced by cassava, soybean, Canavalia, and Tephrosia in the system.
Although all intercrops had an effect on Mussidia infestation, the combination of
maize-Canavalia and maize-Tephrosia proved to be the most effective in the different
locations
The data across locations showed that Mussidia population densities varied
significantly with time of sampling (Figure 2.1). More larvae and pupae were found during
the last sampling when maize was ready to be harvested.
Figure 2.1: Numbers of Mussidia nigrivenella per plant collected per location and per
planting system during the three sampling dates
25
Role of intercropping in the management of Mussidia nigrivenella
Table 2.4: Effect of cropping systems on M. nigrivenella and other maize ear borers’ infestations, ear weight, ear damages at
IITA
Intercrops
No of M.
No of M.
No of E.
No of S.
No of Other
Total ear
Ear weight
% Ear
Ear loss
nigrivenella
nigrivenella
saccharina
calamistis
insects*
borers
(g)
damage
(g)
eggs
larvae+pupae
% Loss
Maize mono
0.10±0.06b
0.54±0.10b
0.16±0.05c
0.30±0.06b
0.75±0.16
1.56±0.21b
119.2±6.4a
13.5±2.5b
13.2±2.3b
11.7±2.2b
Maize-Cass.
0.00±0.00a
0.27±0.06ab
0.06±0.02ab
0.13±0.04a
0.53±0.08
0.95±0.14a
139.1±5.9b
7.3±1.6a
8.8±1.6ab
6.6±1.2ab
Maize-Cowp
0.00±0.00a
0.40±0.07ab
0.10±0.04b
0.18±0.04a
0.66±0.12
1.24±0.20ab
127.6±7.3ab
10.9±2.8ab
9.7±1.4ab
10.4±2.9ab
Maize-Phaseo.
0.00±0.00a
0.41±0.08b
0.12±0.06bc
0.19±0.08a
0.70±0.12
1.32±0.17ab
125.9±8.7ab
11.2±1.8ab
10.3±1.9ab
9.6±1.5ab
Maize-Soyb.
0.00±0.00a
0.39±0.07a
0.09±0.04b
0.16±0.05a
0.57±0.10
1.11±0.14a
133.4±9.6b
10.7±3.9a
8.9±2.4ab
9.3±3.2ab
Maize-Canav.
0.00±0.00a
0.32±0.07a
0.08±0.03ab
0.13±0.04a
0.55±0.09
1.00±0.16a
136.5±6.9b
7.4±1.3a
8.5±1.2ab
6.3±0.9ab
Maize-Sesb.
0.00±0.00a
0.42±0.06a
0.12±0.05bc
0.28±0.12b
0.72±0.16
1.42±0.22b
117.1±6.7a
12.0±3.4b
12.2±2.7b
9.0±2.1b
Maize-Tephr.
0.00±0.00a
0.26±0.05a
0.04±0.02a
0.11±0.03a
0.47±0.11
0.86±0.12a
142.0±8.3b
7.0±1.0a
7.0±1.5a
6.2±1.4a
(7; 712)
(7; 712)
(7; 712)
(7; 712)
(7; 712)
(7; 712)
(7; 230)
(7; 230)
(7; 230)
(7; 230)
0.046
0.034
0.002
0.043
0.062
0.045
0.045
0.048
0.043
0.053
DF**
P
Means within columns followed by the same letter are not signifi cantly different (SNK, P=0.05). *Other insects are Thaumatotibia leucotreta, beetles (Sitophilus zeamais,
Carpophilus sp. and Cathartus quadricollis). Cass: cassava; Cowp: cowpea; Phaseo: Phaseolus lunatus; Soyb: soybean; Canav: Canavalia ensiformis; Sesb: Sesbania rostrata;
Tephr: Tephrosia vogelii. DF** indicates degree of freedom for both treatment and the experimental error.
26
Role of intercropping in the management of Mussidia nigrivenella
No parasitoids were found on M. nigrivenella during the experiment in any of the
locations.
Influence of intercrops on maize yield and on ear borers damages
Ear damage and grain losses in the different locations were significantly lower in the interthan in the monocrop except for maize intercropped with Sesbania. Ear damages in
intercrops were reduced by 34.3-61.1% in Bantè, 19.1-50.2% in Cana, 11.9-84.1% in Djidja
and 11-48.2% at IITA. The percent loss was higher in monocrop, maize intercropped with
cassava, Phaseolus, cowpea and soybean than in maize with Canavalia and Tephrosia. Ear
weight losses were reduced in the intercrops by 22.1-51% in Bantè, 0.9-80.5% in Cana,
13.9-84.1% in Djidja and 11.1-46.8% at IITA. The highest reduction in ear damages and
losses were found in maize intercropped with Tephrosia. However across locations
generally the intercrops have no effect on ear weight (p > 0.05). Across the four
experimental locations ear weight was negatively correlated with the number of ear borers
(Table 2.5) but ear damage increased with the number of the insects found in the ear.
Multiple regressions between ear damage and insect variables showed that the numbers of
M. nigrivenella, E. saccharina, S. calamistis and other insects including T. leucotreta
significantly affected the percentage ear damage and ear losses (Table 2.6).
Table 2.5: Pearson correlation coefficients between maize yield, pest and damage
variables using data across the four experimental locations.
1
2
3
4
5
6
1
1.00
2
-0.31**
1.00
3
-0.18**
0.92**
1.00
4
-0.01
0.01
0.01
1.00
5
-0.13**
0.51**
0.55**
0.03
1.00
6
-0.12**
0.48**
0.41**
-0.01
0.13**
1.00
7
-0.22**
0.68**
0.54**
-0.02
0.23**
0.16**
8
-014**
0.54**
0.45**
-0.03
0.05*
0.12**
9
-0.17**
0.78**
0.75**
-0.01
0.60**
0.35**
*r values ≥ 0.04 have P ≤ 0.05 and **r values ≥ 0.10 have P < 0.01.
7
8
9
1.00
0.17**
0.48**
1.00
0.74**
1.00
1. Ear weight (g); 2. % Ear damage; 3. % Yield loss; 4. Number of M. nigrivenella eggs ; 5. Number of M.
nigrivenella (larvae + pupae); 6. Number of E. saccharina larvae; 7. Number of Sesamia calamistis, 8.
Number of other insects (T. leucotreta + coleoptera larvae) in the ear; 9. Overall larvae in ear
27
Role of intercropping in the management of Mussidia nigrivenella
Table 2.6: Multiple regressions between damage and insect variables
Variables
Coefficient ±
Partial T-
SE
value
Dependent: arcsin√(% Ear damage)
Mean ± SE
Partial
P
10.64 ± 0.208
Independent variables :
log10 (No of M. nigrivenella+1)
25.46 ± 1.43
17.80
0.614 ± 0.013
< 0.0001
log10 (No of E. saccharina+1)
30.89 ± 2.70
11.43
0.118 ± 0.006
< 0.0001
log10 (No of Sesamia sp+1)
48.21 ± 2.62
18.40
0.192 ± 0.005
< 0.0001
log10 (No of Other insects +1)
24.73 ± 1.07
23.02
1.124 ± 0.036
< 0.0001
Intercept = 2.46 ± 0.39
N= 954, F= 653.10, P< 0.0001, R2=
0.73
Dependent: arcsin√(% yield loss)
7.36 ± 0.139
Independent variables:
log10 (No of M. nigrivenella +1)
21.76 ± 1.19
18.29
0.614 ± 0.013
< 0.0001
log10 (No of E. saccharina +1)
16.46 ± 2.26
7.28
0.118 ± 0.006
< 0.0001
log10 ( No of Sesamia sp +1)
32.95 ± 2.18
15.13
0.192 ± 0.005
< 0.0001
log10 (No of Other insects +1)
15.14 ± 0.90
16.84
1.124 ± 0.036
< 0.0001
Intercept =3.59 ± 0.33
N= 942, F= 437.42, P< 0.0001, R2=
0.65
Dependent: g Ear loss
5.60 ± 0.099
Independent variables:
No of M. nigrivenella
1.62 ± 0.22
7.31
0.614 ± 0.013
< 0.0001
No of E. saccharina
1.50 ± 0.45
3.30
0.118 ± 0.006
0.0010
No of Sesamia sp
7.36 ± 0.65
11.30
0.192 ± 0.005
< 0.0001
No of Borers in stem
1.88 ± 0.71
2.64
0.309 ± 0.009
0.0085
No of Other insects
0.28 ± 0.08
3.47
1.124 ± 0.036
0.0006
Intercept = 2.55 ± 0.29
N= 942, F= 71.86, P< 0.0001,
R2=0.28
Role of intercropping in the management of Mussidia nigrivenella
28
Discussion
As shown for stemborers by Schulthess et al. (2004) and Chabi-Olaye et al. (2005)
intercropping reduced attacks of maize ears by M. nigrivenella and other stemborer
species that feed in the ear. Root (1973) and Andow (1992) suggested that the herbivore
were likely to find and remain on host plants that occur in large, dense and pure stands
due to the resource concentration factor. It has been also suggested that when diverse
backgrounds ‘disrupt’ (Vandermeer, 1989) insects from selecting otherwise-acceptable
host plants, the action is mediated through, among other factors, visual camouflage
(Smith, 1969) or deterrent or repellent chemicals (Uvah and Coaker, 1984). Ndemah et
al, (2003) suggested that the negative relationship between the non-host and plant density
and the numbers of larvae were probably due to difficulties encountered by the female
moths in finding host plants for oviposition. Vandermeer (1989) listed three possible
mechanisms responsible for reducing pest infestation in mixed cropping system: (i) the
disruptive-crop hypothesis, in which a second non-host plant species disrupts the ability
of the pest to attack its proper host plant species; (ii) the trap crop hypothesis in which a
second non host plant species attracts the pest away from its primary host; and (iii) the
natural enemy hypothesis, in which the intercropping set up attracts more predators and
parasitoids than the monocrop thereby reducing pests on primary host plant. Although
each treatment had an effect on borer infestation, the most effective intercrops in the
different locations were the treatments where maize was intercropped with Canavalia and
Tephrosia. According to Sétamou et al., (1999), jackbean (C. ensiformis) was the most
suitable host plant for M. nigrivenella development. The high suitability of this cover
crop for M. nigrivenella development and survival compared to maize might have direct
effects on the population dynamics of M. nigrivenella in maize. In our experiments maize
and jackbean seeds were sown simultaneously and both plants reached the suitable stage
for M. nigrivenella attack at the same time; this could explain why low numbers of M.
nigrivenella were found in maize-jackbean intercrop. The low number of M. nigrivenella
observed in Maize-T. vogelii intercrop is probably due to the repulsive effect of T.
vogelii. In semi-field study, oviposition of Mussidia was reduced by the leaf extract of T.
vogelii showing its oviposition deterrent (Agbodzavu, 2005). Moreover these results
suggested that attractiveness and deterrence of the legumes intercropped with maize
Role of intercropping in the management of Mussidia nigrivenella
29
further increase the effectiveness of intercropping in suppressing lepidopterous insects on
maize ear. Visual and chemical stimuli from the host and non-host plants might also
affect the rate at which insects colonize habitats, and their behavior in those habitats.
Moreover in an intercrop, the primary host plant is made less attractive to the herbivore,
and this may depend on the kind of cues, either olfactory or tactile perceived by the
insect. Volatiles emanating from plant tissues had been reported (Elzen et al, 1984;
Udayagiri and Jones, 1992) influencing attractiveness of the plant, which may have also
played vital role in this experiment.
Although it is stipulated that intercropping may enhance the effectiveness of natural
enemies there was no support for this hypothesis in the present study. No parasitoids
were found in any of the treatments including the monocrop in our study. According to
Sétamou et al. (2002), natural enemies of M. nigrivenella are rare in cropping system and
wild habitats in Benin suggesting that the reduction in pest infestation in this study was
not due to parasitism but depended on the performance (attractiveness or repulsiveness)
of each intercrop plant or ovipositional preference of the ear borer.
The effectiveness of the treatments differed from one location to another and with
borer species. According to Sétamou et al., (2000b), the abundance of Mussidia is more
pronounced in the Northern Guinea Savanna than in the other regions under study due to
the abundance of M. nigrivenella host plants. The differences observed in the treatments
toward the infestation of M. nigrivenella and Eldana could be explained by the
differences in the oviposition behavior of the two borers. Eldana, which primarily is a
stemborer that later moves into the ear, (Schulthess et al., 1997) infests plant at the
tasselling stage or later (Kaufman, 1983), whereas the ear borer M. nigrivenella oviposits
on the silk or husks of young and old ears. Moreover M. nigrivenella was recorded on
various plants included the legumes tested in this study (Sétamou et al. 2000a).
Our study has demonstrated that a change in the vegetation diversity could change
the abundance and incidence of maize ear borers. The importance of intercropping as a
method of controlling stem borers in sorghum and maize has been reported by Amoakoatta and Omolo (1983), Ampong-Nyarko et al. (1994), Skovgard and Paets (1996) and
Ayisi et al. (2001). It has been successfully used in reducing infestation of maize stem
Role of intercropping in the management of Mussidia nigrivenella
30
borers especially Busseola fusca Fuller 1901 (Lepidoptera: Noctuidae) (Chabi-Olaye et
al. 2005), Chilo partellus Swinhoe 1885 (Lepidoptera: Pyralidae) (Ampong Nyarko et al.,
1995, Maluleke et al. 2005). Maize-bean intercropping experiments conducted in
Ethiopia during the 1992-cropping season showed that sole maize had significantly high
incidence of stalk borer and earworms as compared to intercropped treatments (Nigussie
and Reddy, 1996). By contrast Schulthess et al. (2004) could not show any effect on the
ear-boring pests such as M. nigrivenella and T. leucotreta by intercropping maize with
cassava maybe because they planted maize before cassava.
There was an increase in the incidence of infestation of M. nigrivenella at the last
sampling date compared to the first one. The low numbers of larvae encountered during
the first sampling might have caused by high immature mortality and high numbers of
larvae at last sampling due to a cumulating of two generations of M. nigrivenella on
maize from milk stage till harvest. According to Sétamou et al. (1999), the generation
time of M. nigrivenella on maize is 37.5 days and M. nigrivenella continues to infest the
ear from milk stage till harvest and even in stores. This oviposition behavior of M.
nigrivenella in field explained the presence of larvae of all stages and pupae in maize ear
during the last sampling in the present study. In contrast to expectation, the high
incidence of borer infestation had little effect on the ear weight, an indication that the
threshold level of the pest was not reached. But the grain losses were affected by the
treatments. This may have great incidence on the aflatoxin content of the maize grains. A
study conducted by Hell et al. (2003) has shown that association of grain legumes or
groundnut with maize would increase aflatoxin in maize. In the present study, the
aflatoxin was not measured in maize samples; therefore in future maize legumes
intercropping studies, care should be taken to assess the aflatoxin content in each
treatment before best crop combinations, which would not only reduce the pest incidence
but also aflatoxin contamination, could be selected.
In conclusion, the findings of this study showed that maize-legumes or cassava
intercrops could reduce M. nigrivenella and other ear borers including T. leucotreta
infestation compared to the sole maize culture. This study showed that an intercropping
system with ‘poor’ hosts of M. nigrivenella could be developed, in a ‘push-pull’ strategy
for the control of M. nigrivenella in small-scale maize farming systems. This strategy will
Role of intercropping in the management of Mussidia nigrivenella
31
involve C. ensiformis as the highly susceptible trap plants (pull) and Tephrosia vogelii as
repellent intercrop (push). Tests are being conducted to determine the susceptible stages
of C. ensiformis the most preferred by the ear borer.
Acknowledgments
This work was financed by the Dutch Ministry of Foreign Affairs, Netherlands. The
authors thank Dr Fritz Schulthess for his useful comments on the early version of this
paper.
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University Press.
CHAPTER 3
The effect of leguminous cover crops and cowpea planted as border rows on
maize ear borers with special reference to Mussidia nigrivenella Ragonot
(Lepidoptera: Pyralidae)
Komi Agboka1,2, Fritz Schulthess, Manuele Tamò1 and Stefan Vidal2
1
International Institute of Tropical Agriculture 08 BP 0932 Tripostal, Cotonou, Republic of
Benin. 2Georg-August-University Goettingen, Agricultural Entomology, Grisebachstrasse 6,
37077 Goettingen, Germany.
Correspondence E-mail: k.agboka@cgiar.org
(Submitted for publication in Phytoparasitica)
Abstract
In southern Benin, the use of cover crops to improve and maintain soil fertility is in the
increase. In the present study, the effect of two leguminous cover crops, Canavalia ensiformis
and Sesbania rostrata, which varied in the onset and duration of their fruiting period, and
cowpea planted as border rows on infestations of maize by the pyralid Mussidia nigrivenella
and of other cob-boring lepidopteran pests was studied in two field trials in 2005. Towards
harvest of both the main and minor season trial, M. nigrivenella densities were higher in the
maize alone than the legume treatments, though the effect depended on the timing of planting
of the cover crop in relation to that of maize. However, pest loads expressed as cumulative
number of feeding-days varied with treatment during the minor season only, and they were
lower on maize with C. ensiformis planted 4 weeks before maize and maize surrounded by S.
rostrata than in the maize alone treatment. There were no discernable trends for other borers
such as the noctuid Sesamia calamistis, the pyralid Eldana saccharina, and the tortricid
Thaumatotibia leuctotreta. Furthermore, M. nigrivenella pest loads were considerably higher
on C. ensiformis than maize. Thus, the lack of significant differences between or the lower
pest loads in some of the treatments as compared to maize alone suggests that there was no
Effect of leguminous cover crops on Mussidia nigrivenella
37
movement of M. nigrivenella from the legumes to maize. Thus, the presence of alternative
host plant species in the vicinity of maize fields does not increase M. nigrivenella attack on
maize.
Per area yields were not different, though in some of the legume treatments, grain
damage and grain losses were higher as compared to the maize alone treatment. However,
grain damage and loss was correlated with other lepidopteran borers, which attack the stem
and ear, rather than M. nigrivenella. Thus a control package has to aim at the entire complex
of maize pests attacking the ears. This should also include the rotation of cover crops or grain
legumes with maize. As shown for other lepidopteran pests in Africa, increasing plant vigour
by improving soil fertility not only increases crop yield but also reduces yield loss.
Keywords: Canavalia ensiformis, cover crops, damage, infestation, maize, Mussidia
nigrivenella,
INTRODUCTION
In West Africa, the pyralid Mussidia nigrivenella (Ragonot) is a polyphagous pest, which
besides maize ears attacks cotton balls, Phaseolus beans and the fruiting structures of many
economically important trees as well as leguminous cover crops such as Mucuna pruriens (L.)
DC. and the jackbean, Canavalia ensiformis (L.) DC. (Silvie 1990, Sétamou et al. 2000a;
Moyal and Tran 1991). In the field, 50% of the plants are usually infested and yield losses
range from 5 to 25% (Moyal and Tran 1991; Sétamou et al. 2000b). Furthermore, M.
nigrivenella continues to feed on maize grains in stores leading to an additional 5% loss. In
addition, grain damage by the borer predisposes maize to pre- and post-harvest infestations by
storage beetles and infections by mycotoxin-producing moulds (Sétamou et al. 1998;
Fandohan et al. 2005).
Several techniques have been tested against M. nigrivenella on maize but none
achieved satisfactory control. Probably because of the cryptic feeding behaviour of the larvae
even systemic insecticides proved to be not very efficient against borers feeding in the ear
(Sétamou et al. 1995, Ndemah and Schulthess 2002). Intercropping maize with both host and
non-host companion crops or planting border rows with grasses reduced oviposition and
larval infestations of stem- and cobborers including M. nigrivenella; however, the results were
Effect of leguminous cover crops on Mussidia nigrivenella
38
not consistent (Ndemah et al. 2002b; Agboka et al. 2006). Given these results, it became
evident that an integrated approach including various control techniques, had to be developed
to control this intractable pest.
Leguminous cover crops can contribute to increased and sustainable crop productivity
through erosion and weed control, biological nitrogen fixation (Vissoh et al. 1998), and
reduction of arthropod pests on the subsequently planted crops (Hokkanen 1991; Chabi et al.
2005a). Because of the high interest of West African farmers in leguminous cover crops such
as C. ensiformis, Tephrosia vogelii Hook. F. Sesbania rostrata Brem. & Oberm. and Mucuna
spp. it is expected that they will become key components of local farming systems (Carsky et
al. 2003). The selection of a cover crop by local farmers, however, should be based not only
on its efficiency in restoring soil fertility, but also on the effects it has on the population
dynamics of pests and natural enemies. As shown by Chabi et al. (2005a) planting leguminous
grain and cover crops during the previous season considerably reduced infestations of maize
by lepidopterous stemborers during the subsequent cropping season. Planting of cover crops
could also divert pests and contribute to the diversity and abundance of natural enemies
thereby affecting pest densities in adjacent crop fields (Altieri 1995; Risch 1981). However,
the introduction of an additional food source in the maize cropping season of southern Benin,
where natural enemies appear to play a minor role in the control of M. nigrivenella (Sétamou
et al. 2002), bears the potential to also increase infestations of maize by this highly
polyphagous pest. In fact, Sétamou et al. (1999) observed high survival and intrinsic rates of
increase of M. nigrivenella reared on pods of C. ensiformis and M. pruriens, explaining the
high infestations found in the field. However, higher attractiveness of cover crops as
compared to maize for ovipositing M. nigrivenella females may also play a role. In addition,
the two cover crops have a considerably less phasic growth habit than maize. Thus depending
on the cultivar, fruiting structures suitable for growth and development of M. nigrivenella are
available for an extended period and thereby could form a source of infestation of the maize
crop. It is therefore suggested that the timing of planting of cover crops should occur in such a
way that the emergence of female moths from mature pods does not coincide with the
occurrence of maize plants in a suitable development stage for oviposition and development
of M. nigrivenella in neighboring crop fields.
Effect of leguminous cover crops on Mussidia nigrivenella
39
The present work aimed at evaluating the effect of the presence of C. ensiformis, S.
rostrata and cowpea, Vigna unguiculata L., planted in the vicinity of maize fields on the
infestation of the crop by pests attacking the ear.
Materials and Method
Location of the experiment
The experiments were conducted in the derived savanna in the south of the Republic of Benin,
at the International Institute of Tropical Agriculture (IITA) research farm in Abomey-Calavi
(latitude 6o24’ N longitude 2o24’E, 12 m above sea level). The site is characterized by a
bimodal rainfall distribution, with peaks in June and October. Mean annual precipitation is
about 1200 mm and mean temperature 25.5oC. The main rainy season usually lasts from
March to July and the minor one from early September to beginning of December. A dry spell
of about four weeks may occur in August. The dry season lasts from December to March.
Two field trials were carried out, one during the main and another during the minor rainy
season of 2005.
Experiment procedures
The maize variety used in both experiments was Quality Protein Maize (QPM) (110-120 days
to harvest). Tasseling is between 35 to 40 days after sowing (DAS) while silking starts at 45
DAS. Maize was sown at a density of 0.4 x 0.75 m (within x between rows) with two seeds
per hole. To accommodate for a gradient in soil fertility, the experimental design for both
trials was a complete randomized block with four replicates. Blocks were separated by 2m
and the plots by 1m. Plot size was 12x12m in maize cover crops treatments and 10x10m in
the maize alone treatments. Two weeks after sowing, a NPK 15–15–15 composite fertilizer
(N, P2O5 and K2O) was applied at a rate of 60 kg per ha, and 45 DAS an additional 50 kg of
urea per ha. Fields were weeded as needed. No insecticide was applied throughout the study
period.
There were five treatments. During the main season, they were (i) maize alone, (ii)
maize plots surrounded with C. ensiformis sown one week before maize (herewith referred to
as Canav1), (iii) maize surrounded with C. ensiformis sown three weeks before maize
(Canav3), (iv) maize with border row of S. rostrata sown three weeks before maize
Effect of leguminous cover crops on Mussidia nigrivenella
40
(Sesbania3) and (v) maize plots surrounded with the erect cowpea cultivar KVx-449
(Cowpea) sown simultaneously. The cover crops species as well as cowpea were sown in two
rows at a spacing of 0.5m within row and 1m between rows, 0.5m from the first maize row. In
jack bean, flowering starts at around 49 days after sowing (DAS) and first pods appear at 56
DAS (Agboka, unpubl. data). The C. ensiformis and S. rostrata treatments were modified
during the minor season. According to laboratory studies carried out during the main season,
rearing of M. nigrivenella on fresh green pods with high content of water failed while it
succeeded more on mature pods (Agboka, unpubl. data). Therefore, border rows of Canavalia
were planted four and eight weeks before maize (herewith referred to as Canav4 and Canav8,
respectively), so that the majority of the pods encountered by M. nigrivenella had low water
content. Sesbania rostrata was sown 4 weeks before maize (Sesbania4).
Data collection
Four destructive samplings were done at biweekly intervals, i.e. at 74, 88, 102 and 116 DAP.
At each sampling, ten plants per maize plot were randomly sampled per sampling occasion.
Ears were thoroughly examined, dissected and the numbers of Mussidia eggs, larvae and
pupae as well as ear damage were assessed according to Sétamou (1996). However, as eggs
were rarely obtained – they are very difficult to detect – cumulative numbers of larvae and
pupae only are presented in the tables. The damage caused by the ear borers was calculated as
the percentage of grains consumed. Numbers of other insects such as Eldana saccharina
Walker (Lepidoptera, Pyralidae), Sesamia calamistis Hampson (Lepidoptera: Noctuidae) and
Thaumatotibia (Cryptophlebia) leucotreta Meyrick (Lepidoptera: Tortricidae) found in the
maize ears were also recorded. In the legume border rows, ten pods of Canavalia, 25 pods of
Sesbania, and 25 pods of cowpea were randomly sampled for assessment of M. nigrivenella
numbers; for logistic reasons sampling of the border rows were done 3-5 days after sampling
maize. At harvest, per area yield of each treatments were estimated using four pre-determined
sub-plots of 1.5m x 2m.
For each treatment, insect-days were calculated according to Ruppel (1983) for each
sampling date, while a cumulative insect-day (CID) index was calculated as CID = Σ0.5
(Pa+Pb)Da-b, where Pa is the population density (mean insects/maize plant at sampling date a,
Pb is the population density at sampling date b, and Da-b is the number of days between a and
b. Feeding days of M. nigrivenella per treatment on per plot basis were calculated as:
41
Effect of leguminous cover crops on Mussidia nigrivenella
CIDx = CIDP * Nx
a)
CIDTA = (CIDLegume * SBR* Dlegume) + (CIDmaize * Smaize * Dmaize)
b)
In equation a) CIDx is insect days per legume or maize plant, CIDP is the insect day per pod or
maize ear and Nx is the number of pod or ear collected per plant. In equation b), CIDTA is the
insect day per total area in plots with legume border rows, CIDLegume and CIDmaize represent
insect day per legume and maize plant, respectively. SBR and Smaize represents area planted to
legumes and maize, respectively, while Dlegume and Dmaize are legume and maize densities,
respectively.
Because M. nigrivenella eggs are not easily detectable, pods were stored at 26 ± 1°C
and RH of 75 ± 5% for ten days to collect not only the already established larvae in the pods
but also additional larvae hatching from non-detected eggs.
Spatial distribution of M. nigrivenella on maize and C. ensiformis
Taylor’s (1961) power law was used to describe the dispersion of larvae and pupae of M.
nigrivenella on maize and C. ensiformis. This law postulates a consistent relationship between
variance S2 and mean m:
S 2 amb
(1)
where b is a measure of dispersion of the species, with b > 1 indicating an aggregated
distribution, b = 1 randomness, and b < 1 a regular distribution, while a is considered a mere
scalar factor without biological meaning. These coefficients were computed by regressing the
natural logarithm of the between plant variance (lnS2) against the natural logarithm of mean
density (lnm), for each field or sampling occasion. A General Linear Model (proc GLM)
(SAS, 1997) was used to compare the b-values.
Wilson and Room (1983) incorporated Taylor’s coefficients (a and b) in a model
describing the relationship between the proportion of infested plants [P(I)] and a mean density
(m) where:
P( I ) 1 e
- m ln (a mb-1) / (a m b -1 – 1)
(2)
(e is the base of natural logarithms). According to Wilson (1982), both a and b are needed to
describe the dispersion of a species, i.e., the more aggregated a species, the smaller P(I) for a
given mean. The P(I) – m curve can be used for a quick estimate of M. nigrivenella densities.
Effect of leguminous cover crops on Mussidia nigrivenella
42
Statistical analysis
Differences in the insect counts per ear among the treatments were analyzed by an analysis of
variance (ANOVA), using the mixed model procedure (SAS, 1997) for repeated measures
over sampling dates. Treatments were considered as fixed effects, while blocks and plants
within replications were considered as random. Wherever the interaction between treatments
and sampling dates was significant, treatments were compared at each sampling date by
means of ANOVA. An F test was used to test the significance of mean differences and least
square mean (LSM) values were computed. The significance level was set at P ≤ 0.05.
Differences in insect feeding days per plant and per plot basis, and cob damage among
cropping patterns were also analyzed by ANOVA, using a GLM procedure. Whenever
significant F values were obtained means were separated by the Student Newman Keuls
(SNK) at P 0.05. Counts were log (x+0.5) and percentages arcsine transformed before
analyses. However, non-transformed means are reported in the tables.
Correlation coefficients were calculated using data pooled across treatments and both
seasons.
Results
Pest infestations
Mussidia nigrivenella larvae were recovered from maize and C. ensiformis but not from S.
rostrata and cowpea. On cowpea, Maruca vitrata Fabricius (Lepidoptera: Crambidae) was the
predominant insect pest.
The effects of leguminous border rows on borer densities on maize varied with
sampling date and season (Table 3.1). In general, M. nigrivenella densities increased towards
harvest. During the main season, differences in pest densities varied with sampling date (F =
75.5, P<0.0001). Around harvest at 116 DAP, they were higher in maize alone than the other
treatments. During the minor season from 88 DAP onwards, M. nigrivenella densities were
always highest in maize alone plots except for 102 DAP, when differences between maize
alone and Canav8 were not significantly different.
43
Effect of leguminous cover crops on Mussidia nigrivenella
Table 3.1: Mean (±SE) number of Mussidia nigrivenella and total borers per maize cob in the different treatments (maize crops
with leguminous border rows and maize alone) and days after planting (DAP) in southern Benin, during the main and minor
cropping season of 2005
Main season
M. nigrivenella
88 DAP
102 DAP
Treatments
74 DAP
116 DAP
74 DAP
Canav3
Canav1
Cowpea
Sesbania3
Maize alone
DF
F
P-value
0.10±0.04aB
0.00±0.00bA
0.17±0.11aA
0.20±0.23aB
0.23±0.11aA
4,145
2.45
0.05
0.00±0.00bA
0.10±0.07aB
0.13±0.13aA
0.00±0.00bA
0.03±0.03aA
4,145
2.48
0.05
0.53±0.29B
0.30±0.13B
0.47±0.18A
0.60±0.40B
0.33±0.13A
4,145
0.10
0.98
1.10±0.36cC
1.93±0.45bC
1.17±0.31cB
1.63±0.49bcC
2.30±0.32aB
4,145
3.55
0.009
Canav8
Canav4
Cowpea
Sesbania4
Maize alone
DF
F
P-value
0.13±0.06aA
0.03±0.03bA
0.00±0.00bA
0.00±0.00bA
0.03±0.03bA
4,145
2.42
0.05
0.03±0.03cA
0.33±0.13bB
0.23±0.11bcB
0.23±0.10bcB
0.93±0.30aB
4,145
3.84
0.0054
0.63±0.31abB
0.07±0.05cA
0.40±0.16bB
0.17±0.07cB
0.80±0.21aB
4,145
3.69
0.0069
Minor season
0.43±0.16bB
0.67±0.21A
0.13±0.06bA
0.93±0.30A
0.50±0.21bB
0.40±0.20A
0.20±0.07bB
0.53±0.16A
1.13±0.29aB
0.52±0.13B
4,145
4,145
4.40
0.88
0.0022
0.48
1.03±0.25A
0.67±0.17B
0.60±0.15BC
1.00±0.17B
1.03±0.30A
4,145
1.0
0.41
Other cob borers
88 DAP
102 DAP
116 DAP
1.33±0.42A
1.03±0.21A
0.87±0.24B
0.87±0.35C
1.27±0.34A
4,145
0.76
0.55
0.80±0.18bA
1.30±0.29aA
1.90±0.47aA
1.20±0.31aAB
1.23±0.24aA
4,145
2.50
0.05
0.33±0.19B
0.63±0.21B
0.40±0.21C
0.77±0.32A
0.27±0.10B
4,145
0.94
0.44
0.57±0.11bA
0.80±0.19bA
0.90±0.23bA
0.67±0.18bA
1.17±0.20aA
4,145
2.43
0.050
0.40±0.18aA
0.57±0.12aA
0.50±0.18aA
0.17±0.07bB
0.17±0.01bC
4,145
2.56
0.04
0.17±0.08B
0.20±0.11B
0.07±0.05B
0.13±0.06B
0.13±0.08C
4,145
0.45
0.77
Canav1, 3, 4, 8 = Canavalia border rows sown 1, 3, 4, 8 weeks before maize, and Sesbania 3, 4 = Sesbania sown 3 and 4 weeks before
maize. Means within columns and season followed by the same lower case letter(s) and within rows followed by the same uppercase
letter(s) are not significantly different at P≤ 0.05 (NSK-test).
Effect of leguminous cover crops on Mussidia nigrivenella
44
Table 3.2: Feeding days of M. nigrivenella (mean ±SE) on maize and
leguminous border rows
Per plant
Treatments
Legumes
Canav3
Canav1
Cowpea
Sesbania3
Maize alone
DF
F
P-value
659.8 ± 88.2aA
838.3 ± 58.5bA
1,6
7.72
0.03
Canav8
Canav4
Cowpea
Sesbania4
Maize alone
DF
F
P-value
3039.9 ± 503.5A
2527.0 ± 323.3A
1,6
0.73
0.4
Maize
Major season
15.9 ±10.2B
19.1 ± 4.0B
17.7 ± 8.1
21.2 ± 12.5
22.9 ± 2.4
4,145
0.36
0.83
Minor season
7.4 ± 3.8aB
1.4 ± 0.7bB
6.3 ± 1.7ab
2.5 ± 0.5b
13.5 ± 0.2a
4,145
4.9
0.019
Per plot (Legumes
and maize)
149247.5 ± 9222.2a
87436.5 ± 4714.8b
6454.9 ± 2958.1c
7728.9 ± 4558.8c
8323.5 ± 862.0c
4,145
151.4
< 0.0001
296674.0 ± 28882.1a
245055.1 ± 17626.9b
4501.5 ± 84.9c
2548.0 ± 819.1c
11805.7 ± 945.8c
4,145
93.1
<0.0001
Means within columns and season followed by the same lower case letter and means per plant within rows
and season followed by the same uppercase letter(s) are not significantly different at P≤ 0.05 (SNK-test)
During both seasons M. nigrivenella feeding days were considerably higher on C.
ensiformis than on maize (F= 157.8 and F= 585.6 with P<0.0001 for Canav3 and Canav1
respectively and F= 101.8 and F=183.1 with P<0.0001 for Canav8 and Canav4 respectively,
Table 3.2). During the main season, feeding days were lower on early compared to late
planted C. ensiformis (F = 7.72; P = 0.03), whereas during the minor season there was no
difference between the two treatments (F = 0.74; P = 0.4). By contrast, during the main
season number of feedings days on maize did not vary with treatment (F = 0.36; P = 0.83),
whereas during the minor season, they were higher on maize alone and Canav8 than Canav4
and Sesbania4. (F = 4.9; P = 0.019). During both seasons, cumulative feeding days on a per
plot basis were highest on maize surrounded by C. ensiformis planted early, followed by C.
ensiformis planted late, and considerably lower but similar on the remaining treatments.
During both seasons, numbers of feeding days by S. calamistis were higher than those
of M. nigrivenella, while E. saccharina and T. leucotreta were less common (Table 3.3).
During the main season, no differences in S. calamistis and E. saccharina feeding days were
observed between treatments. Feeding-days of T. leucotreta were higher on maize alone and
45
Effect of leguminous cover crops on Mussidia nigrivenella
Canava1 than on Canav3 but all three were not different from the other treatments. During the
minor season, S. calamistis feeding days were higher on Canav8 and maize alone than
Cowpea and Sesbania4, while Canav4 was not different from any of these treatments, while E.
saccharina feeding-days were higher for Canav8 than Sesbania4 and maize alone.
Table 3.3: Feeding days (Means ±SE) of M. nigrivenella and of other cob-boring pests on
maize
Treatments
M. nigrivenella
Canav1
Canav3
Cowpea
Sesbania
Maize
F
P
19.1±4.0C
15.9±10.2AB
17.7±8.1B
21.2±12.5B
22.9±2.4C
0.36
0.83
Canav8
Canav4
Cowpea
Sesbania
Maize
F
P
13.3±6.8bBC
6.8±1.2cA
12.4±0.2bB
7.0±0.3cB
32.4±2.6aC
4.31
0.028
S. calamistis
E. saccharina
Main season
29.4±5.0D
9.6±2.1B
25.0±6.1B
8.4±2.0A
30.1±5.3C
11.9±2.9B
28.9±7.0B
8.6±2.9A
29.6±5.6C
11.7±2.9B
0.19
0.80
0.91
0.53
Minor season
16.8±2.7aC
8.9±2.4aB
14.7±3.1abB
6.3±1.9abA
12.8±3.2bB
4.7±1.7abA
10.0±2.6bB
2.3±0.9bA
16.6±2.6aB
2.3±1.4bA
3.06
2.55
0.019
0.042
T. leucotreta
F
P
2.8±1.2bA
6.1±1.6aA
3.7±1.2abA
3.7±0.9ab A
2.8±1.0aA
1.44
0.22
12.4
3.9
8.7
4.9
10.5
<0.001
0.01
<0.001
0.003
<0.001
1.4±0.6A
2.1±1.5A
2.1±0.9A
1.6±0.8A
4.2±1.3A
1.51
0.20
11.8
7.1
6.5
7.2
16.3
<0.001
<0.001
<0.001
<0.001
<0.001
Means within columns and season followed by the same lower case letter and means within
rows and season followed by the same upper case letter(s) are not significantly different at
P≤ 0.05 (SNK-test)
Damage variables and yield
During the main season, per area yields did not vary between treatments, while ear damage
was lower on maize alone, Canav3 and Sesbania3 as compared to Canav1 and Cowpea (Table
3.4). Percent ear damage was lower on Canav1 and Cowpea than the other treatments.
During the minor season, per area yields did again not vary between treatments. Ear damage
was higher in the Canavalia than the maize alone treatment whereas the cowpea and
Sesbania4 treatments were not significantly different from either. There were no significant
differences in grain loss between treatments.
Ear damage and grain loss were not correlated with M. nigrivenella feeding days (R =
0.16, P = 0.38, and R = 0.26, P = 0.16, respectively) but there was a significant positive
relationships with other ear-boring Lepidoptera (R = 0.67, 0.72, respectively, P<0.0001).
46
Effect of leguminous cover crops on Mussidia nigrivenella
Table 3.4: Effect of leguminous border rows on percent plants infested with M.
nigrivenella [P(I)], on maize yields, damage by ear borers and grain loss (means ±
SE)
Treatment
Canav3
Canav1
Cowpea
Sesbania3
Maize alone
DF
F
P-value
P(I)
15.8 ± 6.5
23.3 ± 9.2
21.7 ± 6.8
20.8 ± 6.5
32.5 ±10.1
4, 145
1.52
0.22
Ear damage (%) Yield (kg/Ha)
16.2 ± 2.8b
21.9 ± 2.4a
22.9 ± 3.3a
13.1 ± 1.4b
11.7 ± 1.4b
4, 145
4.84
0.0011
Major season
6338.4±844.0
5267.2±342.3
5339.8±894.9
5626.6±561.9
5964.0±465.5
4, 16
0.58
0.69
Grain loss (%)
11.2 ± 1.9b
12.0 ± 1.5b
20.8 ± 2.9a
12.0 ± 1.9b
15.6 ± 1.9ab
4, 145
3.60
0.0079
Minor season
Canav8
11.7 ± 3.9b 10.0 ± 2.4a
5267.4±492.5
5.8 ± 1.8
Canav4
16.7 ± 4.8b 6.5 ± 1.1a
4654.2±1154.8
3.9 ± 0.9
Cowpea
15.8 ± 4.7b 7.4 ± 1.4ab
6259.4±440.3
4.2 ± 1.3
Sesbania4
13.7 ± 4.5b 6.0 ± 1.6ab
5924.2±186.9
3.3 ± 1.4
Maize alone
31.7 ± 4.5a
4.0 ± 1.1b
7450.0±1395.7
3.1 ± 1.1
DF
4, 145
4, 145
4.16
4, 145
F
2.79
2.61
1.49
1.32
P-value
0.039
0.038
0.28
0.27
Canav1, 3, 4, 8 = Canavalia border rows sown 1, 3, 4, 8 weeks before maize, and
Sesbania3, 4 = Sesbania sown 3 and 4 weeks before maize. Means within column and
season followed by the same lower case letter(s) are not significantly different at P≤ 0.05
(SNK-test).
Spatial distribution of M. nigrivenella
All regression slopes were greater than 1, indicating an aggregated distribution of M.
nigrivenella on the two host plant species used (Table 3.5). They did not significantly vary
with host plant species (F = 0.07, P = 0.81 in main season and F = 0.20, P = 0.68 in minor
season), thus a common slope and intercept was used for fitting the P(I)-m curve (Figure 3.1).
The curves calculated for C. ensiformis and maize fit well the observations and could be used
for a quick estimate of the density ranges shown in figure 3.1.
47
Effect of leguminous cover crops on Mussidia nigrivenella
Table 3.5: Taylor’s Power coefficients (means ±SE) for M.
nigrivenella on maize and Canavalia ensiformis
Host plant
ln (a)
b
Main season
0.81 ± 0.06a
1.12 ± 1.05a
0.89 ± 0.14a
1.35 ± 1.13a
0.82
0.07
0.42
0.81
C. ensiformis
P-value
R2
P
0.32
0.23
0.02
0.0098
Minor season
Maize
0.84 ± 0.05b
1.21 ± 1.04a
0.39
<0.0001
1.79 ± 0.31a
1.57 ± 1.18a
0.26
0.0031
C. ensiformis
F
27.5
0.20
P-value
0.006
0.68
Coefficients within column and season followed by the same letter are
not significantly different at P≤ 0.05
Proportion of infested cobs or pods (P(I))
1.0
0.8
0.6
0.4
0.2
0.0
0
2
4
6
8
10
12
Mean number of M. nigrivenella per cob or pod
Figure 3.1: Proportion of infested cob or pod (P(I)) as function of mean number of M.
nigrivenella per cob; observed (open symbols: maize; closed symbols: Canavalia) and
calculated via equation 2 (line)
Effect of leguminous cover crops on Mussidia nigrivenella
48
Discussion
The data reported here indicate that the presence of leguminous crops in the vicinity of
maize fields do not aggravate M. nigrivenella infestations on maize, irrespective of
when the legume was planted in relation to maize, and irrespective of the status of the
legume species as a host. Thus, although the suitable host C. ensiformis had up to 1800
times higher pest loads than maize, there appeared to have been no movement of M.
nigrivenella to maize. In fact, during the second season, at harvest, all legume
treatments had lower M. nigrivenella densities on maize than the maize alone treatment.
Also, maize surrounded by C. ensiformis planted four weeks before, had lower pest
loads expressed as cumulative feeding days as compared to maize alone and cowpea.
This indicates that C. ensiformis was much more attractive to the ovipositing moth than
maize. The fact that during the minor season C. ensiformis planted 4 weeks before
maize had an effect on pest loads on maize while when planted 1 and 3 weeks before in
the main season or 8 weeks before in minor season it did not, suggests that the growth
stage and/or canopy density of the plants affected the attractiveness of the leguminous
crop to the ovipositing moth. As shown by Ritchie (2000) and Haddad et al. (2001), the
amount of above-ground plant biomass, which however was not assessed in the present
experiment, may have a strong effect on insect abundance. Furthermore the volatile
profile of plants changes with the growth stage (Batten et al. 1995; Zhang et al. 2008),
which might affect the oviposition behaviour of the moth.
The lack of significant differences in pest loads on maize between most
treatments and maize alone also indicates that C. ensiformis did not enhance the activity
of natural enemies – both predators and parasitoids - as suggested for other systems
(Altieri 1995; Risch 1981; Bugg et al. 1991; Tillman et al. 2004). However, parasitoids
of M. nigrivenella are scarce in Southern Benin and appeared to play no role in the
population dynamics of this pest (Sétamou et al. 2002). Similarly, in the present study
no parasitoids were obtained during rearing of larvae in the laboratory from M.
nigrivenella collected from maize or cover crops.
Likewise, planting non-hosts such as cowpea and S. rostrata had little effect on
infestations of maize by M. nigrivenella, though during the minor season maize
surrounded by S. rostrata had lower pest loads than without. Similarly, Ndemah et al.
(2002b) showed that non-hosts such as grasses planted as border rows could reduce
Effect of leguminous cover crops on Mussidia nigrivenella
49
densities of cereal stemborers and of M. nigrivenella on maize. It was suggested that
grasses acted as a barrier to the adult moths in search of a suitable host plant, which
would explain the variability of the efficacy of this control technique (Ndemah et al.
2006, 2007; Matama-Kauma et al. 2006) since only well established borders had an
effect. We therefore recommend testing perennial non-hosts as barrier crops and achieve
a gradient of barrier effect by cutting back the non-host at different times before
planting maize.
A more efficient technique for reducing borer densities on maize proved to be
the intercropping of non-host species with maize, because the presence of the non-host
plants hampers host finding by the ovipositing moth, and thus reducing the number of
egg batches deposited on maize (Ndemah et al. 2003; Schulthess et al. 2004; ChabiOlaye et al. 2005b; Wale et al. 2007; Songa et al. 2007). When diverse backgrounds of
plants ‘disrupt’ insects from selecting otherwise acceptable host plants, the action is
mediated through, among other factors, visual camouflage (Smith, 1969) or
deterrent/repellent chemicals (Altieri et al. 1978; Uvah and Coaker 1984). Furthermore,
both young and old instars of several African stemborer species disperse from the
original oviposition site to other plants (Kaufmann 1983; Berger 1989, 1992). Thereby,
the chances of encountering a suitable host plant is reduced in mixed cropping systems
with non-host plant species leading to high mortality in the dispersing larvae (Ndemah
et al. 2003; Schulthess et al. 2004; Chabi-Olaye et al. 2005b; Wale et al. 2007; Songa et
al. 2007). Thus, Agboka et al. (2006) studying maize-legumes and cassava mixed
systems showed that maize intercropped with C. ensiformis and T. vogelii reduced M.
nigrivenella infestation in maize crop, the first acting as a trap crop and the latter as a
repellent crop.
Some of the legume treatments used in our experiments also lowered pest loads
of S. calamistis and E. saccharina on maize, while others increased them. The reasons
are not obvious because both stemborer species only attack plants of the Poaceae and
Cyperacea families (Gounou and Schulthess 2004; Atachi et al. 2005; Le Rü et al.
2006). Sesamia calamistis only oviposits on pre-tasseling plants (Kaufmann 1983;
Sémeglo 1997) and females avoid plants with egg batches; the resulting distributional
pattern is thus regular to random (Sétamou and Schulthess 1995). Thus, in some
treatments the border rows might have acted as barrier crops, while in others they might
Effect of leguminous cover crops on Mussidia nigrivenella
50
have arrested the ovipositing moth and kept it from moving to other fields. Again, the
effects were not consistent and varied with season.
In general, differences between treatments in insect (i.e., borer-days, percentage
of infested plants) and damage variables (ear damage, grain loss) were not consistent,
and treatments did not have any effect on per area yields. Thus, planting leguminous
border rows as a mean of controlling M. nigrivenella appears not to be economically
meaningful. However, the major finding of the present study is that the presence of
leguminous cover crops or grain legumes in the vicinity of maize fields does not
increase M. nigrivenella densities on maize. Moreover, as shown by Chabi-Olaye et al.
(2005a), grain legumes and cover crops enhance yields and reduce yield losses in maize
crops subsequently planted in the same field by improving plant vigour. It is obvious
that a single control option will not produce satisfactory control of the complex pest
problem caused by lepidopteran maize pests, and as proposed by Chabi-Olaye et al.
(2006) an IPM package including crop rotation with leguminous cover or grain crops or
direct application of synthetic fertilizer, mixed cropping and timely applications of
insecticides or botanicals targeting not only M. nigrivenella but all stem- and earborers
is required.
Acknowledgments
This study is part of a project funded by the Dutch Ministry of Foreign Affairs (DGIS).
The authors are grateful to the technicians of the Cereal Stem and Ear Borers
Laboratory at IITA-Benin.
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CHAPTER 4
Effects of plant extracts and oil emulsions on the maize ear-borer
Mussidia nigrivenella Ragonot (Lepidoptera: Pyralidae) in laboratory and
field experiments
Komi Agboka1, 2, Agbodzavu K. Mawufe3, Manuele Tamò1 and Stefan Vidal2
1
International Institute of Tropical Agriculture, 08 BP 0932 Tripostal, Cotonou, Republic
of Benin. 2Georg-August-University Goettingen, Agricultural Entomology,
Grisebachstrasse 6, 37077 Goettingen Germany. 3University of Lomé, Ecole Supérieure
d’Agronomie BP 1515 Lomé Togo.
(Submitted for publication in International Journal of Tropical Insect Science)
Abstract
Aqueous extracts of Tephrosia vogelii and Hyptis suaveolens, and of oils of Azadirachta
indica and Jatropha curcas, as well as the pesticide Furadan 5G were evaluated for their
insecticidal activity against the maize earborer Mussidia nigrivenella in laboratory and field
experiments. In general, treated plants had a strong deterrent effect on ovipositing M
nigrivenella. The ODIs (oviposition deterrence index) were highest with neem oil at both
concentrations, J. curcas at 5% and H. suaveolens at 20%. In addition, egg hatch was
adversely affected by neem and Jatropha oils; it decreased with an increase in
concentrations of oil emulsions and varied between 3-25.5% for neem and 6-16% for J.
curcas. The LC50 calculated were 1.3% and 0.8% respectively for neem and J. curcas. By
contrast, larval survival was not affected by the oil treatments. In the field, Furadan, neem
and J. curcas oils significantly reduced the number of M. nigrivenella larvae by 16-49.2%,
while aqueous extracts of T. vogelii and H. suaveolens were similar to the control
consisting of emulsified water. The treatments did not significantly influence cob weight,
and only neem oil at both concentrations and furadan significantly reduced ear damage and
consequently grain losses. These results showed that oil emulsions of A. indica and J.
Corresponding Author: Tel: +22921350188, Fax: +22921350556, E-mail: k.agboka@cgiar.org
Effect of plant extracts and oil emulsions on the ear-borers
58
curcas oils act not only as oviposition deterrent but also as ovicides. The prospects for
possible inclusion of botanicals into integrated M. nigrivenella control in maize cropping
systems are discussed.
Keywords: Aqueous extracts, Azadirachta indica, botanicals, integrated pest management,
Jatropha curcas, oviposition.
Introduction
Mussidia nigrivenella Ragonot 1888 (Lepidoptera: Pyralidae) is one of the key pests
attacking maize ears in West Africa (Moyal, 1988; Bosque-Pérez and Mareck, 1990;
Shanower et al., 1991; Moyal and Tran 1991 a, b; Silvie, 1993; Sétamou et al., 2000). In
field-grown maize, reported yield losses vary between 5 and 25% (Moyal & Tran, 1991b)
with additional losses of 10-15% in stores (Sétamou et al., 2000). Moreover, M.
nigrivenella damage predisposes maize to pre- and post-harvest infestation by coleopteran
pests, Aspergillus flavus Lk. Fr. (Deuteromycetes: Monoliales) infections and subsequent
aflatoxin contamination (Sétamou et al., 1998). Hence both the quantity and quality of
maize are affected (Sétamou et al., 1998).
Currently available control options include sun-drying of the cob after harvesting,
and insecticides (Sétamou, 1999), but none provides satisfactory control. Probably due to
the cryptic nature of the larvae and the timing of application, M. nigrivenella is particularly
difficult to control with insecticides (Moyal, 1988; Sétamou et al., 1995; Ndemah and
Schulthess, 2002). Moreover, insecticides are often not affordable to African peasant
farmers. Therefore, biopesticides such as neem products extracted from seeds of the neem
tree, Azadirachta indica Juss (Meliacae), which are locally available, are of special interest.
They are categorized as broad spectrum insecticides and alternatives to synthetics (Isman,
2006, Immaraju, 1998). Juan and Sans (2000) and Carpinella et al. (2002) showed that
extracts of neem seeds and fruits had antifeedant activity in larvae of Sesamia nonagrioides
(Lefebre) or Spodoptera eridania (Lepidoptera: Noctuidae). Crude extract of A. indica
showed growth inhibitory, antifeedant and toxic effects against two noctuids, cabbage
looper, Trichoplusia ni (auth.) and armyworm Pseudaletia unipuncta (Akhtar et al., 2008).
Effect of plant extracts and oil emulsions on the ear-borers
59
In Africa, apart from neem products, other extracts derived from indigenous plants such as
Hyptis suaveolens L. (Lamiacae), Tephrosia vogelii (Fish bean) Hook F. (Leguminosae)
and Jatropha curcas (physic nut) L. (Euphorbiacae) recently gained attention with regard to
their insect pests control potential. According to Gaskins et al., (1972) leaves of Tephrosia
species contain at least four compounds that possess insecticidal properties. Likewise, H.
suaveolens has been recently shown to possess insecticidal properties (Perry, 1980) and,
among others, was effective against the cowpea weevil during storage (Fatope et al., 1995).
An ovicidal effect of J. curcas oil has been demonstrated on Phthorimaea operculella
Zeller (Lepidoptera: Gelechiidae) (Shelke et al., 1987). Botanicals have been successful
against a number of maize pests in Africa. Mugoya and Chensembu (1995) reported that
aqueous fresh-leaf extracts of T. vogelii reduced the incidence of the spotted stalk borer
Chilo partellus Swinhoe (Lepidoptera: Crambidae) in maize in Zambia. Siddiqui et al,
(1990) tested neem products against the spotted stalk borer, and Bruce et al. (2004) against
the stemborers Sesamia calamistis and Eldana saccharina, while Bekele et al. (1997) and
Ogendo et al. (2008) used indigenous plant extracts against stored maize pests. The present
work aimed at assessing the efficacy of botanicals occurring in West Africa in controlling
M. nigrivenella.
Materials and methods
Extraction and formulation of A. indica and J. curcas oils
Neem oil extraction followed a protocol described by Lale and Abdulrahman (1999). Ripe
neem fruits were sun-dried before oven drying at 50oC for 72 hours. Kernels obtained after
decortication, using a mortar and pestle, were ground in an electric blender. The neem seed
powder obtained was then moistened and kneaded till oil started oozing. The neem oil,
which was analyzed by Trifolio-M GmbH, Germany, contained ≈ 0.009% azadirachtin.
Neem oil was formulated with a water and emulsifier solution (soap without any detergent)
to prepare the different concentrations of neem oil emulsion.
The protocol for the extraction of J. curcas oil followed a method developed by
Atchall (1999). Shelled seeds of physic nut were treated like the neem seeds and then
ground. Five kilograms seed paste were soaked in 37.5 l of water. The mixture,
Effect of plant extracts and oil emulsions on the ear-borers
60
homogenized using an agitator, was then boiled for 5 hours. The volume of the mixture was
maintained constant by adding water (approximately 5 l/hour). After two hours, the
foaming cream formed on the surface of the mixture was collected periodically. The cream
- a mixture of water, oil cake, and oil - was heated for 30 min to retrieve oil floating on the
solid residue. The oil thus obtained was oven dried at 105o C for 15 min. and formulated as
required for the experiments.
Preparation of aqueous extract of T. vogelii and H. suaveolens
Aqueous extracts at 15 % and 20 % were prepared by soaking 3.75 and 5 kg pounded fresh
plant material (leaves and fruits, respectively) in 25 liters of water, leaving it for 12 hours,
and then filtering it through muslin cloth. A solution of emulsifier was added to each
preparation before field application.
Insect culture
A laboratory culture of M. nigrivenella originating from specimens collected from field
grown maize in the Southern Guinea savanna of Benin was established at IITA. The insects
were continuously reared for two generations on Canavalia ensiformis (L) (Fabacae) pods
following the protocol developed by Sétamou et al. (1999). Pieces of mature jack bean pods
were infested with red eye-spotted eggs (egg stage after five days with a visible red point)
collected from the oviposition cage. The pieces were then maintained in 14 cm high and 11
cm diameter plastic containers, and incubated at 26 ± 2oC and a 12:12 (L:D) photoperiod.
At pupation the pupae were collected and transferred to oviposition cages.
Oviposition behavior
For the oviposition experiment, maize plants were produced in pots. Silking plants were
transferred to metallic cages. 2 m high, 2m long, and 1 m wide cages (blocks) were used for
this study and repeated five times. All cages were covered with a netting material to avoid
external infestations and to prevent the experimental moths from escaping. At the dough
stage, each treatment (except Furadan) was assigned to a pot containing two plants.
Approximately eight hours after applying the treatment, five newly-emerged pairs of M.
Effect of plant extracts and oil emulsions on the ear-borers
61
nigrivenella were released in the center of each cage in a Petri dish supported by a
cylindrical tube placed in soapy water to keep away predators such as ants. Newly emerged
insects were used in the study, as M. nigrivenella has no pre-oviposition period and lay the
maximum eggs during the first two days (Sétamou et al., 1999). Five days later, cobs were
sampled and examined under a binocular microscope. Eggs deposited were counted and
recorded. Oviposition deterrence index for the extracts and oils was calculated using the
formula: [(C-T)/(C+T)]*100 (Akhtar and Isman, 2003) where C= number of eggs laid on
the control and T = number of eggs laid on the treated cobs.
Toxicity to eggs and larval survival
Eggs (2-3 days old) laid on tissue papers were collected from the oviposition cage and
adjusted to 50 eggs per tissue paper. These tissues were treated with different
concentrations (0, 2.5, 5, 10 and 100%) of neem and physic nut oils and allowed to be airdried for one hour. The treated tissue papers were then transferred to C. ensiformis pods.
The pods were introduced into plastic containers (20 cm long, 12 cm diameter, and 10 cm
high) and stored in the laboratory at 27±2oC and about 70% RH. After 6 days the numbers
of hatched eggs were recorded, and the numbers of larvae still alive were counted after 7
days. The treatments was replicated four times
Topical toxicity of neem and J. curcas to second instar larvae
Sets of second instars larvae were topically treated with the different concentrations of the
oils emulsions and fed Canavalia pods by applying the treatment on the anterior pronotum
of the second instar larvae using a microliter syringe. The larvae were placed in the C.
ensiformis pod for feeding. Larval mortality was recorded every week. The number of
larvae that reached the pupal stage was also recorded in both experiments. The treatments
were replicated four times.
Field trial
The experiment was conducted to evaluate the efficacy of plant extracts and oils in
controlling M. nigrivenella in field conditions. The study was carried out at the
Effect of plant extracts and oil emulsions on the ear-borers
62
International Institute of Tropical Agriculture (IITA)-Benin station in Abomey-Calavi
(6o24’N, 2o24’E), Republic of Benin, during the first growing season of 2004. The site is
located in the derived savanna characterized by a bimodal distribution of rainfall with peaks
in June and September, and an annual precipitation of about 1200 mm. During our trials,
monthly mean rainfall recorded was 189.2 mm and temperatures ranged from 18.5o C to
32.6°C, with a minimum in September and a maximum in October.
A 4-month maize variety QPM (Quality Protein Maize) was used in this study. The
experiment was laid out in a complete randomized block design consisting of ten
treatments, each replicated four times. The experimental plots measured 12.5 m × 7 m.
Plots were separated by 2 and blocks by 3 m. Alleys were sown with sorghum three weeks
before planting maize in order to reduce interaction between treatments. Maize was sown at
three seeds in a pocket a spacing of 0.4 m within rows and 0.75 m between rows. Two
weeks after sowing, the crop was thinned down to two plants per pocket. NPKSB 14-23-145-1 fertilizer was applied 14 and 45 days after sowing at a rate of 60 kg/ha for each
application.
The treatments consisted of aqueous extracts of H. suaveolens and T. vogelii at
concentrations of 15 and 20%, oil emulsions of A. indica and J. curcas at concentrations of
2.5 and 5% and of the synthetic insecticide Furadan 5 G (5% of active ingredient).
Emulsified water and an untreated check served as controls. The concentrations of plant
extracts used in the present trial are commonly used by local farmers against cowpea pests
(Tamo, unpublished data).
The botanical treatments and the control were applied three times, i.e. at the soft
dough stage, approximately 70 days after sowing (DAS), and two subsequent applications
at two-weekly intervals, according to the infestation pattern of M. nigrivenella in the field
(Moyal and Tran, 1991a). At each application, the whole ear was sprayed including the
silks. Because of its persistence, Furadan was applied only once at the rate of 2g per plant
by placing the granules between the stem and the leaf immediately below the ear.
A week after each spray, a sample of ten cobs was randomly taken from each plot.
The cobs were taken to the laboratory and checked thoroughly for eggs before being dehusked. However, as eggs were rarely obtained – they are very difficult to detect –
Effect of plant extracts and oil emulsions on the ear-borers
63
cumulative numbers of larvae and pupae only are presented in the tables.
M. nigrivenella and other borer’s densities
Different stages of larvae and pupae of M. nigrivenella and other borers species found in
the maize ear such as Eldana saccharina Walker 1865 (Lepidoptera: Pyralidae) and
Sesamia calamistis Hampson 1910 (Lepidoptera: Noctuidae) were recorded. The density of
M. nigrivenella at each sampling date was also determined.
Larval survival and parasitism
The data collected here aimed at examining whether the treatments have an effect on larvae
and parasitism. All larvae collected were therefore kept in the laboratory at 27±2oC and
70% RH to record larval mortality and parasitism.
Cob weight and damages
The effects of plant extracts and oils on cob weight and damages by cob borers were
determined. At harvest, a last sampling was done to assess ear weight, damages and grains
losses. The damage caused by the ear borers was calculated as the percentage of grains
consumed by the borer and/or contaminated by fungi. The loss (in g) was calculated as the
difference between the initial weight of the ear and the weight of the ear after removing the
damaged grains.
Statistical analysis
Differences in the insect counts per ear among the treatments in field trial were analyzed by
analysis of variance (ANOVA), using the mixed model procedure (SAS, 1997) for repeated
measures over sampling dates. Treatments were considered as fixed effects while plants
within replications were considered as random. Percentages were arsine and counts were
log (x+1) transformed before analyses. Least square means (LSM) of treatments across
sampling date and within sampling date and of sampling date within treatment were
separated using the t-test. Means of eggs hatching and larval survival in laboratory
experiment were separated by Student-Newman and Keuls’ test. Significance was set at p
Effect of plant extracts and oil emulsions on the ear-borers
64
≤ 0.05. Number of eggs deposited on treated and untreated plants in oviposition experiment
was analyzed by a non parametric ANOVA using Kruskal Wallis test.
Results
Oviposition behavior
Plant extract and oil emulsion treatments significantly reduced oviposition on the plants
offered. More eggs were laid by M. nigrivenella on untreated than treated plants (DF = 8,
χ2 = 29.3, P = 0.0003; Figure 4.1). The oviposition deterrence index (ODI) was
significantly higher with 5% J. curcas, both concentrations of neem oil and H. suaveolens
at 20% compared to the other treatments and control (F = 12.12, P<0.0001) indicating
complete oviposition deterrent effects by neem, J. curcas oils and H. suaveolens extract at
their respective concentrations.
120
Mean ODI (%)
c
b
100
c
c
b
c
b
b
80
60
40
20
a
0%
Em
uls
if i e
r
veo
l2
15%
H.
su a
20
%
a ve
ol
H.
su
e lii
15%
vog
T.
%
5%
e lii
vog
T.
Ne
em
2 .5
%
Ne
em
as
5
J. c
ur c
J. c
urc
as
2 .5
%
0
Treatments
Figure 4.1: Oviposition deterrence index (ODI) of the extracts and oils
65
Effect of plant extracts and oil emulsions on the ear-borers
Toxicity to eggs and larval survival
Hatching of M. nigrivenella eggs was adversely affected by neem and Jatropha oils (DF=8,
F=14.96, P<0.0001), and it decreased with increasing concentrations of the oils applied
(Table 4.1). Only 3 to 6% of eggs hatched in the 100% oils treatments with neem and
Jatropha, respectively, as compared to 66% in the control treatments. LC50 calculated for
neem and J. curcas oils were 1.3% and 0.8% respectively. Percentages of larvae developing
to the 5th instar and pupae were >75% in all treatments (Table 4.1).
Topical toxicity of neem and J. curcas to second instar larvae
Topical application of oil emulsion on second instar larvae did not have any significant
effect on their survival when compared to the control (DF = 8, F = 1.27, P = 0.32), and
pupae formation was >80%. (Table 4.2)
Table 4.1: Mean percentage (± SE) of egg hatching after treated with neem and J.
curcas oils emulsions and survival of M. nigrivenella to pupae
% egg hatch
Concentration
(%)
Neem
J. curcas
% larval survival
neem
J. curcas
2.5
25.5 ± 5.3b
16.0 ± 4.9b
96.8 ±1.9
100.0 ± 0.0
5
18.5 ± 4.3bc
11.0 ± 2.1b
100.0 ± 0.0
75.0 ± 15.0
10
11.5 ± 4.1c
8.5 ± 1.3bc
100.0 ± 0.0
100.0 ± 0.0
100
3.5 ± 2.2d
6.0 ± 1.4c
100.0 ± 0.0
83.3 ± 16.7
66.0 ± 9.1a
66.0 ± 9.1a
97.2 ± 1.9
97.2 ± 1.9
1.3±0.2
0.8±0.1
Control
LC50
Means in a column followed by the same lower case letter(s) are not significantly
different (DF= 7, 27; F=14.96, p<0.0001).
Effect of plant extracts and oil emulsions on the ear-borers
66
Field experiment
M. nigrivenella and other borer’s densities
Significantly fewer M. nigrivenella larvae were recorded on plots treated with Furadan, A.
indica and J. curcas than in the controls (df = 10, F = 7.27, P<0.0001) but there were no
significant differences between concentrations of oil emulsions (Table 4.3). Tephrosia
vogelii and H. suaveolens aqueous extracts did not significantly affect M. nigrivenella
densities, except for the 20% concentration of H. suaveolens.
Neem and Jatropha oils, at both concentrations, Furadan, and extracts of T. vogelii
at 20% significantly reduced the numbers of E. saccharina larvae but only neem oil and
Furadan had an effect on S. calamistis (Table 4.3).
Table 4.2: Survival (mean ± SE) to pupa stage of second instar larvae of M.
nigrivenella topically treated with neem and J. curcas oils emulsions
% Larval survival*
Concentration
(%)
Neem
2.5
89.0 ±1.4
88.3 ± 2.9
5
87.0 ± 2.6
87.8 ± 3.9
10
88.4 ± 5.1
86.8 ± 2.2.0
Pure
85.0 ± 5.1
86.5 ± 5.1
Control
90.1 ± 1.0
90.1 ± 1.0
J. curcas
* No differences were found in all treatments (df= 8, F = 1.27, P = 0.32)
67
Effect of plant extracts and oil emulsions on the ear-borers
Table 4.3: Effects of emulsions of neem and J. curcas oils, Furadan, and aqueous plant
extracts of T. vogelii and H. suaveolens on M. nigrivenella and other cob borer
infestations
Number of larvae per cob (mean ± SE)
Treatments
M. nigrivenella
S. calamistis
E. saccharina
J. curcas oil 2,5%
0.29±0.06bc
0.29±0.05a
0.20±0.05b
J. curcas oil 5%
0.14±0.03c
0.30±0.055a
0.20±0.05b
A. indica oil 2,5%
0.14±0.03c
0.22±0.04b
0.11±0.03b
A. indica oil 5%
0.15±0.03c
0.19±0.04b
0.17±0.04b
T. vogelii extract 15%
0.53±0.11a
0.30±0.05a
0.37±0.06a
T. vogelii extract 20%
0.52±0.11a
0.30±0.05a
0.19±0.04b
H. suaveolens extract 15%
0.49±0.09ab
0.37±0.07a
0.41±0.08a
H. suaveolens extract 20%
0.34±0.10b
0.33±0.05a
0.40±0.08a
Furadan
0.13±0.03c
0.19±0.04b
0.10±0.03b
Emulsifier solution
0.53±0.09a
0.38±0.07a
0.44±0.06a
Control (Untreated check)
0.55±0.11a
0.40±0.09a
0.42±0.04a
DF
10, 1716
10, 1716
10, 1716
F
6.11
3.05
4.37
P
< 0.0001
0.001
< 0.0001
Means in column followed by the same letter(s) are not significantly at P ≤ 0.05 (SNK)
Densities of M. nigrivenella varied significantly with sampling date and tended to
increase towards harvest (df =3, F=16.4, P<0.0001) (Table 4.4). They were significantly
lowest at the second sampling date (P<0.007). In addition, in the oil treated plots, M.
nigrivenella densities tended not to vary with sampling date (Table 4.4).
Larval survival and parasitism
Survival of M. nigrivenella larvae from treated field was not affected by the treatment (DF
= 10, F = 1.57, P = 0.12) and mortality varied from zero to 3.2% only.
No natural enemies were recorded on M. nigrivenella but Cotesia spp. cocoons were
obtained from one S. calamistis larva.
68
Effect of plant extracts and oil emulsions on the ear-borers
Table 4.4: Mean ± SE number of Mussidia nigrivenella per maize cob in the different botanical and control treatments
at different days after sowing (DAS)
Sampling dates (DAS)
Treatments
74
88
102
116
J. curcas oil 2.5%
0.33±0.13abAB
0.13±0.08bB
0.25±0.11bcAB
0.45±0.18bA
J. curcas oil 5%
0.15±0.07cA
0.13±0.06bA
0.10±0.05cA
0.18±0.07cA
A. indica oil 2.5%
0.23±0.08bcA
0.08±0.04bA
0.15±0.08cA
0.10±0.05cA
A. indica oil 5%
0.12±0.05cA
0.08±0.04bA
0.23±0.10c A
0.18±0.06cA
T. vogelii extract 15%
0.15±0.07cA
0.08±0.04bA
0.70±0.30aB
1.18±0.30aC
T. vogelii extract 20%
0.40±0.13aA
0.13±0.06bB
0.68±0.27abC
0.88±0.31aC
H. suaveolens extract 15%
0.28±0.11bA
0.10±0.05bA
0.93±0.28aB
0.68±0.19abB
H. suaveolens extract 20%
0.20±0.06bcA
0.13±0.05bA
0.58±0.0.36abB
0.45±0.13bB
Furadan
0.10±0.05cA
0.05±0.03bA
0.08±0.04cA
0.28±0.10bcA
Emulsifier solution
0.51±0.17aA
0.35±0.08aA
0.43±0.13abA
0.83±0.29aB
Control (Untreated check)
0.45±0.12aA
0.30±0.10aA
0.40±0.21bA
1.05±0.37aB
DF
10, 429
10, 429
10, 429
10, 429
F
2.02
1.92
1.97
3.50
P
0.03
0.047
0.04
0.0004
Means within column followed by the same lower case letter(s) and within row followed by uppercase letter(s) are not
significantly different at P ≤ 0.05
Effect of plant extracts and oil emulsions on the ear-borers
69
Cob weight and damage
The treatments did not significantly influence cob weight (P = 0.45, Table 5), and only
neem oil at both concentrations and Furadan significantly reduced ear damage (DF = 10,
F = 2.01, P = 0.038) and consequently grain losses (DF = 10, F = 2.25, P = 0.019).
Discussion
The results of field’s trials showed that larval population of M. nigrivenella can be
significantly reduced through the application of oil emulsions of A. indica and J. curcas,
which were as efficient as Furadan 5 G. By contrast, plant extracts of T. vogelii and H.
suaveolens were not efficient. Neem oils and pure compounds of neem have been found
to exhibit ovipositional deterrent effects on many crop pests including lepidopteran,
homopteran and dipteran species (Singh and Singh, 1998, Schmutterer 1990, Isman 1996,
Bruce et al. 2004, Showler et al., 2004). According to Udayagiri and Mason (1995)
chemical cues play a major role in host selection. In the ovipositional test, M.
nigrivenella tended not to oviposit on maize plants treated with the oils indicating a
repellent effect. Similar results have been observed by Bruce et al., (2004), who found
that application of neem oil at 0.075 ml/plant lead to a reduction in number of egg laid by
S. calamistis and E. saccharina of 88 and 49%, respectively, compared to the control.
Oviposition deterrence was also observed in Liriomyza spp. (Diptera: Agromyzidae)
(Webb et al., 1983, Hossain and Poehling, 2006, Seljåsen and Meadow, 2006) and the
beet armyworm (Greenberg et al., 2005). Loery and Isman (1993) suggest that this
deterrence results from a variety of compounds working in concert with another,
producing different behavioral responses, which vary in magnitude between species.
Deterrent and ovicidal effects have also been reported for J. curcas (Adebowale and
Adedire 2006, Boateng and Kusi 2008).
The reduction of M. nigrivenella larvae in the field could also be due to reduced
egg viability as indicated by the findings of the laboratory experiment. Although eggs are
supposed to be strongly protected by the impermeable chorion, which may inhibit the
penetration of neem and J. curcas products, egg hatch was adversely affected by both
oils. Schmutterer (1990) stated that the ovicides action of neem treatments is common,
Effect of plant extracts and oil emulsions on the ear-borers
70
and the product can obstruct the egg aeropyle, thus impeding the respiratory changes
during the embryonic development. Similarly, neem oil also affected the viability of S.
calamistis and E. saccharina (Bruce et al., 2004), and of Chilo partellus (Lepidoptera:
Pyralidae) (Siddiqui et al. 1990) eggs. Also, Schulz and Schüter (1983) showed changes
in the ooplasm and vitelligenesis, which is necessary for oocytes maturity, resulting in
egg sterility. This ovicidal effect is advantageous because larvae are killed before they
can cause damage.
In this study contact toxicity of the oils on larvae could not be observed as nearly
all larvae treated with oils developed to pupae. This indicated that 2nd instars larvae were
not susceptible to neem and J. curcas oils used in the present experiment. At 100% the
larvae demonstrated very low susceptibility to the oils and this result is very relevant, if
we consider that in most studies, neem oil has caused insect mortality at doses between
0.1 and 5% (Schmutterer, 1990). The low contact toxicity of neem oil against M.
nigrivenella larvae could be due to low azadirachtin (0.009%) content of the oil.
However, adults of treated larvae were not reared to determine whether the treatments
affected fitness. For example, Bruce et al. (2004) showed that neem oil reduced the
fecundity of S. calamistis and E. saccharina. These findings indicate again that the
treatments in the fields did not kill the larvae but deterred oviposition and affected the
hatching of eggs. By contrast, in other studies neem and Jatropha deterred feeding of the
larvae, when they were incorporated in the diet (Zabel et al., 1999). In laboratory tests
conducted by Ratnadass et al., (1997), artificial diet supplemented with extracts of nuts of
J. curcas at 0.01% and 1% crude oil concentration, yielded 100% of mortality of
Busseola fusca Fuller (Lepidoptera: Noctuidae) and S. calamistis larvae. However, under
natural conditions – except for first instar larvae – the larvae live cryptically inside the
ear and may not be affected by the treatment. Thus, the treatments should be targeted
towards the first larval instar, before they penetrate the ear.
71
Effect of plant extracts and oil emulsions on the ear-borers
Table 4.5: Effects of emulsions of neem and J. curcas oils, Furadan, and aqueous plant extracts of T. vogelii
and H. suaveolens on ear weight and loss, and damage caused by M. nigrivenella and other cob borers (mean ±
SE)
Treatments
Ear weight(g)
% ear damage
Ear loss (g)
% grain loss
J. curcas oil 2.5%
99.8±7.8a
13.8±4.0b
10.5±2.9b
12.5±3.2b
J. curcas oil 5%
120.3±1.9a
7.5±2.2ab
7.7±1.5ab
8.4±2.0ab
A. indica oil 2.5%
106.6±10.1a
5.2±1.9a
4.1±1.0a
5.1±1.4a
A. indica oil 5%
116.3±8.2a
6.9±2.2a
6.8±1.71a
7.3±1.8a
T. vogelii extract 15%
130.5±10.8a
15.7±4.1b
15.6±2.2b
14.6±2.6b
T. vogelii extract 20%
112.7±9.7a
11.7±3.5b
9.5±2.4ab
10.5±2.8ab
H. suaveolens extract 15%
126.3±9.4a
14.0±3.3b
12.6±2.6b
10.6±2.3b
H. suaveolens extract 20%
118.7±9.0a
11.6±2.7b
11.9±1.7b
10.9±1.8b
Furadan
124.8±10.7a
8.3±2.3a
7.0±1.6a
6.9±1.7a
Emulsifier solution
121.2±8.1a
12.0±3.1b
11.5±0.5b
10.9±3.2b
Control (untreated check)
117.6±7.7a
11.7±2.3b
12.3±1.9b
12.0±2.0b
DF
10, 429
10, 429
10, 429
10, 429
F
0.98
2.01
2.88
2.25
P
0.45
0.038
0.003
0.019
Ear weight and damage were determined at harvest. Means in a column followed by the same lower case letter(s)
are not significantly different at P ≤ 0.05 (SNK).
Effect of plant extracts and oil emulsions on the ear-borers
72
Compared to untreated plots, maize treated with oil emulsions of J. curcas at 5%
and neem at both concentrations were protected from M. nigrivenella attack for more
than one week indicating a long-lasting effect. Moreover M. nigrivenella density in oil
treated plots tended to be constant over sampling dates indicating that the oil treatments
protect the maize ear from further infestations. In Nigeria, Olaifa and Adenuga (1988)
have demonstrated that under field condition during the dry season, neem products
prepared from the seeds appeared to lose their efficacy after 11 and 14 days. Likewise,
Schmutterer (1990) stated that under field conditions a foliar application of most
commercial neem formulations persists for 5 to 7 days. The differential effects of neem
and J. curcas oils observed on S. calamistis and E. saccharina might be because the two
borers attack maize at different plant growth stages. Sesamia calamistis only oviposits on
pre-tasseling plants (Kaufmann, 1983; Sémeglo, 1997), while E. saccharina infests the
plant at or after the tasseling stage, but both species also feed on the ear (Kaufmann,
1983). In the present study, plants were treated at silking, thus S. calamistis larvae were
already present in the stem and well protected against J. curcas oil. However, they might
have been affected by the neem oils, which can have systemic properties (Thoeming et
al., 2003, Weintraub and Horowitz, 1997). By contrast, at silking both E. saccharina
oviposition behaviour and its eggs could be affected by the oils as showed by Bruce et al.
(2004).
Although Tephrosia species and H. suaveolens have been reported to be sources
of a number of compounds with toxic and deterrent activities toward insects (Simmonds
et al., 1990, Machocho et al 1995, Morris 1999) their aqueous extracts did not have any
significant effect on M. nigrivenella larvae compared to neem and J. curcas, even though
they reduced oviposition by M. nigrivenella. This inefficacy to reduce significantly larval
population could be due to their low persistence and characteristics of their active
compounds, or they were faster washed-off by rain than oil emulsion. Also, rotenone one of T. vogelii bioactive compounds- is not soluble in water (Anonymous, 1999), which
might explain the results obtained. It is therefore recommended to use other solvents
(alcohol, acetone…etc.) rather than water or add a good emulsifier or use their essential
oils to achieve significant results.
Effect of plant extracts and oil emulsions on the ear-borers
73
In the present experiment, only neem oils significantly reduced ear damage and
grain losses. Neem products have shown to be systemic (Hossain and Poehling, 2006), a
property which was not yet demonstrated for J. curcas products. Thus neem might also
act as feeding inhibitor of larvae present in the ear, though feeding deterrence appears to
be more acute in sap sucking insects like the Western flower thrips Frankliniella
occidentalis (Thysanoptera: Thripidae) (Thoeming et al., 2003).
In conclusion the potential of neem and J. curcas in M. nigrivenella control has
good prospects. However, oils including aqueous extracts of seeds have to be tested in
environments with higher infestations as prevalent in the Southern Guinea Savannah
(Sétamou, 1996) before being included in an IPM program currently being developed.
Acknowledgments
This study was financed by the grant from the Dutch Ministry of Foreign Affairs (DGIS).
The authors thank Prof Dr Sanda Komla at the University of Lomé/ Togo for his
technical assistance in oils extraction.
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CHAPTER 5
The importance of Mussidia nigrivenella Ragonot (Lepidoptera:
Pyralidae) as a post-harvest pest in different storage structures in Benin
Komi Agbokaa, b, Fritz Schulthessc, Manuele Tamòa, Kerstin Hella and Stefan Vidalb
a
International Institute of Tropical Agriculture 08 BP 0932 Tripostal, Cotonou Republic
of Benin; bGeorg-August-University Goettingen, Agricultural Entomology,
Grisebachstrasse 6, 37077 Goettingen Germany; cPostfach 508-4, 7004 Chur,
Switzerland.
Correspondence E-mail: k.agboka@cgiar.org, Tel: +229 21350188, Fax: +229 21 350556
(Submitted for publication in Journal of Stored Products Research)
Abstract
In West Africa, the most damaging lepidopteran pest of maize ears is the pyralid
Mussidia nigrivenella. Although it is mostly described as a field pest, it can be found
feeding on stored maize up to the 4th month. A survey was conducted in Benin in 2006 to
assess M. nigrivenella infestations in different maize storage systems in the Southern
(SGS) and Northern Guinea Savanna (NGS). In SGS and NGS the percentage of infested
stores decreased from 86.7% to 26.7% and from 51.4% to 14.3%, respectively, during the
first 28 weeks of storage. During the same time, mean numbers of M. nigrivenella per
cob decreased from 0.36 to 0.04 across both zones. All larval stages, but mostly 3rd to 5th
instars, were frequently found even after more than 12 weeks, indicating that M.
nigrivenella either reproduced in storage or that development was delayed. Highest M.
nigrivenella incidence of 16.8% and 14.4% were found in the “Ava” and crib stores,
respectively. Infestations were highest in “Ava” and lowest in maize grain stored in
polyethylene bags or in mud silos. In a laboratory experiment, presence of post-harvest
beetles negatively affected the bionomics of the cob borer, indicating strong interspecific
competition.
Keywords: Cob borer; infestation; maize; storage time; storage system; beetles
Importance of Mussidia nigrivenella in storage
80
Introduction
Corn (Zea mays L.) is an important staple crop in West Africa providing food and income
to farmers. In Benin, maize is generally harvested late to facilitate drying. It is stored on
the cob with or without the husk cover either in wooden granaries, under the roof or on
the floor inside the houses, or as grains in clay containers such as mud silos or in
polyethylene bags (Fiagan, 1994; Hell et al., 2000). Stored maize can be infested by a
variety of insects, among them the maize weevil, Sitophilus zeamais Motschulsky
(Coleoptera: Curculionidae) and the larger grain borer, Prostephanus truncatus (Horn)
(Coleoptera: Bostrichidae), which cause losses exceeding 20% (Pantenius, 1988;
Borgemeister et al., 1998; Meikle et al., 2002; Schneider et al., 2004).
The maize cob borer Mussidia nigrivenella Ragonot (Lepidoptera: Pyralidae),
although frequently reported to infest maize in the field (Moyal and Tran 1991a,b,
Shanower et al. 1991, Gounou et al, 1994, Sétamou 1996), has also been shown to feed
on stored maize (Sétamou 1996). In the field, female moths lay their eggs on the silks,
where young larvae feed for a few days before progressing to the grains. In the field,
typically more than half of the cobs are infested by the borer (Whitney, 1970, Sétamou,
1996), and reported yield losses measured at harvest vary between 5 and 15% (Moyal and
Tran, 1991, Sétamou et al, 2000). In addition, Mussidia nigrivenella damage predisposes
maize to pre- and post-harvest infestations by storage beetles and fungal pathogens such
as the aflatoxin producing Aspergillus flavus Lk. Fr. (Sétamou et al, 1998) and Fusarium
spp. (Ako et al., 2003). Hence, both the quantity and the quality of maize are affected by
M. nigrivenella.
The egg-to-adult development time of M. nigrivenella on maize at 26±2oC and
65±5 relative humidity (rh) is roughly 38 days (Bordat and Renand, 1987; Moyal and
Tran, 1991b; Bolaji and Bosque-Pérez, 1998; Sétamou et al., 1999). Thus, the presence of
M. nigrivenella in maize stores after more than two months might indicate that it also
infests stored grain or that the life cycle is extended under storage conditions. In spite of
the fact that M. nigrivenella could infest stored maize (Ratnadass, 1987; Tran, 1987) and
other stored products such as cacao beans (Potter, 1931, Evans, 1952, Varshalovich,
1975), seeds of Canavalia sp. and of Phasesolus sp. (Buyckx, 1962, Le Pelley, 1959),
Importance of Mussidia nigrivenella in storage
81
and soya beans (Moyal, 1988), few studies exist on its importance as a storage pest
(Sétamou, 1996). The objective of the present study was to assess the status of M.
nigrivenella as a pest of stored maize and to evaluate the influence of different storage
structures and the presence of storage beetles on the levels of borer infestations.
Material and methods
Surveys
Four surveys for M. nigrivenella in stored maize were conducted from July 2005 to
February 2006 in the Southern (SGS) and the Northern Guinea Savanna (NGS), which in
previous studies showed the highest prevalence of the borer (Sétamou et al., 2000). The
SGS is characterized by a bimodal rainfall pattern with precipitations averaging 1100 –
1500 mm, allowing for two maize growing seasons, while the NGS has a monomodal
rainfall distribution with less than 1100 mm rainfall and one cropping season only. Three
villages were selected in SGS and seven in NGS depending on the availability of stores in
each zone. In each village, five stores were randomly selected and sampled four times,
once just after harvest (i.e. 0 week after storage), and at 4, 12 and 28 weeks thereafter.
(The description of the storage structure is given in the next section). Stores made from
plant materials, where maize was stored on the cob, were divided into four sections, and
15 cobs were randomly chosen from each. For mud silos and polyethylene bags, in which
maize is stored as grain, approximately 3 kg of grains were taken with a probe. Samples
were taken to the laboratory for determination of numbers of all pest species per cob or
grain sample. For each sampling period and location, the percentage of infested stores
and for each store the percentage of cob or grain sample was calculated.
On-station experiment: effect of storage methods on infestations by M. nigrivenella
The trial was conducted in Ouesse (08°29.521 N and 002°26.046 E) to test the effect of
four store types on borer infestation over a 28 weeks period. During the study, the
monthly ambient temperature varied from 25 to 31° C and the relative humidity from 33
Importance of Mussidia nigrivenella in storage
82
to 76% (Figure 5.1). The improved IITA maize variety DMR-LSR-W (hereafter referred
to as DMR) was used. It is a white seeded cultivar that reaches maturity at approximately
110 days. DMR is resistant to downy mildew (Peronosclerospora sorghi Weston &
Uppal) and to maize streak virus. The treatments consisted of two indigenous and two
improved store types with four replicates for each, i.e. 1) The standard storage structure
named “Ava”, used to store maize as cob with husk; 2) polyethylene bags and 3) mud
silos, in which maize grains are stored in bulk; and 4) cribs where maize is stored as cobs
without husk. “Ava” is a traditional, cylindrical structure with walls made of woven
vegetable material. The cobs with the husks are laid out in a circular fashion to build a
hollow cylinder of about 1.5 m in diameter on a 1.2 m platform. The experimental
structure was rodent protected by metal sheets (http://www.fao.org/inpho/index-f.htm). In
the experimental stores, about 300kg of maize were stored. The mud silo is a hollow
cylinder built with a mixture of clay and grasses (mainly sorghum stems or rice straw).
The maize crib is an improved narrow structure, in the form of a rectangular basket, 1.2m
high, 0.6m wide and about 2.2m long, made of bamboo (http://www.fao.org/inpho/indexf.htm); in the present experiment, maize was stored as de-husked cobs. The top of all
structures, except the polyethylene bags, were covered with a thatched roof to ensure
protection from rain. The treatments were all arranged in randomized complete blocks
with four replications. The blocks consisted of farmers located at about 1km from each
other. No insecticides were used and no insects were released into the structures. The
changes in damage and insect populations over time were monitored by regular
samplings as described above. Mussidia nigrivenella damage was identified by its
characteristic feeding habit as described by Sétamou et al. (1998); M. nigrivenella larvae
start feeding from the tip of the cob and produce conspicuous amounts of silky frass. The
percent damage (y) was calculated according to Boxall (1986) as y = (B / A) x 100,
where A is the number of all grains and B is the number of grains damaged by M.
nigrivenella. In addition, the percentage of damage caused by beetles was calculated by
counting the number of grains damaged over the total number of grains.
The moisture content of the samples from each store type was determined
according to the International Organisation for Standardisation (1979) routine method. A
sub-sample was ground (Romer Grinding Subsampling Mill®, Union, U.S.A), transferred
83
Importance of Mussidia nigrivenella in storage
to a metal container and weighed. The sample was then dried for two hours at 130 °C,
and re-weighed in the container. The corn moisture was determined by the following
formula MC = 100 ((Wi–Wd)/Wi), with MC = moisture content, Wi = initial weight and
32
80
30
70
60
28
50
26
40
24
Temperature
Humidity
22
30
Relative Humidity (%)
Mean temperature (oC)
Wd = weight after drying.
20
20
10
Jul
Aug Sept
Oct
Nov
Dec
Jan
Feb
Mar
Apr
Months
Figure 5.1: Mean monthly temperature and Relative humidity at Ouesse
Laboratory experiment: effect of the presence of storage beetles on the development of
M. nigrivenella
Fifty grams of maize grain were placed into 1 liter jars and infested with storage
beetles and M. nigrivenella. The following treatments were applied: i) M. nigrivenella
alone, ii) M. nigrivenella with P. truncatus, iii) M. nigrivenella with S. zeamais and iv)
M. nigrivenella with P. truncatus and S. zeamais. Thereby, 50 eggs of M. nigrivenella at
Importance of Mussidia nigrivenella in storage
84
the red-spotted eyes stage, 10 pairs of less than 2 weeks old S. zeamais or 10 pairs of P.
truncatus originating from six to eight week old colonies were used. The jars were
covered with a mesh lid and incubated at 27 ± 1o C and 75 ± 2% r.h. Each treatment was
repeated eleven times in completely randomized blocks. The contents of the jars were
monitored every day for 6 weeks for numbers of larva, pupa and moth. At the end of the
experiment, the development time of the larvae and pupae, and the number of pupae were
determined.
Data analysis
Maximum likelihood analysis using the proc logistic model (SAS Institute, 1997) for
categorical variable was applied to survey data to identify the effects of storage period,
zone and storage structures on the presence of M. nigrivenella. Differences in insect
counts per ear/grain sample and in percentages of grain damaged and grain moisture
content among the storage systems in the on-station experiment were analyzed by
analysis of variance (ANOVA) using the Generalized Linear Model (GLM) procedure of
SAS for repeated measures over sampling dates. In the laboratory experiment,
developmental time, numbers of pupae formed and pupal weight were analyzed via
analysis of variance (ANOVA) using the Generalized Linear Model (GLM). Least square
means (LSM) were separated using the t-test. Percentages were arcsinx- and number of
M. nigrivenella log10(x+1) transformed. Correlation coefficients among different insects
were calculated using data pooled across zones.
Results
Surveys
Mussidia nigrivenella was found at all sampling dates. Overall, the logistic regression
models showed that the store system and storage duration had significant impact on the
abundance of M. nigrivenella (Table 5.1). The highest odds ratios for M. nigrivenella
absence were found between 12 and 28 weeks after storage. After 28 weeks of storage,
85
Importance of Mussidia nigrivenella in storage
beetles such as S. zeamais and Cathartus quadricollis Guerin (Coleoptera: Silvanidae)
were the most prevalent species followed by P. truncatus, while M. nigrivenella,
Carpophilus sp. (Coleoptera: Nitidulidae), Tribolium sp. (Coleoptera: Tenebrionidae)
represented less than 5% of all species collected (Table 5.2). Lepidopteran stem borers
such as Sesamia calamistis Hampson (Lepidoptera: Noctuidae) and Eldana saccharina
Walker (Lepidoptera: Pyralidae) were collected up to 4 weeks of storage only and they
were not included in Table 5.2.
Table 5.1: Logistic regression analysis of the effect of storage duration, storage
systems and the ecological zone on the abundance of Mussidia nigrivenella
Parameter
DF Estimate SE
Intercept
Store
Store
Store
Zone
Week
Week
Week
1
1
1
1
1
1
1
1
Ava
Cribs
Mud silos
SGN
0
12
28
3.73
-2.37
-2.05
-1.13
-0.38
-0.34
0.805
1.68
0.27
0.26
0.26
0.28
0.14
0.14
0.18
0.24
Wald
χ2
190.59
80.34
61.86
16.48
7.83
5.45
20.21
50.95
P-value
<.0001
<.0001
<.0001
<.0001
0.0051
0.0195
<.0001
<.0001
Odds
ratio
0.09
0.13
0.32
0.68
0.71
2.24
5.35
Table 5.2: Densities and relative importance (%) of insect
species in stored maize in the Guinea Savannas of Benin after
28 weeks of storage
Insect species
Mussidia nigrivenella
Prostephanus truncatus
Sitophilus zeamais
Cathartus sp.
Carpophilus sp.
Tribolium sp.
Mean ± SD
0.17±0.0082c
0.37±0.051c
1.04±0.058b
2.42±0.108a
0.08±0.0059d
0.20±0.012c
% of total insect
3.92d
8.57c
24.44b
56.58a
1.81e
4.67d
Means in a column followed by the same letter(s) are not significantly different
at P ≤ 0.05 (t- test)
Multiple regressions showed that the numbers of Catharthus sp. and Carpophilus
sp. were positively and the numbers of P. truncatus and S. zeamais negatively related
with M. nigrivenella densities (r2=0.061, P<0.0001; Table 5.3). Percentages of cob or
86
Importance of Mussidia nigrivenella in storage
grain samples and of granaries infested, and the number of M. nigrivenella per cob/grain
sample varied significantly with agro-ecological zone and duration of storage. The
percent infested stores (DF = 1, 200; F = 5.3; P = 0.018) and numbers of M. nigrivenella
per cob (F = 5.6; P = 0.02) was higher in the SGS than in the NGS, but the percentage of
infested cobs was higher in the NGS than the SGS (DF = 1, 12000; F = 5.6, P = 0.02,
Table 5.4).
Table 5.3: Multiple regression analysis of total Mussidia nigrivenella
and storage beetles present in maize cobs
Variables
Intercept
Prostephanus truncatus
Sitophilus zeamais
Catharthus sp.
Carpophilus sp.
Tribolium sp.
R2
Estimates
0.023
-0.021
-0.030
0.087
0.076
-0.018
0.061
Standard Error
0.0014
0.0089
0.0058
0.0044
0.0150
0.0099
P-value
< 0.0001
0.018
< 0.0001
< 0.0001
< 0.0001
0.064
Prior to analysis, number of insects were log10(x + 1)-transformed
In each zone and across zones the percentage of stores infested by M. nigrivenella
decreased significantly with sampling date (DF = 3, F = 4.6; P = 0.008; Table 5.5 and
5.6). Cob borer counts decreased from harvest to 28 weeks after storage. This trend was
significant in the NGS, while in SGS there was an increase of the M. nigrivenella
numbers from harvest to 4 weeks after storage and a subsequent decrease thereafter until
the 28th week (Table 5.5).
Table 5.4: Store and cob/sample infestation (%), and densities per cob
of Mussidia nigrivenella in the Southern (SGS) and Northern (NGS)
Guinea Savanna in Benin
zones
% storage infestation
SGS
66.67±9.95a
NGS
38.57±6.74b
% cob infestation
6.78±1.24b
8.77±1.59a
Number of M. nigrivenella
0.20±0.02a
0.15±0.01b
Means (±SE) within rows followed by the same letter(s) are not significantly different at P≤0.05 (t-test)
87
Importance of Mussidia nigrivenella in storage
Table 5.5: Effect of storage duration on the infestation by Mussidia nigrivenella of
farmers’ stores in Southern (SGS) and Northern Guinea Savanna (NGS)
Zone
SGS
Weeks in
storage
0
4
12
28
% store
infested
86.67±6.67a
93.33±6.67a
60.0±20.00b
26.67±17.64b
% cob infestation
in stores
11.2±3.08a
16.0±3.60a
4.53±1.40b
3.33±2.28b
Number of M.
nigrivenella
0.23±0.03b
0.41±0.05a
0.08±0.02c
0.06±0.01c
0
4
12
28
51.43±15.65a
51.43±15.56a
37.14±11.90ab
14.29±5.71b
16.06±4.11a
6.29±1.78b
3.46±1.08c
1.41±0.75c
0.41±0.03a
0.12±0.01b
0.06±0.01c
0.02±0.01c
NGS
In each zone, means ±SE within columns followed by the same letter(s) are not significantly different at P
≤ 0.05 (t- test)
Table 5.6: Effect of storage duration on the infestation of M. nigrivenella in farmers’
stores across zones (means ±SE)
Weeks after storage
0
4
12
28
% store
infestation
62.0±12.09a
64.0±12.58a
44.0±10.24ab
18.0±6.29b
% cob infestation
per store
14.57±3.0a
9.20±1.75a
3.78±0.86b
2.0±0.87b
Number of M.
nigrivenella
0.36±0.03a
0.21±0.02b
0.07±0.01c
0.04±0.01c
Means within columns followed by the same letter(s) are not significantly different at P ≤0.05 (t- test)
On-station experiment: Effect of storage methods on the infestation of M. nigrivenella
The storage structures and the duration of storage significantly affected the percentage of
cobs infested by M. nigrivenella (DF = 3, 960; F=9.2, P<0.0001 and F= 8.3, P= 0.0001,
respectively) and the number of larvae (DF = 3, 960; F= 42.9, P<0.0001 and F = 41.9,
P<0.0001), respectively). Percentages of cob infested were highest in “Ava” followed by
the cribs (Table 5.7). The percentages of grain sample infested and the number of larvae
in the mud silo and polyethylene bags were significantly lower than in the other two
stores (DF = 3, 960; F=9.6 P<0.0001 and F= 70.1, P<0.0001, respectively). In all
structures the percentages of cob infestation and the number of M. nigrivenella larvae
88
Importance of Mussidia nigrivenella in storage
decreased with storage time (Table 5.7). From harvest throughout storage, a reduction of
more than 70% of cob infestations was observed in all structures. All developmental
stages but mostly 3rd to 5th instars larvae and/or pupae could be found in “Ava” and cribs
after 28 weeks, while lower or no infestations were observed in the mud silo and
polyethylene bags.
Table 5.7: Number of and overall means (across sampling dates) of Mussidia
nigrivenella and mean percentage of cob/grain sample infested in different store
types (means ±SE)
Store types
0
Weeks after storage
4
12
28
“Ava”
Cribs
Mud silos
Polyethylene
bags
0.35±0.05a
0.32±0.04a
0.11±0.02b
0.08±0.02b
Number of M. nigrivenella
0.31±0.04a 0.13±0.03a
0.22±0.03b 0.11±0.02a
0.08±0.02c 0.09±9.02a
0.03±0.01c 0.0±0.0b
0.07±0.02a
0.04±0.01b
0.02±0.01b
0.0±0.0c
Overall
0.21±0.02a
0.17±0.02b
0.07±0.01c
0.03±0.01d
“Ava”
Cribs
Mud silos
Polyethylene
bags
26.0±11.14a
25.5±2.63a
11.0±6.46b
6.0±1.42b
Infestation (%)
25.0±4.20
9.0±3.11
18.0±8.13
10.5±1.71
7.5±4.27
7.5±2.22
3.0±1.0
0.0±0.0
7.0±3.70
3.5±1.71
1.5±0.96
0.0±0.0
Overall
16.75±3.66a
14.38±2.91a
6.88±2.02b
2.25±0.75c
Means within columns followed by the same letter(s) are not significantly different at P ≤ 0.05 (t-test)
Similarly, the damage caused by M. nigrivenella varied significantly with storage
structure and storage time. It was highest in “Ava” and lowest in polyethylene bags
(Table 5.8). In all storage structures, percent feeding damage tended to be constant during
storage except in “Ava” where it increased slightly from 0 to 4 weeks after storage and
then remains stable thereafter. Grain feeding damage by M. nigrivenella remained low in
the mud silo and polyethylene bags throughout storage. In the present experiment,
damage caused by beetles – mostly P. truncatus and S. zeamais – reached 37.5% in
“Ava”, 32.6% in cribs, and 21.5% in polyethylene bags after 12 weeks (data not shown
here).
89
Importance of Mussidia nigrivenella in storage
Table 5.8: Percentage grain damaged by M. nigrivenella in different stores (means
±SE)
store type
“Ava”
Cribs
Mud silos
Polyethylene bags
F
P
0
8.0±1.14a
7.45±1.93a
3.15±1.42b
2.45±0.28b
14.61
0.0013
Weeks after storage
4
12
10.3±1.15a 9.55±1.33a
6.4±1.27b 5.45±1.0b
2.75±1.23c 2.34±1.03c
2.07±1.01c 1.97±0.45c
22.54
31.61
0.0003
<0.0001
28
-*
-
Means within columns followed by the same letter(s) are not significantly different at P ≤ 0.05 (t-test). *
Percentage of grain damaged by M. nigrivenella was not measured at 28 weeks after storage because grains
were heavily infested with beetles.
The moisture content of the maize grains in all stores decreased from around 18%
to <12% after 12 weeks of storage and thereafter slightly increased to 13% (figure 5.
2).There was no difference in moisture content in grain between storage type across
sampling date (DF=3, F= 0.63, P=0.53), and neither at 12 (DF=3, F=1.76, P=0.18) and 28
weeks (F=0.98, P=0.14) after storage.
Moisture content of maize grain (%)
20
18
Ava
Cribs
Mud silos
Polyethylene Bags
16
14
12
10
8
0
4
8
12
16
20
24
28
32
Sampling time (weeks)
Figure 5.2: Moisture content of maize grain in the different store types
90
Importance of Mussidia nigrivenella in storage
Table 5.9: Effect of mixed infestations with storage beetles on Mussidia nigrivenella immature development and survival
(means ±SE)
Developmental time (days)
Larvae
Pupae
Total
Number of pupae
Pupae weight (mg)
M. nigrivenella alone
18.80±0.30c
10.17±0.33a
29.0±0.52b
18.11±0.21a
100.75±1.59a
M. nigrivenella + P. truncatus
20.53±0.62ab
10.13±0.22a
30.7±0.70ab
14.34±0.22b
89.13±0.90bc
M. nigrivenella + S. zeamais
19.44±0.32bc
10.21±0.25a
29.7±0.43ab
9.29±0.13c
93.00±2.55b
M. nigrivenella + both beetles
21.09±0.16a
10.30±0.12a
31.4±0.24a
7.95±0.25d
87.00±1.09c
F
6.78
0.09
4.33
426.35
13.30
P
0.0009
0.97
0.01
<0.0001
0.0004
Treatments
Means in column followed by the same letter(s) are not significantly different at P ≤ 0.05 (t-test)
Importance of Mussidia nigrivenella in storage
91
Laboratory experiment: effect of the presence of storage beetles on the development of
M. nigrivenella
In the presence of storage beetles, egg to pupae development time and, thus, total
development time increased significantly (DF =4, 44; F = 6.8; P = 0.0009 and F = 4.3; P
= 0.01) though developmental time of pupae was not affected (DF = 4, 44; F = 0.03; P =
0.98). Likewise, larval survival and numbers of Mussidia pupae was considerably
reduced in the presence of storage beetles (DF = 4, 44; F = 617.7; P<0.0001; Table 5.9).
Moreover pupae were heaviest in the M. nigrivenella only treatment (DF =, 4, 44;
F=13.30, P=0.0004).
Discussion
Sétamou (1999) found that the pest densities and grain damage increased with delay in
harvest indicating that in the field M. nigrivenella oviposits and develops on mature
maize cobs. In the present study, M. nigrivenella was found feeding on maize cobs after
more than 6 months of storage. The life cycle of M. nigrivenella is around 38 days (Bolaji
and Bosque-Pérez, 1998; Sétamou et al, 1999), thus theoretically allowing for several
overlapping populations on stored maize. The present experimental set-up, however, does
not allow for determining if the presence of M. nigrivenella at 6 months after storage was
due to re-infestation of stored maize or the result of an extended life cycle under storage
conditions; the scarcity of young larval stages indicates the latter. Also, grain damage
remained on a similar level up to the 12th week indicating that most of the grain damage
occurred at the beginning and that M. nigrivenella was not very active during storage.
This rather suggests low feeding activity by M. nigrivenella later in the storage season
indicating a delayed development of the borer under storage condition.
The reduction of M. nigrivenella densities with storage time could be due to adverse
environmental conditions (i.e. a combination of high temperature and low air and grain
moisture content). Most storage insects are able to survive and multiply rapidly on well
dried grain. However grain dried to below 12% mc inhibits the development of most
Importance of Mussidia nigrivenella in storage
92
species to some extent (FAO, 1994). As shown by Fields and Korunic (1999) the lower
moisture content of the grain, the greater mortality. Thus the moisture content below 13%
observed in the stores after 12 weeks of storage in this study probably affected the
survival of M. nigrivenella. However, since moisture contents did not vary between
storage types the differences of M. nigrivenella infestations were due to other factors, e.g.
varying levels of infestations of the grain by storage beetles, which also affected
populations growth rates of the borer. In the present surveys, a negative relationship
between the numbers of storage beetles such as P. truncatus, S. zeamais, Tribolium sp.
and M. nigrivenella infestations was observed. Similarly, the laboratory experiment
showed that the presence of the beetles increased larval development time and mortality.
This suggests a strong interspecific competition between the various grain-feeding
insects. Compton and Sherington (1999) found no M. nigrivenella larvae in maize cobs
heavily colonized by beetles. Storage pests such as the larger grain borer may
preferentially attack the germ of the grain, thus removing a large percentage of the
protein and vitamin content whereas weevils feed mainly on the endosperm removing
carbohydrates mostly (Khare and Mills, 1968; Subramanyam et al., 1987; Demianyk and
Sinha, 1988; Vowotor et al., 1998). It is suggested that poor quality grain would affect
the bionomics of M. nigrivenella. Larsen et al. (2005) describe how resource depletion
influences the per capita growth rate of insect species competing for the same resources;
for example, the reason responsible for S. zeamais’s rapid elimination of Sitotroga
cerealella (Olivier) (Lepidoptera: Gelechiidae) is its superiority in colonizing and
monopolizing new patches.
The varying levels of infestation observed in the present study could also be
explained by differences in initial egg/larval load between the different forms of stored
maize (i.e. with husks vs. dehusked, shelled etc.). In traditional “Ava” stores, in addition
to the larvae already present in the cob, eggs laid on the surface of the husk or silks as
observed by Sétamou (1999) may still hatch and attack the cobs. Although high mortality
of 90% of first two instars larvae are common (Moyal and Tran, 1991b), these additional
infestation would augment the number of M. nigrivenella present in the ear. By contrast,
in the cribs eggs and some of the hatched larvae might have been removed when the ears
were dehusked. Furthermore, the husks might form a protection to M. nigrivenella from
93
Importance of Mussidia nigrivenella in storage
adverse environmental effects and from general predators such as ants, and in addition
reduce attacks of the grain by storage beetles (Kossou et al., 1993).
Another important factor influencing population development is the temperature
in the granary and the aeration pattern both depending on the storage structures. Contrary
to the traditional “Ava” and the cribs, bags and mud silo are tightly closed allowing for
little aeration. In addition, in hermetically closed bags and mud silos where air diffusion
is prevented or reduced, the respiratory process of the biotic components in the bulk
(grains, fungi, insects, etc.) O2 and produces carbon dioxide CO2 (Bartosik et al., 2001).
This new atmosphere, rich in CO2 and poor in O2 might suppress, deactivate, or reduce
the reproduction and/or development capacity of lepidopterous insects such as M.
nigrivenella and other insects like bruchids as observed for hermetic storage of cowpea
seeds
using
triple
bagging
in
Cameroon
(http://www.entm.purdue.edu/entomology/research/cowpea/Extension%20bulletins/PDF
%20publications/Tripple%20Bagging.pdf). Furthermore, closed stores also form a barrier
to invading M. nigrivenella moths and storage beetles, which might partly explain the
differences in borer infestations between open and closed stores.
Although, M. nigrivenella did not cause considerable losses in stored maize, they
appear to be one of principal disseminators of fungi such as A. flavus and Fusarium sp. in
granaries. As shown by several authors, insect feeding renders the grain susceptible to A.
flavus infection, resulting in higher potential aflatoxin levels of grain in both field and
during storage (Sétamou et al., 1998; Hell et al., 2000; Fandohan et al., 2005). According
to Beti et al. (1995) humidity build-up might occur through convection and metabolic
activity of pests thereby increasing moisture levels permitting fungal spores to persist for
longer time in the granary and increase the risk of aflatoxin contamination. To overcome
this risk, maize should be dried below <15% water content to ensure unfavorable
conditions for fungal growth (Hell et al., 2000).
The present findings suggest that storing maize as bulk grains in closed structures
or polyethylene bags would reduce additional damage caused by M. nigrivenella in
storage. As shown for bruchids attacking cowpea seeds (Chauhan et al., 2002), solar
heating of the grain in polyethylene bags could also reduce initial infestations by M.
Importance of Mussidia nigrivenella in storage
94
nigrivenella and storage beetles. However, additional research is required to assess how
hermetically closed structures affect the build-up of aflatoxin producing fungi.
Acknowledgements
This study is part of a project funded by the Dutch Ministry of Foreign Affairs (DGIS).
The authors are grateful to the technicians of the Cereal Stem and Ear Borers Laboratory
at IITA-Benin.
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CHAPTER 6
Surveys for natural enemies of Mussidia spp and other pyralids in
Malaysia: perspectives of bio-control of the maize cob borer Mussidia
nigrivenella in West Africa
Komi Agboka1,2, Schulthess F., Laurence G. Kirton3, Manuele Tamò1 and Stefan Vidal2
1
International Institute of Tropical Agriculture 08 BP 0932 Tripostal, Cotonou Republic of Benin 08 BP
0932 Tripostal, Cotonou Republic of Benin. 2Georg-August-University Goettingen, Agricultural
Entomology, Grisebachstrasse 6, 37077 Goettingen Germany. 3 Forestry Research Institute Malaysia
(FRIM)
Correspondence E-mail: k.agboka@cgiar.org
(In preparation)
Abstract
In West Africa, the pyralid M. nigrivenella is a polyphagous pest, which besides maize
ears attacks cotton balls, Phaseolus beans, and the fruiting structures of many
economically important trees such as shea-butter tree (Butyrospermum parkii) and Parkia
biglobosa. In West Africa, natural enemies appear to play no role in the population
dynamics of the pest. It is hypothesized that parasitoids may regulate other Mussidia
species such as M. pectinicornella and other pyralids occurring in Malaysia on Parkia
speciosa. Surveys were therefore conducted in South-East Asia to assess the pest status of
Mussidia pectinicornella? or other pyralids on Parkia sp. and to identify promising
parasitoids to be introduced into West Africa. In Malaysia, P. speciosa pods were
subjected to serious borer attacks. Though pod infestations could reach 80% the percent
seeds attacked within a pod was less than 20%. The most common parasitoids were the
braconid Bracon spp. (64%), followed by the eurytomid Eurytoma sp. (32%) and the
pteromalid Sphaeripalpus sp. (4%). Overall, mortality caused by parasitoids reached
<40% hence they could be considered a key mortality factor in the population dynamics
of the Mussidia spp in Malaysia.
Keywords: Bracon spp., Malaysia, Mussidia spp., Parkia speciosa
Natural enemies of Mussidia spp. in Malaysia
101
Introduction
In West Africa, the pyralid M. nigrivenella (Ragonot) is a polyphagous pest, which
besides maize ears attacks cotton balls, Phaseolus beans, and the fruiting structures of
many economically important trees such as shea butter-tree (Butyrospermum parkii (G.
Don) Kotschy) (Sapotaceae) and Parkia biglobosa (Jacq.) Benth.) (Leguminosae) (Silvie
1990, Moyal and Tran 1991, Sétamou et al., 2000a). Though, pest incidence in maize
fields is usually more than 50%, yield losses range from 5 to 25% only (Moyal and Tran
1991, Sétamou et al., 2000b). However, M. nigrivenella continues to feed on maize
grains in stores leading to an additional 5% loss. In addition, grain damage by the borer
predisposes maize to pre- and post-harvest infestations by storage beetles and infections
by mycotoxin-producing moulds (Sétamou et al., 1998; Fandohan et al., 2005).
Currently, no technologies are available that provide satisfactory control of M.
nigrivenella. Pesticides and botanicals are only partly efficient due to the cryptic feeding
behavior of lepidopteran larvae in the ear (Sétamou et al. 1995, Ndemah and Schulthess
2002, Agboka et al. submitted). Intercropping maize with both host and non-host
companion crops or planting border rows with grasses reduced oviposition and larval
infestations of stem- and cobborers including M. nigrivenella; however, the results were
not consistent (Ndemah et al. 2002a, Agboka et al. 2006, submitted). Surveys on wild
and cultivated host plants of M. nigrivenella in West Africa and Mussidia spp. in Kenya
in East Africa, yielded a paucity of natural enemy species and low parasitism; from most
host plants no parasitoids were obtained and they appeared to play no role in the
population dynamics of the pest (Sétamou et al., 2002; Muli et al., 2008).
According to Janse (1941), five species of Mussidia occur in Africa and one species
in Asia but their taxonomic status and their distribution are not well known, and they are
not always considered as pests in their ecological zones (Muli et al. 2009). In Malaysia
and Thailand, Parkia speciosa Hassk., commonly called “petai” is an economically
important non-wood tree (Wooh and Poh, 1998). Its pods are consumed by the local
people. The pod-boring larvae of the pyralid moth Mussidia pectinicornella Hamps. and
the torticid moth Argyroploce illepida Btlr. were frequently reported to infest the ripening
seeds of P. speciosa (Kalshoven, 1981).
Natural enemies of Mussidia spp. in Malaysia
102
The main objective of the present work was to conduct surveys of Mussidia spp. or
other pyralids and their parasitoids on Parkia spp. in Malaysia to identify potential new
association parasitoids for introduction into West Africa.
Materials and Methods
In 2005, from August to September, Parkia pods were collected from whole-sell markets
in different States of Malaysia. Depending on the market size and the number of pods
sellers, 1-5 sellers were chosen and 20-100 pods (five to twenty inflorescences) were
randomly selected from each seller.
The samples collected were brought to the laboratory of the Forest Research Institute
Malaysia (FRIM) and dissected. All larvae collected were maintained in the seeds
attacked from the pod and put in rectangular boxes (10cm x 15 cm x 10 cm). Late instars
larvae were maintained on an artificial diet developed for M. nigrivenella by Bolaji and
Bosque-Pérez, (1999). The larvae were reared to adulthood to record parasitism. The
identification of the moths is not yet done however, samples were sent to a pyralid
specialist in Germany. Larval parasitoids collected were identified by Dr Georg Goergen
at the International of Tropical Agriculture Museum (IITA, Benin). The number of larvae
per pod, percent pod infestation in each site surveyed, percent seed infestation in each
pod and the number of parasitoid pupae on dead larvae were determined. In each location
parasitism was defined as the number of parasitoid pupae collected on dead larvae per
total number of larvae collected).
Results
Incidence and level of infestation
Lepidopteran species were found infesting P. speciosa. Parkia pod infestation ranged
from 21.6% to more than 82.2% while seed infestation varied from 1.9% to less than
19.6% (Table 6.1). Two to three larvae could be frequently found in one pod. The mean
number of larvae was 1.32 per pod. But each seed bore only one larva.
103
Natural enemies of Mussidia spp. in Malaysia
Table 6.1: Infestation by Parkia pod borers and their parasitism in different
localities of Peninsular Malaysia and pod originated from Thailand
Seed infestation
Pod infestation
Number of
Pod origin
(%)
(%)
larvae/pod
Parasitism (%)
Pasar Borong
Thailand
Tapah
Gombak
Bidor
Kampung
Seri Menanti
KampungIbol
19.6
19.5
14.9
7.3
9.1
9.3
1.9
9.8
81.2
67.6
21.6
50.4
39.4
47.0
28.6
37.5
1.53
1.43
2.13
1.0
1.03
1.39
0.29
1.08
2.2
21.3
10.2
0
6.0
4.5
0
38.4
All lepidopteran larvae recorded showed the same feeding behaviour: first they feed
on the tip of the green kernel beginning to destroy the germ and then the cotyledon
leaving frass in the seed (Photo 6.2). Late instars larvae, tunneled through the seed and
escaped from leaving an exit hole. In the case of heavy infestation, the whole seed from
the inside is consumed. During the survey no eggs and pupae were observed.
Some hymenoptera were also found infesting the pods but their damage was not
important and limited to the perisperm.
Photo 6.1: Parkia pod borer
Photo 6.2: Damage by the pod
borer
104
Natural enemies of Mussidia spp. in Malaysia
Parasitism
Three larval parasitoids were found parasitizing the 3-4 instars larvae. In Malaysia,
parasitism ranged from 2.2 to 38.4%, while in Thailand it was 22% (Table 6.2). Three
genera were identified, namely Bracon spp. (Hym.: Braconidae) accounted for 64%,
Sphaeripalpus sp. (Hym.: Pteromalidae (4%) and Eurytoma sp. (Hym.: Eurytomidae)
(32%). Neither egg nor pupal parasitoids were observed.
Table 6.2: Larval parasitoids recorded on borers infesting Parkia speciosa in
Malaysia
Parasitoid species
Order: Family
Bracon sp.
Hymenoptera: Braconidae
Sphaeripalpus sp.
Hymenoptera: Pteromalidae
Eurytoma sp
Hymenoptera: Eurytomidae
Discussion
In Malaysia P. speciosa is subjected to serious borer attacks. They caused considerable
amount of damage in the infested seed, rendering it unfit for consumption. Although the
larvae were not yet identified it appear that there might be two different species indicated
by the two different colours of the late instar larvae. Reports on pest infestation on Parkia
spp. in india and Malaysia (Kolshoven, 1981) indicated that the pod-boring larvae of the
pyralids moths M. pectinicornella Hamps. and the torticid moth, Argyroploce illepida
Btlr.
infest
the
ripen
seeds
in
the
field
(http://www.worldagroforestrycentre.org/sea/Products/AFDbases/af/asp/SpeciesInfo.asp?
SpID=1258 [Accessed 2009 Jan 14) while the crambid Cadra cautella Walker infested
the stored seed of Parkia spp. (Thanglam et al. 2003). Mussidia ssp infesting P. speciosa
will be confirmed by an accurate identification using molecular tools.
During the three weeks survey, no pupae were found suggesting that the pod borer
infests the pods when they matured and ripe and that the survey period was too short to
Natural enemies of Mussidia spp. in Malaysia
105
observed all different instars including the pupae. This indicated that larval duration is
more than three weeks on Parkia. In the laboratory larvae collected took more than 40
days to become pupae in the seeds as also observed by Thanglam et al. (2003).
Parasitoids, not yet known at species level, were found regulating the borers’
damages as indicated by preliminary survey conducted by Jiraporn (2004, personal
communication) in Thailand on Parkia pod borer. Sétamou et al. (1999) also found
Bracon sesamiae parasitizing the maize cob borer M. nigrivenella in West Africa.
Although the parasitism was low in some localities the wasps appeared to have potential
to reduce moth populations. But one shortcoming is that to date the genus Bracon
encompasses 573 described species. This may render the identification to species level
very tedious. Sphaeripalpus spp. belonging to the Miscogasterinae, which are parasitoids
of Diptera burrow in or mining the soft tissues of plants. Eurytoma spp. can display
phytophagous or parasitic habits. In some instances members of this genus are
hyperparasitoids of Braconidae attacking larvae of Lepidoptera. Although these
parasitoids are adapted to the climatic condition similar to the one in West Africa giving
a prospect for new association for M. nigrivenella, an accurate identification of their
Phycitinae hosts including Mussidia sp. coupled with suitability tests should be done
before the use in the bio-control of the maize cob borer.
Acknowledgements
The authors are grateful to Dr Jiraporn, P. Entomologist at National Research Center of
Thailand (NRCT), who sent us specimen from Thailand and to Dr. Goergen Georg for
identifying the parasitoids.
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Sétamou, M., Schulthess, F., Poehling, H.-M. and Borgemeister, C. 2000. Monitoring and
modeling of field infestation and damage by the maize ear borer Mussidia
nigrivenella Ragonot (Lepidoptera: Pyralidae) in Benin, West Africa. Journal of
Economic Entomology 93, 650-657.
Silvie, P. 1993. Nouvelles données sur Mussidia nigrivenella Ragonot Lepidoptera:
Pyralidae) au Togo. Insect Science and its Application 14, 643-649.
Thanglam R., Damayanti, M. and Sharma, G.J. 2003. Cadra cautella Walker
(Lepidoptera: Crambidae: Phycitinae) – a pest on Parkia timoriana (DC.) Merr. In
Manipur. Current Science 85 (6), 25
Woon, W.C. and Poh, L.Y. 1998. The economic value of Parkia speciosa (petai) in
Peninsular Malaysia. Forestry Department, Peninsular Malaysia and Forest Research
Institute, Malaysia. 78 pp.
CHAPTER 7
General discussion
Maize is an important component of the farming systems and the diet of many people,
and is increasing in importance as it expands into the drier savanna zones of West Africa.
However, the stability of maize production in West Africa is limited, among others, by
cob boring pests. The cob borer, Mussidia nigrivenella Ragonot (Lepidoptera: Pyralidae)
is one of the key borers attacking directly the maize grain in West Africa (Bosque-Pérez
& Mareck 1990; Shanower et al. 1991, Moyal & Tran 1991). Its biology and ecology
have been well studied (Sétamou, 1999). However, no detailed control strategies have
been developed against the pest. Management approaches developed in the present study
focused on botanical formulations with special emphasis on neem and Jatropha curcas,
habitat
management
particularly
maize-legume
intercropping,
trap
crops
and
redistribution or new association as biological control for sustainably controlling the
maize cob borer M. nigrivenella.
As shown for stemborers by Schulthess et al. (2004) and Chabi-Olaye et al. (2005)
intercropping reduced attacks of maize ears by M. nigrivenella and other stemborer
species that feed in the ear. In the present study, the most effective intercrops in reducing
M. nigrivenella attacks in the different locations were the jack bean Canavalia and
Tephrosia. According to Sétamou et al. (1999), jackbean was the most suitable host plant
for M. nigrivenella development. The high suitability of this cover crop for M.
nigrivenella development and survival compared to maize might have direct effects on
the population dynamics of M. nigrivenella in maize by reducing its density as observed
in this study. The cob borer would lay more eggs and survive more on matured pods thus
preventing high infestation of maize cobs. The low number of M. nigrivenella observed
in Maize-T. vogelii intercrop is probably due to the repulsive effect of T. vogelii. In a
semi-field study, oviposition of Mussidia was reduced by the leaf extract of T. vogelii
(Agbodzavu 2005, cf. chapter 4). Moreover these results suggest that the attractiveness or
deterrence of the legumes intercropped with maize further increased the effectiveness of
intercropping in suppressing lepidopterous insects on maize ear. Visual and chemical
General Discussion
109
stimuli from the host and non-host plants might also affect the rate at which insects
colonize habitats, and their behavior in those habitats (Risch 1983, Ndemah et al. 2003).
Moreover in an intercrop, the primary host plant is made less attractive to the herbivore,
and this may depend on the kind of cues, either olfactory or tactile perceived by the
insect. Volatiles emanating from plant tissues had been reported to influence
attractiveness of the plant (Elzen et al. 1984, Udayagiri and Jones 1992), which may have
also played vital role in this experiment. This study showed that an intercropping system
with host plants of M. nigrivenella could be developed, in a ‘push-pull’ strategy (Khan et
al. 1997) for the control of M. nigrivenella in small-scale maize farming systems. This
strategy will involve C. ensiformis as the highly susceptible trap plants (pull) and
Tephrosia vogelii as repellent intercrop (push) (cf. Chapter 3).
The data reported in chapter 3 indicate that the presence of leguminous crops in the
vicinity of maize fields do not aggravate M. nigrivenella infestations on maize,
irrespective of when the legume was planted in relation to maize, and irrespective of the
status of the legume species as a host. Thus, although the suitable host C. ensiformis had
up to 1800 times higher pest loads than maize, there appeared to have been no movement
of M. nigrivenella to maize. Also, maize surrounded by C. ensiformis planted four weeks
before, had lower pest loads expressed as cumulative feeding days as compared to the
control. This indicates that C. ensiformis was much more attractive to the ovipositing
moth than maize. The fact that during the minor season C. ensiformis planted 4 weeks
before maize had an effect on pest loads on maize while when planted 1, 3 in the main
season or 8 weeks before in minor season it did not, suggests that the growth stage and/or
canopy density of the plants affected the attractiveness of the leguminous crop to the
ovipositing moth. As shown by Ritchie (2000) and Haddad et al. (2001), the amount of
above-ground plant biomass, which however was not assessed in the present experiment,
may have a strong effect on insect abundance. Furthermore the volatile profile of plants
changes with the growth stage (Batten et al. 1995; Zhang et al. 2008), which might affect
the oviposition behaviour of the moth. A more efficient technique for reducing borer
densities on maize proved to be the intercropping of non-host species with maize,
because the presence of the non-host plants hampers host finding by the ovipositing
moth, and thus reduce the number of egg batches deposited on maize (Ndemah et al.
General Discussion
110
2003; Schulthess et al. 2004; Chabi-Olaye et al. 2005b; Wale et al. 2007; Songa et al.
2007. The major finding of the present study is that the presence of leguminous cover
crops or grain legumes in the vicinity of maize fields did not increase M. nigrivenella
densities on maize. Moreover, as shown by Chabi-Olaye et al. (2005a), grain legumes
and cover crops enhance yields and reduce yield losses in maize crops subsequently
planted in the same field by improving plant vigor. It is obvious that a single control
option will not produce satisfactory control of the complex pest problem caused by
lepidopteran maize pests, and as proposed by Chabi-Olaye et al. (2006) an IPM package
including crop rotation with leguminous cover or grain crops or direct application of
synthetic fertilizer, mixed cropping and timely applications of insecticides or botanicals
targeting not only M. nigrivenella but all stem- and earborers is required.
Field and lab experiments showed that oil emulsions of A. indica and J. curcas oils
act not only as oviposition deterrent but also as ovicides (cf. chapter 4). Possible
inclusion of botanicals into integrated M. nigrivenella control has good prospects. The
results of field’s trials showed that larval population of M. nigrivenella can be
significantly reduced through the application of oil emulsions of A. indica and J. curcas,
which were as efficient as Furadan 5 G. Neem oils and pure compounds of neem have
been found to exhibit ovipositional deterrent effects on many crops pests including
lepidopteran, homopteran and dipteran species (Singh and Singh, 1998, Schmutterer
1990, Isman 1996, Bruce et al. 2004, Showler et al., 2004). According to Udayagiri and
Mason (1995) chemical cues play a major role in host selection. In the ovipositional test,
M. nigrivenella tended not to oviposit on maize plants treated with the oils indicating a
repellent effect.
Mussidia nigrivenella was found feeding on maize cobs after more than 6 months of
storage, suggesting that the borer not only completes its development but also reproduces
under storage conditions (cf. chapter 5). However the densities of M. nigrivenella in
stores decreased with storage duration. These reductions in pest infestations were due to
many factors such adverse environmental conditions (i.e. a combination of high
temperature and low air and grain moisture content), the presence of storage beetles
mainly Sitophilus zeamais and Prostephanus truncatus, and the storage systems. Our
findings suggest that storing maize as bulk grains in more hermetic structures or
General Discussion
111
polyethylene bags rather than in traditional “ava” or cribs would reduce additional
damage caused by M. nigrivenella in storage but care should be taken concerning the
moisture content of the grains which could increase the fungal infections.
In search for natural enemies to be introduced in West Africa against M.
nigrivenella, three parasitoids were found parasitizing M. pectinicornella and sympatric
species infesting Parkia speciosa in Malaysia (Chapter 6). Although these parasitoids and
the one found in East Africa (Muli et al. 2009) are adapted to the climatic condition
similar to the one in West Africa giving a prospect for new association for M.
nigrivenella, suitability tests should be done before the use in the bio-control of the maize
cob borer.
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115
ACKNOWLEDGEMENTS
This project was funded by the Dutch Ministry of Foreign Affairs (DGIS), Netherlands.
The three month research and study grant from the German Academic Exchange Service
(DAAD) to me was an important financial support to complete this Thesis.
I am most indebted to my supervisor Dr. Manuele Tamò for the initiation of the project
and giving me the opportunity to gain professional experience through the management
of the project and during the practical work.
My heartfelt thanks go to Prof. Dr. Stefan Vidal for accepting to be my university advisor
and first referee. His consistent collaboration and advices are highly appreciated.
My sincere gratitude goes to Dr. Fritz Schulthess, co-supervisor of this research work,
who followed my progress through valuable discussions, comments and suggestions.
I wish to thank Dr. Chabi-Olaye Adenirin for statistical assistance and for critically
reviewing early version of most chapters of the present dissertation.
I am grateful to the technicians Ogouchi Edouard and Massin Medard of the Cereal Stem
and Ear Borers Laboratory, the administration staff and associated scientists at IITABenin.
I express my deepest thanks to my family especially my brothers, Agboka Agbeko Kodjo
and Mebo Lievin who never give up encouraging me to make my dream true and also to
my wife Georgette Essotena and our lovely daughter Merveille Seyram who endured the
periods of my absence from home in Togo, with remarkable fortitude.
116
List of publications
1) Agboka, K., Schulthess, F., Chabi-Olaye, A., Labo, I., Gounou, S. & H. Smith
(2002). Self-, intra, and interspecific host discrimination in Telenomus busseolae
Gahan and T. isis Polaszek (Hym.: Scelionidea), sympatric egg parasitoids of the
African cereal stem borer Sesamia calamistis Hampson (Lep.: Noctuidae).
Journal of Insect Behavior 15: 1-12).
2) Agbéko K., Tounou, Komi Agboka, Katharina Raupach, Hans-Michael Poehling
and Christian Borgemeister, 2002. Entomopathogenic fungi and an egg parasitoid:
can they collaborate? New strategies for biological control of the greenhouse
leafhopper Empoasca decipiens Paoli. Poster presented at the 2002 ESA Annual
Meeting and Exhibition. Fort Lauderdale, FL.
3) Komi Agboka, Agbeko Kodjo Tounou, Hans-Michael Poehling, Katharina
Raupach & Christian Borgemeister 2003. Searching and oviposition behaviour of
Anagrus atomus L. on four host plants of the green leafhopper Empoasca
decipiens, Journal of Insect Behavior, vol 16, no 5, 667-678)
4) Komi Agboka, Agbeko Kodjo Tounou, Hans-Michael Poehling, Katharina
Raupach & Christian Borgemeister, 2004. Life-table study of Anagrus atomus L.
(Hymenopera: Mymaridae), an egg parasitoid of the leafhopper Empoasca
decipiens Paoli (Homoptera: Cicadellidae) BioControl 49: 261-275.
5) Tounou A.-K., Agboka, K., Poehling, H.-M., Raupach K., Langewald, J.,
Zimmermann, G. & Borgemeister, C. 2003. Evaluation of the Entomopathogenic
Fungi
Metarhizium
anisopliae
and
Paecilomyces
fumosoroseus
(Deuteromycotina: Hyphomycetes) for Control of the Green Leafhopper
Empoasca decipiens (Homoptera: Cicadellidae) and Potential Side Effects on the
Egg Parasitoid Anagrus atomus (Hymenoptera: Mymaridae). Biocontrol Science
and Technology vol 13, no 8, 715-728.
6) Komi Agboka, 2005. Is biological control a viable option to African farmers?
African Technology Development Forum (ATDF) Journal, Volume 2, Issue 1
117
7) Komi Agboka, Gounou Saka and Tamò Manuele. 2006. The role of maizelegumes-cassava intercropping in the management of maize ear borers with
special reference to Mussidia nigrivenella Ragonot (Lepidoptera: Pyralidae).
Annales de la Société Entomologique de France, 42 (2-3).
8) Komi Agboka, Fritz Schulthess, Manuele Tamò and Stefan Vidal. The effect of
leguminous cover crops and cowpea planted as border row on maize ear borers
with special reference to Mussidia nigrivenella Ragonot (Lepidoptera: Pyralidae).
(Submitted to Phytoparasitica)
9) Komi Agboka, Agbodzavu K. M., Tamò, M. and Vidal, S. Effects of Tephrosia
vogelii Hook (Leguminosae), Hyptis suaveolens L. (Lamiacae) extracts and oils
Emulsion of Neem and Jatropha curcas L. (Euphorbiacae) on the maize ear borer
Mussidia nigrivenella Ragonot (Lepidoptera: Pyralidae) in the field and
laboratory. (Submitted to International Journal of Tropical Insect Science)
10) Komi Agboka, Fritz Schulthess, Manuele Tamò, Kerstin Hell and Stefan Vidal.
The importance of Mussidia nigrivenella Ragonot (Lepidoptera: Pyralidae) as
post-harvest pest in different storage structures in Benin. (Submitted to Journal of
Stored Products Research).
11) Komi Agboka, Fritz Schulthess, Kirton, L.G., Manuele Tamò and Stefan Vidal.
Surveys for natural enemies of Mussidia spp. and other pyralids species in
Malaysia: perspectives of bio-control of the maize cob borer Mussidia
nigrivenella in West Africa (In preparation).
118
CURRICULUM VITAE
Name:
Date of Birth:
Place of Birth:
Nationality:
Marital situation:
Sex:
Address:
AGBOKA Komi
31. 12. 1971
Gati-Soun (Republic of Togo, West Africa)
Togolese
Married with one daughter
Male
International Institute of Tropical Agriculture (IITA)-Benin,
08 BP 0932 Tripostal Cotonou Benin
Tel: +229 21 35 01 88/ Fax: +229 21 35 05 56
E-mail: k.agboka@cgiar.org; zagboka@hotmail.com
SUMMARY OF EDUCATION
2006-2009: PhD Student, Georg-August University, Goettingen
2000-2002: M.Sc., in Horticulture, University of Hanover, Institute of Plant diseases and
Plant protection (IPP)
1992-1998: Agronomy, Faculty of Agriculture, University of Lomé-Togo.
1983-1991: Secondary School, Tabligbo, Togo
1977-1983: Primary School, Gati-Soun, Togo
WORK EXPERIENCE
Since 2007: Consultant of the International Center of Insect Physiology and Ecology
(ICIPE)-Kenya at IITA-Benin.
Sept. 2003 – Sept. 2006: APO, Entomologist/Ecologist at IITA-Benin
June 1998 – August 2000: Research Associate at IITA- Benin
TRAININGS
08 – 21 March 2009: International DAAD Alumni Summer School 2009 in “Post Harvest
technologies –High Tec for food security and food safety”, Cologne and
Goettingen - Germany
11 August – 01 September 2001: Laboratory training course on vegetable leafhopper and
leafhopper egg parasitoids biology, ecology and behavior at Imperial College
at Wye (London, UK), Department of Ecology and Entomology.
04 March – 31 March 2001: Training course on formulation and optimization of
pesticides at Bayer Ltd. Leverkusen (Germany), Department of Plant
Protection.
119
Declaration
I, Komi, Agboka, hereby declare, that the work presented in this thesis is my own and has
not been submitted for a degree in any other University.
K. AGBOKA
I certify that, this thesis has been supervised by:
Prof. Dr. Stefan VIDAL
Dr. Manuele TAMÒ
Dr. Fritz SCHULTHESS