Journal of Nematology 35(3):259265. 2003.

The Society of Nematologists 2003.

Efficacy of Steinernematid Nematodes Against Three Insect Pests of

Crucifers in Quebec1
G. Belair,2 Y. Fournier,2 and N. Dauphinais2
Abstract: Steinernematid nematodes were evaluated against the three major cruciferous insect pests: the imported cabbageworm
Artogeia rapae, the diamondback moth Plutella xylostella, and the cabbage looper Trichoplusia ni. LC50 values of S. carpocapsae All, S.
feltiae UK, S. feltiae 27, and S. riobrave 335 were 18.2, 3.6, 5.7, and 8.3 on A. rapae L2; 24.5, 2.3, 6.0, and 15.5 on P. xylostella L3; and
10.1, 4.7, 9.5, and 7.8 on T. ni L2, respectively. Insect mortality from the nematode species and isolates was modulated by
temperature. Maximum mortality (100%) was recorded for A. rapae L2 from S. riobrave at 30 C, 95.8% from S. feltiae, and 91.7% from
S. feltiae 27 at 25 C and 75.7% from S. carpocapsae at 30 C. Mortality of A. rapae L2 increased with contact time to nematode.
Mortality of 76% and 78% was achieved for S. carpocapsae and S. feltiae, respectively, after 12-hour exposure. Susceptibility of A. rapae,
P. xylostella, and T. ni larvae to entomopathogenic nematodes increased with larval age development. The addition of adjuvants
Corn Oil (0.9%, 1.8%, 3.6%), Leafshield (3.0%, 6.0%, 12.0%), Seaweed (0.1%) and Agral (0.05%) significantly increased the
density and survival rate of S. carpocapsae on cabbage leaves compared to water only. At 20 C and 70% relative humidity (RH),
survival rates of S. carpocapsae All, S. feltiae UK, and S. riobrave 335 on cabbage leaves were 43%, 2%, and 0% after 4 hours following
application. Under field conditions, foliar applications of S. carpocapsae provided 35.3% and 33.0% control of A. rapae (L3-L5) on
Brussels sprouts and broccoli in 1996 and 24.9%, 19.4% and 14.9% on Brussels sprouts, broccoli, and cauliflower, respectively, in
1999. Based on our field results, foliar applications of S. carpocapsae do not provide an acceptable level of A. rapae control under
Quebecs environmental conditions.
Key words: Artogeia rapae, cabbage looper, diamondback moth, entomopathogenic nematodes, foliar application, imported cab-
bageworm, Plutella xylostella, Trichoplusia ni.

In North America, three lepidopterous species com- lated, and applied as biopesticides (Kaya and Gaugler,
monly occur on cruciferous crops: the imported cab- 1993).
bageworm, Artogeia (=Pieris) rapae (L.) (Lepidoptera: Infectivity of steinernematid and heterorhabditid
Pieridae); the diamondback moth, Plutella xylostella (L.) species has been documented against a broad range of
(Lepidoptera: Plutellidae); and the cabbage looper, insect pests in a variety of habitats with some successes
Trichoplusia ni (Hubner) (Lepidoptera: Noctuidae) but also with many failures (Begley, 1990; Belair et al.,
(Chagnon et al., 1990; Harcourt, 1963). These species 1999; Jaques, 1967; Kaya and Gaugler, 1993; Morris,
are potential pests for many cruciferous crops in Que- 1985; Wang and Li, 1987). Foliar applications of EPN
bec, which is the second most important production were generally not effective in reducing insect pest
area of crucifers in Canada (Harcourt, 1963; Richard populations (Begley, 1990) because nematodes are
and Boivin, 1994). In Quebec, insecticide applications adapted to the soil environment. The exposure of EPN
are the major control technique used against crucifer- on foliage to extreme temperature (Grewal et al., 1994;
ous pests (Chagnon et al., 1990). Alternative control Kaya, 1990; Molyneux, 1984, 1985), ultraviolet (UV)
measures such as biopesticides are needed to avoid in- light (Gaugler and Boush, 1978; Gaugler et al., 1992),
sect resistance to pesticides and hazards to the environ- and rapid fluctuation in moisture that causes desicca-
ment. tion (Baur et al., 1995; Simons and Poinar, 1973; Wom-
Entomopathogenic nematodes (EPN) are symbioti- ersley, 1990) reduces their potential as biocontrol
cally associated with the bacteria Xenorhabdus spp. and agents against foliage-feeding insects. Accordingly, EPN
Photorhabdus spp. When these bacteria are released into applied to foliage must be protected from these detri-
the insect hemocoel, they cause septicemia and death mental environmental effects by avoiding high tem-
of the insect in 24 to 48 hours (Kaya and Gaugler, perature and UV radiation with evening applications
1993). EPN, especially in the Steinernematidae, have a (Gaugler and Boush, 1978; Wang and Li, 1987) and
great potential as biological control agents against ag- desiccation by using adjuvants or antidesiccants (Baur
ricultural and horticultural insect pests because of their et al., 1997; Glazer and Navon, 1990). These additives
wide host range (Cabanillas et al., 1994; Poinar, 1990). are useful when nematodes are applied to waxy and
Furthermore, they can be easily mass-produced, formu- glaborous leaves such as many cruciferous crops (Baur
et al., 1997; Wang and Li, 1987).
In this study, we investigated the susceptibility of A.
rapae, P. xylostella, and T. ni larvae to EPN in laboratory
Received for publication 9 October 2002. and greenhouse trials and evaluated the efficacy of fo-
1
This is contribution No. 335/2003.07.01R of the Horticultural Research liar applications against A. rapae under natural field
and Development Centre, Agriculture and Agri-Food Canada, Saint-Jean-sur-
Richelieu, Quebec, Canada J3B 3E6. conditions in cruciferous crops.
2
Horticultural Research and Development Centre, Agriculture and Agri-
Food Canada, 430 Gouin Blvd., Saint-Jean-sur-Richelieu, Quebec, Canada J3B
3E6.
Materials and Methods
The authors thank Nicole Simard for dedicated technical assistance.
E-mail: belairg@agr.gc.ca
Nematodes: For laboratory and growth chamber ex-
This paper was edited by S. Patricia Stock. periments, the EPN strains Steinernema carpocapsae All, S.
259
260 Journal of Nematology, Volume 35, No. 3, September 2003

feltiae 27, and S. riobrave 335 were obtained from Biosys Effect of temperature on efficacy of EPN: The effect of
(Palo Alto, CA), and S. feltiae UK was obtained from temperatures (15, 20, 25, and 30 1 C) on EPN against
MicroBio Limited (Hertfordshire, UK). The nematodes A. rapae L2 was assessed. Nematodes were inoculated at
were cycled on Galleria mellonella larvae by the method the rate of 100 IJ per larva in 0.6 ml water. Thirty larvae
of Dutky et al. (1964), and infective juveniles (IJ) were per nematode species and temperature were used. This
stored at 5 1 C up to 1 month before use. Percentage experiment was carried out four times for each combi-
viability, based on movement in water, was determined nation of nematode and temperature for a total of 120
with a dissecting microscope. The J2 were not used if larvae per treatment. Petri dishes were incubated in
their viability was lower than 75%. Nematode concen- growth chambers in the dark with 70% RH. Mortality
trations were adjusted according to their viability level. was noted at 36 hours after contact between the insect
For field experiments, the nematode supply of S. carpo- and the nematodes.
capsae was obtained from Biosys (BioVector) and Micro- Effect of contact time: The effect of contact time of A.
Bio Limited in 1996 and 1999, respectively. rapae L2 with S. carpocapsae All and S. feltiae UK was
Insects: Three insect pests of crucifers were used in evaluated. Nematodes were inoculated at the rate of
this study: the imported cabbageworm (Artogeia rapae 100 IJ per larva in 0.6 ml water. Thirty insects were used
(L.)), the diamondback moth (Plutella xylostella (L.)), for each nematode species and exposure time. The ex-
and the cabbage looper (Trichoplusia ni (Hubner)). Ar- periment was performed four times. After 0, 1, 2, 4, 6,
togeia rapae was reared on a wheat-germ diet (Webb and 8, 10, and 12 hours of exposure to nematodes, all in-
Shelton, 1988), P. xylostella was cultured on a wheat- sects were transferred to nematode-free dishes with a
germ-based artificial diet (Biever and Boldt, 1971), and cabbage leaf disk, and mortality was recorded after an
T. ni was maintained on a modified pinto bean diet additional 72 hours.
where myacin was replaced by aureomycin (Glass and Insect stage: The efficacy of S. carpocapsae All against
Roelofs, 1985). Insects were reared between 21 to 27 C different larval stages of A. rapae L2-L3-L5, P. xylostella
depending on the species, with a 16-hour light/8-hour L3-L4, and T.ni L2-L3 was tested. All larvae were exposed
dark photoperiod and at about 65% relative humidity to S. carpocapsae All at the concentrations of 0, 5, 25, 50,
(RH). 100, 200 IJ per larva in 0.5 ml of water except for A.
Plants: Broccoli (Brassica oleracea L. var. italica cv. Em- rapae, where the rate of 200 IJ was not used. For A. rapae
peror), Brussels sprouts (Brassica oleracea L. var. gemmi- the experiment was performed three times for a total of
fera cv. Jade Cross), cabbage (Brassica oleracea L. var. 120 larvae per treatment, and in the case of P. xylostella
capitata cv. Bartolo), and cauliflower (Brassica oleracea L. and T. ni only one experiment was carried out for a
var. botrytis cv. White-Rock) were grown in individual total of 40 larvae per treatment. Percentage mortality
4-liter pots containing a 50:50 mixture of sand and or- data were recorded after 72 hours.
ganic soil. The greenhouse temperature was main- Growth chamber experiments: All growth chamber
tained at 20 C, with a light regime of 16 hours light/8 experiments were conducted in the dark at 20 1 C,
hours dark. Broccoli, Brussels sprouts, cabbage, and 70% RH.
cauliflower were grown until they had 10, 20 to 22, 18, Persistence on leaves: Steinernema carpocapsae All, S. fel-
and 10 leaves, respectively. tiae UK, and S. riobrave 335 were sprayed on the foliage
Laboratory conditions: Petri dishes (5-cm-diam.) lined of cabbage plants (10 leaf stage) cv. Bartolo at the rate
with Whatman No. 1 filter paper were used for all labo- of 2,000 IJ/ml with Agral 0.05%. For each nematode
ratory experiments. Nematodes were always deposited species, six plants were used. Each plant was sprayed
on the filter paper in 0.5 or 0.6 ml water. Insect larvae until runoff with a manual 1-liter plastic sprayer. The
were transferred individually into each petri dish with a survival rate was estimated after 0, 1, 2, 4, 8, and 12
cabbage leaf disk (1-cm-diam.) as a food source. Cab- hours following application time. At these time points,
bage leaf disks were cut from cabbage grown in the three leaves were randomly sampled on the same seed-
greenhouse. All experiments were carried out in the ling. Each leaf was punched once to obtain a leaf disk of
dark at 20 1 C, 70% RH, unless otherwise specified. 5.5-cm diam. Three leaf disks from the same plant were
Pathogenicity of four EPN: Steinernema carpocapsae All, S. washed on both sides by applying approximately 60 ml
feltiae 27, S. feltiae UK and S. riobrave 335 were tested of water from a wash bottle. The water containing
against A. rapae second instar (L2), P. xylostella third nematodes was recovered in a glass tube topped with a
instar (L3), and T. ni second instar (L2). Forty larvae for glass funnel. Following a 2-hour settling period, the
each insect species and nematode species combination nematodes were concentrated by removing the super-
were used. Steinernema riobrave 335 and S. carpocapsae All natant. The number of living and dead nematodes were
were tested at the rate of 0, 5, 25, 50, 100, 200 IJ per recorded after 24 hours.
larva. An additional rate of one IJ per larva was applied Adjuvants: The effect of six adjuvants on the survival
for S. feltiae 27 and UK to the listed insects. This experi- of S. carpocapsae All on cabbage leaves was tested. These
ment was conducted three times (n = 120). Mortality were: Agral 90 (Syngenta International AG, Basel, Swit-
data were recorded after 72 hours. zerland), Seaweed Acadie (Distrival Canada, Fortier-
 Entomopathogenic Nematodes Against Crucifer Pests: Belair et al. 261

ville, Quebec), Citowett Plus (DuPont, Mississauga, On- 48 hours after nematode application by determining
tario), Corn Oil (United Agri Products, Dorchester, the number of living and dead A. rapae larvae per plant.
Ontario), Leafshield (Aquatrols Corp. of America, A larva was scored dead if it failed to respond to me-
Cherry Hill, NJ), and Super Spread (Wilbur-Ellis, San chanical stimulation. All recovered larvae were depos-
Francisco, CA). Each adjuvant was tested at three con- ited in multicell plates and returned to the laboratory
centrations. Aqueous solutions of the various adjuvants for observation. One week later, larvae were dissected
were mixed with the nematode suspension to provide a to observe the presence or absence of nematodes inside
nematode concentration of 2,000 IJ/ml. The solutions the cadavers.
were sprayed on the leaves with a 1-liter plastic hand Air temperature and relative humidity data were
sprayer until runoff on the foliage of cabbage plants monitored at 2 m from the soil surface and provided
(10-12 leaf stage) cv. Bartolo. Six plants were used for from a weather station located on the experimental
each treatment (adjuvant x concentration). A water farm, approximately 0.5 km from the study site.
control was included. After 12 hours, three leaves were Statistical analysis: LC50 values for each insect species
randomly sampled on each plant. The nematode recov- were computed with a Probit analysis (Polo-PC, LeOra
ery and survival estimate methods follow the same pro- Software, Berkeley, CA). Mortality or survival data were
cedures as described in the previous experiment. transformed with arcsin (x) and were analyzed by
Field experiments: The efficacy of foliar applications of analysis of variance (ANOVA) followed by the Waller-
S. carpocapsae against A. rapae in the field was assessed Duncan k-ratio t-test (Proc GLM, SAS Institute, Cary,
on Brussels sprouts, broccoli, and cauliflower at the NC). Data are expressed as percentage mortality or sur-
experimental farm of Agriculture and Agri-Food vival means with standard errors. Only untransformed
Canada at lAcadie (4518N, 7321W). Two field trials data are presented.
were conductedone in 1996 (trial 1) on Brussels
sprouts and broccoli and one in 1999 (trial 2) on the Results and Discussion
same crops plus cauliflower. Brussels sprouts, broccoli,
and cauliflower plots were 30 m wide and 4 m long. Laboratory experiments: The four EPN studied were
Each plot contained 40 rows and 9 plants per row. For highly pathogenic to A. rapae, P. xylostella, and T. ni.
trial 1, Brussels sprouts and broccoli were transplanted Steinernema feltiae UK was the most virulent, closely fol-
on 21 June 1996. For trial 2, Brussels sprouts and broc- lowed by S. feltiae 27, S. riobrave, and S. carpocapsae
coli seedlings were transplanted on 15 June 1999 and (Table 1). LC50 values ranged from 3.6 to 18.2 for A.
cauliflower on 9 July 1999. Plants were planted 45 cm rapae L2, from 2.3 to 24.5 for P. xylostella L3, and from
apart within a row and 75 cm between rows. 4.7 to 10.1 for T. ni L2 (Table 1). These results are
Two treatments were made: (i) nematode + Agral similar to previous reports by Baur et al (1995), Morris
0.05% and (ii) Agral 0.05% alone. The nematode sus- (1985), and Ratnasinghe and Hague (1995) for all
pension was stirred to prevent nematodes from settling three species.
during spray-tank application. Nematodes were applied The efficacy of EPN was modulated by temperature.
at sunset on 2 September 1996 (trial 1) and on 24 Maximum mortality was recorded for A. rapae L2
August 1999 (trial 2) with a Comet MC 25 Portotata (100%) from S. riobrave at 30 C, 95.8% from S. feltiae
equipped with a handgun sprayer (between 483 and and 91.7% from S. feltiae 27 at 25 C, and 75.7% from S.
1,379 kPa) until runoff at the rate of 4 billion/ha. carpocapsae at 30 C (Table 2). At 15 C, average A. rapae
The nematodes were sprayed on six random 2-m mortality rates by EPN ranged from 1.7% to 19.2%.
double rows for each treatment in each crop. Eighteen Although no significant difference was detected be-
plants for each treatment and each crop were randomly tween isolates, both S. feltiae strains were more effective
chosen. The first and last plant on each treated row than S. carpocapsae and S. riobrave. At 20 C, EPN were
served as a buffer and were not sampled. significantly more effective than at 15 C except S. rio-
Insect mortality caused by nematodes was evaluated brave. Again, S. feltiae strains performed similarly and

TABLE 1. LC50 values and 95% confidence limits (CL) of four entomopathogenic nematodes against Artogeia rapae, Plutella xylostella, and
Trichoplusia ni.

A. rapae L2 P. xylostella L3 T. ni L2
Steinernema
species Strain LC50a 95% CL LC50 95% CL LC50 95% CL

S. carpocapsae All 18.2 11.827.3 24.5 18.332.4 10.1 7.313.8

S. feltiae UK 3.6 2.45.3 2.3 1.43.4 4.7 3.46.4
S. feltiae 27 5.7 3.78.4 6.0 4.48.0 9.5 6.912.8
S. riobrave 335 8.3 5.312.3 15.5 11.520.5 7.8 5.510.7
a
LC50 values = number of IJ per insect needed to reach 50% mortality.
262 Journal of Nematology, Volume 35, No. 3, September 2003

TABLE 2. Mortality of Artogeia rapae L2 (after 36 hour time expo-

sure) as affected by nematode species and temperature.

Steinernema species
Temperature
(C) S. carpocapsae All S. feltiae UK S. feltiae 27 S. riobrave 335
a
15 1.7 cA 19.2 cA 10.0 cA 4.2 cA
20 36.7 bAB 70.8 bA 57.9 bA 10.0 cB
25 65.8 abB 95.8 aA 91.7 aA 89.2 bA
30 68.2 aB 61.7 bB 48.3 bB 92.5 aA
a
Values in the same column followed by the same lowercase letter and in the
same row followed by the same uppercase letter are not significantly different
from (P 0.05) one another as determined by Waller-Duncan k-ratio t-test.

were significantly more effective than S. carpocapsae and

S. riobrave. At 25 C, all EPN were significantly more Fig. 1. Mortality of Artogeia rapae L2 as affected by contact time to
effective than at 20 C, where S. feltiae strains and S. Steinernema carpocapsae All and S. feltiae UK (100 IJ/larvae at 20 C).
riobrave were significantly more pathogenic that S. car-
pocapsae. At 30 C, the infectivity of S. riobrave increased,
S. feltiae strains decreased, and S. carpocapsae remained carpocapsae and S. feltiae caused 76% and 78% mortality,
unchanged when compared to 25 C (Table 2). Many respectively, and no significance difference between
other studies have shown that temperature influences the two species was detected (Fig. 1). Similar results
the nematodes location as well as infection and killing have been observed for many lepidopteran pests under
of insect (Grewal et al., 1994; Kaya, 1990; Molyneux, controlled conditions (Baur et al., 1995; Jaques, 1967;
1984, 1985). Molyneux (1984) noted a correlation be- Morris, 1985), confirming that an exposure time of at
tween the temperature optima of various species and least 6 to 8 hours to the nematodes is necessary to reach
strains of Steinernema and Heterorhabditidis and their geo- a significant level of larval mortality.
graphic origins, where nematodes from the tropics had The susceptibility of A. rapae larvae to S. carpocapsae
higher temperature optima than those from temperate All increased with larval development (P < 0.0007) (Fig.
regions. Steinernema riobrave, which is native to the 2A). Maximum mortality rates were: 93.3% with 200 IJ
Lower Rio Grande Valley of Texas (Cabanillas et al., per L2 larva, 95.5% with 200 IJ per L3 larva, and 100%
1994), was the most pathogenic nematode under high- with 50 IJ per L5 larva (Fig. 2A). Similarly, susceptibility
temperature conditions in our experiment. Molyneux of P. xylostella increased with larval development (P <
(1984) also has demonstrated that S. feltiae is a poor 0.01) (Fig. 2B). Maximum mortality rates were 82.4%
survivor at high temperature, probably because of its with 200 IJ per L3 larva and 90% with 100 IJ per L4 larva
high motility and respiration, which rapidly exhausts (Fig. 2B). Trichoplusia ni L2-L3 were very susceptible to
food reserves. This could explain why S. feltiae 27 and nematode infection (Fig. 2C). The highest mortality
UK were more pathogenic than S. carpocapsae to A. ra- rates were 98.3% with 100 IJ per L2 larva and 100% with
pae, except at 30 C. Our results regarding the patho- 100 IJ per L2-L3 larva (Fig. 2C). Our results on the
genicity of S. carpocapsae to A. rapae under different efficacy of S. carpocapsae against different larval stages
temperatures are in accordance with those observed by are in accordance with those observed by Kaya (1985),
Ratnasinghe and Hague (1998), who demonstrated who demonstrated that the susceptibility of insect to
that the optimal temperature range for the infectivity of EPN increased with larval development.
S. carpocapsae against Plutella xylostella was between 20 Growth chamber experiments: Survival rate of S. carpocap-
and 30 C with an optimum at 25 C. Steinernema carpo- sae All on cabbage leaves was higher than S. feltiae UK
capsae is known to be tolerant to high temperature and and S. riobrave 335 (Fig. 3). After 1 hour, the survival of
desiccation stress. This is related to its specific habitat, S. feltiae UK and S. riobrave was significantly reduced (P
which is near the soil surface (Campbell and Gaugler, < 0.0001) when compared to S. carpocapsae (Fig. 3).
1993; Glazer and Navon, 1990; Kaya, 1990; Simons and Furthermore, after 4-hour exposure, the survival of S.
Poinar, 1973; Womersley, 1990). Nematodes that live feltiae UK and S. riobrave were 2% and 0%, respectively,
near the soil surface are generally more tolerant to in comparison with 42.8% for S. carpocapsae All (P <
high-temperature stress and desiccation than nema- 0.0001) (Fig. 3).
tode species that are present deeper in the soil (Kaya, The addition of adjuvants except for Seaweed
1990). (0.05%, 0.1%) significantly increased the average total
Mortality of A. rapae L2 significantly increased with number (P < 0.0001) and the average number of living
exposure time to S. carpocapsae (P < 0.0001) and S. feltiae nematodes per unit leaf area (P < 0.0001) when com-
UK (P < 0.0001) (Fig. 1). These nematodes killed 50% pared to the water control (Table 3). Corn Oil (0.9%,
of the larvae with a 6-hour exposure. After 12 hours, S. 1.8%, 3.6%), Leafshield (3.0%, 6.0%, 12.0%), Seaweed
 Entomopathogenic Nematodes Against Crucifer Pests: Belair et al. 263

the water control with the exception of Seaweed at

0.05%, which reduced nematode survivorship on the
leaves (Table 3).
Steinernema carpocapsae was chosen for subsequent
field trials because of its availability for field trials and
higher survival rate when exposed to desiccation on
leaf surface (Baur et al., 1995; Simons and Poinar, 1973).
The use of EPN against foliage pests is commonly per-
ceived to be limited by their temperature range (Gre-
wal et al., 1994; Molyneux, 1985), their ability to survive
desiccation (Baur et al., 1995; Simons and Poinar, 1973;
Womersley, 1990), and UV radiation (Gaugler and
Boush, 1978). Thus, nematodes applied to foliage must
be protected from these detrimental and often lethal
effects. Adjuvants are known to indirectly enhance des-
iccation survival of IJ by reducing the evaporation rate
of droplets and decreasing the number of nematodes
lost during application. The majority of adjuvants in
our study increased the number of IJ per unit area and
their survival rate when compared to the water control,
but the number of nematodes (total and living) recov-
ered from cabbage foliage was lower than that observed
on apple leaves in a previous study, where the same
adjuvants were used (Belair et al., 1999). These differ-
ences could be related to the physical properties of
cabbage vs. apple leaves. Glazer (1992) demonstrated
that the leaf surface is an important factor affecting
nematode survival. His study demonstrated that S. car-
pocapsae (Mexican strain) IJ survival was higher on the
pubescent leaves of tomato (Lycopersicon esculentum
Mill.) and soybean (Glycine max (L.) Merr.) than on the
glaborous leaves of pepper (Capsicum frutescens L.) and
bean (Phaseolus vulgaris L.) plants. Pubescence stabi-
lizes the microclimate near the leaf surface by affecting
Fig. 2. Mortality of early instars of A) Artogeia rapae, B) Plutella relative humidity, temperature, and light (Baur et al.,
xylostella, and C) Trichoplusia ni, as affected by S. carpocapsae All con- 1995; Glazer, 1992). Furthermore, the wax layer on a
centrations.
leaf surface can decrease the adherence of water drop-
(0.1%), and Agral (0.05%) increased the survival of lets to leaves. This is probably the case for cabbage
nematodes (P < 0.0001) in comparison with the water leaves that are glaborous and waxy. The adjuvant Agral
control (Table 3). All other adjuvants were similar to (0.05%) was retained for further trials based on effi-
cacy, cost, and availability.
Field experiments: Foliar applications of S. carpocapsae
provided 35.3% and 33.0% control of A. rapae on Brus-
sels sprouts and broccoli, respectively, in trial 1 (1996)
and 24.9%, 19.4%, and 14.9% on Brussels sprouts,
broccoli, and cauliflower, respectively, in trial 2 (1999).
No mortality was observed on crucifer plants treated
with Agral alone (Table 4). The number of A. rapae
larvae observed on each crop was not significantly dif-
ferent from the control (Table 4). Crop type did not
affect the efficacy of S. carpocapsae in either experi-
ments. At application time, air temperature and relative
humidity were 22.9 C and 75% in 1996 and 24.4 C
and 65% in 1999. From application time (7h00 PM) to
Fig. 3. Effects of time on survival of three entomopathogenic sunrise (6h00 AM), average air temperature was 16.3 C
nematodes on cabbage leaves. and 18.9 C in 1996 and 1999, respectively.
264 Journal of Nematology, Volume 35, No. 3, September 2003

TABLE 3. Effect of adjuvants on density and survival of Steinernema carpocapsae All on cabbage leaves after a 12-hour exposure time (20 C
and 70% relative humidity).

Percent concentration
Adjuvant (v/v) Total IJ/cm2 Living IJ/cm2 % Survival
a
Control (water) 2.9 0.5 fg 2.1 0.5 i 64.9 fg
Corn Oil 1.8 9.9 0.5 abc 8.8 0.4 ab 89.2 a
Leafshield 12.0 9.6 1.5 bcd 8.3 1.3 abc 85.4 ab
Corn Oil 0.9 9.7 1.2 bcd 7.9 1.2 abcd 80.4 bc
Leafshield 3.0 10.8 2.4 bc 8.4 1.9 abcd 78.4 bcd
Corn Oil 3.6 10.5 1.5 ab 8.3 1.2 ab 78.2 bcd
Seaweed 0.1 3.1 0.6 f 2.4 0.5 i 77.0 cde
Leafshield 6.0 13.6 1.6 a 10.3 1.0 a 76.3 cde
Agral 0.05 7.3 0.6 d 5.5 0.6 efg 75.4 cde
Citowett Plus 0.4 9.4 0.6 bcd 7.1 0.6 bcdef 74.5 cdef
Agral 0.1 7.6 0.6 bcd 5.6 0.5 defg 73.7 cdef
Super Spread 0.1 10.2 0.7 ab 7.5 0.7 abcde 73.5 cdef
Super Spread 0.2 7.8 0.6 bcd 5.8 0.6 cdefg 73.3 cdef
Seaweed 0.2 5.6 1.7 e 4.1 1.2 h 72.9 cdef
Agral 0.025 9.1 0.2 bcd 6.5 0.4 bcdef 71.1 defg
Citowett Plus 0.1 8.4 1.2 bcd 5.8 0.8 cdefg 69.1 defg
Super Spread 0.4 7.4 0.5 cd 5.1 0.4 fgh 68.8 efg
Citowett Plus 0.2 7.3 0.3 cd 4.6 0.2 gh 62.4 g
Seaweed 0.05 2.2 0.7 g 1.0 0.6 j 32.0 h
a
Values in columns followed by the same letter are not significantly different (P 0.05) according to the Waller-Duncan k-ratio t-test.

In our study, laboratory trials were not good predic- study, the poor field efficacy was attributed to rapid
tors of field efficacy. Even though nematodes were ap- nematode desiccation and, to a lesser extent, to the
plied in both experiments at sunset to protect nema- application method. Alternatively, Wang and Li (1987)
todes from radiation and desiccation (Gaugler and reported that S. carpocapsae DD-136 caused 89.4% mor-
Boush, 1978; Gaugler et al., 1992), S. carpocapsae pro- tality of Pieris rapae in 72 hours in field trials when hu-
vided low efficacy levels against A. rapae. This low nema- midity was nearly 100% for the 15 hours following eve-
tode activity can be related to many factors, including ning applications. The discrepancy between our field
desiccation caused by unfavorable moisture conditions results and those reported by Wang and Li (1987)
on the leaf surface, short contact period with the insect could be attributed to rapid desiccation of EPN caused
pest, and low night temperature. In most cases foliage- by the lower relative humidity, which was between 65%
feeding lepidopteran larvae are highly susceptible to and 75% at application time. Nematode activity on the
infection by EPN in petri dishes but are rarely effective leaf surface also may have a significant effect on their
in the field (Kaya and Gaugler, 1993). For example, efficacy against insect pests. Search strategies of EPN
Jaques (1967) evaluated the DD-136 strain of S. carpo- should be considered when nematodes are used as bio-
capsae against five different foliage-feeding pests of logical insecticides against foliage-feeding insects. Stein-
apple in the laboratory and field. He showed that S. ernema carpocapsae is known to be one of the least motile
carpocapsae DD-136 was very effective in killing the win- EPN because of its sit-and-wait searching strategy (Ishi-
ter moth Operophtera brunata in the laboratory, but field bashi and Kondo, 1990). The sit-and-wait strategy of S.
application did not result in larval suppression. In this carpocapsae consists of remaining stationary in the ab-
sence of stimulus (Lewis et al., 1992). This behavior
TABLE 4. Mortality of Artogeia rapae following foliar applications increases the time taken for the nematode to contact a
of Steinernema carpocapsae on cruciferous crops under field conditions.
potential host and thus reduces its efficacy in unfavor-
Treatment
able habitats such as foliage. Finally, low night tempera-
ture also could have played an even more significant
Crop No. larvae/plant Nematode + Agral Agral alone
role in reducing field efficacy. As mentioned previously,
Trial 1 average night temperature was below 20 C in both
Broccoli 16 a 33.0 13.5 aAa 0.0 0.0 aB trials, and the minimum temperature recorded was
Brussels sprouts 15 a 35.3 3.1 aA 0.0 0.0 aB
Trial 2
near 15 C. In this study, these low temperatures re-
Broccoli 20 a 19.4 3.5 aA 0.0 0.0 aB duced drastically the efficacy of all EPN, including S.
Brussels sprouts 22 a 24.9 2.7 aA 0.4 0.4 aB carpocapsae.
Cauliflower 19 a 14.9 4.1 aA 0.0 0.0 aB Based on our field results, S. carpocapsae does not
a
For both experiments, values in the same column followed by the same provide an acceptable level of control of A. rapae under
lowercase letter and in the same row followed by the same uppercase letter are
not significantly different from (P 0.05) according to the Waller-Duncan
Quebecs environmental conditions. Although great
k-ratio t-test. potential exists for large-scale use of EPN, further stud-
 Entomopathogenic Nematodes Against Crucifer Pests: Belair et al. 265

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