Bulletin of Environment, Pharmacology and Life Sciences

Online ISSN 2277 1808

Bull. Environ. Pharmacol. Life Sci.; Volume 1 [8] July 2012: 65 - 71

Original Article

All Rights Reserved Academy for Environment and Life Sciences, India
Website: www.bepls.com

Mosquito Repellency of Whole Extracts and Volatile oils of

Ocimum americanum, Jatropha curcas and Citrus limon
T. C. *Kazembe and M. Chaibva
Deapartment of Science and Maths Education, Faculty of Education,
University of Zimbabwe, P. O. Box MP167, Harare, Zimbabwe
E-mail kazembet@rocketmail.com
Mobile: 263 733414334
ABSTRACT
The study was carried out to evaluate the efficacies of the crude extracts and of the essential oils from three plants which are
used as mosquito repellents. The crude extracts were obtained from the leaves of Ocimum americanum and Jatropha curcas,
and from fruit peels of Citrus limon by dry distillation and the volatile oils were isolated from the crude extracts using
separating funnels. The mosquito repellency of the crude extracts and of the volatile oils were evaluated using the humanbait technique, whereby hands treated with a pre-determined minimum dose of the repellent were exposed to mosquitoes
and the extent of repellency determined, using DEET as standard, revealing that the oils were much more repellent than the
crude extracts. The mixtures of crude extracts and the mixtures of volatile oils generally gave higher protection than their
respective single repellents. Thus, the components of the different repellents appeared to reinforce each other.
Key words: Mosquito repellents; crude extracts; volatile oils; Ocimum americanum;Jatropha curcas; Citrus limon

INTRODUCTION
The global incidence of malaria has been estimated at 300 - 500 million clinical cases annually,
causing 1.5 - 2.5 million deaths each year. More than 90% of these occur in sub-Saharan Africa
where severe malaria and death affect mainly children of rural areas with little access to health
care services [1]. Malaria causes substantial losses to national economies in terms of lost
productivity, costs of treatment, school and work absenteeism, and funeral costs [2, 3]. Economists
believe that malaria is responsible for a growth penalty of up to 1.3% per year in some African
countries, worsening the poverty burden [3, 4].
Conditions that favour mosquito breeding, for example the natural disasters like cyclone Eline
which promoted the breeding of mosquitoes, have led to increases in malaria cases in Zimbabwe,
increasing drug resistance of Plasmodium falciparum to chloroquine and fansidar, and increasing
mosquito resistance to DDT-based mosquitocides [5].
The intensity of the malaria burden varies substantially even between regions of the same country
[6]. In Zimbabwe, approximately 5.5 million people out of a population of 12.5 million live in
malaria endemic areas [7]. The inhabitants of these areas could guard against mosquito bites by
spraying their houses/huts with mosquito repellents or with mosquitocides [8], or by using
personal protection measures [9]. Personal protection has the added advantage of giving
protection in outdoor areas but it is becoming increasingly difficult due to increasing resistance of
mosquitoes to pesticides and repellents [9]. DEET, a commercial repellent which has been in
worldwide use since 1957, has been reported to have disadvantages associated with its activity as
a solvent of paints, varnishes, and some plastic products such as watch crystals, frames of
spectacles, and certain synthetic fabrics. There have also been concerns over its toxicity. Its
continuous application has been reported to cause in-folding of the epidermis and a thickened
dermis [10-12].
Thus, there is need to evaluate plant-based repellents in order to supplement conventional control
methods. Mosquito repellent properties of plants were well known before the advent of synthetic
chemicals [13]. A wide range of plants have been used for centuries for repelling mosquitoes and
other insects using varying techniques such as burning plant materials to generate smoke that
repels mosquitoes [14], hanging bruised fresh plants in houses [15], and placing potted plants
inside houses [16].
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Reports from clinics and non-governmental organizations in Africa, where 80%of the worlds
malaria burden exists, indicate that the poorer members of society are now using traditional
medicine at least for economic reasons [17, 18]. Mosquitocidal and mosquito repellent properties
of plants have been investigated over the years, revealing that people use plants because they are
cheap, effective, and locally available [8]. The repellency of plants may differ dependent on the
region or cultivar of growth [19].
MATERIAL AND METHODS
This naturalistic inquiry involves evaluation of the efficacy of crude extracts of some selected
plants and oils extracted from the crude extracts as mosquito repellents against laboratory-reared
Aedes aegypti mosquitoes, using the human-bait technique [20, 21]. Hands treated with a predetermined minimum dose for both the whole extract and the extracted volatile oils were exposed
to mosquitoes and the extent of repellency determined based on the relationship:
% repellency = [(Nc Nt) / Nc] x 100, where Nc is the number of mosquitoes landing on the control
subject, and Nt is the number of mosquitoes landing on the treated subject (Oshaghi et al., 2003).
Mosquitoes, which had been starved for one hour prior to repellency tests, were then released into
a 5-liter cage where they found the host (treated hand). The untreated hand was used as a negative
control while the one treated with DEET was used as a standard or positive control. Experiments to
determine the landing time, the exposure time, and the dose finding experiments were carried out.
The repellency experiments were conducted using each of the whole extracts, and using ethanol as
control and DEET as standard, performing each test three times, replacing the mosquitoes and
rotating the volunteers. The number of mosquitoes landing on the control, on the treated hands,
and on the one treated with DEET were recorded. The procedure was repeated using mixtures of
whole extracts and further repeated using the extracted volatile extracts, and finally using mixtures
of the volatile oils.
Citrus limon, Jatropha curcas, and Ocimum americanum were chosen for this study because of their
historical medicinal use as well as their use in mosquito control by the rural people of Zimbabwe
do not appear to have been studied in Zimbabwe although similar plants growing in other regions
of the world have been reported. It is desirable to establish if the Zimbabwean plants will show the
efficacy reported for similar plants from other regions, since the growing environment of a plant
affects its chemical composition.
Citrus limon (Rutaceae)
Citrus limon is thought to have originated from India and introduced into Italy toward the end of
5th century. Lemons have been used to control malaria in the form of mosquito repellents over the
centuries all over the world and have been used as food and food additives [19, 22, 23].
Jatropha curcas (Euphobiaceae)
The origins of Jatropha curcas is still uncertain but it is believed that the plants originated from
Mexico and Central America [24] and is now cultivated worldwide for the latex from its bark, and
oil from its seeds [25]. The oil is used to treat skin ailments and as cosmetic cream and the leaves
are used to repel mosquitoes in some parts of Zimbabwe by hanging them in houses or by burning
them during the day to control mosquitoes during the evening (personal observation).
Ocimum americanum (Lamiaceae)
Ocimum americanum is commonly known as Lime Basil, an annual plant which grows under full
sun to partly shady conditions in average soils. The plant, as well the as oils from it, have received
considerable attention for their potential medicinal properties. The leaves have been shown to
have antibacterial essential oils [26]. The seeds germinate easily, producing the plant which is used
for culinary purposes as a fragrance accent for soups, salads, and fish and is good a tea as well [27].
The juice of the leaves of the plant is used for the treatment of catarrh and the volatile oils from the
plant have been shown to be mosquito repellent and to have larvicidal activity [28].
About 1.0 kg of each of the leaves of O. americanum and J. curcas, and about 1.0 kg of fruits of C.
limon were gathered in Mt Darwin in February 2007 and transported to the Department of
Chemistry, Bimdura University of Science Education, Bindura, Zimbabwe, for processing. The
samples of leaves O. americanum and J. curcas were crushed (mortar and pestle) and spread on the
laboratory bench overnight. The crushed leaves of each plant (300 g) were heated at about 120oC
in a round-bottomed flask of the distillation apparatus until the dry distillation was complete,
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cooling the condenser with cold water and collecting the distillate in 100 cm3 conical flasks. The
procedure was repeated with 300 g of C. limon fruit peels which had been cut to small pieces. The
distillates (the whole extracts) consisted of the volatile compounds, including water, which were
released from the raw material by the heat. These were allowed to cool to room temperature, their
volumes and masses recorded, and then kept at 4oC until required for further experiments.
Extraction of volatile oils from the whole plant extracts
The distillate from each plant sample (50 cm3) was separated into the aqueous and oil phases using
a separating funnel, draining off the aqueous phase until only the oil remained, yielding O.
americanum (4.4 cm3), C. limon (5.1 cm3), and J. curcas (4.0 cm3) oils. These oils were kept at 4oC in
stoppered 10 cm3 plastic sample tubes until they were tested for mosquito repellency [28].
Preparation of mixtures for mosquitoe repellency tests
The extract mixtures were prepared on the basis of the minimum doses established through dose
finding experiments.
Thirty-five laboratory- reared 5-8 day old mosquitoes which had been starved for an hour were
paled in a 5-litre cage. The starving reduced the time needed for the mosquitoes to start landing on
the host in search of a meal. Limiting the number of mosquitoes to 35 made it easier to count the
mosquitoes landing on the host. The mosquito cage had a mosquito-netting on top and a muslin
sleeve on the side for introducing and removing the mosquitoes.
Repellency experimental design
A special glove with an opening measuring 6 cm by 6 cm, giving an open area of 36 cm 2, was used
in each of the experiments. The edges of the opening were lined out with a masking tape. Using a
dropper to apply each test repellent, a 0.5 cm3 dose was applied on to the open area of the hand
and the % repellence during the 3-minute exposure time was determined. The dose was increased
by 0.5 cm3 for each succeeding experiment, calculating the % repellence after each dose, until a
dose that gave 100 % repellence during the 3-minute exposure time was achieved (Figure 1). This
dose was the minimum amount of extract that gave complete protection from mosquito landing
and was used in all experiments. The % repellency (% protection) was calculated basing on the
relationship: % repellency = [(Nc-Nt)/Nc] x100 where Nc is the mean number of mosquitoes
landing on the control subject, and Nt is the mean number of mosquitoes landing on the treated
subject [19]. Percentage protection is defined as the average number of bites received by the
subjects in the treated trial relative to that of the control [19].
For each repellent, the minimum dose established in the dose finding experiment was applied to
the exposed area of the hand. The hands of the respective volunteers were placed for 3 minutes in
the cage containing mosquitoes which had been starved for an hour. This was repeated at 30
minute intervals until repellency was completely lost. Three replicates were run for each repellent
and in each replicate different volunteers were used to nullify any effect of skin differences on
repellency. Before each test, the skin of volunteers was washed using unscented soap and the
repellent being tested was applied to the exposed skin. After the application, the hand was not
allowed to be rubbed, touched, or wetted. An untreated hand was used as control and the one with
DEET was used as a standard. All experiments were run at ambient temperature (27 2o C) and
relative humidity of 80 10 %. The numbers of mosquitoes landing were recorded and the mean
percentage protection was calculated [19].
Data analysis
The mean protection time from replicate tests was used as the standard measure of repellency for
all test repellents against Aedes aegypti mosquitoes. Two-way analysis of variance (ANOVA) was
used to determine the significance of the differences in repellency at 95 % confidence level
between different test samples. All P values are two sided, and a P value of less than 0.05 was
considered to indicate statistical significance.
RESULTS
The minimum volumes that gave 100 % protection from Aedes aegypti mosquitoes were
established from the dose finding experiments and these were applied on to the exposed areas of
the hand in all experiments. The results show that repellent activity was dose dependent with oils
requiring lower doses than whole extracts, and mixtures requiring lower doses than single test
repellents.
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The results indicated that the minimum dose for O. americanum oil was 1 cm3, that for C. limon oil
was 1.5 cm3, and that for J. curcas oil and O. americanum extract was 2 cm3, that for C. limon extract
was 2.5 cm3 and that for J. curcas extract was 3 cm3. Hence in all experiments involving O.
americanum oil, the dose used was 1 cm3 and in those involving C. limon oil the dose was 1.5 cm3. In
all experiments involving J. curcas oil and O. americanum extract the dose was 2 cm3, and in those
involving C. limon extract the dose was 2.5 cm3 and 3 cm3 in those involving J. curcas extract.
The minimum dose for O. americanum / C. limon extracts mixture was 1.5 cm3 and that for O.
americanum / J. curcas extracts mixture and for J. curcas / C. limon extracts mixture was 2 cm3.
Hence in all experiments involving O. americanum / C. limon extracts mixture, the dose used was
1.5 cm3. In all experimrnts involving americanum / J. curcas extracts mixture and for J. curcas / C.
limon extracts mixtures the dose of 2 cm3 was used. The minimum dose for the mixtures O.
americanum / C. limon, O. americanum / J. curcas, and J. curcas / C. limon oils was 1.5 cm3. Hence in
all experiments involving these mixtures of oils, the dose used was 1.5 cm3.
Table 1: Percentage mean repellency of whole plant extracts against Aedes aegypti mosquitoes
Plant extract
100% repellence (hours)
O.americanum
1.5
C. limon
1.0
J. curcas
0.5
O.a /C.l
1.5
C.l /J.c
0.5
O. a / J.c
1.0
O.a /J.c /C.l
2.0
Key
O. a = O. americanum C. = C. limon J. c = J. curcas
O. a /C. l = O. americanum / C. limon mixture
C. l /J .c = C. limon / J. curcas mixture
O. a /J. c / C. l = O. americanum / J. curcas / C. limon mixture

Repellence below 70% (hours)

3.5
2.5
2.0
5.0
4.5
4.0
6.0

Table 2. Percentage mean repellency of volatile oils and their mixtures against Aedes aegypti
mosquitoes
Time spent giving
Time in Hours
repellence (hours)
O.americanum
1.5
C. limon
1.5
J. curcas
1.0
O.a /C.l
2.0
C.l /J.c
1.0
J. c / O. a
1.0
O.a /J.c /C.l
2.0
Key
O. a = O. americanum C. = C. limon J. c = J. curcas
O. a /C. l = O. americanum / C. limon mixture
C. l /J .c = C. limon / J. curcas mixture
O. a /J. c / C. l = O. americanum / J. curcas / C. limon mixture

100%

Time for repellence to fall below

70%
5.5
5.0
4.0
4.0
4.5
6.0
8.0

DISCUSSION
The ideal mosquito repellent would be the one that gives 100 % protection against mosquito bites
over the desired time. Obtaining such a plant based repellent that gives such a high protection over
long periods of time is not easy. A cut-off point for acceptable percentage biting protection needs to
be chosen for discussions of effective repellencies of plant-based repellents. Citrus limon which
gave 71 % protection against A. stephensi has been described as giving acceptable percentage
biting protection, hence effective, and Melissa oil which gave 60 % protection was described as not
effective [19]. For our discussion, we chose 70 % protection as effective and acceptable percentage
biting protection, and describe levels below 70% as ineffective.
2 (a) Mean % repellency of whole plant extracts
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O. americanum whole extract gave 100 % protection for 1.5 hours whilst that of C. limon and J.
curcas gave 100 % protection for 1.0 hour and 0.5 hour respectively. The effectiveness of J. curcas
fell rapidly and approached the cut-off point after 2.0 hours, when it became 74 %, whilst that of O.
americanum and C. limon were 94 % and 80 %, respectively. The effectiveness of C. limon fell to 73
% after 2.5 hours compared to that of O. americanum which fell to 73 % after 3.5 hours (Table 1).
2 (b) Mean % repellency of extracted volatile oils
O. americanum and C.limon oils gave 100 % protection for 1.5 hours whilst J. curcas gave 100 %
protection for 1.0 hour. The effectiveness of O. americanum and C. limon fell more or less at equal
rates, C. limon falling to 71 % after 5.0 hours and O. americanum reaching 71 % after 5.5 hours,
compared to J. curcas which reached 70 % 4.0 hours post application (Table 2). Thus, the effective
protection times of oils were roughly double those of the whole extracts.
2 ( c) Mean repellency of mixtures of whole extracts
O. The mean repellencies of whole extracts of americanum, C. limon, and their mixtures
The mixture was a more effective repellent than either of the single extracts. It would appear that
the mixtures acted in synergism, improving the effectiveness to 5.0 hours post application for the
mixture, compared to 2.5 hours for C. limon and 3.5 hours for O. americanum (Table 1).
(ii) Mean repellency of whole extracts of O. americanum, J. curcas and their mixtures
That the mixture gave 100% protection for 1.0 hour post application compared to O. americanum
and J. curcas which gave 100 % protection up to 1.5 and 0.5 hours, respectively, would suggest that
the components of the two extracts interacted in a way that lowered the repellency of the
components of O. americanum, resulting in depressed repellent effects for the mixture. However,
the overall effectiveness of the repellents was improved from 3.5 hours for O. americanum and 2.0
hours for J. curcas to 4.0 hours for the mixture. Thus, overall, the components of the extracts appear
to act in way that enhances the effects of one another (Table 1).
(iii) Mean repellents of whole extracts of C. limon, J. curcas, and their mixtures
The mixture gave 100 % protection for 0.5 hour compared to J. curcas and C. limon
which gave 0.5 hour and 1.0 hour, respectively. Thus, the components of J. curcas appeared to
interact with the components of C. limon in a way that suppressed the components of C. limon. But
2.0 hours post application they appeared to reinforce each other resulting in the mixture giving
better protection than either of the single extracts, raising the effectiveness of the mixture to 4.5
hours post application, compared to 2.0 hours for J. curcas and 2.5 hours for C. limon (Table 1).
2 (c ) Mean repellency of mixtures of oils of test repellents
The mixture of oils of O. americanum, C. limon gave 100 % protection for 2.0 hours compared to O.
americanum and C. limon which gave 100 % protection for 1.5 hours each. In general the
effectiveness of the mixture was higher than that of either of the single volatile oils. The
effectiveness of the mixture persisted for 8.0 hours post application compared to that of O.
americanum which fell off after 5.5 hours and that of C. limon which fell off after 5.0 hours. Thus the
components of the oils reinforced each other to give a better repellent (Table 2).
(ii) Mean repellency of oils of curcas, C. limon, and their mixture
The mixture gave 100 % protection for 1.0 hour compared to 1.5 hours for J. curcas and 0.5 hour
for C. limon. However, the effectiveness of the mixture was generally higher, 76 % at 4.5 hours post
application and falling to 64 % at 5.0 hours, compared to J. curcas which gave 70 % at 4.0 hours
post application falling to 68 % at 4.5, and C. limon which gave 71% at 5.0 hours post application
and falling to 68 % at 5.5 hours.
(iii) Mean repellency of oils of J. curcas, O. americanum, and their mixtures
The effectiveness of the mixture persisted for 6.0 hours post application, giving 71 % protection
compared to O. americanum oil which gave 71 % protection at 5.5 hours and J. curcas which gave
70 % protection at 4.0 hours post application. The oils of J. curcas appeared to suppress the
repellency of the oils of O. americanum at higher concentration in the first two hours post
application, but as the concentrations fell off due to evaporation the two oils appear to reinforce
each other and raise the overall effectiveness of the mixture. Results showed that extracted
volatile oils were significantly more effective than whole plant extracts. This might be due to the
greater concentration of bioactive components that repel mosquitoes in oils than in the bulkier
solutions of whole extracts. Hence O. americanum oils with protection time of 5.5 hours were better
than C. limon and J. curcas oils with protection times of 5.0 hours and 4.0 hours respectively. Their
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respective whole extracts had protection times of 3.5, 2.5, and 2.0 hours, respectively. Results of
statistical analysis revealed significant differences between whole extracts and extracted volatile
oils (P less than 0.05) against Aedes aegypti mosquitoes for all the plants evaluated. Thus, extracted
oils were more effective mosquito repellents than their respective whole extracts; mixtures of oils
were more effective repellents than their single oils, and their repellencies were not significantly
different from Deet over the first two or three hours.
CONCLUSIONS
Extracts from different mosquito repellent plants could be prepared and tested and produce
effective mosquito repellents which could compete or supplement repellents which are currently
on the market.
ACKNOWLEDGEMENTS
The authors would like to express their gratitude to Messers Makuvaza, Chiwade and Muchenje of
the National Institute of Health Research, Ministry of Health, Harare, Zimbabwe, for assistance in
carrying out laboratory experiments.
REFERENCES
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.

WHO.(1997). Vector control methods for use by individuals and communities, Geneva.
Snow RW. (1999). Estimating mortality, morbidity and diability due to malaria among Africas non-pregnant
population, Bulletin of the World Health Organization; (77): 624-640.
Roberts D, et al. (2004). Malaria Controland Public Health. Emerg. Infect. Dis. 10 (6).
Boivin MJ. (1990). Effects of early cerebral malaria on cognitive ability in Senegalese children, Journal of
Developmental and Behavioral Pediatrics ; 23(5): 353-64.
WHO. (1998). Roll Back Malaria: A global partnership. Geneva. World Health Organization.
Greenhood BM. (1999). Malaria mortality and morbidity in Africa. Bulletin of the World Health Organization; 77
(8): 617-618.
Midzi S. et al. (2004). Essential actions to support the attainment of the Abuja targets, Zimbabwe RBM country
consultative mission final report, Harare.
Lukwa N. et al. (1999). Peoples Perceptions about Malaria Transmission and Control in a locality in Zimbabwe.
Central African Journal of Medicine; 45 (3):64-68.
Ranson H. et al. Identification of a novel class of insect glutathione S-transferases involved in resistance to DDT in
the malaria vector Anopheles gambiae. Biochemical Journal. 2001; 359: 295-304.
Liu WK. et al.(1987). Toxic effects of mosquito coil (a mosquito repellent) smoke on rats. Properties of the mosquito
coil and its smoke. Toxicology Letters ; 39: 223-30.
Qui HHW, McCall JW. (1998). Pharmacokinetics, formulation, and safety of insect repellent DEET: A review, J. Am.
Mosq. Contr. Assoc. 1998; 14: 12-27.
Al-Sagaff I. et al.(2001). Toxic effects of Diethyltoluamide and Dimethylphthalate creams as mosquito repellents on
rabbits skin. Journal of Anatomical Society of India, ; 50 (2): 148-152.
Curtis CF. et al. (1989). Natural and Synthetic repellents. In Appropriate technology in vector control. Ed. CF Curtis,
CRC Press. Boca Raton FL ; pp 75-92.
Sharma VP, Ansari MA. (1993). Personal protection from mosquitoes (Diptera: Culicidae) by burning neem oil, in of
the American Mosquito Control Association 9: 359-360.
Waka M. et al. (2006). The effect of repellents: Ocimum forsklei and DEET on the response of Anopheles stephensi to
host odours. Medical and Veterinary Entomology; 20: 373-376.
Seyoum A. (2002). Repellency of five potted plants against Anopheles gambiae from human baits in semi-field
experimental huts. American Journal of Tropical Medicine and Hygiene, 2002; 67: 191-195.
Prozesky EA, et al. (2001). In vitro antiplasmodial activity and cytotoxicity of ethnobotanically selected South
African Plants. Journal of Ethnopharmacology ; 76: 239-45.
Zirihi, G. N., et. al.(2005). In vitro antiplasmodial activity and cytotoxicity of 33 West African plants used for
treatment of malaria, Journal of Ethnopharmacology ; 98:81-5
Oshaghi MA, et al.(2003). Repellent Effects of Extracts and Essential Oils of Citrus limon (Rutaceae) and Melissa
officinalis (Labiatae) Against Main Malaria Vector, Anopheles stephensi (Diptera: Culicidae), Iranian Journal of Public
Health ; 32 (4)
Schreck CE, McGovernTP. Repellents and other personal protection stratergies against Aedes albopictus. J. Am.Mosq.
Contr. Assoc. 1989; 247-252.
WHO(1996). Informal Consultation: a rapid dipstick antigen capture assay for the diagnosis of falciparum malaria.
Bulletin of the World Health Organization; 74 (1): 47-54.
Andrew MW. (1983).Agricultural Innovation in the Early Islamic World: The Diffusion of Crops and Farming
Techniques, Cambridge University Press 1983
Brown I.(2002). The Royal Horticultural Society New Encyclopaedia of Herbs and their Uses Dorling Kindersley
London.
Blackwell WH.(1990). Poisonous and medicinal plants, New Jersey, USA, Prentice Hall.

~ 70 ~

Kazembe and Chaibva

25.
26.
27.
28.

Mujaju C, Zinanga F. (2006). Initiation of the Community Conservation of Forests Programme: The national
Genebank of Zimbabwe and Community Technology Development Trust..
Cimanga K, et al. (2002). Correllation between Chemical Composition and antibacterial activity of essential oils of
Some aromatic medicinal plants growing in the Democratic Republic of Congo, Journal of Ethnopharmacology; 79: 2,
213-220.
Sand Mountain Herbs c/o Larry Chandier 321 County Road 18 Fyffe, AL 35971 Email
Info@SandMountainHerbs.com.). Retrieved 2 August, 2007.
Tawatsin A, Wratten SD, Scott RR, Thavara U, Techadamrongsin Y. (2001). Repellency of Volatile Oils from plants
against three mosquito vectors. Journal of vector ecology ; 26 (1): 76-82

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