Eect of plant volatile oils in protecting stored cowpea
Vigna unguiculata
(L.) Walpers against
Callosobruchus
maculatus
(F.) (Coleoptera: Bruchidae) infestation
N. Raja
a, S. Albert
a, S. Ignacimuthu
a,*, S. Dorn
ba
Entomology Research Institute, Loyola College, Chennai 600 034, India
bApplied Entomology, Eidgenossische Technische Hochschule, Clausiusstr 25, CH-8092 Zurich, Switzerland
Accepted 30 March 2000
Abstract
Adult Callosobruchus maculatus (F.) were introduced into cowpea seeds which were stored in containers with volatile oils derived from Mentha arvensis, M. piperata, M. spicata and Cymbopogon nardus. The numbers of eggs laid, adult mortality, adult emergence and subsequent seed damage were studied for four months. All oils signi®cantly in¯uenced all parameters (P< 0.05) and results with dierent parameters were generally parallel. Signi®cant dierences for at least some time/parameters combinations indicated an order of potency of M. spicata > M. piperata > M. arvensis > C. nardus.72000 Elsevier Science Ltd. All rights reserved.
Keywords: Mentha arvensis; M. piperata; M. spicata; Cymbopogon nardus; Volatile oils; Callosobruchus maculatus;
Vigna unguiculata
1. Introduction
Cowpea, Vigna unguiculata (L.) Walpers, is an important edible legume crop gaining recognition in India as a staple crop. It is mainly cultivated in dry lands. Cowpea is a very good source of vegetable protein for millions of people. The estimated global post-harvest losses caused by insect damage, microbial deterioration and other factors are of the order of
0022-474X/00/$ - see front matter72000 Elsevier Science Ltd. All rights reserved. PII: S 0 0 2 2 - 4 7 4 X ( 0 0 ) 0 0 0 1 4 - X
www.elsevier.com/locate/jspr
* Corresponding author. Tel.: +91 44 826 5542; fax: +91 44 826 5542.
10±25% (Matthews, 1993). In India, 12.5 million tonnes of edible legumes are produced every year and nearly 18.6% of cowpea alone is damaged by bruchids during storage (Agarwal et al., 1988). The bruchid beetle Callosobruchus maculatus(F.) has been associated with dried legumes for thousands of years (Mitchell, 1983; Messina, 1991). Synthetic chemical pesticides have been used to protect grains but their widespread use has led to the development of pest resistance (Champ and Dyte, 1976; Zettler and Cuperus, 1990; White, 1995). Alternatives to synthetic chemical insecticides are highly desirable (Xie et al., 1995). Research on the use of natural pesticides for crop protection and storage is increasing because of their low toxicity to human beings (Ivibjaro, 1983; Zehrer, 1984; Fagoonee, 1987; Schmutterer, 1987; Tanzubil, 1987; Raja et al., 1998). Plant volatile oils have been used in the protection of stored grains (El-Nahal et al., 1989; Saxena and Mathur, 1976; Risha et al., 1990; Gbolade and Adebayo, 1993). In the present study, volatile oils from Mentha arvensis L., M. piperata L., M. spicata L. and Cymbopogon nardus (L.) Rentle, were studied for their deterrent eects on oviposition and their ovicidal and insecticidal actions againstC. maculatus.
2. Materials and methods
2.1. Callosobruchus maculatus
The legume pest C. maculatus was obtained from our stock culture maintained in a glass jar at 31228C and 60±70% r.h. on cowpea seed as culture medium.
2.2. Volatile oils
Volatile oils from M. arvensis, M. piperata, M. spicata and Cymbopogon nardus were procured from the Central Institute of Medicinal and Aromatic plants, Lucknow, India.
2.3. Experimental design
Plastic containers (6 cm diameter5 cm height) with tight ®tting lids were used as exposure chambers. One drop (0.01 ml) of pure oil was smeared on the inner topside of the container. No further oil was applied during the 4 months of the study. One hundred uninfested cowpea seeds were placed in each of the treated containers and then two pairs of newly-emerged adults of C. maculatus were introduced into each. Containers without volatile oil were maintained as controls and each control and treatment replicated ®ve times. Observations were made for 4 months on the test material held under laboratory conditions.
2.4. Egg-laying, adult emergence and seed damage
were also released into the container. The adult emergence was recorded continuously from the time of ®rst emergence to the last emergence over a period of 30±40 days. Every day newly-emerged adults were removed to avoid further egg laying on the seeds. The numbers of seeds damaged by the feeding of C. maculatus larvae were recorded after completion of adult emergence.
2.5. Mortality determination
Ten pairs of adult C. maculatus were released into each of another series of volatile oil-treated containers. After a 24 h exposure period the containers were opened and the dead beetles were removed and recorded. Knocked-down adults were regarded as alive if they showed continued movement of their appendages by the touch of a ®ne brush. After observation, the containers were tightly closed. After every 30 days, new batches of 10 pairs of insects were released into each container for the 4 months of the trial. Every month the numbers of dead insects were recorded and the percentage of mortality was calculated and corrected using Abbott's formula (Abbott, 1925).
2.6. Statistical analysis
All the data collected were subjected to statistical analysis without transformation using one way analysis of variance (ANOVA). The means were separated using the Least Signi®cant Dierence test (LSD). In view of the wide dierences in variance at month 1, the LSD values were not calculated for these means.
3. Results
Oils of M. arvensis, M. piperata and M. spicatasigni®cantly reduced the number of eggs laid for a period of 3 months and C. nardus for a period of 2 months (P< 0.05, Table 1). At the 2 and 3-month intervals the reduction due to M. spicata was signi®cantly greater than that due
Table 1
Number of eggs laid (means2SD,n= 5) byCallosobruchus maculatus on fresh batches of cowpea seeds added to containers treated with volatile oils at various times prior to exposure
Container holding period (months)
Source of oil 1 2 3 4
Cymbopogon nardus 26.425.3 113.027.7 186.4213.2 221.8232.4
Mentha arvensis 7.821.5 63.228.2 161.428.9 217.0216.1
Mentha piperata 3.221.6 42.227.7 128.228.8 219.6229.4
Mentha spicata 1.421.1 24.225.2 82.228.9 190.2211.8
Control 192.628.1 193.029.1 196.4212.4 218.0224.7
to other treatments (P< 0.05). Adult mortality was high in all the oil treatments compared with the control (Table 2). In addition all treatments signi®cantly reduced adult emergence (Table 3, P < 0.05) and the number of seeds damaged (Table 4, P < 0.05) for at least 2 months. At 3 months the reduction in adult emergence with C. nardus was signi®cantly less than that due to other treatments. At 4 months M. spicata was the only treatment to reduce adult emergence and the number of seeds damaged. Consideration of the data from all parameter/time combinations indicated an order of potency M. spicata> M. piperata> M. arvensis>C. nardus.
4. Discussion
The marked decline in egg laying was perhaps a consequence of the mild suppressing eect exerted by these volatile oils on the beetles' mating Ð a decisive factor in¯uencing the subsequent number of eggs laid by the beetle (Engelmann, 1970). The current results are in agreement with the report of Schmidt et al. (1991) who have reported that Acorus calamus oil vapour treatment for 96 h could be satisfactory for controlling the adults and their egg laying.
Table 2
Percentage mortality of adult Callosobruchus maculatus after 24 h exposure on cowpea seed in containers treated with plant oils at various times prior to the commencement of exposure
Container holding period (months)
Source of oil 1 2 3 4
Cymbopogon nardus 45 35 10 0
Mentha arvensis 55 70 40 5
Mentha piperata 70 70 45 0
Mentha spicata 100 80 50 10
Control 0 0 0 0
Table 3
Number of adults of Callosobruchus maculatus emerged (mean2SD, n= 5) from fresh batches of cowpea seeds added to containers treated with plant oils at various times prior to exposure
Container holding period (months)
Source of oil 1 2 3 4
Cymbopogon nardus 7.223.8 64.226.8 153.0215.2 197.4227.1
Mentha arvensis 1.420.6 38.626.5 126.6217.1 179.4218.8
Mentha piperata 0 15.823.4 88.626.4 187.2219.5
Mentha spicata 0 9.8622.9 29.624.2 150.0216.9
Control 158.2210.1 176.827.4 171.029.1 184.2223.6
The drastic reduction in adult emergence that was recorded could also in part be due to low hatchability of eggs. It is probable that oil vapours diused into eggs and aected the physiological and biochemical process associated with embryonic development. These ®ndings corroborate the observations recorded for peppermint and citronella oil vapours on Earias vittella eggs (Marimuthu et al., 1997) when signi®cant reduction in seed damage was recorded in M. spicata and M. piperata oil treated containers. In that case protection of cowpea seeds for up to 2 months was mainly due to reduced oviposition, low adult emergence and high adult mortality, and this agrees completely with the results of the present investigation. From this study it is quite obvious that the bioactive principles of the four oils are responsible for checking the population build-up of C. maculatus in cowpea seed storage. The application of these oils in any integrated pest management strategy to protect stored grains is likely to be advantageous, as they are economically viable, environmentally safe and socially acceptable.
Acknowledgements
The authors are grateful to Novartis Foundation, Basel, Switzerland for providing ®nancial assistance to carry out this research work.
References
Abbott, W.W., 1925. A method for computing the eectiveness of an insecticide. Journal of Economic Entomology 18, 265±267.
Agarwal, A., Lal, S., Gupta, K.C., 1988. Natural products as protectants of pulses against pulse beetle. Bulletin of Grain Technology 26, 154±164.
Champ, B.R., Dyte, C.E., 1976. Report of the FAO global survey of Pesticide susceptibility of stored grain pests. FAO Plant Production and Protection Series, No. 5.
El-Nahal, A.K.M., Schmidt, G.H., Risha, E.M., 1989. Vapours ofAcorus calamusoil a space treatment for stored product insects. Journal of Stored Products Research 25, 211±216.
Engelmann, F., 1970. The Physiology of Insect Reproduction. Pergamon Press, New York.
Fagoonee, I., 1987. Use of neem in vegetable crop protection in Mauritius. In: Schmutterer, H., Ascher, K.R.S. Table 4
Number of seeds damaged by feeding ofCallosobruchus maculatus (mean2SD) in fresh batches cowpea added to containers at various time prior to exposure
Container holding period (months)
Source of oil 1 2 3 4
Cymbopogon nardus 6.023.3 47.027.2 85.427.0 93.825.9
Mentha arvensis 1.220.5 35.626.4 85.625.7 91.424.7
Mentha piperata 0 12.021.9 63.625.9 95.424.7
Mentha spicata 0 7.421.9 20.622.1 73.628.8
Control 90.827.3 92.428.2 93.025.9 94.424.0
(Eds.), Natural Pesticides from the Neem Tree (Azadirachta indica A. Juss) and other Tropical Plants. Proceedings of the Third International Neem Conference, Nairobi, Kenya. Eschborn, Germany, pp. 419±429. Gbolade, A.A., Adebayo, T.A., 1993. Fumigant eects of some volatile oils on fecundity and adult emergence of
Callosobruchus maculatusF. Insect Science and Its Application 14, 631±636.
Ivibjaro, M.F., 1983. Preservation of cowpea Vigna unguiculata (L.) Walp. with neem seed Azadirachta indica A. Juss. Protection Ecology 5, 171±182.
Marimuthu, S., Gurusubramaniam, G., Krishna, S.S., 1997. Eect of exposure of eggs to vapour from essential oils on egg mortality development and adult emergence in Earias vittella(F.) (Lepidoptera : Noctuidae). Biological Agriculture and Horticulture 14, 303±307.
Matthews, G.A., 1993. Insecticide application in stores. In: Matthews, G.A., Histop, E.C. (Eds.), Application Technology for Crop Protection. CAB International, London, pp. 305±315.
Messina, F.J., 1991. Life history variation in a seed beetle adult egg-laying vs larval competitive ability. Oecologia 85, 447±455.
Mitchell, R., 1983. Eects of host plants variability on the ®tness of sedentary herbivorous insects. In: Denno, R.F., McClure, M.S. (Eds.), Variable Plants and Herbivores in Natural and Managed Systems. Academic Press, New York, pp. 343±370.
Raja, N., Albert, S., Ignacimuthu, S., Ofuya, T.I., Dorn, S., 1998. Evaluation of some plants for use in the control of cowpea weevilCallosobruchus maculatus(Coleoptera: Bruchidae). Applied Tropical Agriculture 3, 34±39. Risha, E.M., El, Nahal K.M., Schmidt, G.H., 1990. Toxicity of vapours ofAcorus calamusL. oil to the immature
stages of some stored product Coleoptera. Journal of Stored Products Research 26, 133±137.
Saxena, B.P., Mathur, A.C., 1976. Loss of fecundity inDysdercus koenigii (F.) due to vapours of Acorus calamus
oil. Experientia 32, 315±316.
Schmidt, G.H., Risha, E.M., El-Nahal, A.K.M., 1991. Reduction of progeny of some stored product Coleoptera by vapours ofAcorus calamusoil. Journal of Stored Products Research 27, 121±127.
Schmutterer, H., 1987. Fecundity reducing and sterilising eects of neem seed kernel extracts in the Colorado potato beetle Leptinotarsa decemlineata. In: Schmutterer, H., Ascher, K.R.S. (Eds.), Natural Pesticides from the Neem Tree (Azadirachta indica A. Juss) and other Tropical Plants. Proceedings of the Third International Neem Conference, Nairobi, Kenya. Eschborn, Germany, pp. 351±360.
Tanzubil, P.B., 1987. The use of neem products in controlling the cowpea weevil, Callosobruchus maculatus. In: Schmutterer, H., Ascher, K.R.S. (Eds.), Natural Pesticides from the Neem Tree (Azadirachta indicaA. Juss) and other Tropical Plants. Proceedings of the Third International Neem Conference, Nairobi, Kenya. Eschborn, Germany, pp. 517±523.
White, N.D.G., 1995. Insects, mites and insecticides in stored grain ecosystems. In: Jayas, D.S., White, N.D.G., Muir, W.E. (Eds.), Stored Grain Ecosystems. Marcel Dekker, New York, pp. 123±168.
Xie, Y.S., Fields, P.G., Isman, M.B., 1995. Repellency and toxicity of azadirachtin and neem concentrations to three-stored product beetles. Journal of Economic Entomology 88, 1024±1031.
Zehrer, W., 1984. The eect of the traditional preservatives used in northern Togo and neem oil for control of storage pests. In: Schmutterer, H., Ascher, K.R.S. (Eds.), Natural Pesticides from the Neem Tree (Azadirachta indica A. Juss) and other Tropical Plants. Proceedings of the Second International Neem Conference, Rauiscbhholzhausen, Germany. Eschborn, Germany, pp. 453±460.
Zettler, J.L., Cuperus, G.W., 1990. Pesticide resistance in Tribolium castaneum (Coleoptera:Tenebrionidae) and
