Effects of Three Medicinal Plant Products on Survival, Oviposition and Progeny Development of Cowpea Bruchid, Callosobruchus maculatus (Fab.) [Coleoptera: Chrysomelidae] Infesting Cowpea Seeds in Storage

Powders from three medicinal plants were evaluated for their efficacy as contact and fumigant insecticides on cowpea bruchid, Callosobruchus maculatus (Fab.) in the laboratory at ambient tropical conditions of temperature and relative humidity. The plant powders tested included Capsicum frutescens L. (fruit and seed), C. annum Miller (fruit and seed) and Citrus sinensis Osbeck (peel). The powders were applied at rates 0.0 (control), 2g and 3.0g/20g of cowpea seeds either directly for contact with the insect pest or in plastic containers to assess fumigant toxicity of their volatiles. Results of contact toxicity assay showed that powders of C. frutescens and C. annum seeds were more effective against the adult C. maculatus evoking 100% mortality within 2 days of application at 3g/20g of cowpea seeds. There was no progeny development of the bruchid in samples treated with Capsicum species. The survival of the bruchid from eggs to adults when treated with the plant powders showed that there was significantly (P 0.05) more % progeny development in the control (69.32%) compared to others. However, the results of fumigant assays showed that C. sinensis had the highest insecticidal activity causing 281.25% mortality of C. maculatus within 4 days of application at rate 3g/20g of cowpea seeds. This study showed that all the tested plant products were toxic to cowpea bruchid and the powders can be mixed with cowpea seeds to prevent hatching of the eggs thereby helping in their management