Efficacy of plant extracts on the toxicity, ovipositional deterrence and damage assessment of the cowpea weevil, Callosobruchus maculatus (Coleoptera: Bruchidae)

A laboratory experiment was conducted to investigate the efficacy of different plant derivatives against the development of the cowpea weevil, Callosobruchus maculatus (F) (Coleoptera: Bruchidae) fed on cowpea, Vigna unguiculata (W) seeds. The leaf extracts of romatic plants, Murraya koenigii and Azadirachta indica (A.Juss) were evaluated for their growth, adult mortality and oviposition inhibition of C. maculatus. The results revealed that the extracts of the two plant species caused a considerable reduction in the number of weevils. The combination of neem seed kernel extract and leaf extract of M. koenigii was the most effective in checking insect infestation and allowing the least number of F1 adults to emerge from the seeds over other treatments. Acetone leaf extracts of M. koenigii were more toxic to adult beetles compared to ethanolic extracts. Thus, the botanicals acted as insect antifeedant and the order of toxicity of various treatments on cowpea weevil were: combination of neem seed kernel extract + M. koenigii leaf extract > neem > M. koenigii.