Response of Callosobruchus maculatus (Coleoptera: Chrysomelidae: Bruchinae) to extracts of cashew kernels

Cashew kernels were extracted with six different solvents namely methanol, ethanol, water, acetone, pet-ether and n-hexane. The different extraction products were evaluated on C. maculatus adults for their mortality, ovicidal and adult emergence effects. The long-term protectant ability of the cashew kernel extracts and water absorption capacity of the treated cowpea seeds were also investigated. The results obtained showed that the steam distillate was most toxic to C. maculatus. The least toxic extracts on the insect were those of methanol and ethanol. The extracts drastically reduced oviposition in C. maculatus. The cowpea seeds treated with steam distillate had the lowest water absorption capacity, while the highest water absorption capacity was obtained in grains treated with ethanol and methanol. At 2.0% v/w cashew kernel extracts, the percentage water absorption capacity of cowpea seeds increased with increase in the interval of submergence. Steam distillate and the extracts of n-hexane, pet-ether and acetone completely prevented infestation and damage of the treated cowpea seeds for a period of three months as there was neither weight loss nor damage in the treated grains. In the grains treated with the methanol and ethanol extracts, damage of 20.17% and 9.76% were recorded, respectively. The results obtained from this study revealed that extract of cashew kernel is effective in controlling cowpea storage bruchid, C. maculatus and could serve as an alternative to synthetic insecticides for the protection of stored cowpeas against bruchids.