Effect of Neem Powder (Azadirachta indica A. Juss) on the Control of Cowpea Weevils [Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)] in Cowpea Beans

Abstract

The cowpea weevils [Callosobruchus maculatus (F.)] are the primary pest affecting grain and seeds of stored cowpea beans. The control of this insect comprises expensive methods such as fumigation or spraying of chemicals, which are unfeasible for small farmers. The use of insecticidal plants, such as the neem tree (Azadirachta indica), may stand out as a cheaper alternative. This study evaluates the bioactivity of neem powder on the control of weevils in cowpea seeds. We tested four types of powders according to the part of the plant from which it originated: leaves, fruits, bark, and the mixture of these three parts in the same proportion. The bioassay of the action spectrum and the insecticidal effects were assessed using four doses of each type of powder: 0.25%, 0.50%, 0.75%, and 1.00% per 20g of beans. The fruit powder repelled weevils at the lower doses used, while leaf powder, bark, and the mixture were neutral. Although neem powder reduced the survival of insects, the reduction was slow, showing mild toxicity. Neem powder may be an alternative for the control of cowpea weevils in storage units. However, the efficiency of the control depends on the part of the plant and dosage used.