The Insecticidal Activity of Neem and Palm Kernel Oils on Bean Weevil (Callosobruchus maculatus F.) (Coleoptera: Chrysomelidae: Bruchinae) Infestations of Stored Cowpea (Vigna unguiculata L. Walp)

Abstract

Even though it has been established that neem oil has insecticidal properties, its desirability as a plant-based insecticide is unsuitable owing to the sulfurous odour it deposits on the grain(s) that makes it bitter and impinges on its acceptability. For this reason, another oil of plant origin, palm kernel oil (PKO), was admixed with it to reduce the bitter taste and test for their bioinsecticidal potential on the insect pest of stored cowpea seeds. The general objective was to determine the combined effect of neem and palm kernel oils in controlling bean weevil infestations of stored cowpea. The results showed that the treated seeds recorded a significantly higher ( $p<0.05$ ) mortality of adult Callosobruchus maculatus (Coleoptera: Chrysomelidae: Bruchinae), a reduction in oviposition, and a decrease in the number of emerged insects with the interval of treatment application, and the seeds that were treated had a significantly lower adult emergence hole ( $p<0.05$ ) and a reduction in % grain damage ( $p<0.05$ ), and the weevil perforation index (WPI) was <100%. The findings of this study suggest that admixing neem oil and palm kernel oil has the potential insecticidal efficacy of controlling the bean weevil of stored cowpea, and based on the quantity of palm kernel oil mixed with neem oil, the seeds treated tend to have varying levels of bitterness and sulfurous odour deposit.