Comparative biocidal activities of some crude plant species powders against the cowpea weevil (Callosobrochus maculatus (F.)(Coleoptera: bruchidae))

Abstract

Callosobruchus maculatus is one of the most important pests of cowpea in storage causing severe economic damage to the grain. This study investigated the efficacies of three plant materials (Azadirachta indica, Calotropis procera and Chromolaena odorata) leaves against the cowpea weevil. Concentrations of 0.1, 0.25 and 0.5g of the plant powders were used on 10g of grains with 10 adult weevils in each and a Control (untreated) in triplicates. The results showed significant (P< 0.05) negatively effects of the plant materials on the survival of C. maculatus at the highest concentration. In all trails, mean daily mortality in adult C. maculatus were significantly(p<0.05) increased. All plant powder type were effective but concentration-dependent, with C. procera recording significantly (P < 0.05) higher mortality at the various concentrations while C. odorata, elicited the least mean daily mortality. The lowest LD₅₀ (0.63g) was obtained with C. procera. These plants materials were found to also affect the egg-laying capacity of C. maculatus. Treatment with C. odorata recorded significantly(P<0.05) higher number of eggs laid at all concentrations, though the egg-laying capacity was also concentration-dependent; whereas C. procera recorded the least number of eggs laid. All the three plants powders tested demonstrated significant insecticidal potency on stored cowpea weevils, with C. procera and C. odorata showing significantly higher and lower insecticidal potentials respectively. These findings will help in solving problem associated with food security especially with respect to stored produce.