Efficacy of Neem and Papaya Leaf Powders on the Cowpea Bruchid Callosobruchus maculatus (Coleoptera: Chrysomelidae)

Abstract

Callosobruchus maculatus Fab (Coleoptera: Chrysomelidae) is a pest that causes enormous damage to cowpea stocks. To limit this damage, farmers resort to synthetic insecticides despite their consequences on the environment and human health. The objective of this study was to evaluate the efficacy of neem and papaya leaf powders as an alternative to control C. maculatus pests of Vigna unguiculata Walp. stocks (Fabaceae). Five hundred grams (500 g) of cowpea seeds contained in one-litre glass jars were infested with 10 pairs of C. maculatus aged 24 hours. Each of the powders was used to treat the seeds at 20, 40, 60 g/kg cowpea in each jar respectively. For each dose of each biopesticide used, four batches (Batch 1, Batch 2, Batch 3 and Batch 4) were prepared and monitored after 1, 2, 3 and 4 months of storage respectively. The rate of reduction of the C. maculatus population, and the weight losses of the cowpeas, were determined. The results showed that after 4 months of cowpea storage, neem caused, at doses of 20, 40 and 60 g/kg, a significant reduction in the bruchid population by 42.58±6.97%; 79.1±5.31% and 84.27±5.7%; while at the same doses, papaya reduced the population by 14.32±4.53%; 42.18±5.83% and 64.86±8.03% compared to the negative control. No bruchids emerged from seeds treated with the synthetic insecticide (BEXTOXIN: fumigant) used at the dose of 0.25 g/kg during all storage periods. All doses significantly reduced cowpea weight losses, especially with the higher doses. Neem leaf powder was more effective than papaya leaf powder. Neem leaf powder could therefore be used as an alternative to synthetic chemicals in pest management of cowpea stocks.