Genotypic Variation in Cowpea (Vigna unguiculata (L.) Walp.) for Resistance to Pulse Beetle (Callosobruchus maculatus F.) and the Protective Effects of Botanical Powders

Abstract

Cowpea (Vigna unguiculata (L.) Walp.) is a significant grain legume commonly grown in tropical and subtropical regions and is an important source of protein, vitamins, and minerals for humans and livestock. Nevertheless, storage losses caused by the pulse beetle, Callosobruchus maculatus (F.), continue to constrain cowpea production and storage, particularly in sub-Saharan Africa. This study assessed varietal resistance and botanical powders as alternative protectants against C. maculatus infestation under in vitro conditions at the Savannah Agricultural Research Institute (CSIR-SARI), Nyankpala, Ghana. The experiment used a split-plot factorial arrangement in a randomised complete block design (RCBD) with three replications. The main plots comprised four cowpea varieties (Padituya, Songotra, Apagbaala, and Zaayura), while the subplots comprised five protectant treatments (untreated control, neem seed powder, basilicum powder, hyptis powder, and Phostoxin). Data were collected on oviposition, developmental period, adult mortality, progeny emergence, grain damage, and grain weight loss. Significant interaction effects between variety and protectant were observed for oviposition, adult emergence, and mortality of C. maculatus. Songotra and Zaayura recorded lower oviposition, adult emergence, grain damage, and grain weight loss than Apagbaala and Padituya. Phostoxin produced the lowest adult emergence and highest mortality, while neem seed and basilicum powders similarly reduced oviposition, progeny emergence, and grain damage. Hyptis powder provided comparatively lower protection. These findings indicate that combining resistant varieties, particularly Songotra and Zaayura, with neem seed or basilicum powder may improve the protection of stored cowpea grains and provide a more environmentally favourable alternative to synthetic insecticides.