Entomotoxicity of some agro-wastes against cowpea bruchid, Callosobruchus maculatus (Fab.) [Coleoptera: Chrysomelidae] infesting cowpea seeds in storage

Cowpea, Vigna unguiculata is a popular agricultural produce known as poor man's meat among Africans because it is very cheap and affordable. In spite of its importance, its infestation by cowpea seed bruchid, Callosobruchus maculatus has been a major constrain hindering its storage. Considering the high level of infestation of cowpea by C. maculatus and the high level of pollution caused by agricultural products, this research investigated the entomotoxicant effectiveness of rice husk, wheat husk and groundnut pod ash and powder in the control of cowpea beetle in storage. This study was carried out under laboratory condition of ambient temperature 28 ± 2 °C and 70 ± 5% relative humidity. The wastes (rice husk, groundnut pod and wheat husk) were pulverized separately and another portion was burnt to ashes at 525 °C. The powders and the ashes were analyzed for their proximate composition, phytochemical content (powders) and silica content (ashes). The powders and the ashes were tested at 0.1, 0.2, 0.3, 0.4 and 0.5 g/20 g of cowpea. Rice husk ash resulted in the highest mortality of 100% of adult beetles at dosage of 0.5g/20g cowpea after 96 h post-application. Wheat husk ash at 0.4 and 0.5 g per 20 g cowpea seed had the highest protectant ability on cowpea as it reduced fecundity to 4.67% and prevented adult emergence, seed damage and weight loss. The ash of the wastes caused more mortality of the adult beetles than their powders. The results obtained showed that the wastes caused high mortality of C. maculatus. It was also found that the wastes had some phytochemicals which might be responsible for the recorded high mortality. The findings showed that the tested agro-wastes have a promising insecticidal potential against C. maculatus, and can be used as possible alternatives to synthetic chemical insecticides for the control of stored product insects.