Abstract:Over the years, several studies have been conducted to discover new botanicals that could be used to control stored product insect pests. The efficacy of two plant leaf powders, Moringa oleifera and Senna alata, in reducing post-harvest losses caused by Callosobruchus maculatus in the cowpea variety, Ife-brown, was assessed under laboratory conditions at 24 hrs, 48 hrs, and 72 hrs. Each of the plant powders was tested by exposing the beetles to various dosages of 0.5, 1.0 and 2.0 g in five replications. Pirimiphos-methyl at 0.015 g was used as a standard check in the experiment. Each experimental unit was infested with five pairs of adult insects in the sex ratio 1:1, male: female. Callosobruchus maculatus was subjected to contact and fumigant toxicity assays. Results revealed that adult mortality significantly increased with time but not with increasing concentrations. Moringa oleifera at 0.5g compared favourably with Pirimiphos-methyl after 72 hours, with 82.0% adult mortalities. Senna alata applied at 1.0 g had the highest fumigant effect on adults, with a percentage mortality of 73.3%. Oviposition (62.6) and adult emergence (46.0) were significantly reduced on cowpea seeds treated with 0.5 g of M. oleifera leaf powder compared with Pirimiphos-methyl, having a population of 80.2 and 64.1, respectively.