Susceptibility and reproductive capability of Callosobruchus maculatus (Coleoptera: Bruchidae) to Datura metel extracts as potential cowpea grains protectant

Abstract

In this study we evaluated the toxicity of Datura metel on susceptibility and reproductive capability of Callosobruchus maculatus (Coleoptera: Bruchidae). Datura metel leaves powder was extracted with hexane, ethyl acetate, chloroform, acetone and methanol using Soxhlet apparatus and tested at 50, 100 and 150 µl/20 g cowpea seeds corresponding to 2.5, 5 and 7.5 µl/g. Mortality of C. maculatus, percentage reduction of eggs laid, egg hatchability, reduction in adult emergence, infestation, tolerance and weight loss were calculated at a different time of exposure. The lowest LD₅₀ (0.202 µl) recorded was with ethyl acetate extract at 96 h of exposure, followed by methanol extract (9.45 µl) at 72 h of exposure. The mortality rate after 96 h exposure was ethyl acetate > methanol > acetone > hexane > chloroform. At 2.5 and 5 µl/g, methanol extract significantly (p < 0.05) reduced percent egg laid (59.92% and 59.31% respectively). Ethyl acetate extract of D. metel resulted in the lowest percentage of egg hatchability at 2.5 µl/g (15.0%), 100 µl (22.63%) and 7.5 µl/g (23.89%). Percent reduction in adult emergence was highest in methanol extract treated grains at 5 µl/g (89.33%) and 7.5 µl/g (91.67%). While, percent tolerance was lowest in ethyl acetate treated grains at 2.5 µl/g (72.80%) and 7.5 µl/g 58.67%) respectively. The lowest percentage weight loss in 7.5 µl/g was 2.50% (chloroform), followed by methanol (2.57%) and ethyl acetate (2.87%) with no significant difference (p > 0.05) among used solvents. D. metel proved effective against C. maculatus infestation and enhanced storability of cowpea grains.