Comparative Pesticidal and Repellent Effects of Some Selected Plant Species on Cowpea bruchid (Coleoptera:Bruchidae)

Abstract

Toxic and repellent effects of four plarts belonging to the family Lamiaceae against the stored legume pest. Callosobruchus maculatus (Coleoptera.Bruchidae) were investigated. Several bioassays were carried out under ambient laboratory conditons. to evaluate 'the effects using powdered leaves of Hyptis suaveolensii..). Mentha l'iridis(L.). Ocimum !!r(ltissimul11(L.). and Ocimum S(lI1Clllll1(L.). Repellency tests were conducted using four (2.5.5.0. 7.5 and IO.Og) doses of powders from each plant in a multi-choice bio-assay apparatus and observations were recorded 3 hours after the exposure of adult C maculatus beetles to the treatments. Observations on toxicity were obtained with five doses (1.0, 3.0. 5.0, 7.0 and 10.Og) of each plant after 6. 18 and 24 hours of exposure using a no-choice bio-assay apparatus. In each experiment. 50.0 g of mung bean (Vigna radio/a) seeds were ILlixcd with different doses of leaf powders separately before the introduction of the adult 58 beetles. All four plants at all doses produced significantly higher (p< 0.05) toxic and repeller: effects :1 (p< 0.05) C maculatus when compared with the controls. The highest repeltency (96.45%) in C. maculatus was}bserv~!d after 3 hours with the dosage of IO.Og of powdered leaves of M. viridis. This was followed by H. suaveolens. 0. gratissimum and 0. sanctum eliciting repellent effects of 83.72%.77.07% and 74.63% respectively. Just after 4 hours. a hundred percent mortality was observed when the beetles were exposed to 5.0 g of leaf powder of M. viridis. Furthermore. 0. gratissimum also elicited relatively high mortality in the beetles at the dose of 109.When compared with the other three plants M. viridis was extremely effective in inducing both repellent and toxic activities in the beetles. In general. the strong repellent and insecticidal properties of the leaves of these four plants especially those of M viridis suggest that stored legumes can be efficiently protected from C maculatus infestations