Laboratory Evaluation of Residual Phytotoxicity of Some Plant Powders to the Merchant Grain. Beetle, Oryzaephilus mercator Fauvel (Coleoptera: Silvanidae), Infesting Stored Kernels of Irvingia gabonensis

Abstract

Investigations were conducted on phytochemical composition and residual toxicity of seven plant powders (which had been stored for 4 months) to the merchant grain beetle, Oryzaephilus mercator Fauvel, infesting kernels of Irvingia gabonensis. Beetle mortality data taken at days 1,3,5 and 7 post-infestation showed that all test plants excluding M. myristica caused higher level of beetle mortality than occurred in control. Cashew nut shell, Anacardium occidentale, powder was the most potent (cumulative mean mortality of 52.5 %) matching the efficacy of pirimiphos-methyl, which served as insecticide check in addition to an untreated control. It was followed by powders of J. curcas (35.0 %) and P. guineense (30.2 %), while the least toxic was M myristica. Mortality value for the latter (%), though numerically lower, was not significantly different from those of C. citratus (%) and X. aethiopica (%). Mean residual toxicity increased with duration of exposure The least number of adults emerged from pirimiphos-methyl treated jars, followed by A. occidentale powder, -while M myristica was the least potent. Phytochemical analysis revealed varied proportions of typical plant constituents such as phytates, flavonoids, hydrogen cyanides, alkaloids, tannins, oxalates, phenols and saponins some of which are responsible for the residual action of the tested plants.