Contribution of different constituents to the toxicity of the essential oil constituents of <i>Vernonia amygdalina</i> (Compositae) and <i>Xylopia aetiopica</i> (Annonaceae) on maize weevil <i>Sitophilus zeamais</i> Motschulsky (Coleoptera: Curculionidae)

Abstract

The lethal toxicity of the major constituent of the essential oils of Vernonia amygdalina and Xylopia aetiopica, and of selected blends of these against Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae) was compared with those of the full blends of the essential oils. The compounds were assayed in amounts and proportions present in the minimum 100% lethal dose of the essential oils. The major component of X. aetiopica was found to be largely responsible for the toxic action of its essential
oil against S. zeamais, On the other hand the toxic action of V. amygdalina was due to the combined effects of its constituents, either with or without significant individual toxic action of their own against the insects. The implication of these results and their implication in screening and using plants and their phytochemicals for S. zeamais control is highlighted.