Digenous Plants Against Three Stored Product Beetles

ABSTRACT Toxicity and protectant potential of isoeugenol, limonene and essential oil of Hyptis spicigera against Sitophilus zeamais (Motsch.), Callosobruchus maculatus F. and Tribolium castaneum (Herbst.) and the effect of the oils on germination of maize and cowpea were investigated in the laboratory using contact toxicity, grain treatment and repellency assays. The effects of acetone extracts from leaf and seed of Hyptis spicigera on oviposition and adult emergence of C. maculatus were also investigated in the laboratory. Isoeugenol, limonene and essential oil extract of H. spicigera applied topically could not kill any significant number of the three beetle species. Grains treated with isoeugenol and limonene killed at least 30% of C. maculatus and T. castaneum but the two compounds and essential oil extract of H. spicigera were not toxic to S. zeamais. Isoeugenol and limonene did not cause inhibition of the development of eggs, larvae and pupae of T. castaneum and S. zeamais but these completely inhibited the development of eggs and larvae of C. maculatus. Maize and cowpea seeds treated with isoeugenol and limonene were less damaged by S. zeamais and C. maculatus compared to the controls. The essential oil extracts of H. spicigera, isoeugenol and limonene evoked strong repellency against the three beetle species. The repellency was strongest against S. zeamais in H. spicigera treated grain. All the three oils did not have effect on the viability of cowpea and maize seeds and hence did not affect their germination. Acetone extracts of both leaf and seed powder of H. spicigera caused a decline in the oviposition and adult emergence of C. maculatus.