Pesticidal Potential of the Leaves of Ocimum Casilicum linn. and Hyptis spicigera lam. on Callosobruchus maculatus F. (cowpea weevils) family lamiaceae

Abstract

A laboratory study was conducted on the pesticidal potentials of the aromatic plants Ocimum basilicum Linn and Hyptis spicigera Lamarck both of the family Lamiaceae against Callosobruchus maculatus (cowpea weevils), a pest of stored cowpeas. The essential oils produced by these plants which are a complex mixture of terpenes, sesquiterpenes, their oxygenated derivatives and other aromatic compounds were obtained by steam or hydro/hot-distillation method using a soxhlet extractor. 70g portions of Ocimum basilicum and Hyptis spicigera powdered leaves were separately extracted sequentially using the solvents; Hexane, ethylacetate, acetone, methanol and water in order of increasing polarities. Phytochemical screening of the both plant leaves showed the presence of alkaloids, cardiac glycosides, in all the extracts; flavournoids, tannins, steroids and carbohydrates in most of the extracts; while saponins and anthraquinones tested virtually absent. The extracts of both plants were tested for pesticidal activity against untreated cowpea seeds using cowpea weevils. Within the experimental time of 24-72hrs using 100mg and 200mg of 100mg/ml concentration, the solvent extracts generally demonstrated a knock down and mortality activity. Hexane extracts showed 80% mortality and 66.67% knockdown while acetone extracts showed 75% mortality and 60%knockdown. The effects were significant for both plants at P>0.05. Both plants exhibited an increase in effect with increasing concentration of the extracts.