Bioactivity of some natural products against the cowpea storage weevil <i>Callosobruchus Maculatus</i> L.

Abstract

This work was carried out to evaluate the insecticidal activity of extracts from 14 plant species of Ghanaian origin against Callosobruchus maculatus adults under laboratory conditions. Phytochemical screenings of the 14 plant species were performed using standard laboratory methods to determine the types of secondary natural products present in the plant species. Aqueous, petroleum ether and ethanolic extracts of the 14 plant species were screened for their bioactivity against Artemia selina in a brine shrimp lethality test. The pesticidal activities of the plant products against Callosobruchus maculatus were investigated in laboratory experiments. Contact toxicity (filter paper impregnation method), grain treatment with plant products for insect population and mortality assays, and also effect of the plant products on grain damage were obtained and compared with Actellic Super EC (synthetic insecticide) during a three-month observation period. Cymbopogan winterianus oil caused the highest mortality, least damage to grains and the highest antireproductive effect. All grain-protective properties of the natural products were concentration and time dependent. Extracts of Cassia alata showed good potential in protecting cowpea and gave better protection than the powder, whilst Griffornia simplicifolia did not significantly protect the grains. Phytochemical investigations of the plants revealed the presence of terpenes, saponins, tannins, glycosides, alkaloids, anthraquinones and flavonoids. The presence of some of these compounds may be responsible for the pesticidal action of the plants.

Keywords: Phytochemical screening, Extracts, Insecticidal, Brine shrimp lethality test, Cowpea.