Pesticidal activity of certain plant extracts and their isolates against the cowpea beetle Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae: Bruchinae)
Different extracts from seven plant species were assayed against the cowpea beetle (Callosobruchus maculatus) in the laboratory. The plants were extracted sequentially with petroleum ether, chloroform and ethyl alcohol. The petroleum ether extract of each was fractionated into sap and unsap, then identified by GC chromatography. Also compounds isolated from chloroform and alcohol extracts of Citrullus colocynthis and petroleum ether extract of Nicandra physaloides were tested for their toxicity against the adult beetle. The sensitivity of the adults to various crude extracts revealed great variation in effectiveness. Petroleum ether and chloroform extracts of Nicandra physaloides proved to be the most toxic in comparison to other extracts tested, while petroleum ether extracts of Curcuma longa proved to be the least effective. All the fatty acid fractions of the seven plant species were toxic to the adult beetles at the tested concentrations. N. physaloides, Schinus terebinthifolius and Dodonaea viscosa resulted in 100% mortality of adults at the highest concentration tested (1.0%). Using 1.0% unsap fraction of Dodonaea viscosa resulted in 100% mortality between the adults. The least percentage mortality between the adult beetles recorded (22%) was for unsap fraction of T. orientalis at concentration of 0.0625% but increased to 80.0% mortality at concentration of 1.0%. The compounds isolated from chloroform and alcohol extracts of C. colocynthis and petroleum ether extract of N. physaloides proved to be highly efficient against C. maculatus adults.