Larvicidal Efficacies, Insect Growth Regulatory Activities and Vectorial Fitness of Sterculia setigera Bark Extracts against Culex quinquefasciatus Mosquitoes - Diptera: Culicidae.

Abstract

Mosquitoes are not only a nuisance as biting insects; they are also involved periodically in transmitting diseases to human and animals. Frequent use of insecticides for mosquito control has caused development of resistance, adverse effect on non –target organisms and serious environmental concern. This study was conducted to determine the phytochemical constituents of bark (S.setigera) and evaluate its vectorial fitness potential, insect growth regulatory efficacies and mosquito larvicidal activities against Culex quiquefasiatus. The egg rafts of culex quinquefasciatus mosquitoes were collected from some breeder habitat within the study area and were incubated using standard protocol. The barks of the plant were extracted using methanol and n-hexane. Four concentrations 0.00625, 0.0125, 0.025 and 0.05 were used for n-hexane and 0.2, 0.3, 0.4 and 0.5 were used for methanol respectively. The test procedure was carried out according to World Health Organisation protocol for insecticide testing. The bark of S.setigera reveals important bio-active phytochemicals namely; flavonoids, tannins, saponins, alkaloid, steroid, anthraquinone, and cardiac glycoside. The methanol and n-hexane of the bark of S.setigera significantly elongated the developmental survivorship of Culex quinquefasciatus. The results obtained for larvicidal bioassay of methanol and n-hexane extracts of the bark of Sterculia setigera showed significant (p<0.05) effect on the species. The results also indicated a dose-and – time dependent toxicity of the plant. i.e. the higher the concentration and period of time, the higher the mortality. The LC50 and LC90 of the methanol extracts of the bark of Sterculia setigera were 0.25mg/L and 0.42mg/L While LC50 and LC90 of the bark of n-hexane extract were 0.01mg/L and 0.04mg/L respectively. The results of this study, suggested that the plant species, S.setigera, possess promising bio-active phytochemicals for larvicidal and growth disruptive agents for effective mosquito vector control.