Influence of Bacillus thuringiensis var. israelensis on mosquitocidal, longevity and fecundity of malarial vector, Anopheles stephensi liston (Insecta: Diptera: Culicidae)

Mosquitoes are vectors of many human diseases and cause environmental nuisances. Due to their large geographical distribution and abundance, Anopheles stephensi represent the most important mosquito species in India. The management of these disease vectors using conventional pesticides has failed because of the high reproductive ability, development of insecticide resistance of mosquito species and environmental pollution. These reasons are leading to a search for novel molecules. As so the Bacillus thuringiensis var. israelensis (Bti) provide effective alternatives to broad spectrum larvicides in many situations with little or no environmental impact. Taking into account environmental benefits including safety for humans and other non-target organisms, reduction of pesticide residues in the aquatic environment, increased activity of most other natural enemies and increased biodiversity in aquatic ecosystems, their advantages are numerous. Bioassay was conducted to test the larval, pupal, and adult toxicity, longevity and mosquito fecundity. The mosquitocidal activity of Bti was tested at different concentrations, ranging between 10 to 40 ppm, against the different larval stages (1st instar to 4th instar) of Anopheles stephensi. Bioassays were done on newly moulted larvae under laboratory conditions. The technical material showed a high level of activity with mortality recorded for treated and following stages and happened after incomplete development. For the same treated series a significant decrease was also recorded in the longevity of the adult. In other experiments the compound was applied against the fourth instars larvae and its effects was investigated on fecundity of female emerged from larval treated series. The results showed that Bti reduced significantly the laying egg number, egg hatchability and the percentage of fecundity.