Efficacy of aqueous suspension and granular formulations of Bacillus thuringiensis (Vectobac) against mosquito vectors

The efficacy of aqueous suspension (AS) and granular (G) formulation of Bacillus thuringiensis var. israelensis (Vectobac) was tested against the immatures of mosquito vectors in the laboratory and under field conditions. Laboratory tests showed that the aqueous suspension was relatively more effective against Culex quinquefasciatus than Aedes aegypti and Anopheles stephensi, the respective LC 50 values being 0.046, 0.060 and 0.190 mg/l. In stream pools, with the application of Vectobac AS at 1.2 l/ha, more than 80% reduction in immature density of Anopheles larvae (Anopheles fluviatilis and Anopheles culicifacies) was observed for 2–8 days, and at 2.4 l/ha for 3.5–9.0 days. At the dosage of 7.0 kg/ha of the granular formulation, a reduction in immature density by more than 80% was observed for 2–9 days. In polluted habitats such as cesspits, U-drains and cement tanks, the effectiveness of Vectobac AS lasted for 1–4 days when applied at 1.2 and 2.4 l/ha, and Vectobac G was effective for 1–3 days at application rates of 7.0 and 14.0 kg/ha against C. quinquefasciatus. There was no significant difference in the effectiveness between the two formulations and the two application rates.