Larvicidal persistence of formulations of Bacillus thuringiensis var. israelensis to control larval Aedes aegypti

After detection of resistance to the organophosphate temephos in populations of Aedes aegypti in Brazil, corncob granule (CG) and water-dispersible granule (WDG) formulations of Bacillus thuringiensis var. israelensis (Bti) were introduced in routine focal treatments. Larvicidal persistence and the influence of exposure to sunlight on VectoBac formulations of Bti were compared in 250-liter fiberglass water containers. Production of pupal Ae. aegypti in containers was used to indicate control. In untreated containers, survival of larvae was always above 95%. A temephos sand granule formulation used as reference treatment maintained 100% control throughout the 12-wk period in all situations. Under sunlight exposure, control dropped below the 90% level in the 2nd week after treatment at both dosages of VectoBac CG (1 and 2 g/50 liters) and VectoBac tablet (T) formulation at 1 tablet/100 liters. VectoBac T at 1 tablet/50 liters provided 2 wk of 100% control. VectoBac WDG at dosages of 1 and 2 g/500 liters provided 100% control for 3 wk. Without sunlight exposure (covered containers), VectoBac CG provided 9 wk of continuous 100% control and 5 wk of continuous 100% control, respectively, at 1 and 2 g/50 liters. The VectoBac T formulation at both dosages initially provided 2 wk of 100% control. After this period, the control level fluctuated between 96 and 100%. VectoBac WDG provided continuous 100% control for 7 wk for the lower dosage and for 6 wk for the higher dosage. At both dosages of WDG, 100% control was achieved in 11 wk out of the 12-wk period.