Integration of Bacillus thuringiensis H-14 formulations and pyriproxyfen for the control of larvae of Aedes aegypti and Aedes albopictus

Studies were carried out on the bioefficacy and residual activity of Bacillus thuringiensis israelensis H-14 (Bti) (water-dispersible granules of VectoBac ABG 6511 and liquid formulations of VectoBac: 12AS) and pyriproxyfen (insect growth regulator, Sumilarv 0.5%) as direct applications for control of larvae of Aedes aegypti and Aedes albopictus. Two dosages of each Bti formulation (285 and 570 international toxic units [ITU]/liter) and the integration of both Bti formulations and pyriproxyfen were used for residual tests with 45-liter earthen jars for a period of 4 wk. In 1 test series, the treated water was replenished daily with 6 liters of seasoned untreated water. In the 2nd test series, the water in the jars was topped up to the 40-liter level during evaluation. Neither Bti formulation remained effective for a full week. Water-dispersible Bti granules provided effective initial control activity against Ae. aegypti and Ae. albopictus for both test designs (with replenishment and without replenishment of water). The higher dosage (570 ITU/Iiter) for both Bti formulations was only partially effective at the end of 1 wk after being diluted. After 1 wk, water-dispersible Bti granules provided greater larval mortality than did liquid Bti formulation against both mosquito species when integrated with pyriproxyfen. Pyriproxyfen (79.5 and 159 mg/liter) on its own showed low larvicidal activity but provided very effective control of adult emergence. In this study, integration of Bti (285 and 570 ITU/liter) with pyriproxyfen (79.5 mg/liter) extended the duration of partial larval control somewhat, but live larvae persisted throughout the 4-wk test. The integration effect was more obvious when water-dispersible Bti granules were integrated with pyriproxyfen than when liquid Bti was used. Integration of Bti with pyriproxyfen had a negative effect on adult emergence, which was completely inhibited by pyriproxyfen after day 1. Daily replenishment of water increased Bti activity and provided slightly better larval control. Aedes albopictus and Ae. aegypti were both completely susceptible to the higher concentration of Bti and pyriproxyfen in both test designs (with replenishment and without replenishment of water).