Evaluation of biological and chemical insecticide mixture against Aedes aegypti larvae and adults by thermal fogging in Singapore

To improve the operational efficiency of dengue vector control in Singapore, larvicide and adulticide were applied together by thermal fog generator (Agrofog AF40). The mixture consisted of Bacillus thuringiensis var. israelensis (Vectobac 12 AS) as biological larvicide at 1.5 L/ha and pirimiphos-methyl (Actellic 50 EC) as adulticide at 100 g ai/ha, diluted 10-fold with water. Aerosol of this mixture was evaluated against the mosquito Aedes aegypti (L.) (Diptera: Culicidae) in bioassays using cages of 10 adult females exposed at heights of 0.3-2.4 m and distances of 3-12 m from the hand-held generator. Cups containing 200 mL water were treated at ground level by exposure to the aerosol application at the same distances from the generator. Subsequent larval bioassays on days 1, 7, 14, 21 and 28 post-spray involved exposing 20 larvae/cup for 48 h. Droplets had VMD 57 microm and female mosquitoes were killed by 2 s exposure to the aerosol at 3 m. We obtained 92-100% mortality of the adult mosquitoes and 100% control of larvae at 3 m distance, but only 10-13% mortality at 12 m from the fogger. In treated cups, larvae showed high mortality (92%) when exposed for 48 h even 1 month post-treatment. Results demonstrate the practical advantage of using this mixture of Vectobac 12AS and Actellic 50 EC for simultaneous control of Aedes adults and larvae, with prolonged larvicidal efficacy in treated containers.