Efficacy Evaluation of Deltamethrin and Cypermethrin Against Insecticide-resistant and -susceptible Strains of Dengue Vector Aedes aegypti

Abstract

The objective of this study was to assess knockdown and insecticidal effects of deltamethrin and cypermethrin in order to identify appropriate concentration of the chemicals for the control of insecticide resistant strains of Aedes aegypti, the dengue vector in Thailand. The concentration used in this study was at 0.025, 0.05, 0.1, 0.15 and 0.2 g a.i./m2; and the mosquitoes were Aedes aegypti strains from Rayong and Chanthaburi Provinces compared with laboratory susceptible strain using World Health Organization susceptibility test. It was found that the two field populations of Ae. aegypti showed moderate resistance to deltamethrin and high resistance to cypermethrin. The toxic effect of deltamethrin was observed at the doses of 0.15 and 0.2 g a.i./m2with 100.0% mortality in both field populations while cypermethrin gave 91.3-97.0% mortality for Rayong population and 89.8-92.4% mortality for Chanthaburi population. Deltamethrin also provided a faster knockdown effect than cypermethrin. Therefore, further studies are needed to evaluate the residual effect of deltamethrin applied with the active ingredient at 0.15 and 0.2 g/m2. Spraying residual insecticides on potential resting places of adult Ae. aegypti, especially in dengue endemic areas facing insecticide resistance in dengue vectors, can be considered a supplementary method to be used in combination with the major methods (insecticide space-spraying and larviciding) for dengue vector control.