Mortality and Knockdown Effects of Deltamethrin and Cypermethrin on Plywoodsurface against Laboratory and Field Strains of Aedes aegypti

Abstract

Deltamethrin and cypermethrin have been used for Aedes aegypti mosquito control, a primary vector of dengue viruses in Thailand. The objective of this study was to determine the lethal and knockdown effects of Emulsifiable concentrate (EC) formulations of deltamethrin at doses of 0.025, 0.05, 0.1, and 0.2 g/m², and cypermethrin at doses of 0.1, 0.3, 0.5 and 0.7 g/m² sprayed on unpainted plywood against Ae. aegypti. Background insecticide susceptibility of the Chanthaburi strain of Ae. aegypti was compared with a lab susceptible strain showing the field strain was highly resistant to 0.05% concentrations of both chemicals. At 30-min test exposure, the Chanthaburi strain with deltamethrin EC at 0.025 g/m² produced a 34% knockdown and 10% mortality after 48-hour post-exposure, while the highest dose (0.2 g/m²) had a higher knockdown (83.3%) but relatively low mortality (18.8%) showing significant post-exposure recovery. Cypermethrin EC at 0.1 g/m² displayed low knockdown effect (26.5%) and mortality (6.1%), while at 0.7 g/m², it produced a much greater knockdown response (83.7%) but high recovery with only 26.8% final mortality. Conversely, deltamethrin at 0.025-0.2 g/m² showed complete knockdown, but only at 0.1-0.2 g/m² gave >80% mortality in the laboratory strain. Similarly, cypermethrin (0.1-0.7 g/m²) provided 100% knockdown and high mortality (92-100%) after 48 hours holding time.