Pyrethroid Resistance in Association with the Use of Insecticide Impregnated Bed Nets

Abstract

Abstract

There has been concern about whether pyrethroid tolerance or resistance will be selected in anophelines and other mosquitoes through the use of pyrethroid-impregnated bed nets. Pieces of nylon netting impregnated with different concentrations of lambda-cyhalothrin and permethrin were used for mosquito selection, to investigate the development of pyrethroid tolerance or resistance in adult Aedes aegypti and Anopheles maculatus. The WHO susceptibility test kits were lined inside with insecticide-impregnated nylon netting and mosquitoes were exposed for periods of 30 seconds to 4 minutes. Mortality was scored after a 24-hour observation period. The LT₅₀ values and the resistance ratio or increased tolerance in each generation were determined. The exposure of 9 generations of Ae. aegypti to 0.015 g/m² lambda-cyhalothrin, and 8 generations of Ae. aegypti to 0.15 g/m² permethrin produced 2.6-fold and 2.8-fold tolerance, respectively, whereas 5 generations of An. maculatus exposed to 0.1 g/m² permethrin showed 1.4-fold tolerance. The pattern of increased tolerance levels to lambda-cyhalothrin and permethrin by both mosquito species indicated no evidence for the development of pyrethroid resistance.

Keywords : pyrethroid-impregnated bed nets, pyrethroid tolerance, Aedes aegypti, Anopheles maculatus