Studies of the susceptibility of Aedes aegypti (Diptera: Culicidae) from Timor‐Leste to pyrethroid and organophosphate insecticides

Aedes aegypti is the mosquito vector of dengue worldwide and also occurs in far northern Queensland, where cases of dengue occur annually. Aedes aegypti from colonies established from Townville, Queensland, Australia, and Dili, Timor-Leste, were exposed in bottle bioassays to determine their susceptibility to three pyrethroids, the organophosphate, malathion and two commercial pyrethroid-based products: Reslin (R) (50 g/l bioresmethrin) and Aqua-K-Othrine (R) (20 g/l deltamethrin) both containing the synergist, piperonyl butoxide. Aedes aegypti from Dili, Timor-Leste, were resistant to permethrin, lamda-cyhalothrin and resmethrin, but were susceptible to malathion and the two pyrethroid products. Biochemical microplate assays were used to measure activity levels of three enzymes (oxidase, esterase and glutathione-S-transferase), and there were no significant increases in the activity of oxidase and glutathione-S-transferase, but an increase in esterase activity in A. aegypti from Dili was detected. The study showed that mosquitoes originating in Timor-Leste are tolerant of pyrethroid insecticides used in Australia and monitoring of insecticide susceptibility in A. aegypti introduced into Australia needs to be maintained to ensure that adequate control of dengue vectors is achieved.