The F1534C voltage-sensitive sodium channel mutation confers 7-to 16-fold resistance to pyrethroid insecticides in Aedes aegypti

BACKGROUND Recent outbreaks of dengue and Zika have emphasized the importance to effectively control Aedes aegypti, which vectors the viruses causing these diseases. Pyrethroid insecticides are primarily used to control adult A. aegypti, especially during disease outbreaks. However, pyrethroid resistance in A. aegypti is an increasing problem. Mutations in the voltage-sensitive sodium channel (Vssc) are a common mechanism of pyrethroid resistance. The F1534C mutation is common and distributed globally in A. aegypti populations, but previous studies disagree about the role of this mutation in conferring resistance to pyrethroid insecticides. RESULTS We isolated a congenic strain (1534C:ROCK) which was closely related to a susceptible strain Rockefeller (ROCK), but was homozygous for the 1534C Vssc allele. We determined resistance levels against eight insecticides that target the VSSC: six pyrethroids, DDT and DCJW (the bioactivated metabolite of indoxacarb). The resistance levels ranged from 7- to 16-fold, and resistance was inherited as an incompletely recessive trait. We also found a novel 367I+1520I+1534C allele, in addition to the 1534C and 1520I+1534C alleles, in mosquitoes from Thailand. The T1520I mutation did not increase pyrethroid resistance beyond what was conferred by the F1534C mutation alone. CONCLUSION The F1534C Vssc mutation is common in A. aegypti populations and confers 7- to 16-fold resistance to pyrethroids, DDT, and DCJW in Aedes aegypti. These resistance levels are considerably less than previously reported for the S989P+V1016G mutations. Our results provide useful information for resistance management, specifically the levels of resistance conferred by the most common Vssc mutation in A. aegypti. (c) 2020 Society of Chemical Industry