Glycine to valine substitution in the short intracellular linkers of domain II enhances I1011M-mediated sodium channel resistance to Type I pyrethroids, but not Type II pyrethroids.

Pyrethroids are widely used against agricultural pests and human disease vectors due to their broad insecticidal spectrum, fast action, and low mammalian toxicity. Unfortunately, overuse of pyrethroids has led to knockdown resistance (kdr) caused by mutations in voltage-gated sodium channels. Mutation I1011M was repeatedly detected in numerous pyrethroid-resistant Aedes aegypti populations from Latin American and Brazil. In addition, mutation G923V was first reported to coexist with I1011M in permethrin/DDT-resistant Ae. aegypti, whether G923V enhances the I1011M-mediated pyrethroid resistance in sodium channels remains unclear. In this study, we introduced mutations G923V and I1011M alone or in combination into the pyrethroid-sensitive sodium channel AaNa1-1 and examined the effects of these mutations on gating properties and pyrethroid sensitivity. We found mutations I1011M and G923V + I1011M shifted the voltage dependence of activation in the depolarizing direction, and none of mutations affect the voltage-dependence of inactivation. G923V and G923V + I1011M mutations reduced the channel sensitivity to both Type I and Type II pyrethroids. However, I1011M alone conferred resistance to Type I pyrethroids, not to Type II pyrethroids. Interestingly, significant synergism effects on Type I pyrethroids were observed between mutations G923V and I1011M. The effects of all mutations on channel sensitivity to DDT were identical with those to Type I pyrethroids. Our results confirm the molecular basis of resistance mediated by mutations G923V and I1011M and may contribute to develop molecular markers for monitoring pest resistance to pyrethroids.