A Single Crossing-Over Event in Voltage-Sensitive Na ⁺ Channel Genes May Cause Critical Failure of Dengue Mosquito Control by Insecticides

Abstract

The voltage-sensitive sodium (Na ⁺) channel (Vssc) is the target site of pyrethroid insecticides. Pest insects develop resistance to this class of insecticide by acquisition of one or multiple amino acid substitution(s) in this channel. In Southeast Asia, two major Vssc types confer pyrethroid resistance in the dengue mosquito vector Aedes aegypti, namely, S989P+V1016G and F1534C. We expressed several types of Vssc in Xenopus oocytes and examined the effect of amino acid substitutions in Vssc on pyrethroid susceptibilities. S989P+V1016G and F1534C haplotypes reduced the channel sensitivity to permethrin by 100- and 25-fold, respectively, while S989P+V1016G+F1534C triple mutations reduced the channel sensitivity to permethrin by 1100-fold. S989P+V1016G and F1534C haplotypes reduced the channel sensitivity to deltamethrin by 10- and 1-fold (no reduction), respectively, but S989P+V1016G+F1534C triple mutations reduced the channel sensitivity to deltamethrin by 90-fold. These results imply that pyrethroid insecticides are highly likely to lose their effectiveness against A. aegypti if such a Vssc haplotype emerges as the result of a single crossing-over event; thus, this may cause failure to control this key mosquito vector. Here, we strongly emphasize the importance of monitoring the occurrence of triple mutations in Vssc in the field population of A. aegypti.

Author Summary

Pyrethroids are one of the major classes of insecticides that is widely used to control mosquito vectors. The target site of pyrethroids is found in the voltage-sensitive Na ⁺ channel (Vssc) consisting of about 2100 amino acid residues. In this study we generated several types of Vssc with a single or multiple mutations, expressed in Xenopus oocytes, and examined their electrophysiological properties using two-electrode voltage clamp method. We confirmed that Aedes aegypti Vssc harboring a triple mutations exhibited extremely high levels of resistance to pyrethroid insecticides. This Vssc type can be generated by a single crossing-over event of two resistant Vssc genes that are widely distributed in Southeast Asia, one of the greatest dengue endemic areas. Our results highlight the importance of intensive monitoring for the triple mutations in Vssc in the A. aegypti mosquito.