Comparing organophosphate and pyrethroid resistance levels of Aedes aegypti (Diptera: Culicidae) in frequent and infrequent application areas of Taiwan

Abstract

Aedes aegypti mosquitoes spread a number of diseases that cause significant impacts to public health. In Taiwan, Ae. aegypti are mainly controlled using chemical insecticides, but previous studies indicate that Ae. aegypti may have developed resistance to several insecticides. We hypothesized that Ae. aegypti resistance levels could be affected by insecticide application frequencies and therefore compared transcriptome information, expressions of metabolic resistance genes, and gene mutations of field adult mosquitoes collected from Kaohsiung City (frequent application area, insecticides applied once a week) and Tainan City (infrequent application area, insecticides applied only when dengue cases were discovered); a laboratory strain was established as control. Next-generation sequencing was used to identify potential resistance genes from four main detoxification categories, bioassays were used to determine knockdown effects and mortality rates, and point mutations relating to target resistance were further analyzed. A total of 50 detoxification differential transcripts were identified following comparison with the laboratory strain, and more differential transcripts were found in mosquitos collected from the frequent application area (Kaohsiung). Mosquitoes from areas with frequent applications displayed lower mortality rates, confirming a difference in resistance levels. Additionally, mosquitoes from frequent application areas showed higher levels of resistance to pyrethroids compared with organophosphates. We found silent mutations at G923, L982, and A1007, as well as point mutations at S989P, V1016G, F1534C, and D1763Y. V1016G occurred in all four strains we collected, indicating that pyrethroid resistance in Ae. aegypti has begun to develop in all regions.