102 - Phenotypic and genotypic insights into mosquito insecticide resistance in Thailand (2021-2024)
Wednesday, March 5, 2025
9:30 AM – 9:40 AM AST
Location: 208 B
Abstract: Background: This study provides a comprehensive investigation into both phenotypic and genotypic insecticide resistance in mosquito populations across Thailand from 2021 to 2024. The aim was to evaluate the extent of resistance in Aedes and Anopheles mosquito populations, two key vectors for dengue and malaria, respectively, using both WHO tube tests for phenotypic resistance and genetic sequencing for knockdown resistance (kdr) mutations.
Methods: Field colonies of Aedes and Anopheles mosquitoes were established from endemic regions, totaling 54 colonies (43 Aedes spp. and 11 Anopheles spp.). Phenotypic resistance was assessed using WHO tube tests with pyrethroids (bifenthrin, deltamethrin, permethrin, λ-cyhalothrin) and an organophosphate (pirimiphos-methyl). Genotypic resistance was evaluated in Ae. aegypti populations by sequencing specific kdr gene mutations.
Results: From 2021 to 2024, Ae. aegypti populations exhibited widespread resistance to bifenthrin and permethrin, with mortality rates below 90%. However, susceptibility to deltamethrin was observed in some strains. Resistance profiles in Ae. albopictus varied by strain and insecticide. Most Anopheles populations were susceptible, though the An. minimus TAK-PP strain from Tak Province displayed potential resistance to deltamethrin. Genotypic analysis identified kdr mutations in 70-75% of Ae. aegypti populations, with the F1534C mutation being the most prevalent. Additional heterozygous mutations (S989P, V999A, T1520I) contributed to resistance. Notably, over 50% of mosquitoes that survived insecticide exposure did not possess any mutations in the kdr gene regions studied, suggesting alternative mechanisms of resistance. Conclusion: The increasing insecticide resistance observed in Aedes populations in Thailand, particularly to pyrethroids, poses significant challenges for vector control. The identification of widespread kdr mutations highlights the importance of genetic monitoring in resistance management. Ongoing surveillance and adaptive vector control strategies are crucial to mitigating the rise of resistance in mosquito populations and maintaining the efficacy of insecticide-based interventions.
