Resistance phenotyping and kdr genotyping in Aedes aegypti and Aedes albopictus from Thailand

Insecticide resistance profiles and underlying mechanisms are essential for developing effective and sustainable vector control strategies. This study aimed to investigate the insecticide susceptibility profiles and kdr genotypes in field populations of Aedes aegypti and Ae. albopictus. Bioassays were conducted on six Ae. albopictus and two Ae. aegypti populations towards deltamethrin, lambda-cyhalothrin, pirimiphos-methyl, and bendiocarb. Piperonyl butoxide (PBO) synergism and kdr genotyping of the Vssc gene were conducted. Against pyrethroids, Ae. aegypti and four out of six Ae. albopictus populations exhibited resistance. PBO restored full susceptibility across Ae. albopictus populations but not against Ae. aegypti, suggesting metabolic resistance involving cytochrome P450 monooxygenese. All tested mosquitoes were susceptible to pirimiphos-methyl. F1534C and V1016G kdr mutations were detected in both populations of Ae. aegypti. For the F1534C locus, the resistant allele Cys1534 was predominant but population specific. At codon 1016, Gly1016 was present but less frequent than Val1016, with resistant homozygotes population specific. These findings highlight heterogeneous resistance profiles across provinces and species, underscoring the need for vector and location-specific vector control strategies. PBO synergist addition remains viable option for managing Ae. albopictus resistance but pyrethroid alternatives such as pirimiphos-methyl and bendiocarb offer an interspecies option for controlling Aedes vectors.