Pyrethroid Insecticide Resistance of Aedes albopictus and Aedes aegypti (Diptera: Culicidae) across the Hawaiian Islands

Background Aedes albopictus (Skuse, 1894) and Aedes aegypti (Linnaeus, 1762) (Diptera: Culicidae) are invasive species in the Hawaiian Islands as well as other islands of the Pacific and serve as the primary vectors of arboviruses like dengue virus. Despite its significance to public health, data on their insecticide resistance remains limited. Knowledge of the level of insecticide resistance is critical in developing effective mosquito control strategies, especially when an arboviral disease outbreak occurs. Methods This study investigated the phenotypic and genotypic resistance of Hawaiian Ae. albopictus and Ae. aegypti to permethrin, one of the commonly used pyrethroids. Genomic sequences of 93 Ae. albopictus samples from four Hawaiian Islands (Kaua‘i, O‘ahu, Maui, and the Island of Hawai‘i) were screened for non-synonymous mutations in the voltage-gated sodium channel (VGSC) gene (chromosome 3: 345,142,499 − 345,663,668). Phenotypic resistance to permethrin was assessed using a modified Centers for Disease Control and Prevention (CDC) bottle bioassay on Ae. albopictus and Ae. aegypti collected from two socio-environmentally distinct sites. Results Among 4,101 single-nucleotide polymorphisms (SNPs) identified in the VGSC region of Ae. albopictus genomes from for Hawaiian Islands, 61 were classified as synonymous. No non-synonymous mutations were found, suggesting an absence of genotypic resistance to pyrethroids in these populations. In phenotypic assays, over 97% of Ae. albopictus and all Ae. aegypti individuals were knocked down within 10 minutes of permethrin exposure. These high knockdown rates indicate that both species remain phenotypically susceptible to permethrin. Conclusions This study is the first study reporting the phenotypic insecticide resistance profile of Hawaiian Aedes mosquitoes. Hawaiian populations of Ae. albopictus and Ae. aegypti remain susceptible to pyrethroids, as demonstrated by the absence of VGSC mutations and high knockdown rates in permethrin bioassays. While no genotypic and phenotypic resistance was detected in these two Aedes species, monitoring for resistance in other mosquito species and through alternative mechanisms is needed.