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 such as 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 on the Island of Hawai‘i.

Results

Among 4101 single-nucleotide polymorphisms (SNPs) identified in the VGSC region of Ae. albopictus genomes from four Hawaiian Islands, 44 were classified as synonymous in the coding DNA sequence (CDS) region. No non-synonymous mutations were found in the CDS region, suggesting an absence of genotypic resistance to pyrethroids in these populations. In phenotypic assays, all individuals from the two Ae. aegypti populations and the Ae. albopictus population from Miloli‘i were completely knocked down within 10 min of permethrin exposure, indicating that both species remain phenotypically susceptible to permethrin. However, knockdown rates of less than 97% observed in the Ae. albopictus population from Kawaihae suggest early signs of the development of phenotypic resistance.

Conclusions

This study is the first to report the phenotypic insecticide resistance profile of Hawaiian Aedes mosquitoes. Hawaiian populations of Ae. albopictus and Ae. aegypti remain susceptible or are in the stage of developing resistance 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.

Graphical Abstract