287 - Thermal stress and pyrethroid resistance in the invasive mosquito Aedes aegypti

Abstract: The invasive mosquito Aedes aegypti poses significant public health risks in California urban environments, where high summer temperatures coincide with peak mosquito biting activity increasing the risk of dengue virus transmission. This study investigated the relationship between thermal stress and pyrethroid resistance in Ae. aegypti Madera, CA populations. Using CDC bottle bioassays with CDC technical grade λ-cyhalothrin (10 µg/mL), time-mortality data was collected from three temperature-treated wild-type F₀ female Madera strain (MAD) female mosquito groups (18 °C, 26 °C, and 34 °C) and compared to the ROCK lab susceptible strain. Optimally treated (26 °C) MAD strain mosquitoes had the highest mortality rate 30 min post-exposure, inferring temperature treatment influences survivability of MAD strain mosquitoes. An ultra-low volume spray (ULV) field trial at three sites, one site per temperature treatment, was conducted with wild-type F₀ MAD female Ae. aegypti and the susceptible ROCK strain using commercial grade Demand CS to bridge understanding of technical resistance and practical resistance in the field. All temperature treated MAD groups had an overall knockdown rate of ~ 0%, 1-hour post-exposure and a knockdown rate of ~ 3%, 12-hours post-exposure. This suggests that MAD strain mosquitoes are highly resistant to field application of Demand CS, revealing that lab-based bottle bioassays may not accurately predict real-world outcomes. Pools of surviving and knocked down/dead mosquitoes were collected from each assay and field trial for RNA extraction and RNA-seq. Expression analysis of the genes of interest (HSP70, HSP20, HSP83, CYP9J32, CYP9J28, CYP6M11, CYP6BB2, V410L, V1016I, and F1534C) will characterize the transcriptomic response to pyrethroid exposure in MAD Ae. aegypti. Findings from this study will provide insights into the relationship between thermal stress and pyrethroid resistance, and guide vector control strategies by identifying resistance markers in field populations to enable more targeted Ae. aegypti management in California.