Target-site resistance genotype impacts temperature-dependent pyrethroid toxicity in Aedes aegypti

Authors: DAGG, KENDRA - University Of Florida; Estep Iii, Alden; FAROOQ, MUHAMMAD - Anastasia Mosquito Control District; QUALLS, WHITNEY - Anastasia Mosquito Control District; BURGESS, EDWIN - University Of Florida

Submitted to: Pesticide Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/18/2026
Publication Date: 6/19/2026
Citation: Dagg, K.A., Estep Iii, A.S., Farooq, M., Qualls, W.A., Burgess, E.R. 2026. Target-site resistance genotype impacts temperature-dependent pyrethroid toxicity in Aedes aegypti. Pesticide Biochemistry and Physiology. 222:107217. https://doi.org/10.1016/j.pestbp.2026.107217.
DOI: https://doi.org/10.1016/j.pestbp.2026.107217

Interpretive Summary: Resistance to the limited number of insecticide classes remains a major challenge in mosquito control. Resistance surveillance often relies on high throughput toxicological assays conducted under standard laboratory conditions that do not reflect environmental variation, particularly temperature. Laboratory conditions may obscure resistance phenotypes, leading to misinterpretation of resistance status. Here, University of Florida and USDA Mosquito & Fly Research Unit scientists examined how different resistance mutations in Aedes aegypti affected the relationship between temperature and toxicity. We examined well characterized strains at 3 field relevant temperatures using 3 standard assessment methods. Notably, we found that while the laboratory methods were sensitive to changes in temperature, temperature did not significantly change adulticide efficacy. These findings emphasize the complex interactions between resistance and temperature and demonstrate that these interactions can vary based on the specific intervention.

Technical Abstract: Resistance to the limited number of insecticide classes remains a major challenge in mosquito control. Resistance surveillance often relies on high throughput toxicological assays conducted under standard laboratory conditions that do not reflect environmental variation, particularly temperature. Temperature is known to impact insecticide toxicity, with many pyrethroids demonstrating a negative temperature coefficient (i.e. increase in toxicity as temperature decreases). Thus, laboratory conditions may obscure resistance phenotypes, leading to misinterpretation of resistance status. Here we examined how different pyrethroid resistance target-site knockdown (kdr) mutations in Aedes aegypti affected the relationship between temperature and toxicity. Two laboratory and three field-type congenic strains, differing in F1534C and V1016I kdr mutations, were tested against a type I (permethrin) and type II (deltamethrin) pyrethroid. Toxicological responses were assessed at three ecologically relevant temperatures (19°C, 25°C, 31°C) through 1) electrophysiological recordings of larval central nerves exposed to concentrations of insecticide, 2) adult topical assays, and 3) wind tunnel assays at 100% and 50% label rates of a formulated adulticide. Nerve firing rates varied by strain, temperature, and insecticide, with permethrin generating greater temperature dependent differentiation at all concentrations compared to deltamethrin. Between 19°C and 25°C, topical application demonstrated shifts in the negative temperature coefficient of toxicity based on congenic background, kdr type, and insecticide, with no differences observed between 25°C and 31°C. Temperature did not significantly affect adulticide performance in wind tunnel assays. These findings suggest that temperature may alter resistance phenotypes in kdr mutant Ae. aegypti emphasizing the complex interactions between genetic mutations and temperature.