P23 - Establishing the Window of Selection (WoS) and the level of resistance of knock down resistant (kdr) mutations for Aedes aegypti mosquitoes topically treated with deltamethrin

Abstract: Perpetual use of insecticides has led to the emergence and persistence of insecticide resistance. Insecticide resistance is a major threat that prevents effective mosquito population control and consequently results in continued mosquito-borne disease transmission. Knockdown resistance (kdr) confers resistance against pyrethroids – the main insecticide class used for disease prevention. Selection for kdr occurs within the Window of Selection (WoS), which establishes the concentration range of xenobiotic that exerts positive selection for resistance. Fundamentally, selective pressure is highest within the WoS when all genotypes containing resistant alleles – heterozygous and homozygous-resistant organisms – survive. However, heterozygous mosquitoes are infrequently included in resistance studies and models. Additionally, male mosquitoes are less included because they are of lower epidemiological relevance. In this study, we establish the WoS of deltamethrin for Aedes aegypti kdr strains (including heterozygotes and males) using topical bioassay application and establish the level of resistance (LoR) of each strain and sex. Strains included in this study originate from Florida where deltamethrin has been historically used, and contain zero, one, or two alleles of kdr mutations V1016I and F1534C. Results determine the upper bound of the WoS to exceed the amount of deltamethrin recommended for mosquito control by the U.S. Environmental Protection Agency. Therefore, we can assume applications following these recommendations are selecting for kdr. The LoR was significantly different between the heterozygous and homozygous-resistant strains, supporting the inclusion of heterozygotes in future research and modeling. Lastly, results show no significant difference in the LoR between males and females of the same strain when comparisons are mass-relativized. This suggests that males could be used for resistance surveillance, increasing their flexibility. Continuation of this work will improve our understanding of which insecticide treatments create the greatest selection for resistance and will improve our modeling of insecticide resistance evolution.