Reduced effectiveness of repellents in a pyrethroid-resistant strain of Aedes aegypti (Diptera: culicidae) and its correlation with olfactory sensitivity.

BACKGROUND: The mosquito, Aedes aegypti (Diptera: Culicidae), is a vector of dengue fever, zika, chikungunya, and yellow fever viruses, and in many areas possesses significant levels of resistance to pyrethroids. Behavioral performance was assessed in 15, 30, and 60 min exposures in a high throughput vapor phase spatial repellency assay to three contact repellent standards: N,N-diethyl-3-methylbenzamide (DEET), ethyl 3-[acetyl(butyl)amino] propanoate (IR3535), and 2-undecanone, as well as pyrethrum extract, transfluthrin, and metofluthrin in susceptible (Orlando) and a pyrethroid-resistant Puerto Rico strain of Aedes aegypti. Additionally, electroantennographic studies were used to investigate the antennal sensitivities to these compounds in both strains.

RESULTS: Resistance was found to all tested insect repellents in the Puerto Rico strain of Ae. aegypti. Resistance ratios at the different time points were about 2 for DEET, 3 for 2-undecanone, and 12 for IR3535. Resistance was also observed to pyrethrum extract (∼9-fold), transfluthrin (∼5-fold), and metofluthrin (∼48-fold) in repellent behavioral response. Electrophysiological analysis found decreased antennal sensitivity to all repellents tested, consistent with their behavioral effects.

CONCLUSION: The reduced sensitivity to these repellents may represent a fitness cost arising from the kdr mutation present in Puerto Rico Aedes aegypti. This work highlights the need for understanding collateral effects from the evolution of pesticide resistance in mosquitoes, and the importance of finding alternative strategies to control resistance development. © 2019 Society of Chemical Industry.