Insecticide resistance, particularly to pyrethroids, in mosquitoes is a looming threat to effective pest control. Pyrethroids are frequently employed to manage mosquito populations, but excessive exposure may encourage resistance development and hamper long-term efforts. Urban settings also have multiple avenues, including concrete surfaces and catch basins, by which pesticides may be retained and released over extended periods of time. This study, conducted in collaboration with several California vector control agencies, measured pyrethroid concentrations in catch basins along with resistance in associated populations of mosquitoes to determine the presence of a relationship between the two. Samples of water and various solids were collected from several urban catch basins in Woodland, Elk Grove, and Ontario, CA. Mosquitoes from the Culex pipiens species complex were caught near or in basins and used to raise colonies to a specific age for testing. Environmental samples were extracted for 8 pyrethroid analytes, and reared mosquitoes were subjected to resistance bottle bioassays using permethrin. Pyrethroids were detected in all catch basin samples, with the most prevalent analytes being bifenthrin, permethrin, and fenpropathrin. All field-caught mosquitoes exhibited permethrin resistance, and resistance ratios were determined by comparing their LT50 with that of positive lab colony CQ1. Correlations between pyrethroid concentrations and resistance ratios were not statistically significant, likely indicating that the number of basins sampled was not high enough. Subsequent work will focus on catch basin constituents’ direct effects on mosquito development and resistance.

Pyrethroid residues in urban catch basins and their relationship with permethrin resistance in Culex pipiens mosquitoes

ACS Fall 2020 Virtual Meeting

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