UC Riverside

Pyrethroid insecticides frequently contaminate urban runoff and are transported to downstream waterways. Due to their high hydrophobicity, these insecticides have a propensity to partition from surface water into sediment, where they may be slow to degrade. Past studies have shown adverse impacts to aquatic ecosystems, where many fish and invertebrates are especially susceptible to pyrethroids. Apart from non-target toxicity, pyrethroid pollution risks exposure to larval mosquitoes, which are nuisance pests and vectors for disease across the world. Urban species of mosquitoes often lay their eggs in underground storm drain systems due to their tendency to accumulate standing water and detritus. In this exposure scenario, selection pressure may be exerted on populations of larvae, increasing their resistance to pyrethroids. Pyrethroids are one of the few types of insecticides used for adult mosquito control in the United States, and a reduction of their efficacy imposes costs on pest management operations. Though pyrethroid contamination of urban water bodies, like streams, is well-documented, specific information on their occurrence within storm drain systems along with their influence on current mosquito populations is lacking. In the first study of this dissertation, the prevalence of pyrethroid residues in water from urban catch basins, which are storm drain structures that accept runoff, was determined. Results showed that pyrethroids were present in nearly every sample, with the pyrethroid bifenthrin being the most frequently detected analyte. In the second study, pyrethroid distribution across catch basins, open channels, and stormwater outfalls in a storm drain system was assessed. Pyrethroids were detected in every sediment, algae, and biofilm sample, and bifenthrin concentrations in catch basin water were notably elevated compared to those in other structures. In the third study, larval mosquitoes of strains established from field-collected populations were exposed to bifenthrin at an environmentally relevant concentration for multiple generations, and parameters associated with permethrin resistance in adults were measured. It was found that mosquito strains were already highly resistant to permethrin and that the treatment increased survival after exposure to permethrin for one of the strains, which may indicate that exposure effects may differ significantly by strain. The results of this dissertation research highlight the ubiquity of pyrethroids in urban storm drains and suggest that they may play a role in maintaining, or even encouraging the development of, pyrethroid resistance in mosquitoes.