Does mosquito control reduce the aquatic invertebrates in Spring Creek, Laramie, Wyoming?

Many towns in the western United States control mosquitoes to reduce the threat of West Nile Virus; however, little is known about how these insecticides may affect other animals. Broadly applied insecticides may alter populations of non-target invertebrates. Permethrin is commonly used to reduce adult mosquitoes including in Laramie, Wyoming; however, the insecticide is more toxic in water. The insecticide may be of particular concern to aquatic ecosystems in close proximity to urban areas. We measured the density and biomass of drift and benthic invertebrates before and after mosquito control in Spring Creek, a spring stream that runs through Laramie, Wyoming. The intent of our project was to quantify the effects of incidental exposure of non-mosquito aquatic invertebrates to Permethrin. Drifting invertebrates were collected before, immediately after (~3-6 hours), and one day after (~28 hours) insecticide application. We collected five benthic samples using a Hess sampler from each site before Permethrin application in June and after two months of application in August. We observed a significant increase in the abundance, biomass, and richness of drifting invertebrates immediately after the application of Permethrin. Insects drift to escape from danger or unsuitable conditions. Analysis of benthic samples is still underway. Increases in drifting invertebrates may alter ecosystems by changing resources available to fish and riparian birds. Understanding the unintended ecological impacts of pest control practices can help develop more effective management approaches.