Evaluation of nontarget effects of methoprene applied to catch basins for mosquito control

The mosquito larvicide methoprene is a juvenile growth hormone mimic that is widely used to control mosquito larvae in stormwater catch basins. This study addresses two concerns pertaining to methoprene's use for mosquito control. First, measurements of methoprene concentrations were made from water in catch basins that had been treated with methoprene and from an adjoining salt pond near where the treated catch basins emptied. The concentrations of methoprene in catch basins and at drainage outlets after application at the rates currently used for mosquito control in southern Rhode Island were 0.5 ppb and lower, orders of magnitude below what has been determined as detrimental to organisms other than mosquitoes. Second, the effects of methoprene on the communities that live in catch basins were evaluated both in simulated catch basins in the laboratory and in actual catch basins in the field. We found no evidence of declines in abundances of any taxa attributable to the application. Furthermore, we found no consistent changes in community-level parameters (e.g., taxonomic richness, and dominance-diversity relationships) related to methoprene application in either field or laboratory trials.