Effects of dimilin® on freshwater litter decomposition

Abstract

AbstractThe pesticide Dimilin® (diflubenzuron) is widely used on forests in Maryland to control gypsy moths, and it may enter streams via leaf litter. We measured the effects of Dimilin on stream leaf litter processing using artificial leaf packs treated with the pesticide. Over the entire study period (464 degree days) the Dimilin‐treated packs were processed more rapidly than control packs. There was a continuous loss of Dimilin from the packs, apparently due to leaching. Both Dimilin‐treated and control packs were quickly colonized by macroinvertebrates and the maximum total macroin‐vertebrate biomass occurred when about 50% of the leaf‐pack biomass remained. The macroinvertebrate community in the leaf packs was typical for western Maryland. There was little difference in the macroinvertebrate communities on the Dimilin‐treated and the control packs; any possible differences between treatments were probably obscured by recolonization of the packs by invertebrate drift. Bioassays were conducted using two shredder macroinvertebrates (Tipula abdominalis and Platycentropus radiatus) to compare growth and mortality when they were fed untreated and Dimilin‐treated tulip poplar leaves. Mortality was significantly higher and growth significantly lower in the shredders fed Dimilin‐treated leaves.