Toxicity of the systemic insecticide, imidacloprid, to forest stream insects and microbial communities.

Imidacloprid was added to laboratory aquatic microcosms at concentrations of 12, 24, 48 and 96 microg/L to determine effects on leaf-shredding aquatic insect survival and feeding rates, and on aquatic microbial decomposition of leaf material. Survival of the stonefly, Pteronarcys dorsata, was significantly reduced at 48 and 96 microg/L. There was no significant mortality of the cranefly, Tipula sp., but most surviving tipulids were very sluggish and non-responsive to prodding at 48 and 96 microg/L. Leaf decomposition by these leaf-shredding insects was significantly reduced at all test concentrations. There were no significant adverse effects on microbial decomposition of leaf material.