Long-term effects of fenoxycarb on two mayfly species in artificial indoor streams

The effects of the juvenile hormone analog fenoxycarb (CAS No. 72490-01-8) were investigated in artificial indoor streams. The results from aufwuchs and two mayfly species (Rhithrogena semicolorata and Ephemerella ignita) are presented. Four concentrations ranging from 0.05 to 50 μg/L (with a spacing factor of 10) were tested. Fenoxycarb disappeared rapidly from the water phase (DT50≈5 days in the highest concentration, less in the other concentrations). Physico-chemical parameters and aufwuchs were not affected by fenoxycarb. The mayfly R. semicolorata, introduced at the start of the experiment, was affected by treatments of 5 and 50 μg/L. For the larvae in the streams a LC50 of 3.3 μg/L and for the larvae in the enclosures a LC50 of 2.5 μg/L were calculated. The second species (E. ignita) was introduced 72 days after the application, at which time no fenoxycarb was detectable in the water of the streams (limit of detection of 0.5 ng/L). The emergence of E. ignita was affected in the highest treatment (50 μg/L). Ninety percent of the emerged imagoes showed morphological abnormalities at the abdomen.