Aquatic Hyphomycetes in Insecticide-Treated and Untreated Streams

We compared the aquatic hyphomycete assemblage in a small headwater stream, where both shredder abundances and production had been dramatically reduced by the insecticide methoxychlor, with the aquatic hyphomycete assemblages in two reference streams containing high abundances of insect shredders. Concentrations of conidia being transported in the water of the treated stream were higher than those in the reference streams during much of the year (8 of 13 samples taken every 4 wk). The species composition (both number of species and the percent each contributed to the total) of conidia in transport was similar among the three streams. Aquatic hyphomycete assemblages on maple leaves colonized at 4-wk intervals over an annual cycle exhibited a similar pattern in that fungi sporulated at higher frequencies in the treated stream than in the reference streams, but the fungal species composition was similar in the three streams.