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Abstract

Plecoptera taken by the aid of emergence traps on two very different streams in Lower Austria during 1972-74 have been studied. Plecopteran communities are described and their ecological significance is discussed after comments on faunistics, taxonomy and morphology. Flight periods and sex-ratios are considered. The unknown life history of a large species contributing much of the biomass is elucidated from supplementary benthos samples. Some limitations of the emergence trap method under extreme conditions are discussed. Plecopteran emergence is between 1400-4100 mg dry weight/m²/yr in the outlet of a pond, 830-1200 mg/m²/yr in a permanently cool mountain torrent. Total biomass of all emerging insects is also much smaller in the cool stream and this appears to be the only large fraction of total secondary net production, as there are no fish or other large populations of permanently submerged animals in that stream. Therefore, this torrent appears to be much less productive than other streams studied with similar methods so far.