Light-Trapping of Caddisflies at the Thaya (Lower Austria), a River Influenced by Pulsating Hypolimnetic Water Release

Adult Trichoptera were caught from September 1999 to September 2000 at the Thaya River at Hardegg, Lower Austria, using a Jermy‐type light trap. From a total of 11,711 specimens caught, the most abundant species were Psychomyia pusilla (Fabricius), Lepidostoma hirtum (Fabricius), Lasiocephala basalis (Kolenati), Agapetus ochripes Curtis and Sericostoma flavicorne Schneider. In nine out of the eleven most abundant species the sex ratios significantly differed from 1:1, with an excess of females. Of the meteorological parameters tested, only the effect of air temperature was significant. An upstream shift of faunal zonation patterns from epipotamon to meta‐ and hyporhithron could be detected at the station which is influenced by hypolimnetic water release.