Datensatz

Zusammenfassung

Schreierbach, a torrential mountain stream near Lunz, lower Austria, has a constant temp. of 6°C, which makes it a special biotope. As suggested by the 2nd biocoenotic principle of Thienemann (1920), its fauna is less diverse than that of other streams in the region. Emerging merolimnic insects are practically the only faunal component, and Dictyogenus alpinum is the most important contributor to total biomass. Its ecology was poorly known. Small larvae of Dictyogenus feed predominantly on Aufwuchs and detritus. The essentially carnivorous larger larvae also do so to some extent, at least at times. Adults do not feed, eggs are produced from biomass accumulated during the larval stage. Conditions in Schreierbach prolong egg incubation and slow larval growth thereby extending the normal 2-year cycle of D. alpinum to a 3-year period. Need of eggs to experience a number of degree days sufficient for development during the warm season is suggested as a factor controlling the spring to early summer flight periods common to all semivoltine Plecoptera of northern temperate latitudes.