Life cycle of Arctopsyche ladogensis (trichoptera) in a regulated Norwegian river

Abstract

AbstractThe life cycle of the net‐spinning caddisfly, Arctopsyche ladogensis (Kolenati), was studied at a site 25 km below a major catchment transfer dam on the large Norwegian river, the Glomma. The site experiences 25–50% of pre‐impoundment flows during winter and at times during summer. The sampling frequency varied between 2 and 3 weeks in mid‐summer to every 2 months during winter. There were five larval instars. In the fifth instar there was a clear size bomodality, the females being larger than the males. Pupae were present during the spring flood. The adult flight period extended from early June until mid‐July. There was a mixture of one‐ and two‐year life cycles, with a semivoltine cycle dominating. Such life cycle flexibility is advantageous in adapting to changed temperature and flow regimes in regulated river systems.