The abundance and temporal distribution of caddisflies (Insecta: Trichoptera) caught by light traps on the Austrian Danube from 1986 to 1987

1. Adult Trichoptera were caught for 1 year (May 1986 to June 1987) on the banks of the Danube at Altenwörth, Lower Austria, using a set of three Jermy‐type light traps. From a total of 62,693 specimens caught, the most abundant species were Brachycentrus subnubilus Curtis (Brachycentridae), the two hydropsychids Hydropsyche bulgaromanorum Mal. and Hydropsyche contubernalis McL., Tinodes waeneri L. (Psychomyidae) and the leptocerid Ceraclea dissimilis Steph. 2. The total catch included sixty‐five of the 278 Austrian species from thirteen families. Hydroptila pulchricornis Pictet and Oecetis notata Ramb. were new to the Austrian fauna. 3.Of the meteorological parameters tested, only air temperature seemed to influence flight activity. 4. Twenty‐four species were studied in detail; Halesus tesselatus Ramb. was the only autumn species, the remainder being summer species. In Tinodes waeneri, the flight period was divided into two well‐defined peaks. 5. Of the total, 49.9% were caught during the first third of the night, 39.1% in the second and 11.0% in the last third. 6. In seventeen species the sex ratio was significantly different from 1:1, and it changed during the night. 7. The indication of water quality by light trap catches of caddisflies is discussed.