Flight of Trichoptera (caddisflies) north of the Arctic Circle: seven years light-trapping in alpine Scandinavian birch forest

Light traps might not perform well under the bright summer nights at high latitudes. Trichoptera were caught in light-traps at Abisko, northern Sweden, 1970–1976. Among the 45 species col- lected, the family Limnephilidae was the most species-rich. Apatania stigmatella (Zetterstedt, 1840) made up 92% of the 65,400 specimens collected, and mostly in traps in open, dry birch forest. The species composition among these traps was surprisingly simi- lar and differed greatly from these in dense birch forest, near small water bodies and near bogs. Most species started to fly at the end of July or later. The temporal pattern of Apatania stigmatella and Limnephilus borealis (Zetterstedt, 1840) was similar over these years, and the median day (when 50% of the catch was reached) being 11 and eight days, respectively. In traps with a fluorescent lamp, the temporal pattern for Apatania stigmatella was 5–13 days later than in a trap with a strong mercury vapor lamp. Sex ratios varied among species, but most species were male-dominated. The unique light conditions at high latitudes did not preclude the use of light traps, but they appeared to bias catches towards species with a late flight period, and catches were sensitive to the light source used.