Life cycle of Chaetopteryx villosa (Fabricius, 1798) (Trichoptera: Limnephilidae) in a lowland‐ and a mountain‐stream in western Norway

Abstract

Chaetopteryx villosa is a common species in west Norwegian streams and rivers, ranging from sea level up to about 1250 m a.s.l. In lowland areas the species is univoltine.'bverwintering in the first and second instars and growing rapidly during the next spring and early summer. Pupation starts in August and the imaginai period lasts from late September to mid-October. In the mountains the species is semivoltine, overwintering as eggs during the first winter and in the fourth and fifth instars during the second winter. Pupation starts in mid-July and the prepupae- pupae period is approximately seven weeks. The imaginai period lasts from mid-August to early October.

Both in the lowlands and in the mountains all instar larvae construct cases preferably of sand grains, with a varying amount of organic particles. In the lowlands the cases of early instar larvae contain more organic material than the cases of corresponding instars in the mountains. Third instar larvae show no differences in utilization of organic material, while the old larvae in the mountains incorporate a higher amount of organic material than those in the lowlands.

Imagines are reluctant to fly. In the lowlands most imagines were found hidden during the day, particularly early in the flight period, while in the mountains the imagines were active in the daytime. The imagines selected resting places where they were well concealed.

The females emerged with maturing ovaries. Mating was observed during most of the imaginai period, and the pairs could remain in copulation for several days. In the lowlands females contained an average of 112 eggs as compared to 138 eggs in the mountains, but the individual variation in egg number was high.