The life histories of<i>hydropsyche siltalai</i>döhler, 1963 and<i>h. pellucidula</i>(curtis, 1834) (trichoptera, hydropsychidae) in a west norwegian river

Abstract

Abstract Only two Hydropsychidae, Hydropsyche siltalai and H. pellucidula inhabit the Oselven river system in Western Norway. Both complete their life cycles in one year, having fairly synchronous moulting patterns. H. siltalai flies in late summer and early autumn; the median day of the flight was 15 and 17 August for males and females, respectively. Females with mature eggs were found throughout the flight period, and first instar larvae in September and early October. The species overwintered mainly as fourth instar larvae. H. pellucidula flies in early summer, the median day of the flight was 17 June for females. Females containing eggs were found in the first part of the flight period; after 5 July only a few empty ones were taken. First instar larvae were found in late July and early August, and the species overwintered in the fifth instar. In spite of its late flight period, H. siltalai overwintered in an advanced larval instar. It is suggested that this is an adaptation to the low water temperatures in Western Norway during spring and early summer. Competition with fifth instar larvae of H. pellucidula for crevices during the winter is thought to be reduced by character displacement.