Life History of a Net-spinning Caddisfly, Parapsyche shikotsuensis in a Headwater Stream of Hokkaido, Northern Japan

Abstract

The life history of a net-spinning caddisfly, Parapsyche shikotsuensis was studied in a headwater stream, a tributary of Ichankoppe Creek, Eniwa, Hokkaido, northern Japan, 1994-1996. This species is univoltine with an early and mid-summer adult period. Females deposit eggs either above- or underwater on cobbles and wood debris. Early instar larvae appear in August, and almost all of them develop to fifth instar by December. Larvae grow and develop even in winter. Larvae live on riffles, wood debris and the submerged leaves and stems of living riparian plants. Second, third and fifth instar larvae were found at a relatively high density in riffles. Gut contents of larvae are mostly composed of animal fragments (55-95%) and vascular plant fragments (5-45%). The animal-fragment frequency in the guts was relatively low in fourth instar larvae and in October. Moreover, a comparison among the same instar larvae collected in different months showed that animal-fragment frequency was low in October for third, fourth and fifth instar larvae.