Seasonal changes in the composition of aquatic macroinvertebrates in an outlet stream of Lake Ô-ike, Tsugaru Jūniko Lakes, northern Japan, with special reference to adult chironomid fauna and relationships between hydropsychid trichopterans and their parasitic chironomid, Polypedilum kamotertium

Seasonal changes in the occurrence of benthic macoinvertebrates, especially of parasitoid chironomid (Polypedilum kamotertium) and the host hydropsychids (Hydropsyche orientalis and Cheumatopsyche spp.) were studied in a stream in the Tsugaru-Jūniko Lakes in northern Japan. P. kamotertium was the most dominant among more than 61 species of adult chironomids collected by means of a light-trap at the stream. Infection of larval P. kamotertium on hydropsychid pupae was found from May through September, and this period coincided with those of pupae and adults of the host hydropsychids. The results suggest that the life history of P. kamotertium is regulated by those of the host hydropsychids. The prevalence of P. kamotertium on the hydropsychid pupae ranged from 8% to 32% in the stream, thus the parasitism could make a considerable impact on host hydropsychid populations.