Life cycles and larval and pupal habitats of eleven Japanese Rhyacophila (Trichoptera) species at the mountain streams in central Honshu

Abstract

The life cycles and microhabitats involved in aquatic stages of eleven Rhyacophila Stephens, 1836 species living in two neighboring Japanese mountain streams in Nara Prefecture, central Honshu, were investigated. Eight species had univoltine life cycles; seven species had spring to early summer emergence seasons. One species had an autumnal emergence. Four univoltine species had periods where no larvae or pupae were collected in aquatic stages, possibly a period of egg diapause. Three species had bivoltine life cycles, with early summer and autumn emergence seasons. Rhyacophila nipponica Iwata, 1927, R. manuleata AV Martynov, 1934, and R. shikotsuensis Iwata, 1927, in the nigrocephala species group Ross, 1956, have larvae which spend most of their larval stage in the hyporheos. The larvae of R. transquilla Tsuda, 1940, also inhabit the hyporheic zone, although the vertical microhabitat used by this species differed from the former three species. All four of these species have hyporheic larval stages, but in these species the first and final instar larvae reside on the surfaces of cobbles. The first instar larvae seem to live on stone surfaces immediately after hatching, and subsequently move to the interstices of sand. Final instar larvae live in the interstices of sandy bottom, and move to stone surfaces for pupation. Eleven species of the genus Rhyacophila had diverse life histories, microhabitat preferences, and experienced differing water temperature regimes during larval stages at the sites. Life history and habitat preference variation enhances the species richness of the genus and coexistence of species in upper stream of the Kinokawa River.