1998 Volume 59 Issue 4 Pages 429-441
I investigated the downstream distribution and annual changes in densities of net-spinning Trichoptera in the Yoshino River, Shikoku, Japan from 1973 through 1996. I found that 13 species of caddis larvae, and Stenopsyche marmorata, Hydropsyche orientalis, H. setennsis and Cheumatopsyche spp. were abundant taxa in the main stream. Macrostemum radiatum had been restricted to the lower reaches of the river, but from 1985 it became abundant and expanded its distribution to the middle reaches just down-stream of a reservoir, Sameura Dam, constructed in 1973. I compared the gut contents of the fifth instar larvae of M. radiatum and S. marmorata, and found that the former species ingested more plankton algae, probably from the reservoir, than the latter. The construction of the reservoir and the rich supply of plankton algae from it probably enhanced the colonization and settlement of Macrostemum larvae.
