Abstract
Effects of insecticides (diazinon, fenthion and fenitrothion) on net-spinning Trichopteran, Hydropsychidae (Hydropsyche orientalis and Cheumatopsyche brevilineata) larvae, which were often dominant species in steams in Japan, were investigated in the laboratory. The 48-h EC50 (effects of going out from nests) values of insecticides (diazinon, fenthion and fenitrothion) for the nested final instar larvae of H. orientalis (Trichoptera) were as well as those of concentrations detected in pesticide-contaminated rivers (48-h EC50 values, 3.8 μg L-1), but C. brevilineata was very insensitive to these three insecticides (48-EC50 values, 280-660 μg L-1). Then effects of each insecticide on the nested final instar larvae of these two species were investigated using rotary flowing water taps. The 50% individuals of the larvae of H. orientalis easily went out from their nests by 5 μg L-1 after six days of applications. And also, multiple effects of two (10 μg L-1) or three (15 μg L-1) insecticides on the species were recognized. However, very few individuals of the larvae of C. brevilineata went out from their nests even by 15 μg L-1 of these three insecticides after two weeks of applications.
