Production of Two Species of Stenopsyche (Trichoptera : Stenopsychidae) in Tohoku District

Production was estimated for the co-existing net-spinning caddisflies, Stenopsyche marmorata and S. sauteri, using the instantaneous growth method, in the Mamigasaki River in Yamagata, Tohoku District. S.marmorata was bivoltine, whereas S.sauteri was univoltine. Annual production for S.marmorata was calculated to be 15.47 g dry weight·m-2 · yr-1, which was the highest value of many reported for Trichoptera, excluding unusual conditions. Production for the overwintering generation of S.marmorata was roughly twice as large as that of the summer generation. Higher production was attained by the overwintering cohort because of heavier fifth instar body weights. Annual production for S.sauteri was 1.08 g dry weight · m-2·yr-1, which was within the range of values reported for many species of Trichoptera. Annual turnover ratio (P/B) was 8.99 for S.marmorata and 3.93 for S.sauteri. Cohort turnover ratios were 5.25 for the overwintering generation and 4.98 for the summer generation. Cohort turnover ratios for the two species were within the range observed for aquatic invertebrates.