Biometric studies of some stoneflies and a mayfly (Plecoptera and Ephemeroptera)

摘要

Aspects of the nymphal/adult developmental change were investigated in biometric studies of several species of Plecoptera: Nemouridae near Schlitz, Hesse, Germany. Preliminary information on the mayfly,Baetis vernusCurtis, is also provided. Nemourid nymphs pass through 3 wing bearing stages before reaching adulthood. Instars can be identified by their characteristic shapes, as expressed by the wing length/head width (WL/HW) ratio. Size does not allow instar discrimination, mainly due to sexual size differences. HW isca10 larger in last instar female than in male nemourid nymphs; exuviae shed at the moult to adult represent about 14 of nymphal ash free dry weight (AFDW). Biomass lost with exuviae during the many larval moults should be accounted for in estimates of production. Freshly emerged nemourid females are about 6 larger and 30 heavier than males. The HW/AFDW relationship is the same in both sexes. Through terrestrial feeding during adult life, males double their weight on average. Mature females are up to three times heavier than freshly emerged ones. They invest about 30 of their final AFDW in reproduction.