BIOMETRIC STUDIES OF SOME STONEFLIES AND A MAYFLY (PLECOPTERA AND EPHEMEROPTERA)

Aspects of the nymphal/adult developmental change were investigated in biometric studies of several species of Plecoptera: Memouridae near S chlitz, Hesse, Germany. Preliminary information on the mayfly, Baetis vernus Curtis, is also provided. Nemourid nymphs pass through 3 wing b earing stages before reaching adulthood. Instars can be identified by their characteristic shapes, as expressed by the wing length/head widt h (WL/HW) ratio. Size does not allow instar discrimination, mainly due to sexual size differences. HW is ca 10% larger in last instar female than in male nemourid nymphs; exuviae shed at the moult to adult repr esent about 14% of nymphal ash free dry weight (AFDW). Biomass lost wi th exuviae during the many larval moults should be accounted for in es timates of production. Freshly emerged nemourid females are about 6% l arger and 30% heavier than males. The HW/AFDW relationship is the same in both sexes. Through terrestrial feeding during adult life, males d ouble their weight on average. Mature females are up to three times he avier than freshly emerged ones. They invest about 30% of their final AFDW in reproduction. Shape of last instar nymphal Baetis was expresse d as the ratio wing length/mesonotum length. It is size-dependent, a c haracteristic, instar-specific shape may not occur in this mayfly. Nym phal and subimaginal exuviae together represent about 14% of last inst ar nymphal dry weight. Females of Baetis are about 55% heavier than ma les. Unlike in Plecoptera, the size/weight (ML/AFDW) relationship diff ers between sexes.