Great Basin Naturalist


Six species of Plecoptera were maintained at four different temperatures, which were constant and higher than occurred in the natural habitat, and three species at two different day lengths. Each animal was weighed each day or each week. Weight of two species in the wild was monitored from periodic collection.

The weight of each animal fluctuated rhythmically, changing about five percent every five days. These short-term fluctuations probably resulted from changes in water content. Molting occurred when a peak weight was predicted from the cycle and involved temporary gain of about 20 percent in weight. Growth probably stopped for some time before molt and was most rapid just afterward. Many animals died at molt.

The time before death was less for univoltine species than for those with longer life cycles. Plecoptera collected in winter from water near 0 C lived for shorter times than did those collected in autumn from water near 10 C. Two species died sooner at higher temperatures and one died sooner with shorter day lengths.

Growth in the laboratory was generally slower than in nature. One species grew faster, while three grew more slowly at higher temperatures. One species grew faster under long- than short-day conditions.

Premature emergence, expected at the higher temperatures, did not occur, except in one animal.