Diapause in the Nymphs of Canadian Winter Stoneflies

The nymphs of several winter stoneflies, Taeniopteryx burksi, T. nivalis, Brachyptera fasciata, Capnia manitoba, Allocapnia granulata, A. pygmaea, and A. vivipara, undergo a diapause during the summer. The diapause determines external morphological changes, which are described. This adaptation enables the species to inhabit streams that reach high temperatures or dry up during the summer; its advantages over the more common embryonic diapause are that it permits the nymphs to grow in both spring and fall and to seek a convenient site in which to aestivate.