Summer diapause and nymphal development inAllocapnia pygmaea(Burmeister), (Plecoptera: Capniidae), in the speed river, Southern Ontario

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Abstract
Summer diapause in Allocapnia pygmaea usually occurs in the fourth instar, and is followed by thirteen post‐diapause instars. There are four distinct growth phases that correspond with the pre‐diapause, diapause, immediate post‐diapause, and late instar stages. There is some evidence that a small number of nymphs postpone diapause until the end of winter, perhaps as an adaptation for surviving unpredictable changes in the environment. The difficulties of using head capsule width frequencies to determine instars are discussed.