CHAPTER 6 



Plecoptera 



By Stanley G. Jewett, Jr. 



U. S. Fish and Wildlife Service, Portland, Oregon 



INTRODUCTION 



This is a relatively small order of aquatic insects 

 with a world fauna of approximately twelve hundred 

 species. Stoneflies require moving water for the 

 . development of the nymphs, and hence the adults are 

 usually found near streams. In some northern regions 

 y the early life history is passed in cold lakes where 

 \ the shore area is composed of gravel, but in most 

 L areas the immature stages are passed in creeks and 

 rivers. There is a marked seasonal succession in 

 the emergence of stoneflies, particularly in the north- 

 ern hemisphere; adult stoneflies can be collected 

 every month of the year in California if the proper 

 locality is visited. 



Adult members of the genus Brachyptera are occa- 

 sionally destructive to soft fruit crops in the Pacific 

 Northwest, where they are reported to feed on the 

 tender buds of these plants (Newcomer, 1918). The 

 principal economic importance of the majority of 

 , species, however, lies in their value as food for 

 - fish. Dimick and Mote (1934) rate stoneflies as the 



second most important order of insects in the diet 

 of Oregon rainbow trout in streams. 



The order is divided into two suborders: the Fili- 

 palpia, in which the nymphs and adults of many genera 

 are primarily vegetarians, and the Setipalpia, in which 

 the nymphs are usually carnivores and the adults 

 are nonfeeding in most genera. The world fauna in- 

 cludes nine families (Ricker, 1951), three of which 

 are primarily Notogaean. Six occur in North America, 

 and all of these are represented in California. Of the 

 approximately four hundred described North American 

 species, eighty-seven are known to occur in Cali- 

 fornia. As the fauna of this state becomes better 

 known, the list of species will probably be increased 

 by at least twenty. 



The system of classification adopted here is that 

 proposed by Ricker (1950, 1952). The keys include 

 the North American fauna to subgenera and the known 

 California fauna to species. Distributional notes 

 are given for genera which occur only within one 

 general region of the continent. Specific names are 

 included for all monotypic genera and subgenera. 

 Synonyms established since the Needham and Claas- 

 sen monograph (1925) are indicated parenthetically in 

 the keys. 



Adult. — The adult stonefly (fig. 6:1) is readily dis- 

 tinguished from other insects with which it might be 

 confused, such as male Embioptera and certain Neurop- 

 tera, by its relatively primitive venation and mouth 



Fig. 6:1. Brachyptera pacifica. a, odult female; b, mandibles 

 in ventral view; c, female terminal abdominal segments; d, labium; 

 e, maxilla; f, labrum, dorsally at left and ventrally at right (New- 

 comer, 1918). 



Fig. 6:2. Plecoptera eggs, o, Pteronarcys dorsato; b, Isogenus 

 frontalis colubrinus. (Needham and Claassen, 1925). 



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