Section 6
Chapter 5,795

Larval identification and instar association in some species of hydropsyche and cheumatopsyche trichoptera hydropsychidae

Mackay, R.J.

Annals of the Entomological Society of America 71(4): 499-509


ISSN/ISBN: 0013-8746
DOI: 10.1093/aesa/71.4.499
Accession: 005794242

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Features of hydropsychid larvae are described which allowed coexisting species in southern Ontario [Canada] to be distinguished while in the first 3 instars; these young stages cannot usually be identified by existing taxonomic keys. Cheumatopsyche differed from Hydropsyche in having a long tapered seta on each antero-lateral corner of the pronotum. Species of Hydropsyche were distinguished according to the length and degree of tapering of the pronotal seta, by background color of head and thoracic sclerites, by round spots and oval patches on the dorsum of the head capsule, and by abdominal setae and scale hairs. After species had been differentiated, measurements of head widths showed that successive instars increased in size in a regular geometric progression (Dyar's Rule). The factor of increase was .apprx. 1.5 in all species. The use of Dyar's Rule is suggested as a taxonomic tool to associate young instars of coexisting hydropsychids with the more easily identified older instars. [Species used were H. slossonae Banks, H. betteni Ross, H. sparna Ross, H. morosa Hagen, H. bronta Ross, H. dicantha Ross, an unidentified species of Hydropsyche, C. gracilis (Banks) and a larger type instar which includes C. campyla Ross and C. pettiti (Banks).].