LIFE HISTORIES OF COEXISTING SPECIES OFCERACLEACADDISFLIES (TRICHOPTERA: LEPTOCERIDAE): THE OPERATION OF INDEPENDENT FUNCTIONAL UNITS IN A STREAM ECOSYSTEM

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Abstract
Bionomics of the stream caddisflies,Ceraclea transversa(Hagen) (=Athripsodes angustusBanks) andCeraclea ancylus(Vorhies) (=Athripsodes ancylus(Vorhies)) were compared with generalized trichopteran life cycles. The univoltine detritus-feedingC.ancylushas five larval instars and a brief adult emergence period.C.transversahas five larval instars but two distinct cohorts, in which larvae of the first cohort feed entirely on freshwater sponge, overwinter as inactive prepupae, pupate, and emerge the following spring. The second larval cohort feeds on sponge until the onset of gemmulation in autumn, then the larvae must overwinter as active third- or fourth-instar detritus-feeders, pupating and emerging later in the summer than the first cohort. The detritus-feedingC.ancyluslarvae have a diurnal feeding cycle. The sand case ofC.ancylusand the silk-secreted case ofC.transversadiffer in shape and composition, although both species initiate case construction using egg mass matrix, silk, and detritus. Emergence, flight activity, sex ratios, and adult survival depart from reported generalizations of caddisfly biology. Neither the validity of generalizing typical life cycles in benthic studies, nor the rationale that congeneric species operate as a functional unit in stream dynamics, is substantiated.