The biology and zoogeography of Helicopsyche borealis (Trichoptera: Helicopsychidae): a Nearctic representative of a tropical genus

Abstract

Members of the caddisfly family Helicopsychidae were present in the Upper Jurassic; the present-day distribution of the genus Helicopsyche shows typical southern continent dispersion, suggesting that it was in existence before the breakup of Pangea. Most of the .apprx. 90 spp. of Helicopsyche are endemic to the tropics, indicating a tropical origin for the genus. At certain locations, e.g., Mexico, Sri Lanka and New Caledonia, pronounced speciation has occurred. Only 2 spp. have successfully colonized North Temperate regions, H. borealis in North America (the most widespread species) and H. sperata in Europe. In a stream in southern Ontario [Canada], H. borealis is probably univoltine although difficulty in separating instars complicates interpretation. Dyar''s Rule was applied to assist in this interpretation. Microdistribution of larvae in the stream was examined and microcurrent regime around single rocks was judged to be an important controlling factor. Microdistribution of larvae in the stream was examined and microcurrent regime around single rocks was judged to be an important controlling factor. Microdistribution extended into the hyporheic zone of the stream bed. The ability to live interstitially is proposed to explain the unique helical shape of the larval case as the case is very resistant to crushing. Case composition was very similar in 5th instar individuals. Larvae were capable of limited case repair but could not build an entire new case. Larval diet, even in the interstices, consisted chiefly of detritus and diatoms, although the proportions of each changed with seasonal availability. Larvae of H. borealis have the ability to regulate their O2 consumption in a low O2 environment and this also fits them for an interstitial life. Comparative biological data for other helicopsychids are presented.