Life history patterns of Hydropsyche bronta and H. morosa (Trichoptera: Hydropsychidae) in summer-warm rivers of southern Ontario

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Abstract
Life history patterns are described for H. bronta and H. morosa in the Credit and Humber rivers of sourthern Ontario. In the lower reaches (stream orders 4 and 5) of these rivers, summer water temperatures exceed 24.degree. C for 3 mo. and reach maximum of 27.degree.-30.degree. C. Here H. morosa appeared to be bivoltine; at least half of the H. bronta population at each of 4 sites was trivoltine. At a 5 site below an impoundment on a 2nd-order tributary to the Humber, H. bronta was bivotine; H. morosa was extremely rate at this site and in upper reaches in general. H. bronta is smaller tahn H. morosa and tends to overwinter in slightly order larval instars than H. morosa. Both these characteristics and the fact than H. bronta is probably living in the optimal part of its habitat range in the Credit and Humber, may explain its ability to be trivoltine.
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