Life History and Habits of Sialis rotunda and S. californica1 in Western Oregon2

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Abstract
Comparative ecological studies of Sialis rotunda Banks and S. californica Banks (Megaloptera: Sialidae) were made in western Oregon from 1966 to 1968. Techniques were developed for rearing both species, and the duration of the life cycles was determined in aquaria, in a laboratory stream, and in the natural habitats. It was found by rearing individual larvae that there are 10 larval instars, and measurements were recorded of body length and head width of all stadia. The duration of each of the life stages was determined. S. rotunda, predominantly a pond or lake species, has 1 generation per year with adults emerging from April to June. S. californica is a larger species, occurs in streams, and development takes 1 or 2 years depending on time of oviposition and availability of prey. Adults emerge from May to July. The density and biomass of Sialis larvae were evaluated throughout the year. As these predators can be very abundant (a maximum of 500/m2 for S. rotunda.) they are capable of exerting a marked effect in reducing the standing crop of the benthic fauna.

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