Biology of the Caddisfly Helicopsyche borealis (Hagen): A Comparison of North American Populations

Abstract

Studies of the caddisfly Helicopsyche borealis (Hagen) in Big Sulphur Creek (Sonoma Co., CA) from 1977-1983 indicated a single-cohort population with a univoltine life cycle. Most adult emergence occurred in May. Larval growth was rapid during summer, decreased in autumn and winter, and increased again in spring; larval instars could not be distinguished using head capsule measurements. Larval densities were as high as 28,000/m2 in August; densities in spring were generally 1-2% of densities the previous autumn. Adult females exhibit 'calling' behavior similar to some Lepidoptera and apparently emit sex pheromones in attracting males. Characteristics of the Big Sulphur Creek H. borealis population that differ from one or more reports on other North American populations include: absence of egg diapause, indistinguishable larval instars, temporally restricted pupation and emergence periods, no hyporheic distribution, and higher thermal tolerances.