Life History and Biology of Sericostoma personatum Spence (Trichoptera)

Abstract

Monthly samples of larvae, pupae and imagines of Sericostoma personatum (Spence) were taken from Wilfin Beck, a small stony stream in the English Lake District. There were six larval instars and eggs were laid underwater. First instars hatched from overwintering eggs in March and from newly laid eggs in June. Both groups of larvae grew rapidly through the summer and reached the sixth instar in October. The larvae overwintered in the sixth instar, started to pupate in April, and started to emerge in May. A third group of larvae hatched in late summer (August to October), overwintered in the second and third instars, started to pupate in July, and emerged until the end of August. Therefore there were at least three separate age groups. Imagines emerged and flew chiefly during the day, whereas the larvae were most active at night. The nocturnal periodicity in larval activity was controlled solely by changes in light intensity and there was no evidence of an endogenous rhythm. Feeding occurred chiefly at night and the diet consisted chiefly of algae, and the leaves of both terrestrial and aquatic macrophytes. Early instars were most abundant near the source and later instars were most abundant in the lower half of the stream. Larvae were neither drifting or crawling downstream under normal flow conditions, but some larvae were swept downstream in spates. The upstream flight of imagines before oviposition may compensate for this downstream movement of larvae from the upper reaches of the stream. Pe3IoMe