Behavioural and Physiological Adaptations to a Variable Habitat in Two Species of Case-Making Caddis Larvae Using Different Food

Abstract

Larvae of Glyphotaelius pellucidus feed on leaves and those of Trichostegla minor graze aufwuchs and are also predators. Both species inhabit temporary pools. Growth rate was more rapid in G. pellicidus and final size was reached earlier in this species. At serious drought most G. pellucidus larvae left their cases, while the T. minor larvae remained within theirs and closed the openings with silk membranes. A high proportion of the T. minor larvae survived drought compared to those of G. pellucidus. Also freezing and O2 deficit were coped with more efficiently by the T. minor larvae suggesting a broad habitat niche with respect to these factors in this species. Functional response at starvation in terms of locomotion differed markedly between the species. The G. pellucidus larvae were active on a constant level irrespective of the duration of the starvation period. The T. minor larvae at first moved significantly more but later less than G. pellucidus. Despite heavy feeding on their cases during the starvation period, the G. pellucidus larvae lost as much as 55% of their initial weight in 25 days. The corresponding value in the T. minor larvae was only 15%. During simulated bird attacks the G. pellucidus larvae did not leave their stout cases, while the T. minor larvae abandoned their fragile cases at the slightest provocation.