Changing the pupal-case architecture as a survival strategy in the caddisfly Annitella amelia Sipahiler, 1998 (Insecta, Trichoptera)

Abstract

In early autumn, pupal cases of the scarce caddisfly species Annitella amelia Sipahiler, 1998 were collected on the shore of a narrow, shallow brook from the northwestern Iberian peninsula, in Spain. Some of the pupal cases had been built as a new tube inside an existing tubular case. Moreover, for pupation, the last instar larvae clearly changed the architecture of the cases by adding internal and/or external grains of substrate at the tips. An architectural study with microCT techniques made it possible to divide each case into equal halves and to indirectly measure the weight of each. As no significant differences were found, it was concluded that pupa equilibrates its case, ensuring that it will lie horizontally on the substrate of the brook and thus avoid more vertical positions that might risk air exposure. The architectural changes could represent a survival strategy during pupation, in which the pupae remain in shallow channels ditches of the small brooks.