Case Abandonment as a Response to Burial by <i>Potamophylax cingulatus</i> (Trichoptera: Limnephilidae) Larvae

Abstract

A flood event in a river will redistribute the bed sediments and may bury benthic insect larvae. To test the responses of case-building caddis larvae under such circumstances, we buried fourth instar larvae of Potamophylax cingulatus (Limnephilidae) in sediment of various grain size diameters (<1, 1–4, 4–10, >10 mm) to a depth of 1 or 2 cm. Depth of burial significantly affected time taken to emerge, individuals buried to 2 cm requiring longer to emerge, particularly if buried in fine (<1 mm) or coarse (>10 mm) sediment. Two thirds of those buried 2 cm deep in fine sediment abandoned their cases before emerging, whereas very few of those buried in coarser sediments and none buried to 1 cm depth emerged without a case. Burial in fine sediment is detrimental to P. cingulatus individuals, to the extent that they will abandon their cases, increasing the risk of predation, in order to facilitate escape. The case mass probably acts as a physical impediment to movement in fine matter, particularly if the animals experience respiratory stress. In coarse sediment, weight of sediment particles may slow down emergence, but not to the extent that individuals resort to case abandonment.