Case‐building of some Trichoptera larvae in experimental conditions: Selectivity for calcareous and siliceous grains

Abstract

The ability of some caddisflies to select calcareous and siliceous grains during case‐building was tested in experimental conditions. This investigation was carried out on Hydropsyche morettii, Limnephilus flavicornis, Micropterna sequax, and Sericostoma pedemontanum; the last of these was collected in a habitat with prevalently calcareous substratum, whereas the remaining species were from marly‐arenaceous ones. Larvae were provided with a substratum mixture made up of travertine and quartzite grains (1.0–1.5 mm in size forming a 1‐cm‐thick substratum). Apart from H. morettii, which only picks up grains in its pupal stage, the remaining species are case‐builders during their larval stage. After being removed from their original case, larvae were reared in Petri dishes kept at a constant temperature of 23° C. Video camera recordings, coupled with the analysis of the number and typology of the grains incorporated into each reconstructed case, gave evidence that evicted individuals exhibited a significant preference in the picking up of grains. The Tukey test indicated, with the exception of H. morettii, a significant preference for travertine grains. Sericostoma pedemontanum preferentially selected travertine grains when reared on a mixed substratum, but it built a case using quartzite when provided exclusively with these grains. This demonstrates that the ancestral impulse to construct a protective shield prevails over the nature of the material. The preferential choice of travertine grains could be due to certain mechanical and chemical silk/grain interaction factors.