Winter prey preference of Perlodes microcephalus (Pictet, 1833) (Plecoptera, Perlodidae) nymphs in an Apenninic creek, northwestern Italy

The feeding habits of Perlodes microcephalus nymphs (Plecoptera, Perlodidae) have been investigated in Caramagna, an Apennine creek located in northwestern Italy. This large species is one of the most representative carnivorous stonelly nymphs in this area, where it is a top-bottom predator in many fishless creeks. Despite its ecological importance, little is known about its trophic ecology. In this study, we examined the gut contents of 35 nymphs during the winter of February 2005. We detected an evident trophic preference for the following taxa: Chironomidae (Diptera) as well as Psychomidae, Glossosomatidae, Hyporhyacophila sp., and other Trichoptera. This preference appears to be independent of the prey's availability in the substratum. Rheostenie taxa, also abundant and widespread in the substratum, were almost absent or seldom found in the diet of P. microcephalus. These results suggest that the trophic preferences of P. microcephalus are more dependent on prey microhabitat preference than on prey abundance.