Nymphal feeding habits of Perla pallida (Plecoptera: Perlidae) from Armenia

The feeding habits of two different populations of Perla pallida from two different streams in Armenia are described. Among Plecoptera, Perlidae have been particularly well studied regarding their feeding habits, but the trophic behaviour of this species all along its distribution area was neglected. This is the first information on the nymphal diet of this species. The aim of the present paper is to describe the feeding habits of P. pallida nymphs, to compare the obtained results between populations from the two streams and to compare the obtained data with those known in other Perla spp. Sixty nymphs from each stream, representing all the present size range, were selected to study the trophic habits by the transparency method. The percentage of various items and the number of prey was recorded. About 60% of the 120 analyzed nymphs had some gut content. The feeding habits of the studied populations of P. pallida in Armenia widely coincide with those observed in other Perla spp. populations all around Europe. The main trophic resources ingested by nymphs of these populations were animal matter (mainly Chironomidae and Ephemeroptera), detritus and diatoms. Significant negative correlations were found between head width and percentage of detritus in both populations. While detritus is an important component of the diet in smaller nymphs, we observed a significant trend to ingest higher size prey by bigger nymphs. Differences in the trophic spectrum width and statistically significant differences between populations were detected for the importance of some resources in the guts (such as detritus, diatoms and Chironomidae). We suppose that these differences reflect the taxonomical composition and abundance of aquatic macroinvertebrates assemblage and thus the quantity and composition of available prey at sampling stations, as well as differences in the availability of detritus and diatoms.