Diel feeding ecology of three species of aquatic insects

Aspects of the diel feeding ecology of the odonate nymphs Anax Junius and Ischnura verticalis and the ephemeropteran Callibaetis fluctuans were examined over a 24-h period in a small pond. Detrital material was the primary food of both A. Junius and I. verticalis. Aquatic insects (mainly C. fluctuans) were the second ranking prey in the diel diet of A. Junius, whereas ostracods were the second most important prey consumed by I. verticalis. Diet overlap between A. Junius and I. verticalis was high ([xbar] = 0.76) when detritus was considered but fell to 0.25 when detrital material was omitted. Food consumption by the odonate nymphs was highest at 0800 h and was generally lowest from 2400 h to 0400 h. Conversely, feeding activity by C. fluctuans peaked between 2400 h and 0400 h with the least feeding occurring at 0800 h. Differences in diel feeding patterns between the ephemeropteran and odonate species may reflect predator avoidance behavior by C. fluctuans.