Alimentation de larves d’Anax imperator Leach dans un milieu naturel (Anisoptera: Aeshnidae)

The variations in food intake have been studied by monthly analyses of the faecal pellets (Sept. 1973 – Sept. 1974). The average number of recognizable prey decreases from June through Dec., then increases. Quantitatively, prey intake appears density-dependent. In the pond under study (Brittany, France) larval Ephemeroptera, Zygoptera (Coenagrion), Heteroptera (Corixidae) and Trichoptera are the relatively more abundant groups, though there are considerable fluctuations in this respect. The remains of prey occurring in faecal pellets show that Anax larvae attack mostly larval Ephemeroptera, Zygoptera, Trichoptera (Phryganea), chironomids, and adult and larval Plea (Heteroptera). These groups, as well as larval Libellulidae and Nymphulea (Lepidoptera), seem to be positively selected. Molluscs, Hydracarina, Crustacea, some aquatic Heteroptera (inch Naucoris and Notonecta), and larval and adult Coleoptera, on the other hand, seem to be avoided. Other groups are preyed upon more or less proportionally to their density. F’actors affecting food intake (relative abundance, size, habits, habitats, stimulative value of potential prey, intra- and interspecific competition) are discussed.