Abstract and Summary
Reactions of ultimate (F0) and penultimate (F-1) instar Anax imperator larvae to six different experimental prey species showed that they selected preferentially chironomid larvae. They then diose, in decreasing order Corixa spec, zygopteran, ephemeropteran and trichopteran larvae and Gastropoda. The last two prey species were usually avoided. This preference order can be related to behavioural characteristics of predatory sequences and to biological characteristics of prey species. Spontaneous prey selection can be modified experimentally by exposure of predators to a given prey species: Anax imperator larvae confined to a diet of chironomid larvae subsequently ate less Corixa spec, than larvae fed only Corixa spec. Anax imperator larvae showed an increase in preference for the more familiar diet after return to a mixed diet of chironomid larvae and Corixa spec. No significant differences were found between the numbers of two prey species eaten by larvae of the two instars tested for the different groups.