THE EFFECT OF COMPLETE VERSUS INCOMPLETE INFORMATION ON ODOR DISCRIMINATION IN A PARASITIC WASP

We studied the function of learning in the parasitoid Leptopilina hete rotoma by looking at discrimination of odour stimuli used in foraging for a host. To optimize the rate of encounters with hosts, these paras itoids are expected to assess the extent to which variation in host-su bstrate odours is reliably associated with variation in the presence o f hosts, that is, substrate profitability. Where the association is re liable, parasitoids should attend to variation in odours and discrimin ate between them; where it is not, they should ignore it. We hypothesi zed that foraging decisions are based on the completeness of informati on the animal has about differences in substrate profitabilities. Our laboratory studies showed that discrimination and non-discrimination o f odour stimuli are dynamic behavioural decisions that can be related to the degree of substrate variation and to an animal's informational state. In wind-tunnel studies, females learned to discriminate between odours from substrates that were qualitatively different, for example , between odours from apple and pear substrates or between yeast subst rates with different C-6, compounds added. They did not discriminate w hen differences were small (e,g. between odours from two apple varieti es or between yeast patches with different concentrations of ethyl ace tate), unless unrewarding experiences provided evidence of the absence of hosts in one of the substrates. Hence, we suggest that non-discrim ination between odour stimuli in L. heterotoma is not a lack of abilit y to discriminate but a functional decision by the parasitoid. (C) 199 8 The Association for the Study of Animal Behaviour.