Learning used as a strategy for host stage location in an endophytic host-parasitoid system

The relationship between host stage selection and foraging behaviour of Pho letesor bicolor Nees (Hymenoptera: Braconidae), a larval parasitoid of Phyl lonorycter spp. (Lepidoptera: Gracillariidae), was investigated under labor atory conditions. The endophytic host develops through two larval stages wi th different feeding habits, accordingly named sap- and tissue-feeders. The parasitoid was able to find and parasitise both larval stages, even though it is most successful in parasitising the sap-feeder stage. The influence of experience in the parasitoid's searching behaviour was observed in a cho ice bioassay. Searching activity increased when either contact experience w ith the sap- or the tissue-feeder host was given. Furthermore, the ability of the parasitoid to locate a sap- or a tissue-feeder infested plant was in fluenced by the type of experience given prior to the bioassay. Naive femal es were less active, and were observed with equal frequency on sap-feeder, tissue-feeder and non-infested plants. In contrast, females that were given previous contact experience with sap-feeders (i.e., the host stage which p rovided the most successful parasitism) were observed foraging more often o n plants infested by the sap-feeders, than on those infested by tissue-feed ers or on non-infested plants. Experience with a tissue-feeder host had no detectable effect on host stage location and only enhanced P. bicolor's for aging activity. The advantages of learning in this tritrophic system are di scussed.