The Effects of Prior Host Experience and Egg Load on Host Acceptance Behavior of the Parasitoid Itoplectis naranyae (Hymenoptera : Ichneumonidae) on Empty Hosts

Oviposition behavior of parasitoids commonly varies among individuals even under controlled laboratory conditions. Some female parasitoids actively oviposit on many hosts whereas the others may show a weak response to hosts, accepting only a fraction of hosts for oviposition. Variation of egg load, i.e. the number of mature eggs that a female carries, can be a major source of such behavioral variation among female parasitoids. In the present study, we assessed the effect of egg load versus prior host experience on host acceptance behavior of Itoplectis naranyae, a major ichneumonid parasitoid wasp inhabiting in rice paddies. Here we used empty host cocoons (parasitized hosts after wasp emergence) to examine the wasps’ responses to hosts that were not available for oviposition but contained useful host information to be learnt. More females that had oviposition experience attacked the test hosts than naive females. Experienced females carried more mature eggs than naive females, suggesting that the difference in host attack rate could be due to the difference either in egg load or in prior host experience. A multiple logistic regression analysis showed that egg load effect was significant while experience was not. Females with a greater egg load were more likely to attack hosts. Thus, egg load was the sole factor affecting the wasps’ decision to attack empty hosts, and, at least in part, explained behavioral variation observed in I. naranyae. The importance of physiological state, i.e. egg load, in determining parasitoid foraging behavior was discussed.