Multiparasitism and host feeding by solitary parasitoid wasps (Hymenoptera: Ichneumonidae) based on the pay-off from parasitized hosts

In general, several parasitoids are associated with 1 host species, leading to competition among the parasitoids. To test whether female parasitoids decided to multiparasitize based on the probability of the offspring survival, multiparasitism and larval competition in the 2 coexisting solitary parasitoids Pimpla nipponica Uchida and Itoplectis naranyae Ashmead were studied. Females of both species readily multiparasitized when time intervals between the attacks were short. However, they avoided multiparasitism with increasing time intervals while they increasingly fed on parasitized hosts. The survival of offspring of the 2nd parasitoid decreased with increasing time intervals between the attacks and was positively correlated with the degree of multiparasitism. The degree of host-feeding in both species was also negatively correlated with offspring survival. These results suggest that females multiparasitized or host-fed on the basis of their offspring survival. Larvae of the 1st parasitoid were killed by the 2nd parasitoid via host-feeding, suggesting that preferential host-feeding on parasitized hosts could be a form of interspecific competition. Multiparasitism and host-feeding strategies in parasitoids were discussed. Further, it was suggested that parasitoid tendencies to feed on parasitized hosts could affect host-parasitoid dynamics and competition among parasitoids.