Influence of oviposition experience on multiparasitism by Pimpla disparis Vierick and Itoplectis conquisitor Say (Hymenoptera: Ichneumonidae).

We evaluated the potential for competition between the exotic ichneumonid parasitoid Pimpla disparis Vierick and the native ichneumonid Itoplectis conquisitor Say, in the form of multiparasitism and destructive host feeding, by examining how previous oviposition experience influenced host selection. Both species commonly attack the host species, bagworm, Thyridopteryx ephemeraeformis (Haworth) (Lepidoptera: Psychidae), in central Illinois. We used in our study adult female parasitoids that were naïve, had previously oviposited into hosts that contained heterospecifics, or had oviposited into hosts that initially were unparasitized. Naïve parasitoids of both species were disinclined to oviposit into hosts that already were parasitized by heterospecific larvae, suggesting that female parasitoids could detect the larvae. However, parasitoids with prior oviposition experience were less selective and oviposited into hosts that already were parasitized and unparasitized hosts. Female P. disparis and I. conquisitor probed parasitized hosts more frequently than unparasitized hosts. Adult female parasitoids of both species rarely directly fed on hosts, but those that did preferred to feed on hosts that already were parasitized. For both parasitoid species, the first larva to colonize a multiparasitized host was the most likely to survive to adulthood.