Interspecific competition between two generalist parasitoids that attack the leafroller Epiphyas postvittana (Lepidoptera: Tortricidae)

Two generalist parasitoids, Dolichogenidea tasmanica (Cameron) (Hymenoptera: Braconidae) and Therophilus unimaculatus (Turner) (Hymenoptera: Braconidae) attack early instars of tortricid moths, including the light brown apple moth, Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae). The two parasitoids co-exist in natural habitats, while D. tasmanica is dominant in vineyards, whereas T. unimaculatus occurs mainly in adjacent native vegetation. This difference suggests possible competition between the two species, mediated by habitat. Here, we report on the extent of interspecific differences in host discrimination and the outcome of interspecific competition between the two parasitoids. The parasitoids did not show different behavioural responses to un-parasitized hosts or those that were parasitized by the other species. Larvae of D. tasmanica out-competed those of T. unimaculatus, irrespective of the order or interval between attacks by the two species. The host larvae that were attacked by two parasitoids died more frequently before a parasitoid completed its larval development than those that were attacked by a single parasitoid. Dissection of host larvae parasitized by both species indicated that first instars of D. tasmanica attacked and killed larval T. unimaculatus.