The effect of interspecific competition between the solitary endoparasitoid Glyptapanteles porthetriae Muesebeck (Hymenoptera: Braconidae) and the gregarious Glyptapanteles liparidis Bouché (Hymenoptera: Braconidae), was investigated in larvae of Lymantria dispar L. (Lepidoptera: Lymantriidae). Host larvae were parasitized by both wasp species simultaneously in premolt to the 2nd or the 3rd host instar or in an additional approach with a 4‐day delay in parasitization by the second wasp species. Host acceptance experiments revealed that both wasp species do not discriminate between unparasitized host larvae and larvae parasitized previously by the same or the other species. In more than 90% female wasps parasitized the larva they encountered first. During the period of endoparasitic development, larvae of the competing parasitoid species never attacked the egg stage of the other species. When host larvae were parasitized simultaneously by both wasp species, the rate of successful development of both species depended on the age of the host larva at the time of its parasitization; G. liparidis emerged successfully from 44% of host larvae parasitized during the premolt to 2nd instar, G. porthetriae from 28%, and in 20% of the hosts both parasitoid species were able to develop in one gypsy moth larva. However, when host larvae were parasitized simultaneously during premolt to the 3rd instar, G. liparidis was successful in 90% of the hosts, compared to 8% from which only G. porthetriae emerged. In the experiments with delayed oviposition, generally the species that oviposited first succeeded in completing its larval development. Larvae of the species ovipositing with four days delay were frequently attacked and killed by larvae of the first parasitizing species or suffered reduced growth. As the secondary parasitoid species, G. porthetriae‐larvae were never able to complete their development, whereas G. liparidis developed successfully in at least 12,5% of the multiparasitized host larvae. Thus, multiparasitism of gypsy moth larvae by both Glyptapanteles species corresponds to the contest type; however, G. porthetriae is only able to develop successfully as the primary parasitoid of young host larvae.

No abstract

No abstract

Gamma radiation-induced pseudoparasitization as a tool to study interactions between host insects and parasitoids in the system Lymantria dispar (Lep., Lymantriidae) Á Glyptapanteles liparidis (Hym., Braconidae)Larvae of the koinobiont endoparasitoid Glyptapanteles liparidis (Hym., Braconidae) need to suppress the immune responses of parasitized Lymantria dispar host larvae while maintaining them at high nutritional quality. We used the method of g-radiation-induced pseudoparasitization to study the effects of the parasitoid's polydnavirus and venom in these processes. To achieve pseudoparasitization, G. liparidis females were irradiated in a cobalt-60 irradiator; such wasps injected during oviposition nonviable eggs along with polydnavirus and venom into the host. Glyptapanteles liparidis eggs or larvae were implanted into unparasitized or pseudoparasitized L. dispar larvae together with or without the parasitoid's teratocytes. Eggs or larvae of G. liparidis implanted into unparasitized hosts were readily encapsulated by the host hemocytes. The further development of the hosts was not impaired. Implantation into pseudoparasitized hosts prevented encapsulation; complete endoparasitic development, however, was only possible when also teratocytes were implanted along with parasitoids into the L. dispar larva. These parasitoids required longer to emerge from the host compared to natural parasitization, but they were able to complete metamorphosis into imagines. Analysis of trehalose levels in the host hemolymph and glycogen in host tissue revealed that G. liparidis polydnavirus/venom is responsible for an alteration of carbohydrate metabolism in L. dispar that is probably beneficial for the developing parasitoid.