Gamma radiation-induced pseudoparasitization as a tool to study interactions between host insects and parasitoids in the system Lymantria dispar (Lep., Lymantriidae)–Glyptapanteles liparidis (Hym., Braconidae)

Abstract

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 γ-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.