Parasitoid wasps

Parasitoid wasps

Parasitoids, and particularly parasitic wasps, represent a diverse and abundant (~10 % of the insects) group. They develop on (ectoparasitoids) or within (endoparasitoids) an arthropod host, ultimately killing the host. They are thus key regulators of arthropod populations and of particular value as natural enemies to control insect pests.

Endoparasitic wasps deeply affect the host physiology by altering its growth, development, metabolism or immune response, what ensures success of parasitism. Such alterations largely result from factors injected into the host by the female wasp at time of oviposition. These factors are produced in specialized tissues of the female genital tract such as the venom gland or the calyx. In certain lineages of the Ichneumonoidea super-family, the calyx cells are the site of production of viral symbionts of the Polydnavirus family, which are essential for successful development of the associated wasp.

Polydnaviruses

Discovered in the 70’, polydnaviruses (PDVs) are characterized by a genome composed of 15 to more than 100 circular dsDNA molecules.
 PDVs are divided into Bracoviruses (BVs) associated to Braconid wasps and Ichnoviruses (IVs), associated to Ichneumonids.

PDVs are stably integrated into parasitoid genomes as proviruses and replicate only in the calyx cells nuclei. Structural genes are present within the wasp genome but not encapsidated.

Viral particles containing the segmented genome are stored in the oviducts and injected into the host hemocele by the females during oviposition.

Inside the Lepidoptera host, PDVs do not replicate but infect several tissues. PDV infection results in alterations in growth, development and metabolism of the parasitized caterpillar and in inhibition of the immune response.

 

Studied biological models

The team research focuses on the interactions between 3 Ichneumonoidea species and their Lepidoptera larvae hosts:

  • Hyposoter didymator (Ichneumonidae; Campopleginae), which parasitizes several Noctuids, associated with an ichnovirus;
  • Macrocentrus cingulum(Braconidae; Macrocentrinae), polyembryonic parasitoid of Ostrinia spp. larvae;
  • Venturia canescens (Ichneumonidae; Campopleginae), which parasitizes Pyralidae larvae, associated with virus-like particles (VLPs).

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Modification date: 17 July 2023 | Publication date: 14 July 2011 | By: Anne-Nathalie Volkoff, B. Duvic