A heritable RNA virus facilitates egg hatching of a parasitoid wasp

Information on the impacts of RNA viruses inhabiting insect hosts is scarce. Here, we studied the effects of a recently described RNA virus, Anagyrus vladimiri Reovirus, on its host, the parasitoid wasp Anagyrus vladimiri (Hymenoptera: Encyrtidae), an important natural enemy of mealybug pest species. We found that Anagyrus vladimiri Reovirus is maternally transmitted with very high fidelity but not paternally. Additionally, Anagyrus vladimiri Reovirus is horizontally transferred at a frequency of 23% from infected to uninfected wasp larvae that develop together inside the same mealybug host (superparasitism). To test the effects of Anagyrus vladimiri Reovirus on A. vladimiri, the virus horizontal transmission was utilized to establish Anagyrus vladimiri Reovirus-infected (RV⁺) and uninfected (RV^-) isogenic wasp lines, a method rarely applied and novel to RNA virus-parasitoid systems. Longevity, developmental time, sex ratio, and fecundity of RV⁺ and RV^-  A. vladimiri were very similar. Nonetheless, the egg hatching rate of RV⁺ wasps was markedly and significantly higher than that of RV^- wasps, especially in hosts that were not superparasitized. Additionally, significantly fewer encapsulation marks (the main form of mealybug immunity) were found around RV⁺ eggs inside parasitized mealybug hosts. Taken together, the data shows that Anagyrus vladimiri Reovirus may benefit A. vladimiri by counteracting the encapsulation immune response of the mealybug. However, why the numbers of offspring in both wasp lines are similar remains unclear. These findings present a rare example of interaction between an RNA virus and a parasitoid and may provide a tool for the improvement of biological control efforts.