A Vertically and Horizontally Transmitted 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, termed AnvRV, on its host, the parasitoid wasp Anagyrus vladimiri (Hymenoptera: Encyrtidae), an important natural enemy of mealybug pests. AnvRV was found to be maternally transmitted with very high fidelity but not paternally. Additionally, AnvRV was horizontally transferred at an efficiency of 23% from infected to uninfected wasp larvae that develop together inside the same mealybug host (superparasitism). To test the effects of AnvRV on A. vladimiri , the virus horizontal transmission was utilized to establish AnvRV-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, less encapsulation marks (the main form of mealybug immunity) were found around RV ⁺ eggs inside parasitized mealybug hosts. Taken together, the data suggest that AnvRV is affecting the mealybugs’ physiology in a way that improves first stages of wasps’ development. 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.