Partitiviruses Infecting Drosophila melanogaster and Aedes aegypti Exhibit Efficient Biparental Vertical Transmission

Partitiviruses are segmented, multipartite double-stranded RNA (dsRNA) viruses that until recently were only known to infect fungi, plants, and protozoans. Metagenomic surveys have revealed that partitivirus-like sequences are also commonly associated with arthropods. One arthropod-associated partitivirus, galbut virus, is common in wild populations of Drosophila melanogaster. To begin to understand the processes that underlie this virus's high global prevalence, we established colonies of wild-caught infected flies. Infection remained at stably high levels over 3 years, with between 63 and 100% of individual flies infected. Galbut virus infects fly cells and replicates in tissues throughout infected adults, including reproductive tissues and the gut epithelium. We detected no evidence of horizontal transmission via ingestion, but vertical transmission from either infected females or infected males was -100% efficient. Vertical transmission of a related partitivirus, verdadero virus, that we discovered in a laboratory colony of Aedes aegypti mosquitoes was similarly efficient. This suggests that efficient biparental vertical transmission may be a feature of at least a subset of insect-infecting partitiviruses. To study the impact of galbut virus infection free from the confounding effect of other viruses, we generated an inbred line of flies with galbut virus as the only detectable virus infection. We were able to transmit infection experimentally via microinjection of homogenate from these galbut-only flies. This sets the stage for experiments to understand the biological impact and possible utility of partitiviruses infecting model organisms and disease vectors. IMPORTANCE Galbut virus is a recently discovered partitivirus that is extraordinarily common in wild populations of the model organism Drosophila melanogaster. Like for most viruses discovered through metagenomics, most of the basic biological questions about this virus remain unanswered. We found that galbut virus, along with a closely related partitivirus found in Aedes aegypti mosquitoes, is transmitted from infected females or males to offspring with similar to 100% efficiency and can be maintained in laboratory colonies over years. This efficient transmission mechanism likely underlies the successful spread of these viruses through insect populations. We created Drosophila lines that contained galbut virus as the only virus infection and showed that these flies can be used as a source for ex