Fungal DNA virus infects a mycophagous insect and utilizes it as a transmission vector

Mycoviruses are usually transmitted horizontally via hyphal anastomosis and vertically via sexual/asexual spores. Previously, we reported that a gemycircularvirus, <i>Sclerotinia sclerotiorum</i> hypovirulence-associated DNA virus 1 (SsHADV-1), could infect its fungal host extracellularly. Here, we discovered that SsHADV-1 could infect a mycophagous insect, <i>Lycoriella ingenua</i>, and use it as a transmission vector. Virus acquired by larvae feeding on colonies of a virus-infected strain of <i>S. sclerotiorum</i> was replicated and retained in larvae, pupae, adults, and eggs. Virus could be transmitted to insect offspring when larvae were injected with virus particles and allowed to feed on a nonhost fungus. Virus replication in insect cells was further confirmed by inoculating <i>Spodoptera frugiperda</i> cells with virus particles and analyzing with RT-PCR, Northern blot, immunofluorescence, and flow cytometry assays. Larvae could transmit virus once they acquired virus by feeding on virus-infected fungal colony. Offspring larvae hatched from viruliferous eggs were virus carriers and could also successfully transmit virus. Virus transmission between insect and fungus also occurred on rapeseed plants. Virus-infected isolates produced less repellent volatile substances to attract adults of <i>L. ingenua</i> Furthermore, <i>L. ingenua</i> was easily observed on <i>Sclerotinia</i> lesions in rapeseed fields, and viruliferous adults were captured from fields either sprayed with a virus-infected fungal strain or nonsprayed. Our findings may facilitate the exploration of mycoviruses for control of fungal diseases and enhance our understanding of the ecology of SsHADV-1 and other newly emerging SsHADV-1-like viruses, which were recently found to be widespread in various niches including human HIV-infected blood, human and animal feces, insects, plants, and even sewage.