Advances in sequencing technologies and bioinformatics have greatly enhanced our knowledge of virus biodiversity. Currently, viromes of haematophagous invertebrates, such as mosquitoes and ixodid ticks, are actively studied. Tabanidae (Diptera) is a widespread family, with members mostly known for their persistent haematophagous behavior. They transmit viral, bacterial and other pathogens, both biologically and mechanically. However, tabanid viromes remain severely understudied. In this study, we used high-throughput sequencing to describe the viromes of several species of Hybomitra, Tabanus, Chrysops, and Haematopota genera, which were collected in Russia. We assembled 14 full coding genomes of the novel viruses, 4 partial coding genomes, as well as several fragmented viral sequences, which presumably belong to another 12 new viruses. All the discovered viruses were tested on their ability to replicate in the mammalian porcine embryo kidney (PEK), tick HAE/CTVM8, and mosquito C6/36 cell lines. In total, 16 viruses were detected in at least one cell culture after three passages (for PEK and C6/36) or 3 weeks of persistence in HAE/CTVM8. However, in the majority of cases, qPCR showed a decline in virus load over time. Nevertheless, four viruses were detected after six passages.

Hymenoscyphus albidus is a native fungus in Europe where it behaves as a harmless decomposer of leaves of common ash. Its close relative Hymenoscyphus fraxineus was introduced into Europe from Asia and currently threatens ash (Fraxinus sp.) stands all across the continent causing ash dieback. H. fraxineus isolates from Europe were previously shown to harbor a mycovirus named Hymenoscyphus fraxineus Mitovirus 1 (HfMV1). In the present study, we describe a conspecific mycovirus that we detected in H. albidus. HfMV1 was consistently identified in H. albidus isolates (mean prevalence: 49.3%) which were collected in the sampling areas before the arrival of ash dieback. HfMV1 strains in both fungal hosts contain a single ORF of identical length (717 AA) for which a mean pairwise identity of 94.5% was revealed. The occurrence of a conspecific mitovirus in H. albidus and H. fraxineus is most likely the result of parallel virus evolution in the two fungal hosts. HfMV1 sequences from H. albidus showed a higher nucleotide diversity and a higher number of mutations compared to those from H. fraxineus, probably due to a bottleneck caused by the introduction of H. fraxineus in Europe. Our data also points to multiple interspecific virus transfers from H. albidus to H. fraxineus, which could have contributed to the intraspecific virus diversity found in H. fraxineus.