This study aims to study new genomes of filamentous viruses forming a new viral family among the Naldaviricetes
Large dsDNA viruses from the Naldaviricetes class are currently composed of four viral families infecting insects and/or crustaceans. Since the 1970s, particles described as filamentous viruses have been observed by electronic microscopy in several species of Hymenoptera parasitoids but until recently, no genomic data was available. This study provides the first comparative morphological and genomic analyses of these filamentous viruses. We analyzed the genomes of seven filamentous viruses, six of which were newly obtained, in addition to the previously sequenced Leptopilina boulardi filamentous virus (LbFV), to gain a better understanding of their evolutionary history. We show these filamentous viruses share all genomic features of the Naldaviricetes and that their core genome comprises five specific genes that distinguish them from their closest relatives the hytrosaviruses. By mining public databases, we also provide evidence that these viruses regularly integrated into the genome of numerous insects, mostly Hymenoptera with parasitoid lifestyle, further suggesting a specialisation of these viruses on these hosts. on this clade/lifestyle.