The first arbovirus from a phytoplasma insect vector.

The leafhopper Euscelidius variegatus is an efficient natural vector of chrysanthemum yellows phytoplasma (CY) and a laboratory vector of Flavescence dorée phytoplasma (FD). A 10,616 nucleotide-long contig, highly similar to picorna-like viruses, was identified through RNA-seq in E. variegatus and named Euscelidius variegatus virus 1 (EVV-1). The virus presence was confirmed by Northern blot and its prevalence determined by RT-PCR: EVV-1 was detected in all the tested insects from the Italian laboratory colony, but absent in two other E. variegatus lab colonies based in France and in California. The whole viral genome was cloned in 11 overlapping fragments and completely re-sequenced by Sanger method. The amino acid sequence, the shape and size of viral particles observed at TEM as well as the phylogenetic analyses suggest that EVV-1 can be a new species of the genus Iflavirus. The presence of virus does not seem to be associated with any evident symptom on E. variegatus laboratory colony. The virus was detected both in phytoplasma-exposed and in non exposed insects, but the viral load measured by RT-qPCR in FD-infected samples was significantly lower than the one of phytoplasma-free insects. This result suggests possible interesting interactions among insects, endogenous bacteria and viruses. The availability of EVV-1 free E. variegatus colonies will allow to characterize viral replication and transmission mechanisms, and will offer the opportunity to produce infectious viral clones and manipulate the expression of endogenous genes by promoting virus-induced gene silencing.