Grapevine leafroll viruses (Grapevine leafroll-associated virus, GLRaV) are present worldwide and transmitted to grapevine only by scale insect vectors (Coccoidea). In France, leafroll disease is present in all vine-growing areas, particularly in north-eastern regions. The biological approach of transmission allowed us to show the capacity of the mealybug Phenacoccus aceris to transmit the viruses GLRaV-1, -3, -4, -5, -6, -9 and the rugose wood viruses Grapevine virus A and B. This study represents the first evidence of the transmission of GLRaV-6 and confirms the absence of mealybug specificity in the transmission of Ampelovirus. First instar nymphs of P. aceris and of Neopulvinaria innumerabilis represent a very efficient development stage in the transmission of leafroll and rugose wood viruses. As a consequence, their vector capacities associated with the high potential of dispersal of these nymphs imply an important risk of natural spread of viruses in an infested vineyard. The entomological monitoring on 4 plots shows that Parthenolecanium corni, Pulvinaria vitis, Heliococcus bohemicus and P. aceris are common in vineyards, each site differing by the specific diversity, the level of infested stocks and the abundance of scale insects on stocks. The epidemiological study proves the role of scales insects in the dispersal of leafroll disease in the vineyards of north-eastern France. In Bonzon, the major role of P. aceris in the rapid spread of the GLRaV-1 is demonstrated. This finding represents the first report in Europe of a natural spread of GLRaV-1. In Marsannay-la-Côte, the incidence of the GLRaV-1 remains low and the colony of P. aceris, not associated to grapevine, seems to have only a very limited role in the disease spread. The molecular epidemiology study in Bonzon reveals an important genetic diversity of GLRaV-1 within a signle plotand supplies for the first time information on the genetic polymorphism of a GLRaV-1population being spread by scale insects.
