Transmission of Grapevine Leafroll-Associated Viruses and Grapevine Virus A by Vineyard-Sampled Soft Scales (Parthenolecanium corni, Hemiptera: Coccidae) †

Grapevine-infecting ampelo- and vitiviruses are transmitted by scale insects belonging to several species, among which is the European fruit lecanium, Parthenolecanium corni (Bouché) (Hemiptera Coccidae). Our objective was to characterize the transmission biology of grapevine leafroll-associated viruses (GLRaV) and grapevine virus A (GVA) by this soft scale species in order to evaluate its ability to spread these viruses. In transmission experiments with nymphs sampled from different vineyards infected with GLRaV 1, 2, 3 and GVA, P. corni transmitted only GLRaV 1 and GVA to healthy vines. GVA was predominantly transmitted along with GLRaV 1, whereas the latter could be transmitted alone from single or co-infected vines. Vineyard-sampled second instar nymphs were more efficient than first instars at transmitting GLRaV 1, whereas both instars displayed similar transmission rates for GVA. Short virus inoculation access periods and the absence of virus in eggs of females living on infected grapevines fulfilled the criteria of non-circulative semi-persistent transmission mode.