Transmission of Grapevine virus A and Grapevine leafroll-associated viruses 1 and 3 by Planococcus ficus and Planococcus citri fed on mixed-infected plants

The Grapevine virus A (GVA) and Grapevine leafroll-associated viruses 1 and 3 (GLRaV-1 and GLRaV-3) are associated with grapevine diseases that induce severe reductions in yield and berry quality. These three viruses are known to coexist in both grapevine and insect vectors, but their cotransmission has been poorly characterised so far. This study investigates the acquisition and transmission of GLRaV-1, GLRaV-3 and GVA by Planococcus ficus and Planococcus citri (Hemiptera: Pseudococcidae) following feeding on multiple-infected plants. The retention and load of the three viruses in the two insect species were analysed. After feeding onto GVA, GLRaV-1 and GLRaV-3 mixed-infected grapevines, nymphs of P. ficus and P. citri showed similar virus acquisition rates and retained low quantities of viruses until the third post-acquisition day. Despite the similar acquisition patterns, the two vectors differed in transmission efficiency: P. ficus showed a higher efficiency in transmitting GVA and GLRaV-3, whereas P. citri transmitted GLRaV-1 more efficiently. When focusing on the virus cotransmission, it appears that GVA could be transmitted to grapevine without GLRaV-1 and/or GLRaV-3 and that the transmission of both GLRaVs could take place in the absence of GVA. This comparative study involving different viruses and vector species improves the current knowledge of the semi-persistent transmission of these three viruses and contributes to the understanding of grapevine virus epidemiology.