Testing three possible insect vectors of grapevine red blotch virus using field transmission studies

Grapevine red blotch associated virus (GRBaV) is the cause of grapevine red blotch disease, which affects crop quality and yield in commercial vineyards worldwide. Although the initial spread was possibly human mediated, the virus continues to spread in vineyards, most likely by an insect vector. Surveys of insects collected in infected vineyards yield a list of mostly leaf hoppers as possible candidate vectors. We focused on three likely candidates based on this survey as well as the biology and abundance of the insects, Spissistilus festinus, Scaphytopius graneticus and Erythroneura elegantula. Twenty field caught insects of one of the three species were caged on known red blotch positive vines for 48 hours, after which the vine was brought back to the lab and the insects were placed on red blotch negative potted vines in the greenhouse for 48 hours. The vines are kept in the greenhouse for scheduled testing of red blotch virus status. The vines from Spissistilus festinus and Erythroneura elegantulahave been held for two years and have continually testedransmit the virus. We found that Scaphytopius from the field and from being caged on infected vines in the field were infected with red blotch virus. This suggests that Scaphytopius can acquire the virus, but we are still testing the vines for red blotch virus to see if Scaphytopius can inoculate uninfected vines, which would suggest Scaphytopius is a vector of red blotch virus.