The grape mealybug (Pseudococcus maritimus) as a vector of GLRAV-3 in Concord vineyards in Washington state

The Grape Mealybug (Pseudococcus maritimus) is a known vector of grapevine leafroll associated viruses (GLRaVs) and is implicated in the potential spread of these viruses within wine grape vineyards (Vitis vinifera cv.).  Grapevine leafroll disease, caused by GLRaVs, is the most devastating viral disease of wine grapes worldwide.  However, in Concord juice grapes (Vitis labrusca), GLRaVs appear to produce latent infections, therefore little attention has been paid to the role of mealybugs as vectors in Concord vineyards.  In Washington State, the most common GLRaV is GLRaV-3 and has been confirmed in Concord vineyards.  In this study, grape mealybugs were reared on Pixie cv. grapes.  First instar crawlers were allowed to feed on an infected grapevine for three days and were then transferred to virus free Concord vines.  Concord vines were tested at intervals of two weeks, one month, three months, and six months.  To detect the virus, plant material was tested using RT-PCR and real-time PCR techniques using primers for various genes for GLRaV-3.  When tested for Hsp70, all Concord samples tested negative.  When tested for the RdRp gene, all Concord samples tested positive for the presence of GLRaV-3.   Samples were also tested for CP, p20a, and p20b.  No virus was detected when tested for p20a or CP but two samples tested positive for p20b.  Based on these preliminary data, it appears that the grape mealybug can vector GLRaV-3 in Concord juice grapes.