Role of grape mealybug (Pseudococcus maritimus) and soft scale species in the spread of leafroll disease-associated viruses in New York Finger Lakes vineyards

Over several years we investigated the role of mealybugs and soft scale insects in vectoring leafroll-associated viruses of grapevines in the Finger Lakes area of New York. Surveys revealed the presence of one mealybug species (grape mealybug Pseudococcus maritimus) and two species of soft scale (Parthenolecanium corni and Pulvinaria innumerabilis), generally at low population levels. Concurrent with the insect survey was a survey of leafroll-associated viruses GLRaV-1 and GLRaV-3, which were found to be at generally high levels in grapevines in the region and also detected in immature and adult mealybugs and immature soft scale species. Assessment of leafroll-associated viruses over a three-year period indicated significant increases of GLRa-V-1 and GLRaV-3 within some vineyard blocks implicating insect vectors as the cause of the spread of the disease. In one vineyard with intermediate levels of leafroll-associated virus and grape mealybug, we treated some blocks with insecticide to control the insect vector while leaving other blocks untreated in a replicated experiment over two years and assessed insect vector populations and virus levels. Insecticide significantly reduced mealybug populations. Influence on leafroll-associated viruses was insignificant in the first year and results for the second season are being processed.