PI(s): Bergh, J Christopher (Project Leader)
Abstract: The grape root borer (GRB), Vitacea polistiformis, is indigenous to the eastern United States and oligophagous on native and cultivated species of Vitis. Recognized as a potentially significant threat to grape production since the late 1800’s, GRB remains an important pest in commercial vineyards. Female GRB moths deposit eggs on weeds and vines in vineyard rows and the tiny neonate larvae must burrow down through the soil to find and establish on vine roots. In Virginia, the larval developmental duration is two years, during which time they grow to a considerable size and create increasingly large feeding channels through the center of main roots. Given the subterranean larval habitat, the adverse effects of GRB infestations are often not recognized until vines show serious symptoms of decline and loss of productivity. Our research has shown that most vineyard blocks in Virginia support some level of GRB infestation, ranging from severe to very light. Current research objectives are to determine the biotic and abiotic risk factors underlying differences in infestation levels among vineyards, to develop a sampling plan based on the spatial distributions of infestations in commercial plantings, and to explore aspects of its plant-insect interactions associated with food-finding by neonate larvae in soil.
A five-year intensive and extensive survey of the abundance and spatial distribution of GRB pupal exuviae in grids of sample vines in commercial vineyard blocks was completed in 2012 and has generated a database of 50 blocks from 20 vineyards. Geospatial statistics and mapping are being used to examine the spatial distribution of infestations and to develop a quantitative sampling plan. Principal Components Analysis will be used to assess the relative contribution of numerous potential risk factors (e.g. rootstock, vine age, cultivar, soil type, etc.) to differences in the extent of infestation among the vineyard blocks surveyed. Laboratory bioassays have revealed that newly-hatched GRB larvae are attracted to volatile stimuli from grape roots. Soil column bioassays are being used to assess the vertical and horizontal movement capabilities of neonates and the distance over which they can perceive the presence of roots. As well, on-going studies seek to measure the rate and success of food-finding by neonate larvae and the effect of incorporating extraneous sources of stimuli derived from grape roots in soil columns.