Project Title: Qualitative Survey of Washington State Vineyards for Potential Insect Vectors of Grapevine Red Blotch Disease
Project Duration 2017-2019
Principal Investigator(s): Doug Walsh
Organization: WSU Entomology / IAREC
Address: 24106 North Bunn Rd, Prosser, WA 99350
Telephone: 509-786-9287
Email: dwalsh@wsu.edu
CO-PI(s): Jonathan O’Hearn
Organization: WSU Entomology
Address: 24106 North Bunn Rd, Prosser, WA 99350
CO-PI(s): Peter Forrence
Organization: WSU Entomology
Address: 24106 North Bunn Rd, Prosser, WA 99350
Project Summary:
The three cornered alfalfa tree hopper Spissistilus festinus has been confirmed to vector an emerging viral pathogen called grape vine redblotch disease (GRBaV). S. festinus is a membracid, native to southern-tier US states, and are ubiquitous in California alfalfa fields. There are 1 million acres of alfalfa in California. There are no records for S. festinus in Washington State. In Oregon S. festinus persists in the Rogue River Valley but not in the Willamette Valley; postulating that S. festinus has a northern threshold? In Oregon in 2015 it was observed that GRBaV was spreading in the Rogue River Valley more rapidly than in the Willamette Valley. This trend changed late-season 2016 as OSU scientists observed rapid spread of GRBaV in the Willamette Valley in the absence of S. festinus. Several other species of membracids are now suspected as potential vectors of GRBaV. In summer 2017 and 18 we completed comprehensive surveys in all the major wine grape appellations in Washington State as well as in alfalfa fields, pear orchards and riparian habitats. In these surveys we captured two species of treehoppers. We captured a single individual adult male Palonica spp. in a riparian habitat east of Prosser in a riparuian habitat along the Yakima river. We think it might be a Palonica pyramidata, but we’re not sure. In numerous locations, specifically riparian habitats, field margins of alfalfa fields, and in pear orchards we captured buffalo treehoppers Stictocephala bisonia. Research had been completed on this insect by USDA-ARS scientists in the mid 20th century centered near Wenatchee, WA. Fortunately, we never captured any buffalo treehoppers in any vineyard we surveyed. We did establish a colony of buffalo treehoppers in summer 2018 and completed transmission assays on grape vines in the greenhouse. As stated above virologists have determined that there can be a latent period greater than 2 years before virus becomes detectable. We are awaiting the results of our transmission assays. What is interesting is that in these transmission assays we permitted the buffalo treehoppers to persist as long as they survived through summer and fall 2018. Eventually they died during winter. In spring 2019 we observed an egg hatch on the potted grape vines in the greenhouse. The buffalo treehopper nymphs progressed through 2 to 3 nymphal instars, but they eventually died prior to achieving adult status. This preliminary data would indicate that grape vines are likely not a preferred host plant for buffalo treehopper.
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