Grapevine red blotch virus (GRBV), the causal agent of red blotch disease (RBD) in grapevine, Vitis vinifera L., is an emerging pathogen of significance to the wine grape industry of Oregon, USA. To address knowledge gaps of GRBV epidemiology, spread of GRBV was evaluated in Oregon vineyards over four years. Insect populations that could potentially transmit GRBV were assessed for biological attributes, and their ability to transmit GRBV was tested under controlled conditions.
Virus spread occurred in all study sites where GRBV was initially present. Field surveys for potential vector species yielded treehopper (Hemiptera: Membracidae) species Spissistilus festinus (Say), Stictocephala basalis (Walker), Stictocephala bisonia (Kopp and Yonke), and Tortistilus albidosparsus (Stål).
In the Willamette Valley, St. basalis immature stages appeared in late May, and adult emergence began in July. Suitable host plants were identified for all life stages. Collections in southern Oregon showed appearance of T. albidosparsus immature stages in April. Adults emerged in late June in Willamette Valley and southern Oregon sites. An edge effect of treehopper feeding damage was apparent at two vineyards.
Populations of St. basalis and T. albidosparsus were maintained in the laboratory and greenhouse. Eggs of St. basalis were deposited behind resting buds of woody plants, while T. albidosparsus deposited eggs along stems of woody plants. Adult feeding and oviposition occurred near apical tips of shoots. Late-instar nymphs of St. basalis emerged as adults on four of five herbaceous plant species in a growth chamber.
Controlled GRBV transmission bioassays on potted grapevines were conducted in 2016–2018 using adults of Sp. festinus, St. basalis and T. albidosparsus. Immature St. basalis were additionally used. No evidence of GRBV transmission was found using St. basalis or T. albidosparsus. A single vine was positive following infestation by Sp. festinus. GRBV was acquired in all species.
Voucher specimens of four treehopper species were deposited in the Oregon State Arthropod Collection, Corvallis, Oregon, USA and at the Smithsonian National Museum of Natural History, Washington, D.C., USA.