Invasive Aphids, Reservoir Hosts, and Endophyte-Mediated Plant-Vector Interactions in Barley Yellow Dwarf Virus Pathosystems: Revisiting Disease Management

Abstract

The cereal aphid-borne barley yellow dwarf virus (BYDV) is the most economically significant viral disease of small grains. Its spread is influenced by complex interactions among plants, virus, aphids, and different biotic and abiotic environmental variables. It is important to integrate these factors with economic thresholds and decision-support tools to develop more effective integrated pest management (IPM) strategies. This dissertation summarizes the roles of a newly invasive cereal aphid, endophyte interactions, and plant reservoirs in BYDV transmission and revisits current management practices across U.S. production systems with an emphasis on effectiveness and profitability. Chapter 1 provides an overview of BYDV biology, epidemiology, and management, highlighting key knowledge gaps related to aphid vectors, reservoir hosts, and environmental drivers of disease risk. Chapter 2 demonstrates the invasive aphid Metopolophium festucae cerealium Stroyan (Hemiptera: Aphididae), is expanding in the western U.S. as a superclone following a likely single introduction. This aphid is unable to transmit BYDV under experimental conditions, and its main impact may be due to direct feeding damage. Chapter 3 explores the role of endophytic tall fescue cultivars as potential reservoirs for BYDV and its aphid vectors. Under experimental conditions, the non-toxic novel endophyte cultivar BarOptima reduces aphid performance compared to wheat and common toxic cultivar KY-31, but it does not affect BYDV transmission. Thus, switching to novel cultivars in grazing lands may limit BYDV spread mainly by reducing aphid populations. Chapter 4 combines agronomic field trials and landscape surveys to assess the roles of management practices and environmental variables in BYDV risk. The results showed that planting date is the main factor affecting BYDV risk. The virus level, and the success and economic benefits of management practices are location specific. Insecticide treatments are economically beneficial only in high aphid pressure situations. Landscape analyses indicated that BYDV incidence in Virginia may be influenced more strongly by regional movement of viruliferous aphids than by nearby vegetation or local reservoir hosts. In Chapter 5, I discuss how my findings help a transition to an adaptive, knowledge-based IPM that considers ecological complexity, environmental variability, and economic thresholds to improve sustainability of small-grain production systems.