Spatiotemporal Patterns of Iris Yellow Spot Virus and Its Onion Thrips Vector, Thrips tabaci, in Transplanted and Seeded Onion Fields in New York

Onion thrips, Thrips tabaci (Lindeman), transmits iris yellow spot virus (IYSV) and is one of the most important pests of Allium crops. IYSV is a member of the species Tospovirus iridimaculaflavi in the genus Orthotospovirus of the family Tospoviridae. This virus typically reduces overall onion bulb quality and weight but can also prematurely kill onion plants. IYSV is neither seed nor mechanically transmitted. Onion fields are typically established via seeds and transplants. A decade ago, onion thrips tended to colonize transplanted fields before seeded fields because plants in transplanted fields were larger and more attractive to thrips than smaller onions in seeded fields. Therefore, we hypothesized that the incidence of IYSV in transplanted fields would be detected early in the season and be spatially aggregated, whereas IYSV would be absent from seeded fields early in the season and initial epidemic patterns would be spatially random. In 2021 and 2022, IYSV incidence and onion thrips populations were quantified in 12 onion fields (four transplanted fields and eight seeded fields) in New York. Fields were scouted four times throughout the growing season (n = 96 samples), and a geospatial and temporal analysis of aggregation and incidence was conducted to determine spatiotemporal patterns in each field type. Results indicated that spatial patterns of IYSV incidence and onion thrips populations were similar early in the season, indicating that transplanted onion fields are no longer the dominant early-season source of IYSV in New York. These findings suggest the need to identify other important early-season sources of IYSV that impact New York onion fields.