Weed hosts of onion thrips (Thrips tabaci) and their role in Iris yellow spot virus epidemiology in onion

Onion thrips, Thrips tabaci, is a yield-reducing pest of onion and the sole vector of Iris yellow spot virus (IYSV), a yield-reducing pathogen of onion. T. tabaci acquire IYSV as first instars when feeding on infected plants and transmit the pathogen to other plants as adults. T. tabaci and IYSV both exploit plant species other than onion, including many weed species. Common hosts for both T. tabaci and IYSV must be identified in order to understand the impact of these hosts on IYSV epidemiology. Perennial, biennial, and winter-annual weeds bordering onion fields are likely sources for T. tabaci and IYSV, but have not been identified. In western New York in 2008 and 2009, common weed species were sampled bi-weekly during the onion growing season. Data were collected near five commercial onion fields in New York's second-largest onion growing region. All weed species were identified in transects along the borders of onion fields, and leaf tissues from more than 60 of the most common perennial, biennial, and winter-annual weed species were collected and numbers of immature thrips were recorded. Thrips larvae from each weed species were reared to adulthood to identify species in which T. tabaci utilize as a host. Preliminary results indicate that T. tabaci can reproduce on at least 18 perennial, biennial, and winter-annual weed species. Of these species, however, only a few were hosts for IYSV and dandelion was the most prevalent. The role of weeds in the epidemiology of IYSV and its management will be discussed.