Identifying weed hosts for onion thrips (Thrips tabaci) and implications for Iris yellow spot virus management in onion

Onion thrips, Thrips tabaci Lindeman, is a serious yield-reducing pest of onion crops, as well as the sole vector of Iris yellow spot virus (IYSV), a yield-reducing pathogen recently confirmed in all major US onion production regions. Thrips tabaci can only acquire IYSV as first instars. Perennial and winter-annual weeds bordering onion fields may be important overwintering sources for IYSV. Identifying weed species that are also hosts for T. tabaci will be important for understanding the spread of IYSV from weeds into onion fields and potential approaches for managing alternate hosts for this disease. To do this, weed populations were sampled bi-weekly through the growing season in five regions in western New York in 2008. All species were identified in transects along the borders of onion fields, and tissues or entire plants from up to 20 of the most common perennial and winter-annual weed species were collected and numbers of immature thrips were recorded. A sub-sample of thrips larvae from each weed species was reared to adulthood to identify species in which T. tabaci utilize as a host. Preliminary results indicate that T. tabaci can reproduce on common burdock (Arctium minus), dandelion (Taraxicum officinale), shepherd’s purse (Capsella bursa-pastoris), and yellow rocket (Barbarea vulgaris). This information will be used to target perennial and winter-annual weeds that might play an important role in the spread of IYSV.