ABSTRACT
Yellow starthistle is an annual from southern Eurasia that is a destructive and invasive weed of grasslands and other environments in the far western United States, particularly Arizona, California, Idaho, Oregon, and Washington. Tephritid flies comprise a substantial component of the insect fauna attacking the heads of yellow starthistle, resulting in reduced seed production. This chapter provides an overview of tephritid flies in the biological control of yellow starthistle. Two species, Urophora sirunaseva and Chaetorellia australis, have been successfully introduced from Greece and established on yellow starthistle in the United States. U. sirunaseva might reduce seed production in two ways: infested heads produce fewer seeds; and the production of lignified galls may act as a resource sink for the whole plant, resulting in the production of fewer total heads by the plant. U. sirunaseva is showing the ability to increase numerically to where it could eventually have considerable impact on yellow starthistle.
