Post-glacial-expansion
Guides
Urophora cardui
Canada thistle gall fly, Thistle Stem Gall Fly
Urophora cardui is a tephritid fruit fly native to Central Europe, from the United Kingdom east to near the Crimea and from Sweden south to the Mediterranean. It has been introduced to North America as a biological control agent for Canada thistle (Cirsium arvense), an invasive weed. The species forms stem galls on its host plant and has been extensively studied for its population genetics, dispersal patterns, and interactions with parasitoids. Despite establishment in eastern Canada, its impact on host weed populations has remained limited.