Spotted knapweed (Centurea stoebe) is a widespread invasive plant in Montana and North America. It is particularly problematic in rangeland and degraded areas and is responsible for increases in erosion, and decreases in livestock forage and overall biodiversity. One way spotted knapweed threatens the native floral diversity is by altering patterns of pollinator visitation, which has the potential to limit native flower reproduction. Thirteen biological control agents have been approved for release to control knapweed and several have become well established in Montana. Their effectiveness however is variable, and may be further compromised by the presence of parasitoids.

In order to illuminate the direct and indirect effects spotted knapweed has on native plant community dynamics my research investigates the multi-trophic interactions between spotted knapweed, pollinators, biological control agents and associated parasitoids. I will observe and record the visitation patterns of pollinators with the goal of identifying which flowers may be at risk of pollen limitation due to decreased pollinator visitation in the presence of spotted knapweed. I will then perform a pollination experiment to determine whether the native flowers are indeed pollen limited or not. I will also be collecting biological control agents from various sites around western Montana to determine if they are being targeted by native parasitoids.

The outcome of this project will further our understanding of how plant-pollinator interactions and biological control agent-parasitoid relationships influence native plant communities threatened by an invasive species. From a management standpoint, the results of this research will provide information to improve the sustainability of biological control, and give managers a better understanding of the mechanisms behind spotted knapweed invasion.

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