The pollinator community of the invasive plant yellow starthistle (Compositae: Centaurea solistitialis) is described for several sites in northeastern Oregon. We collected and identified flower visitors over a three year time period to determine the relative abundance and species composition of the pollinator community that utilizes yellow starthistle. Over 50 species of bees and about 20 species of other potential pollinating insects were collected and identified. Bees represent the dominant group, with over 75% of total numbers. The most common species of bees found visiting starthistle were the introduced honey bee and the alalfa leafcutting bee, representing about 25% of the total bee fauna. Relative abundances and species compositions however, were highly variable among sites and over the 3-year time period, making it difficult to associate pollinator community structure with site plant species composition. The data are discussed within the context of "invasive mutualisms", in which exotic species (honeybees and leafcutting bees) provide services to other exotic species (yellow starthistle).
Keywords: invasive mutualism, Centaurea solstitialis
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