Spotted knapweed (Centaurea stoebe var. micranthos (Gugler)) has caused significant damage to ecosystems and ecosystem services in North America, and has become recognized as a threat to natural areas in the Midwest. In the past decade, three new biological control insects have been released in Michigan: the seedhead feeding weevils Larinus minutus, Larinus obtusus, and the root-feeding weevil Cyphocleonus achates. Here I report the findings of seven data collection efforts related to the biological control of spotted knapweed in Michigan. Both Larinus species established relatively quickly and are capable dispersers, redistributing themselves on a regional level less than a decade after release. Their rate of dispersal increases with time since release. The root-feeder C. achates is slower to establish and has not yet dispersed. Impacts on plant communities have yet to be observed. Seeds of native plants introduced to release sites in 2011 have not yet established. In two studies investigating spotted knapweed's influence on native bee community composition and abundance, we found that while spotted knapweed is very attractive to many native bee species, sites that have greater flowering plant diversity are able to support greater bee abundance and diversity because they extend the period of floral resource availability to include times before and after spotted knapweed's bloom period.
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