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Cirsium pitcheri (Pitcher’s thistle)

We have been studying the demography and genetics of Cirsium pitcheri, a threatened species that occurs around Lake Michigan for more than 20 years. We found that the species is in decline, and that all monitored populations are below replacement rate due to numerous threats including invasive species, predation by goldfinches, and predation by a biocontrol weevil (Larinus planus) that had been introduced to control weedy thistles. In 2011, we began demographic monitoring of the weevil-infested population in Wisconsin to track weevil effects (which has continued to date).  Since then our research team has documented several other weevils impacting C. pitcheri, including the biocontrol weevils, Rhinocyllus conicus and Cleonus piger, as well as Cassida rubiginosa and a Baris species.  Currently we are working on finding ways to control weevils without disrupting pollination, possibly by timing of chemical control or by using scent traps. In 2016, we characterized the pollination network in the dune habitat associated with C. pitcheri. C. pitcheri was found to support more pollinators than any other species in the dune community.

 

Pitcher's thistle