The Laurentian Great Lakes basin houses the world’s largest concentration of freshwater dunes; these dunes in turn support more endemics than any other part of the basin. This 765,000 km2 basin is a living laboratory of natural resources reflecting Pleistocene glacial activity, which results in a rich diversity of globally rare habitat types and regionally endemic species. Yet, this rich biodiversity is exposed to an unsettling and increasing variety of threats, including the incursion of invasive species in addition as well as habitat modification and loss. Cirsium pitcheri is a federally threatened plant endemic to the dunes and shorelines of the upper Great Lakes in Michigan, Indiana, Wisconsin, Illinois, and Canada. Individuals of Pitcher’s thistle typically live for 4-10 years, flower, then die, with no means of vegetative reproduction. Thus, successful seed set is critical for population persistence and survival of this iconic species. We have studied populations of Pitcher’s thistle since 1988 and have documented increasing threats to population viability, including weedy plant species (baby’s breath, Gypsophila paniculata L.) and seed predation by two seed weevil biocontrol agents, Larinus planus (adventive and distributed) at the western and northern edges of the thistle distribution, and Rhinocyllus conicus (introduced and distributed) at the southern edge of the thistle distribution. Application of weevils in the genus Larinus is increasing to control weedy thistles (e.g., Cirsium arvense) and spotted knapweed (Centaurea stoebe L. ssp. micranthos), invasive plants threaten many dune and regional ecosystems, and which often co-occur with C. pitcheri. Weevil infestation can reduce Pitcher’s thistle seed output by 50-95%. Our models suggest such predation can reduce population growth rates by at least 10% and cut time to extinction by half. We propose a two-year monitoring and weevil control study program to: (1) survey and quantify weevil seed predation at severely impacted Cirsium pitcheri sites in WI compared to relatively unimpacted populations in MI, and to assist in completion of a range wide survey for weevils in C. pitcheri populations; (2) document phenology of weevils relative to Pitcher’s thistle (Cirsium pitcheri) and levels of seed damage by weevils where found in WI and northern MI; (3) assess efficacy of several cultural and barrier control methods for the weevils, Larinus planus and Rhinocyllus conicus that are depredating Cirsium pitcheri; (4) determine if there is any association among the weevil (Larinus planus) and the invasive plants, spotted knapweed (Centaurea stoebe L. ssp. micranthos) and Canada thistle (Cirsium arvense); (5) conduct host-specificity feeding experiments to assess if Larinus planus and Rhinocyllus conicus use spotted knapweed as an alternate host and to determine if Larinus minutus and L. obtusus use Cirsium pitcheri as an alternate host; and (6) conduct a workshop/webinar to report on the magnitude of the threats and best management practices to reduce their impacts and promote Pitcher’s thistle recovery. A significant outcome of this project will be a better understanding of the potential impacts to C. pitcheri of Larinus planus and Rhinocyllus conicus, as well as possible methods of weevil control.