Despite their usefulness in integrated pest management programs, there is a growing concern that many introduced biological control agents will eventually begin using non-target species or displace/reduce native species in similar guilds. Two weevils (Rhinocyllus conicus and Trichosirocalus horridus), have been introduced against the Eurasian musk thistle (Carduus nutans). While effective against musk thistle in some areas, R. conicus has been documented to feed on native Cirsium thistles in the north central and western U.S., and T. horridus has been observed at low levels on native C. discolor in Virginia. Non-target feeding of these weevils in meristems, buds, and flowers may impact plant reproduction, especially when combined with impacts of other native endophagous insects that feed on thistles. A study was initiated in spring 2004 to 1) investigate the impact, both on native and introduced thistle species, of the two introduced European weevils, and 2) evaluate the incidence of other endophagous insects within the guild that utilizes meristems and receptacles of thistle species in Tennessee. Populations of native Cirsium species (C. altissimum, C. carolinianum, C. discolor, C. horridulum), as well as exotic thistles (C. vulgare, C. arvense, Carduus nutans) were identified, and plants from sites in each of 15 counties were collected from the field, taken to the laboratory, and examined for herbivory by head and rosette weevils. Extent of weevil infestation on thistles and impact on plant biology will be discussed. Intra-guild comparisons will be made between native and introduced endophages on native and introduced thistles.