Utilization of native thistles (Cirsium spp.) by the Canada thistle rust mite, Aceria anthocoptes

From 2006 through 2008, native Cirsium thistles were sampled in Colorado to detect the presence and estimate the abundance of the non-native Canada thistle rust mite, Aceria anthocoptes. Mites were collected from field populations of all seven native thistles examined: Cirsium canescens, C. calcareum, C. ochrocentrum, C. scariosum, C. scopulorum, C. undulatum, and C. undulatum var. tracyi. In addition, mites from infested Canada thistle plants were able to colonize these seven thistles and a California species (Cirsium occidentale) in laboratory experiments. In field populations, mite abundance on native thistles was typically less but sometimes comparable to populations on the 'presumed' primary host, the invasive weed Canada thistle (Cirsium arvense). A. anthocoptes was collected on native thistles at sites that were >5 km from Canada thistle populations. Utilization of native thistles probably precludes further development of the mite as a Canada thistle biocontrol agent.