Technical Abstract: Quackgrass, Elymus repens, is a perennial grass spreading by vigorous underground rhizomes. Because of its capacity for rapid spread and persistence it is considered as a common weed in many settings worldwide. The cereal rust mite (CRM) Abacarus hystrix is a polyphagous, phytophagous mite attacking quackgrass and many other grasses including wheat. Its feeding causes leaf discoloration and inhibition of seed production. This mite can also transmit plant pathogens. Its role as an agent of quackgrass control was considered since previous work had suggested that populations of this mite colonizing quackgrass may be specifically adapted to that host. The ability to colonize wheat by these quackgrass population should, however, be first excluded. The aim of this study was to estimate whether the CRM quackgrass population can colonize wheat. For this purpose, females mites from quackgrass were transferred, and subsequently reared, on quackgrass (control, n = 132) and wheat (n = 125). Colonization ability was assessed by comparing the mean oviposition rate, mean female survival, and mean number of progeny on each host. Mites had similar success in the colonization of both quackgrass and wheat. The conclusion is that the quackgrass population of CRM is well adapted to wheat and thus cannot be considered as a potential agent against quackgrass.