Mites (Arachnida: Acari) are one of the most diverse groups of organisms associated with bark beetles (Curculionidae: Scolytinae), but their taxonomy and ecology are poorly understood, including in Canada. Here we address this by describing the diversity, species composition, and host associations of mesostigmatic and oribatid mites collected from scolytines across four sites in eastern Ontario, Canada, in 2008 and 2009. Using Lindgren funnel traps baited with α-pinene, ethanol lures, or Ips pini (Say) pheromone lures, a total of 5,635 bark beetles (30 species) were collected, and 16.4% of these beetles had at least one mite. From these beetles, a total of 2,424 mites representing 33 species from seven families were collected. The majority of mite species had a narrow host range from one (33.3%) or two (36.4%) host species, and fewer species had a host range of three or more hosts (30.3%). This study represents the first broad investigation of the acarofauna of scolytines in Canada, and we expand upon the known (worldwide) host records of described mite species by 19%, and uncover 12 new species. Half (7) of the 14 most common mites collected in this study showed a marked preference for a single host species, which contradicts the hypothesis that nonparasitic mites are typically not host specific, at least locally. Moreover, host records from the literature and those of this study together suggest that at a global scale, bark beetle mites have a broad host range, while at a local scale many species are host specific.