The Mite-y Bee: Factors Affecting the Mite Community of Bumble Bees (Bombus spp., Hymenoptera: Apidae)

Parasites and other associates can play an important role in shaping the communities of their hosts; and their hosts, in turn, shape the community of host-associated organisms. This makes the study of associates vital to understanding the communities of their hosts. Mites associated with bees have a range of lifestyles on their hosts, acting as anything from parasitic disease vectors to harmless scavengers to mutualistic hive cleaners. For instance, in Apis mellifera (the European honey bee) the parasitic mite Varroa destructor has had a dramatic impact as one of the causes of colony-collapse disorder. However, little is known about mites associated with bees outside the genus Apis or about factors influencing the makeup of bee-associated mite communities. In this thesis, I explore the mite community of bees of the genus Bombus and how it is shaped by extrinsic and intrinsic aspects of the bees' environment at the individual bee, bee species, and bee community levels. Bombus were collected from 15 sites in the Ottawa area along a land-use gradient and examined for mites. The number of individual mites and number of mite species hosted by particular bee species increased significantly with bee species abundance. In addition, several bee species differed in terms of mite abundance, mite species richness, mite prevalence, and mite diversity at the level of individual bees and at the species level. In particular, individuals of rare bee species tended to have particularly high mite abundance in comparison to other bees. However, geography, site quality, and bee diversity were never significant predictors of mite community attributes at any level of analysis. Overall, the best predictor of bee-mite community attributes is the bee species themselves. Thus, these mite communities were not shaped by the factors that are known to shape the parasite communities of other species (i.e., geographic distance, host diversity), perhaps because of the commensalistic nature of most of the mite species investigated here. These findings have implications for conservation of bumble bees, given that commensals may become cleptoparasitic at high densities and may act as disease vectors