The evolutionary ecology of multi-host parasites is predicted to depend upon patterns of host quality and the dynamics of transmission networks. Depending upon the differences in host quality and transmission asymmetries, as well as the balance between intra- and inter-specific transmission, the evolution of specialist or generalist strategies is predicted. Using a trypanosome parasite of bumble bees we ask how host quality and transmission networks relate to parasite population structure across host species, and thus...