This research will develop a model system for the influence of the microbiome on parasite transmission, potentially improving the health of not only plants, but also humans, animals, and ecosystems. The focal parasites are of national agricultural significance, and tall fescue is a plant of national economic importance, so it may improve sustainable pest management. Available ecological theory, considered together with mechanistic studies, strongly predict that the species composition of a host’s microbiome will influence the role of that host in parasite transmission. Yet, this nexus between the microbiome and parasite transmission remains an open frontier for research. We propose to integrate from individual-level variation among parasites to the transmission dynamics of a multispecies parasite assemblage.