Fungal endophytes are known to play a role in host resistance against plant pathogens. Yet, the effect of endophytes in conifers against bark beetles and their fungal associates are poorly studied. Fungal endophytes occur in all conifer forest systems and hypothesized to be involved in resistance-mediated responses, essentially functioning as an extended phenotype of the host plant. In this study, we test whether fungal endophytes from Pinus ponderosa affect the colonization and reproduction of bark beetles and potentially reduce the growth of bluestain fungi and other beetle-associated fungi. We use in vitro media assays to test effects of endophytic fungal species on plant pathogens and use in vivo assays (endophyte-inoculated logs) to test effects of endophytes on bark beetle colonization, reproduction and larval performance. Our results provide insight into causes of intra- and interspecific variation in bark beetle performance within and across trees, and the potential role of endophytes as extended phenotypes of Ponderosa pine.