Two ophiostomatoid fungi, Ophiostoma clavigerum (Robinson-Jeffrey & Davidson) Harrington and Ophiostoma montium (Rumbold) von Arx, are known to be associated with the mycangia of the mountain pine beetle, Dendroctonus ponderosae Hopkins. However, virtually nothing is known regarding the phoretic fungi carried on the external surface of the exoskeleton of this beetle. In this study, I compared the phoretic fungi of individual D. ponderosae with the fungi carried in their mycangia. As many beetles carried ophiostomatoid fungi on the exoskeleton as in the mycangia; however, the species of ophiostomatoid fungus carried phoretically on an individual beetle was not always the same as was carried in its mycangia. Ophiostoma montium was isolated more often from exoskeletal surfaces than from mycangia, while the reverse was true for O. clavigerum. It appears that O. clavigerum is highly adapted for mycangial dissemination, while O. montium is adapted to phoretic as well as mycangial dissemination. Ophiostoma ips (Rumbold) Nannf. was phoretic on two beetles, indicating that cross-contamination with fungi from cohabiting Ips spp. may sometimes occur. Several non-ophiostomatoid fungi were isolated from exoskeletal surfaces, but none consistently so. All non-ophiostomatoid fungi isolated were common saprophytes often found in beetle-killed trees. Yeasts were also common and were isolated more often from the exoskeleton than from mycangia.
