Ecology of a yeast found in association with the western pine beetle, Dendroctonus brevicomis LeConte

Recent research suggests that ecologically important microbes other than filamentous fungi can be housed within the fungal-transport structures (mycangia) of Dendroctonus bark beetles. The yeast Pichia pini Phaff (Saccharomycetales: Saccharomycetaceae) was isolated from the mycangia of western pine beetle (Dendroctonus brevicomis LeConte) populations in northern Arizona (U.S.A.) with a frequency of 56%. We performed experiments to test if P. pini could survive in the constitutive chemical environment of the pine trees (Pinus ponderosa var Arizonica) that Dendroctonus beetles colonize. We also tested if volatile organic compounds produced by cultures of P. pini affected the radial growth rate of mutualistic and antagonistic species of filamentous fungi with which beetles commonly associate, including Entomocorticium sp. B, Ophiostoma minus, Beauvaria bassiana, and an Aspergillus sp. In addition, we determined the compounds that yeasts were producing using a gas chromatography/mass spectrometry (GC/MS) analysis of headspace volatiles. We found that all isolates of P. pini could be re-isolated from pure pine resin after 48 h. Volatiles produced by yeast colonies significantly enhanced the growth of the mutualistic Entomocorticium sp. B, and inhibited growth of the entomopathogenic B.bassiana. Finally, GC/MS revealed that yeast cultures were producing ethanol, carbon disulfide (CS2), and Ä-3-carene in headspace. The results of these studies are discussed in the context of D. brevicomis community ecology.