Pathogenicity to western larch (Larix occidentalis) of two fungi, Ophiostoma pseudotsugae and Leptographium abietinum, associated with the Douglas fir beetle (Coleoptera: Scolytidae)

Abstract

Abstract1 Pole‐sized, live western larch Larix occidentalis Nutt. were mass‐inoculated with Ophiostoma pseudotsugae (Romb.) von Arx or Leptographium abietinum (Peck) Wingf., two blue‐stain fungi associated with the Douglas fir beetle Dendroctonus pseudotsugae Hopkins, to assess their pathogenicity.2 Inoculation with O. pseudotsugae resulted in significantly greater percentages of necrotic phloem compared with L. abietinum inoculations.3 The percentage of occluded sapwood was significantly greater after L. abietinum inoculations compared with O. pseudotsugae inoculations.4 Within the inoculation band, all trees had more than 60% functional sapwood 4 months after treatment.5 The results suggest that western larch can successfully limit colonization by O. pseudotsugae and L. abietinum.6 The inability of the fungi to thrive in live western larch may be a factor in the consistent failure of Douglas fir beetle broods in this host tree species.