Distribution and taxonomic reclassification of the mycangial fungus of the fir engraver, Scolytus ventralis

The fir engraver, Scolytus ventralis, is a bark beetle that infests true firs (Abies) in western North America. The beetle is known to carry a symbiotic fungus, Trichosporium symbioticum, in pit mycangia located on the heads of adult beetles. We investigated whether this fungus is associated with the beetle across its geographic range and the frequency of its occurrence with egg galleries, larvae, pupae and adult beetles in two major tree hosts. We also used morphology and DNA sequencing to determine the correct taxonomic placement of the fungus. We found the fungus is consistently associated with the beetle across its range and in all life stages. We also determined the fungus resides in the Ascomycota order Ophiostomatales and re-designated it as Ophiostoma symbioticum (Wright) Six nov. comb. We suggest O. symbioticum may be a nutritional mutualist with S. ventralis and that future studies should investigate this possibility.