Filamentous fungal communities associated with the eastern larch beetle (Dendroctonus simplex LeConte) in Minnesota, including new Ophiostomatales species

The eastern larch beetle (Dendroctonus simplex LeConte) is a native and historically nonaggressive inhabitant of Larix laricina trees in North America. Since 2001, however, D. simplex has experienced an uncharacteristic and prolonged outbreak that has impacted trees on approximately 90% of the L. laricina forests in Minnesota. To investigate the fungal communities within D. simplex galleries during this outbreak, we isolated fungi from 56 D. simplex–infested trees across seven sites in Minnesota. We recovered 45 fungal species, including four new species in the order Ophiostomatales, proposed as Graphilbum insulare, sp. nov., Ophiostoma itasca, sp. nov., Ophiostoma minnesotense, sp. nov., and Ophiostoma pseudoips, sp. nov. Additionally, based on phylogenetics and morphological traits, we recommend a new taxonomic classification for Leptographium simplex, comb. nov. previously described as Graphium simplex from D. simplex galleries in Vermont, USA. At the community level, most isolates were in the phylum Ascomycota (82% of the total relative abundance), followed by Basidiomycota (12%). The most frequently isolated orders were Ophiostomatales (59% of the total relative abundance), Hypocreales (9%), and Pleosporales (8%). One species, Grosmannia americana, accounted for more than half of all isolates recovered. These results improve our understanding of the fungi associated with a bark beetle outbreak and an understudied tree species.