Mountain pine beetle mutualist Leptographium longiclavatum presence in the southern Rocky Mountains during a record warm period

We studied blue-stain fungi (Ophiostomataceae: Ophiostomatales) of mountain pine beetle in declining epidemic populations affecting three pine species in Colorado. Using morphological and molecular characterizations, we determined the presence of the mutualist L. longiclavatum in the southern Rocky Mountains of Colorado, where it was as common as the warm temperature adapted O. montium within the insect’s specialized maxillary mycangium. The species was more prevalent than its “sibling species” G. clavigera which is the the common mycangial mutualist documented in USA populations. Findings were made during a two-year period including the warmest year on record in the state (i. e., 2012). Other studies have indicated that L. longiclavatum is more frequent in insect populations occurring in the northern Canadian Rockies diminishing in southern areas of that mountain range, suggesting latitude influences the frequency of this fungal mutualists, due to its better cool temperature tolerances. Our findings suggest Colorado isolates may have a greater tolerance of warmer temperatures than those from the north. These findings also increase our knowledge about the species distribution and the in situ conditions permissive of its occurrence in areas south of the Canadian Rockies.