Fungi associated with the North American spruce beetle, Dendroctonus rufipennis

Fungi were isolated from individual Dendroctonus rufipennis (Kirby) collected from six populations in Alaska, Colorado, Utah, and Minnesota, U.S.A. In all populations, Leptographium abietinum (Peck) Wingfield was the most commonly isolated mycelial fungus (91–100% of beetles). All beetles in all populations were associated with yeasts and some with only yeasts (0–5%). In one population, Ophiostoma ips (Rumbold) Nannf. was also present on 5% of the beetles but always in combination with L. abietinum and yeasts. Ophiostoma piceae (Munch) H. & P. Sydow was found on 2% of beetles in another population. Ceratocystis rufipenni Wingfield, Harrington & Solheim, previously reported as an associate of D. rufipennis, was not isolated from beetles in this study. Ceratocystis rufipenni is a virulent pathogen of host Picea, which has led to speculation that C. rufipenni aids the beetle in overcoming tree defenses and therefore contributes positively to the overall success of the beetle during colonization. However, our results, considered along with those of others, indicate that C. rufipenni may be absent from many populations of D. rufipennis and may be relatively rare in those populations in which it is found. If this is true, C. rufipenni may be only a minor or incidental associate of D. rufipennis and, as such, not likely to have significant impacts on beetle success or population dynamics. Alternatively, the rarity of C. rufipenni in our and others isolations may be due to difficulties in isolating this fungus in the presence of other faster growing fungi such as L. abietinum.