Mite and fungal associates on mountain pine beetles attacking three pines species in northern Colorado

Abstract

During its life cycle, mountain pine beetle (Dendroctonus ponderosae) interacts with phoretic organisms such as mites, nematodes, fungi, and bacteria. The types of associations these organisms establish with the mountain pine beetle vary from mutualistic to antagonistic. The most studied of these interactions are those between beetle and fungi. The least studied are interactions with bacteria, but these have received increased attention recently. Nematodes remain little studied. During 2011 to 2013, I studied phoretic mites arriving to limber (P. flexilis), lodgepole (P. contorta), and ponderosa (P. ponderosa) pines. Species of blue-stain fungi can be hyperphoretic by being carried on mites transported by beetles. Therefore, I studied phoretic fungi transported by mountain pine beetle and the mites arriving to limber, lodgepole, and ponderosa pines. On average, 57% of mountain pine beetles carried phoretic mites, a percentage that increased from 32 to 65% over three years in which mountain pine beetle population declined in our plots. Overall, I found that four of five mite species were common (>10%) on beetles arriving to the three pine hosts, but only T.ips and T. hirsuta were present during all years. The uncommon fifth species, Histiogaster arborsignis, was more frequently found on mountain pine beetle predators in the family Cleridae. Mountain pine beetle phoretic mites were not found on co-arriving insect predators including three species of clerids, Medetera aldrichii, or on parasitic hymenoptera Coeloides sympitys. Co-arriving Dendroctonus beetle species to ponderosa (D. valens) and lodgepole (D. murrayanae) pines also carried a different mite fauna than mountain pine beetles. I report a new species of omnivorous mite, Trichouropoda cf. hirsuta for the Colorado Front Range. The percent of beetles carrying mites increased significantly from 2011 (32%) to 2012 (62%) but did not increased singnificantly from 2012 to 2013 (65%). The average number of mites per beetle did not increased significantly between 2011 (1.23) to 2012 (1.32), but it was significantly greater between 2012 and 2013 (5.19). Within the three years mite assemblages of three species common to mountain pine beetle arriving to lodgepole and ponderosa pines changed significantly on ponderosa pines but did not change significantly on mountain pine beetle arriving to lodgepole pine. Mite assemblages arriving to all hosts within years were the same on male and female mountain pine beetles. During 2012 and 2013 I examined mountain pine beetle associated blue-stain fungi and fungi hyperphoretic on its phoretic mites. Mountain pine beetle carried Grosmannia clavigera and Ophiostoma montium, the two blue-stain species reported from western USA, but also Leptographium longiclavatum reported previously only from mountain pine beetle in Canada. Beetles transported the three blue-stain species to all three pine hosts during the three years. While four common mountain pine beetle phoretic mite species carried some blue-stain fungal species, along with other fungi such as Alternaria, Ceratocystiopsis, Entomocorticium, and Penicillium, among others; only the two most common species, Tarsonemus ips and Trichouropoda hirsuta transported all three blue-stain species present on mountain pine beetle. Overall, the contribution mites made to the total blue-stain transport was approximately 2.0 % of the total transported by the beetle-mite complex in the symbiosis. A general and significant reduction in occurrence of blue-stain transported by both, beetles (77 to 34 %) and mites (77 to 4 %) was found between 2012 and 2013. These two years were, respectively, a warm dry and average temperature and humid years. Mites carrying O. montium significantly increased the probability of finding that fungus on beetles. Although, the overall transport of O. montium by T. ips and T. hirsuta during the two years was small, the type of spores these carry were sexual (ascospores) which could benefit the fungus by increasing the proportion of recombinant sexual types on that species.