Professor of Forest Entomology/PathologyOffice: Bioresearch 104
Professor of Forest Entomology/Pathology; Chair, Department of Ecosystems and Conservation Sciences
My primary research focuses on the evolution and maintenance of symbioses particularly those occurring among bark beetles, ambrosia beetles and fungi. This work includes collaborative efforts with scientists in the US, South Africa, Sweden and Mexico. I also conduct research on various aspects of bark beetle ecology and management, including investigations into how bark beetles may affect the ability of forests to adapt to climate change.
I am an associate editor for the journals Insects, Journal of Economic Entomology, and Agricultural and Forest Entomology.
A.S. Microbiology: 1986, Chaffey College, Alta Loma, CA High Honors
B.S. Agricultural Biology (IPM): 1990, California State Polytechnic University, Pomona, Magna cum laude
M.S. Entomology: 1992, University of California, Riverside
Ph.D. Entomology: 1997, University of California, Riverside Minor: Mycology
Postdoctoral Researcher: 1997. University of California, Berkeley
I conduct both basic and applied research and I am especially drawn to working in that powerful place where the two come together.
On the basic end of the spectrum, my interests are mainly focused on understanding ectosymbioses among bark and ambrosia beetles and fungi. In my research, I investigate how evolution and ecological processes have acted in concert to shape these fascinating, complex symbioses.
On the applied end of the spectrum, my research focuses on bark beetle ecology in relation to forest restoration and climate change. This includes work on mountain pine beetle outbreaks in lodepole and ponderosa pine and the massive die-offs of whitebark pine in North America and the giant Euphorbia tree in southern Africa.
I am also highly committed to science communication. As part of this, I am pursuing a MA degree in the Natural Resource and Environmental Journalism Program at UM, and blog, and tweet science as often as I can.
Watch my TEDx talk.
Check out coverage of our work in National Geographic, Mother Jones, Yale Environment 360, New York Times, and the Missoulian. We have also been featured in the book Empire of the Beetle, Years of Living Dangerously (episode 2) and David Suzuki’s The Nature of Things -The Beetles are Coming (CBC)
Six, D.L. 2003. Bark Beetle-Fungus Symbioses. Pp. 99-116. In: Insect Symbiosis. Eds. K. Bourtzis and T. A Miller. CRC Press.
Six, D.L. 2005. Population genetics of bark beetles and their associated blue-stain fungi with the use or molecular markers. In: Forest Pathology: From Genes to Landscapes. J.E. Lundquist, R.C. Hamelin, and C. Aquirre-Bravo, eds. American Phytopathological Society Press.
Six, D.L. and R. Bracewell. 2015. Dendroctonus. In: Bark Beetles: Biology and Ecology of Native and Invasive Species. F.E. Vega and R. W. Hofstetter (eds.). pp. 305-323.
Six, D. L. and B. A. Mullens. 1996. Seasonal prevalence of Entomophthora muscae and introduction of Entomophthora schizophorae (Zygomycotina: Entomophthorales) in Musca domestica (Diptera: Muscidae) populations on California dairies. Biological Control 6: 315-323.
Six, D. L. and B. A. Mullens. 1996. Distance of conidial discharge of Entomophthora muscae and E. schizophorae conidia. Journal of Invertebrate Pathology 67: 253-258.
Six, D. L. and T. D. Paine. 1996. Leptographium pyrinum is a mycangial fungus of Dendroctonus adjunctus. Mycologia 88: 739-744.
Six, D. L. and T. D. Paine. 1996. A technique for the introduction of fungi to bark beetle mycangia. Journal of Entomological Science 31: 466-468.
Six, D. L. and T. D. Paine. 1997. Ophiostoma clavigerum is the mycangial fungus of the Jeffrey pine beetle, Dendroctonus jeffreyi (Coleoptera: Scolytidae). Mycologia 89: 858-866.
Six, D. L. and T. D. Paine. 1998. The effects of mycangial fungi on development and emergence of Dendroctonus ponderosae and D. jeffreyi. Environmental Entomology. 27: 1393-1401.
Six, D. L. and T. D. Paine. 1999. Phylogenetic comparison of the ascomycetes associated with the mycangia of Dendroctonus bark beetles. Annals of the Entomological Society of America 92: 159-166.
Six, D. L. and T. D. Paine. 1999. Allozyme diversity and gene flow in the bark beetle, Dendroctonus jeffreyi (Coleoptera: Scolytidae). Canadian Journal of Forest Research. 29: 315-323.
Six, D. L. and T. D. Paine. 1999. Allozyme diversity and gene flow in Ophiostoma clavigerum (Ophiostomatales: Ophiostomataceae), the mycangial fungus of the Jeffrey pine beetle, Dendroctonus jeffreyi (Coleoptera: Scolytidae). Canadian Journal of Forest Research 29: 324-331.
Six, D. L., P. Alaback, R. A. Winfree, D. Snyder, and A. Hagele. 2000. Pros and cons of using wilderness areas for biological research. Proceedings of the Wilderness Science in a Time of Change Conference. Missoula, MT. May 23-27, 1999.
Six, D.L., M. Vander Meer, T. H. DeLuca, and P. Kolb. 2002. Pine engraver, Ips pini (Say), colonization of logging residues created using alternative slash management systems in western Montana. Western Journal of Applied Forestry 17: 96-100.
Powell, H. D. W., S. Hejl, and D. L. Six. 2002. Measuring woodpecker food: a simple method for comparing wood-boring beetle abundance among fire-killed trees. J. Field Ornithol. 73: 130-140.
Six, D.L. 2003. A comparison of mycangial and phoretic fungi of individual mountain pine beetles. Canadian Journal of Forest Research. 33: 1331-1334.
Six, D.L. and B.J. Bentz. 2003. The fungi associated with the North American Spruce Beetle, Dendroctonus rufipennis. Canadian Journal of Forest Research. 33: 1815-1820.
Six, D.L., T.C. Harrington, J. Steimel, D. McNew, and T.D. Paine. 2003. Genetic relationships among Leptographium terebrantis and the mycangial fungi of three western Dendroctonus bark beetles. Mycologia 95: 781-792.
Dahlsten, D.L., D.L. Six, N. Erbilgen, K.F. Raffa, A.B. Lawson, and D.L. Rowney. 2003. Attraction of Ips pini (Coleoptera: Scolytidae) and its predators to various enantiomeric ratios of ipsdienol and lanierone in California: implications for the augmentation and conservation of natural enemies. Environmental Entomology 32: 1115-1122.
Six, D.L. and K. D. Klepzig. 2004. Dendroctonus bark beetles as model systems for the study of symbiosis. Symbiosis 37: 207-232.
Klepzig, K.D. and D.L. Six. 2004. Bark beetle fungal symbioses: Context dependency in complex associations. Symbiosis 37: 189-206.
Shelley, R.M. and D.L. Six. 2004. Discovery of the centipede, Scolopocrytops gracilis Wood, in Montana (Scolopendromorpha: Scolopocryptopidae). Western North American Naturalist 64: 257-258.
Dahlsten, D.L., D.L. Six, D.L. Rowney, A.B. Lawson, N. Erbilgin, and K.F. Raffa. 2004. Attraction of Ips pini (Coleoptera: Scolytidae) and its predators to natural attractants and synthetic semiochemicals: Implications for population monitoring in Northern California. Environmental Entomology. 33: 1554-1561.
Waring, K. M. and D.L. Six. 2005. Distribution of bark beetle attacks following whitebark pine restoration treatments. Western Journal of Applied Forestry. 20: 110-116.
Six, D.L. and M. Newcomb. 2005. A rapid method for rating white pine blister rust incidence, severity, and distribution within individual trees in whitebark pine. Northwest Science 79: 189-195.
Mueller, U., N. Gerardo, D. Aanen, D. L. Six, and T. Schultz. 2005. The evolution of agriculture in insects. Annual Review of Ecology, Evolution, and Systematics. 36: 563-595.
Six, D.L., Z.W. de Beer, R.A. Beaver, L. Visser, and M.J. Wingfield. 2005. Exotic invasive elm beetle, Scolytus kirschii, detected in South Africa. South African Journal of Science. 101: 229-232.
Jensen, J. and D. L. Six. 2006. Myrmecochory of the exotic plant, Centaurea maculosa (spotted knapweed), in western Montana: a potential mechanism enhancing invasiveness. Environmental Entomology 35: 326-331.
Bentz, B.J. and D.L. Six. 2006. Ergosterol content of three fungal species associated with Dendroctonus ponderosae and D. rufipennis (Coleoptera: Curculionidae, Scolytinae). Annals of the Entomological Society of America 99: 189-194.
Ortega, Y.K., K. S. McKelvey and D. L. Six. 2006. Invasion of an exotic forb impacts reproductive success and site fidelity of a migratory songbird. Oecologia 149: 340-351.
Adams, A.S. and D.L. Six. 2006. Temporal variation in mycophagy and prevalence of fungi associated with developmental stages of the mountain pine beetle, Dendroctonus ponderosae (Coleoptera: Curculionidae, Scolytinae). Environmental Entomology 36: 64-72.
Yen, T., D.L. Six, and E. Burke. 2006. A rapid culture-independent direct molecular method for detection of Phellinus pini from wood of lodgepole pine (Pinus contorta). Forest Products Journal 56: 107-110.
Six, D.L. and B.J. Bentz. 2007. Temperature determines symbiont abundance in a multipartite bark beetle-fungus ectosymbiosis. Microbial Ecology 54: 112-118.
Six, D.L. and J. C. Adams. 2007. Relationships between white pine blister rust and the selection of individual whitebark pine by the mountain pine beetle. Journal of Entomological Science 42: 345-353.
Lee, S., Breuil, C. Hamelin, R. and D.L. Six. 2007. Genetic diversity and the presence of two distinct groups in Ophiostoma clavigerum associated with the mountain pine beetle, Dendroctonus ponderosae in British Columbia and the northern Rocky Mountains. Phytopathology 97: 1177-1185.
Bleiker, K. and D.L. Six. 2007. Dietary benefits of fungal associates to an eruptive herbivore: potential implications of multiple associates on host population dynamics. Environmental Entomology 36: 1384-1396.
Adams, A.S. and D.L. Six. 2008. Detection of host habitat by parasitoids using cues associated with mycangial fungi of the mountain pine beetle, Dendroctonus ponderosae. The Canadian Entomologist 140: 124-127.
Boone, C.K., D.L. Six, Y. Zheng, and K. F. Raffa. 2008. Parasitoids and dipteran predators exploit volatiles from microbial symbionts to locate bark beetles. Environmental Entomology 37: 150-161.
Boone, C.K., D. L. Six, and K. F. Raffa. 2008. The enemy of my enemy is still my enemy: competitors add to predator load of primary bark beetles. Agricultural and Forest Management 10:411-421.
Adams, A.S., D.L. Six, S. Adams, and W. Holben. 2008. In vitro interactions between yeasts and bacteria and the fungal symbionts of the mountain pine beetle, Dendroctonus ponderosae. Microbial Ecology 56: 460-466.
Bleiker, K. and D.L. Six. 2008. Effects of water potential and solute on growth and interactions of two fungal symbionts of the mountain pine beetle. Mycological Research 113:3-15.
Bleiker, K. and D.L. Six. 2008. Competition and coexistence in a multi-partner mutualism: Interactions between two fungal symbionts of the mountain pine beetle in beetle-attacked trees. Microbial Ecology 57: 191-202.
Six, D.L., W. D. Stone., Z. W. de beer, S.W. Woolfolk, 2009. Ambrosiella beaveri, sp. nov., associated with and exotic ambrosia beetle, Xylosandrus mutilatus (Coleoptera: Curculionidae, Scolytinae) in Mississippi, USA. Antonie van Leeuwenhoek 96:17-29.
Six, D.L. and K. Skov. 2009. Response of bark beetles and their natural enemies to fire and fire surrogate treatments in mixed-conifer forests in western Montana. Forest Ecology and Management 258: 761-772.
Boone, C. K., D.L. Six, and K. Raffa. 2009. Assemblage of Hymenoptera arriving at logs colonized by Ips pini (Coleoptera: Curculionidae: Scolytinae) and its microbial symbionts in westrrn Montana. Canadian Entomologist 141: 172-199.
Raffa, K.F., B. Aukema, B.J. Bentz, A. Carroll, N. Erbilgin, D.A. Herms, J. A. Hicke., R. W. Hofstetter, S. Katovich, B. S. Lindgren, J. Logan, W. Mattson, A. S. Munson, D. J. Robison, D. L. Six, P. C. Tobin, P. A. Townsend, and K. F. Wallin. 2009. A literal use of “forest health” safeguards against misuse and misapplication. Journal of Forestry 107: 276-278.
Bleiker, K.P. S.E. Potter, C.R. Lauzon and D.L. Six. 2009. Transport of fungal symbionts by mountain pine beetles. Canadian Entomology 18: 55-59.
Hansen, A., D.L. Six and Y. Ortega. 2009. Comparison of ground beetle (Coleoptera: Carbaidae) assemblages in Rocky Mountain savannas invaded and un-invaded by an exotic forb, spotted knapweed. Northwest Science 83: 348-360.
Six, D.L. 2009. Climate change and mutualism. Nature Reviews Microbiology 7: 686. Invited editorial.
Hatala, J.A., M.C. Dietze, R.L. Crabtree, K. Kendall, D.L. Six, and P.R. Moorcroft. 2011. An ecosystem-scale model for the spread of a host-specific forest pathogen in the Greater Yellowstone Ecosystem. Ecological Applications 21:1138-1153
Six, D.L. and M. J. Wingfield. 2011. The role of phytopathogenicity in bark beetle-fungus symbioses: A challenge to the classic paradigm. Annual Review of Entomology 56: 255-272.
Wingfield, M. J., M. P. A. Coetzee, P. W. Crous, D. L. Six and B. D. Wingfield. 2011. Fungal phoenix rising from the ashes? IMA Fungus 1: 149-153.
Massoumi-Alamouti, S., D. L. Six, V. Wang, S. Diguistini, J. Bohlman, R.C. Hamelin, N. Feau, and C. Breuil. 2011. Gene genealogies reveal cryptic speciation and host-specificity for the pine fungal pathogen, Grosmannia clavigera. Microbial Ecology 20: 2581-2602.
Six, D.L, de Beer, ZW, Duong, T, Carroll, A. L. and M. J. Wingfield. 2011. Fungal associates of the lodgepole pine beetle, Dendroctonus murrayanae. Antonie van Leeuwenhoek 100: 231-244.
Six, D.L., M. Poulsen, A. K. Hansen, M. J. Wingfield, J. Roux, P. Eggleton, B. Slippers, and T. D. Paine. 2011. Anthropogenic effects on insect-microbial symbioses in forest and savanna ecosystems. Symbiosis 53: 101-121. Cover article
van der Linde, J. A., D. L. Six, and J. Roux. 2011. In press. New species of Gondwanamyces from dying Euphorbia trees in South Africa. Mycologia 104:574-584.
van der Linde, J.A, D. L Six, M. J. Wingfield, and J. Roux. 2011. Lasiodiplodia species associated with dying Euphorbia ingens in South Africa. Southern Forests 73: 165-173.
van der Linde, J.A., J. Roux, M.J. Wingfield, and D.L. Six. 2012. Die off of giant Euphorbia trees in South Africa: Symptoms and relationships to climate. South African Journal of Botany 83: 172-185.
Six, D.L. 2012. Ecological and Evolutionary determinants of bark beetle-fungus symbioses. Insects 3: 339-366.
Biedermann, P. H. W., K. D. Klepzig, Taborsky and D. L. Six. 2013. Dynamics of filamentous fungi in the ambrosia gardens of the primitively eusocial beetle Xyleborinus saxesenii Ratzeburg (Scolytinae: Curculionidae). FEMS Microbial Ecology 83: 711-723.
Addison, A, J.A. Powell, D.L. Six, M. Moore, and B. Bentz. 2013. The role of temperature variability in stabilizing the mountain pine beetle-fungus mutualism. Journal of Theoretical Biology 335: 40-50.
Six, D. L. 2013. The bark beetle holobiont: Why microbes matter. Journal of Chemical Ecology 39: 989-1002. Invited review.
Six, D.L., E. Biber and E. Long. 2014. Management for mountain pine beetle outbreak suppression: Does relevant science support current policy? Forests 5: 103-133. Invited review.
Addison, A., J.A. Powell, D. L. Six and B. J. Bentz. 2015. Integrating models to investigate critical phenological overlaps in complex ecological interactions: the mountain pine beetle-fungus symbiosis. Journal of Theoretical Biology 68: 55-66.
Bracewell, R, and D. L. Six. 2015. Broadscale specificity in a beetle-fungal symbiosis: A spatio-temporal molecular analysis of the mycangial fungi of the western pine beetle. Microbial Ecology 68: 859-870.
Moore, M., J. Powell, B. Bentz, and D.L. Six. 2015. Effects of temperature on growth, sporulation, and competition of mountain pine beetle fungal symbionts. Microbial Ecology 70: 336-347.
Dooley, E., J.A. Powell and D.L. Six. 2015. A comparison of mountain pine beetle (Coleoptera: Curculionidae, Scolytinae) productivity and survival in lodgepole and whitebark pine after a region-wide cold weather event. Forest Science.61: 235-246.
Dysthe, J.C., R. Bracewell, and D.L. Six. 2015. Temperature effects on growth of the fungal symbionts of the western pine beetle. Fungal Ecology 17: 62-68.
Dooley, E, and D.L. Six. 2015. Severe white pine blister rust infection in whitebark pine alters mountain pine beetle (Coleoptera: Curculionidae) attack density, emergence rate, and body size. Environmental Entomology 107: 1384-1394
Bracewell, R. R. and D.L. Six. 2015. Experimental evidence of bark beetle adaptation to a fungal symbiont. Ecology and Evolution 5: 5109-5119.
Vander Linde, J. D.L. Six, W.Z. de Beer, M.J. Wingfield, and J. Roux. 2016. Novel ophiostomatalean fungi from galleries of Cyrtogenius africus (Scolytinae) infesting dying Euphorbia ingens. Antonie van Leeuwenhoek Journal of Microbiology
Bracewell, R.R. and D.L. Six. 2016. Cascading speciation among mutualists and antagonists in a tree-beetle-fungal interaction.
Six, D.L. 2016. A major symbiont shift supports a major resource shift for the bark beetle Dendroctonus brevicomis.
Bentz, B., J. Logan, J. MacMahon, C. D. Allen, M. Ayres, E. Berg, A. Carroll, M. Hansen, J. Hicke, L. Joyce, W. Macfarlane, S. Munson, J. Negrón, T. Paine, J. Powell, K. Raffa, J. Régnière, M. Reid, B. Romme, S. J. Seybold, D. Six, D. Tomback, J. Vandygriff, T. Veblen, M. White, J. Witcosky, D. Wood. Bark Beetle Outbreaks in Western North America: Causes and Consequences. 2009. University of Utah Press. 44 pp.
Department of Ecosystem and Conservation Sciences, College of Forestry and Conservation
Area of Expertise
Bark Beetle Ecology and Management in Relation to Forest Restoration and Climate Change; Ectosymbioses among Bark and Ambrosia Beetles and Fungi
Systems Ecology Title
Professor, Forest Entomology/Pathology
Currently, I work for a period each year in Africa, particularly with members of the Forest and Agriculture Biotechnology Institute (FABI) and the Centre for Tree Health Biotechnology, University of Pretoria, Pretoria, South Africa. This involves applied work with commercial plantation forestry and well as with conservation of indigenous forests. Field work is exciting and includes sites in Namibia, Botswana, South Africa and Zimbabwe. Nothing like working in a rhino preserve or on the banks of the Zambezi to keep you on your toes!
I am a member of several scientific societies including the Entomological Society of America and the International Symbiosis Society. I am a deputy director of IUFRO Section 07.03 Bark and wood boring beetles, sit on the Board of Directors for the Centre for Tree Health Biotechnology, Pretoria, South Africa, and recently on the Advisory Board for ISEFOR, a multi-nation, multi-million dollar, EU-funded project on threats of exotics and climate change to European forests. I am also involved with several national and local conservation groups including Trout Unlimited (Board Member, West Slope Chapter), Watershed Education Network, and Five Valleys Land Trust.
I am an avid fly fisher and fly tier. I LOVE to hike, backpack, cross country ski, and just about anything outdoors that respects nature and the land. Bodybuilding is my way to stay healthy and get rid of stress. I am currently writing a book and hoping it moves beyond a hobby to a reality!