Mountain Pine Beetle Epidemiology in Lodgepole Pine

The following brief synthesis of mountain pine beetle epidemiology is based on host-beetle interaction. In the first part I briefly describe the relationship between the dynamics of lodgepole pine and mountain pine beetle. The second part describes the phases in the infestation cycle and their main characteristics. This synthesis is based on published information on infestation behaviour in western Canada, augmented by personal experience relating to the subject area. Lodgepole pine stand dynamics and the epidemiology of the mountain pine beetle The mountain pine beetle is native to the pine forests of western North America. As a consequence of the close interaction between the mountain pine beetle with its associated blue stain fungi and lodgepole pine (Safranyik et al. 1975), mountain pine beetle epidemiology is a reflection of the population dynamics of lodgepole pine. The female beetles require a minimum bark thickness (Fig. 1) and the presence of bark scales and ridges in the bark to establish successful attacks (Safranyik 1971). Hence, the potential attack sites on the bole are largely determined by the density and distribution of these bark characteristics. Young trees with thin bark and small diameter (dbh) older trees (Fig. 2) are rarely attacked or sustain lethal attacks. Because beetle brood production is much lower in small dbh trees compared with large dbh trees (Fig. 3), populations breeding in small trees grow at much slower rates compared to large trees. Attacks by the mountain pine beetle are mediated by blue stain fungi. The spores of blue stain fungi are carried into the tree by the beetles. The spores germinate quickly, penetrate and kill living cells in both the phloem and xylem (Safranyik et al. 1975). This process aids the establishment of successful attacks in the tree. Trees respond to the invasion by the beetle-blue stain complex with a flow of liquid resin from resin ducts (primary resin) damaged by the attacking organisms and production of additional resin in living cells next to the damaged area (secondary resin). When resin production is rapid and massive and the phloem and sapwood next to the wound becomes impregnated by resinous substances, beetles are killed or repelled and the fungi are confined and die. Mountain Pine Beetle Symposium: Challenges and Solutions. October 30-31, 2003, Kelowna, British Columbia. T.L. Shore, J.E. Brooks, and J.E. Stone (editors). Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre, Information Report BC-X-399, Victoria, BC. 298 p.