Induced terpenoid defenses in lodgepole and jack pine and possible effects on the eastern spread of the mountain pine beetle

The primary host of the mountain pine beetle (Dendroctonus ponderosae Hopkins, MPB) in British Columbia is lodgepole pine (Pinus contorta var. latifolia), but the insect is capable of utilizing several Pinus spp., including jack pine (Pinus banksiana), as hosts. Pines use their terpenoid resin defenses against the MPB, and some terpenoids are toxic to the invading insects. Bark beetles may reverse such defenses by using them as precursors to components of their aggregation pheromone. Comparison of jack and lodgepole pine defenses may help predict risks of beetle infestation in new areas. We sampled phloem tissue from three populations of pine: lodgepole pine stands in southern and central British Columbia and a jack pine stand in Alberta. Samples were analyzed for presence and quantity of 26 terpenoids after wounding the trees to simulate beetle attack. Samples were taken near to the wound site at three time points: just before wounding, two days post-wounding, and 14 days post-wounding. Following wounding, jack pine had lower induced levels of toxic Δ-3-carene. It also had higher induced levels of α-pinene a terpene utilized by MPB to produce aggregation pheromone. These results, along with comparative analyses of other differences in induced terpenoid defenses between the two species of pine, indicate that MPB may be quite successful as it encounters jack pine stands.