Heritability of lodgepole pine defenses against mountain pine beetle: Family does matter

About 13 million ha of lodgepole pine, Pinus contorta var. latifolia, have been killed by mountain pine beetle (MPB), Dendroctonus ponderosae (Coleoptera: Curculionidae) and its symbiotic fungal complex in the current outbreak in British Columbia. Although most trees succumb to the MPB/fungal complex, some appear to escape, tolerate, or resist attack. The surviving trees may possess heritable traits that affect MPB host selection, reproduction, brood success, and fungal symbiont growth. We quantified the genetic variation of lodgepole pine chemical and physical defensive responses against MPB and a component of its fungal complex, Grosmannia clavigera, in 45 open-pollinated pine families at two sites. The quantified responses included host hypersensitive response and levels of particular constitutive and induced terpenoid secondary metabolites. We also assessed other parameters related to tree condition and survival as well as those related to beetle host selection and reproductive success. Our data suggest that resin terpenoid constituents differ significantly among families both before and after simulated MPB/fungal attack. In addition, several other phenotypic traits in lodgepole pine affect MPB colonization and tree mortality. We calculated family mean correlations of such traits that also possessed significant heritability. Constitutive δ-3-carene was negatively correlated with family mean mortality and with levels of several constitutive and induced terpenoids. MPB gallery production, reproduction, and brood development were negatively correlated with the occurrence of hypersensitive reactions. Thus heritable δ-3-carene levels and hypersensitivity reactions negatively impact MPB induced tree mortality and insect reproductive success.