Comparisons of Efficiency of Two Formulations of Verbenone (4, 6, 6-trimethylbicyclo [3.1.1] hept-3-en-2-one) for Protecting Whitebark Pine, Pinus albicaulis (Pinales: Pinaceae) From Mountain Pine Beetle (Colopetera: Curculionidae)

Whitebark pine, Pinus albicaulis Engelm., is a subalpine tree endemic to western North America. This species provides multiple ecosystem services and is suffering widespread mortality from mountain pine beetle, Dendroctonus ponderosae Hopkins. Verbenone is a pheromone produced as D. ponderosae feed, and high air concentrations of verbenone deter D. ponderosae from colonizing trees. Synthetic verbenone has been formulated into products used to prevent D. ponderosae from colonizing trees. We compared the ability of verbenone pouches and SPLAT Verb to protect individuals and small stands of P. albicaulis. With individual trees in Montana, all treated trees survived regardless of verbenone formulation and rate, whereas untreated trees suffered 70 and 90% mortality in 2015 and 2016. In plot experiments in California from 2015 to 2017, and Oregon from 2015 to 2018, verbenone was applied to trees spaced ∼10 m apart, and survival of small (12.7–23 cm DBH = diameter at 1.37 m height), medium (23.1–33 cm DBH) and large (>33 cm DBH) trees was compared. In California, where >80% of untreated trees survived, pouches increased survival ∼2 to 3% and SPLAT Verb increased survival ∼4 to 7% regardless of tree size. In Oregon, verbenone pouches and SPLAT Verb performed similarly on medium and small trees, but large trees had greater survival when treated with SPLAT Verb (∼93%) than pouches (∼82%). Compared to verbenone pouches, SPLAT Verb appears to better protect P. albicaulis from D. ponderosae.