Population densities and tree diameter effects associated with verbenone treatments to reduce mountain pine beetle-caused mortality of lodgepole pine

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.

Presence and roles of myrtenol, myrtanol and myrtenal in Dendroctonus armandi (Coleoptera: Curculionidae: Scolytinae) and Pinus armandi (Pinales: Pinaceae: Pinoideae)

BACKGROUND

Insect pheromones and host volatiles are important for pest control due to their high efficiency and low potential for environmental pollution. The functions of myrtenol, myrtanol and myrtenal in pest-host interactions are unknown. This study aimed to determine the presence of myrtenol, myrtanol and myrtenal in newly emerged and emerged stages of Dendroctonus armandi, and in infected and healthy Pinus armandi, and to identify their roles in tree protection and pest management based on electroantennography (EAG), Y-tube and toxicity experiments.

RESULTS

Gas chromatographic and mass spectrometry (GC-MS) analyses, EAG, Y-tube and toxicity assays revealed the following: (1) myrtenol was found in P. armandi phloem and did not exhibit significant toxicity towards D. armandi; (2) myrtanol was produced by infected P. armandi after D. armandi invasion and had significant toxicity towards D. armandi, especially females; and (3) myrtenal might represent an aggregation pheromone produced by female D. armandi to exert aggregation effects on other females, to help them overcome the resistance of P. armandi jointly and ensure a successful invasion, females remained in an aggregation state from leaving the host to mating in a new host.

CONCLUSION

These findings suggest that myrtanol as a repellent has potential for the protection of P. armandi and that myrtenal could be used to trap and disorient D. armandi. © 2019 Society of Chemical Industry.

Management of Western North American Bark Beetles with Semiochemicals

We summarize the status of semiochemical-based management of the major bark beetle species in western North America. The conifer forests of this region have a long history of profound impacts by phloem-feeding bark beetles, and species such as the mountain pine beetle (Dendroctonus ponderosae) and the spruce beetle (D. rufipennis) have recently undergone epic outbreaks linked to changing climate. At the same time, great strides are being made in the application of semiochemicals to the integrated pest management of bark beetles. In this review, we synthesize and interpret these recent advances in applied chemical ecology of bark beetles for scientists and land managers.

A Novel Semiochemical Tool for Protecting Pinus contorta From Mortality Attributed to Dendroctonus ponderosae (Coleoptera: Curculionidae)

Verbenone (4,6,6-trimethylbicyclo[3.1.1]hept-3-en-2-one) is an antiaggregant of the mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), a notable forest insect capable of causing extensive levels of tree mortality in western North America. Several formulations of verbenone are registered for tree protection, but failures in efficacy are not uncommon, particularly when applied during large infestations. A formulation of (-)-verbenone was developed (Specialized Pheromone & Lure Application Technology [SPLAT] Verb, ISCA Technologies Inc., Riverside, CA) and evaluated for protecting individual lodgepole pine, Pinus contorta Douglas ex Loudon, and small stands of P. contorta from mortality attributed to D. ponderosae. SPLAT Verb applied to individual P. contorta resulted in complete tree protection, while 93.3% mortality occurred in the untreated controls. Significantly fewer P. contorta were killed by D. ponderosae within 0.041-ha circular plots surrounding P. contorta treated with SPLAT Verb compared with the untreated control. In a second study, a smaller percentage of P. contorta were colonized and killed on 0.4-ha square plots treated with SPLAT Verb compared with the untreated control. No significant differences in levels of tree mortality were observed between the untreated control and another formulation of verbenone (7-g pouch) or between the 7-g pouch and SPLAT Verb. In a trapping bioassay, no significant differences were observed among captures in multiple-funnel traps at 1, 2, or 4 m from the point of release of SPLAT Verb. Significantly fewer D. ponderosae were collected at 1 and 2 m compared with 8 m. Significantly more D. ponderosae were captured at the farthest distance evaluated (16 m) than at any other distance. Our data indicate that SPLAT Verb is effective for protecting individual P. contorta and small stands of P. contorta from mortality attributed to D. ponderosae at moderate doses. The high levels of tree protection observed are attributed to the ability of applying release points (dollops) at high densities, and a larger zone of inhibition than reported for other formulations of verbenone. SPLAT Verb was registered by the U.S. Environmental Protection Agency for use on pines, Pinus spp., in 2013.