LAUSR

Abstract Several formulations of the antiaggregation pheromone verbenone (4,6,6-trimethylbicyclo [3.1.1]hept-3-en-2-one) are registered to protect pine trees and forest stands from mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), but failures in efficacy are not uncommon. In 2011–2013, a novel formulation of (−)-verbenone was developed (SPLAT® Verb, 10.0% (−)-verbenone by weight, EPA Reg. No. 80286−20, ISCA Technologies Inc., Riverside, CA, USA) for protecting individual lodgepole pine, Pinus contorta Dougl. ex Loud., and small stands of P. contorta from mortality attributed to D. ponderosae. We evaluated the efficacy of lower doses of SPLAT® Verb than previously considered for tree protection on the Beaverhead-Deerlodge National Forest, Montana, USA, 2014–2015. In an individual tree study, D. ponderosae pressure was not sufficient to adequately challenge the treatments as only 56.7% of the untreated controls died. However, if one additional tree in the untreated control had died, all verbenone treatments (30 g, 50 g, and 70 g of SPLAT® Verb/tree, and one 7-g verbenone pouch/tree) would have been considered efficacious. In a small-scale stand study, fewer P. contorta were colonized by D. ponderosae on 0.41-ha experimental plots treated with 2.5 kg and 3.5 kg of SPLAT® Verb [250 g and 350 g of (−)-verbenone, respectively] and the 7-g verbenone pouch [50 pouches/plot, 350.0 g of (−)-verbenone/plot] compared to the untreated control. No significant difference was observed between 1.5 kg of SPLAT® Verb [150 g of (−)-verbenone] and the untreated control. Fewer P. contorta were killed by D. ponderosae on experimental plots treated with 1.5 kg, 2.5 kg and 3.5 kg of SPLAT® Verb and the verbenone pouch compared to the untreated control. No other significant differences were observed among treatments. Collectively, these data suggest that lower doses of SPLAT® Verb can be used for tree protection than previously considered, and at a substantial cost savings that could make this strategy economically viable for area-wide management of D. ponderosae.