A Test of High-Dose Verbenone for Stand-Level Protection of Lodgepole and Whitebark Pine from Mountain Pine Beetle (Coleoptera: Curculionidae: Scolytinae) Attacks

Abstract

The efficacy of verbenone as a stand-level protectant against mountain pine beetle, Dendroctonus ponderosae Hopkins, attacks was tested in lodgepole and whitebark pine stands at five geographically separated sites, including three consecutive years at one site. Forty and 20 high-dose pouches, with a verbenone emission rate up to 50 mg/d per pouch, were spaced in a grid pattern throughout 0.40-ha plots, replicated up to six times at each site. Although the verbenone treatment did not prevent beetles from dispersing through treated stands, attacking large-diameter trees most frequently, the overall number of trees attacked was, on average, reduced significantly compared with nontreated stands. In a few blocks each year, verbenone-treated plots had more attacked trees than controls. These blocks tended to have a large emerging beetle population, exceeding 140 previously attacked trees within the hectare including and surrounding the treated area. Additional research is needed on the behavioral role of verbenone in mountain pine beetle population dynamics and quantification of the infestation level above which treatment efficacy tends to be reduced.

Evaluation of the push-pull tactic against the mountain pine beetle using verbenone and non-host volatiles in combination with pheromone-baited trees

“…For all other relationships between percentage of red trees and percentage of available trees massattacked, the r 2 values ranged from .0012 to .3293 and the corresponding P values from 0.9239 to 0.0826. This result is in contrast to that found by Bentz et al (2005) in plots treated with high-dose verbenone at 10-m centres. However, Bentz et al (2005) found that verbenone treatment became ineffective when there were ≥ 200 red trees/ha, while the highest density of red trees/ha in our plots was 89 (Table 4).…”

“…Because this was an operational evaluation designed to protect all PSPs to the maximum extent possible, no control plots were left untreated. However, the results are similar to those of Bentz et al (2005), who found that, when compared to control plots, high-dose verbenone protected most trees from attack, but that treatment efficacy was not uniformly consistent. Similarly, Progar (2003Progar ( , 2005 found that verbenone protected treated plots from attack for two successive years, but in the face of an advancing infestation, efficacy was lost thereafter.…”

“…Trees in the PSPs were not protected to a greater extent than those in the remainder of the 50 ϫ 50 m treated areas. The significantly higher percentage of available trees mass-attacked in the outer 0.75 ha in four of the 10 plots, and the generally higher attack in this outer perimeter in all but one plot, agree with the interpretation by Bentz et al (2005) that the effect of high-dose verbenone extended beyond 0.4 ha treated plots into a 20-m wide buffer zone surrounding them.…”

“…This study, and those of Bentz et al (2005) and Progar (2005), indicate that unless policy prohibits other management tactics, e.g., in parks, high-dose verbenone should desirably be applied only if the resource manager is permitted and intends to use the treatment as part of an integrated pest management (IPM) program. Such a program would employ other tactics like removing infested trees by sanitation harvesting, killing resident beetles by using monosodium methane arsonate or falling and burning (Maclauchlan and Brooks 1999), or potentially using the push-pull tactic.…”

“…Deploying high-dose verbenone pouches at 16 points, 10 m apart, in 40 ϫ 40 m plots, with a pheromonebaited lodgepole pine in the centre, reduced the incidence of mass-attacked trees by 72%, significantly lower than a 46% reduction achieved by bubble caps deployed at the same density. Using high-dose verbenone pouches at similar densities, Bentz et al (2005) found significant reductions in mass-attacked lodgepole pine and whitebark pine, P. albicaulis Engelmann, for up to three years. Similarly, treatment with high-dose verbenone resulted in significant reductions in the numbers of lodgepole pines attacked for two successive years (Progar 2003), but over a five-year period in the same location, attack in treated areas was not significantly different from that in control areas (Progar 2005).…”