Area-wide application of verbenone-releasing flakes reducesmortality of whitebark pine Pinus albicaulis caused by the mountainpine beetle Dendroctonus ponderosae

1 DISRUPT Micro-Flake Verbenone Bark Beetle Anti-Aggregant flakes (Hercon Environmental, Inc., Emigsville, Pennsylvania) were applied in two large-scale tests to assess their efficacy for protecting whitebark pine Pinus albicaulis Engelm. from attack by mountain pine beetle Dendroctonus ponderosae Hopkins (Coleoptera: Scolytinae) (MPB). At two locations, five plots of equivalent size and stand structure served as untreated controls. All plots had earlyto mid-outbreak beetle populations (i.e. 7.1–29.2 attacked trees/ha). Verbenone was applied at 370 g/ha in both studies. Intercept traps baited with MPB aggregation pheromone were placed near the corners of each plot after the treatment in order to monitor beetle flight within the plots. Trap catches were collected at 7to 14-day intervals, and assessments were made at the end of the season of stand structure, stand composition and MPB attack rate for the current and previous years. 2 Applications of verbenone flakes significantly reduced the numbers of beetles trapped in treated plots compared with controls at both sites by approximately 50% at the first collection date. 3 The applications also significantly reduced the proportion of trees attacked in both Wyoming and Washington using the proportion of trees attacked the previous year as a covariate in the model for analysis of current year attack rates; in both sites, the reduction was ≥ 50%. 4 The flake formulation of verbenone appears to have promise for area-wide treatment by aerial application when aiming to control the mountain pine beetle in whitebark pine forests.