Trapping Douglas-fir beetle (Dendroctonus pseudotsugae) with pheromone baited multiple-funnel traps does not reduce Douglas-fir (Pseudotsuga menziesii) mortality

Douglas-fir beetle (Dendroctonus pseudotsugae Hopkins) (DFB) causes considerable mortality to Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) in western North American forests. We evaluated the use of semiochemical-baited multiple-funnel traps for the protection of small, high-value stands of trees, such as those occurring in campgrounds, rest areas, and small parks when Douglas-fir mortality caused by populations of DFB were at levels of concern to land managers. At two sites in western Montana in 2004, three treated plots were surrounded by three trapping stations arranged in an equilateral triangle (200 m per triangle side). Similar, untreated plots were used for comparison. More than 2 million DFB were trapped and removed from treated plots during 2004, but this trapping did not protect Douglas-fir at either site. Conversely, the ratio of infested to living trees increased substantially due to trapping at one of the sites. Placing semiochemical lures adjacent to stands of susceptible trees may have concentrated beetles from the surrounding area. Though many beetles were trapped, large numbers of beetles did not enter the traps and consequently attacked trees in our plots. Positioning pheromone traps immediately adjacent to high-value Douglas-fir stands when beetle population densities are high, does not appear to reduce overall tree mortality in target stands and sometimes increases it. However, trapping combined with sanitation and/or and antiaggregant may be a viable treatment.