Using Pheromone-Baited Traps to Control the Amount and Distribution of Tree Mortality During Outbreaks of the Douglas-Fir Beetle

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Forest Science

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Multiple-funnel traps baited with strong aggregation pheromone lures were placed throughout three 259 ha plots in a coniferous forest in northeastern Oregon during an outbreak of the Douglas-fir beetle (Dendroctonus pseudotsugae). In addition to Douglas fir (Pseudotsuga menziesii), other tree species found within the plots included ponderosa pine (Pinus ponderosa), western larch (Larix occidentalis), grand fir (Abies grandis), lodgepole pine (Pinus contorta), Engelmann spruce (Picea engelmannii) and alpine fir (Abies lasiocarpa). Mean numbers ( SEM) of Douglas-fir beetles collected per plot for the entire flight periods of 1992 and 1993 were 277 921 40 447 and 268 834 37 088, respectively. Mean numbers ( SEM) of the most abundant predator, Thanasimus undatulus, collected per plot in 1992 and 1993 were 43 527 3553 and 35 652 3514, respectively. Tree mortality caused by Douglas-fir beetles was concentrated around the trap sites in the treated plots, even though traps were located an average of 40 m from the nearest host tree. Managers can influence the spatial distribution of tree mortality during an outbreak by selective placement of traps across the landscape. Selective trap placement, plus the removal of trapped beetles from the population, may reduce tree mortality within the general area.