REDUCTION OF DOUGLAS-FIR BEETLE INFESTATION OF HIGH-RISK STANDS BY ANTIAGGREGATION AND AGGREGATION PHEROMONES

A combination of antiaggregation and aggregation pheromones was tested for protecting stands of Douglas-fir (Pseudotsuga menziesii (Mirb.) F rance) at high risk for infestation by the Douglas-fir beetle (Dendroc tonus pseudot-sugae Hopkins). The antiaggregation pheromone, 3-methylc yclohex-2-en-1-one (MCH), was applied in a bubble capsule formulation to the perimeter of 1-ha circular plots at a rate of 60 g/plot. Treate d plots also had three or four clusters of four Lindgren funnel traps baited with frontalin, seudenol, 1-methylcyclohex-2-en-1-ol, and ethan ol located outside of the plot but within 160 m of the boundary. Mean (+/-SE) accumulated catches in all traps per plot were 73 658 +/- 19 7 21 Douglas-fir beetles and 12 892 +/- 2 513 Thanasimus undatulus (Say) , a predator of the Douglas-fir beetle. The mean percentage of Douglas -fir trees greater than or equal to 20 cm DBH that were mass attacked was reduced by 80% within the treated plots compared with the untreate d plots. However, there was an eightfold increase in the percentage of trees mass attacked in the area outside the treated plots in the vici nity of the funnel traps. The net effect of the treatment was to conce ntrate mass-attacked trees within a limited area outside of the protec ted stand. Our results indicate that Douglas-fir beetle antiaggregatio n and aggregation pheromones can be used effectively to reduce the pro bability of infestation in small, high-value stands.