Tests of Three Pheromones to Induce or Disrupt Aggregation of Douglas-Fir Beetles (Coleoptera: Scolytidae) on Live Trees

Two-hundred-seventy live trees were treated with 3 Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins, pheromones (frontalin, 3-methyl-2-cyclohexen-1-one, and trans-verbenol) and with the host volatiles I±-pinene and camphene, alone and in combination. Frontalin induced beetle attacks but most attacks were unsuccessful and few beetles were trapped. The highest proportion of “spillover” attacks occurred in trees surrounding those treated with frontalin. Methylcyclohexenone disrupted attraction and prevented attack. The role of trans -verbenol in regulating beetle behavior was unclear, but it did not attract beetles by itself, nor did it repress the attractiveness of frontalin. Chopping, to release the odor of resin, did not influence treatment results. Attacks in the younger trees (about 50-80 years old) were unsuccessful. These results indicate that methylcyclohexenone should be tested to determine its ability to prevent attacks in susceptible stands.