Attack Density Regulation: a New Approach to the Use of Pheromones in Douglas-fir Beetle Population Management12

The Douglas fir beetle, Dendroctonus pseudotsugae Hopkins, normally mass attacks Douglasfir, Pseudotsuga menziesii (Mirb.) Franco, at a density of 8–10 females/0.1 m2. An attack at this density kills the tree and establishes a new beetle brood. When the aggregation pheromone Douglure (2 attractants and 2 host cofactors) and a natural aggregation inhibitor 3-methyl-2-cyclohexen-l-one (MCH) were placed on or near live hosts simultaneously and in varying ratios, the colonization behavior of the Douglas fir beetle was altered. These alterations in behavior affect number of attacks, total height of attack, length of parent galleries, and proportion of successful galleries. Below a threshold of 4–6 attacks/0.1 m2 of bark surface, the females were unsuccessful in establishing a brood, and the tree survived. These results suggest a new concept (the pest population sink), which modifies the behavior of this pest with chemicals.