Semiochemical interruption of Dendroctonus rufipennis (Coleoptera: Curculionidae) in Alaska and Colorado, U.S

Spruce beetle, Dendroctonus rufipennis (Kirby) (Coleoptera: Curculionidae), poses a significant threat to mature spruce (Picea spp.) in western North America. We evaluated 3-methylcyclohex-2-en-1-one (MCH), the primary anti-aggregation pheromone of D. rufipennis, for tree protection at 3.5 and 7 g MCH/tree (SPLAT MCH, ISCA Inc., Riverside, CA) alone and in combination with acetophenone + (E)-2-hexen-1-ol + (Z)-2-hexen-1ol (PLUS) or with linalool + β-caryophyllene + (Z)-3-hexanol (AKB). Dendroctonus rufipennis colonization and subsequent mortality of individually treated spruce and of untreated spruce within 0.041-ha circular plots (11.3-m radius) surrounding individually treated spruce were assessed in two studies, one on the Kenai Peninsula, Alaska, and one on the San Isabel National Forest, Colorado. In a third study, we evaluated two release devices containing MCH, SPLAT MCH, and Synergy Shield MCH Double Bubble caps (Synergy Semiochemical Corp. Delta, BC), for tree protection at three doses (1, 3, and 7 g MCH/tree) on the Kenai Peninsula. In each study, treated trees and untreated control trees were baited with frontalin, the primary aggregation pheromone of D. rufipennis, to induce D. rufipennis attacks. Separately, we conducted three zones of inhibition studies to determine maximum inhibition from semiochemical point sources (treated spruce) based on D. rufipennis captures in baited traps. All semiochemical treatments, except SPLAT MCH alone, significantly reduced D. rufipennis colonization of treated spruce and neighboring spruce in all studies compared to the controls. All semiochemical treatments significantly reduced the mortality of treated spruce and neighboring spruce in all studies compared to the controls. Only two (of 300) semiochemical-treated spruce died during these studies while 47% to 80% mortality occurred in the controls (32 of 50 spruce across all studies). Maximum inhibition was statistically constant to 4 m from semiochemical point sources in Alaska and to 12 m in two separate studies in Colorado. The implications of these results are discussed.