Log colonization by Ips sexdentatus prevented by increasing host unsuitability signaled by verbenone

Sudden increments of breeding material after windstorms, forest fires, or inappropriate management practices help bark beetles such as Ips sexdentatus Boerner (Coleoptera: Curculionidae: Scolytinae) increase in numbers and colonize standing healthy pine trees. Preventing bark beetles from arriving to susceptible trees or logs may have great relevance for bark beetle management. Recent studies have reported inhibition of the aggregation response of I.sexdentatus using verbenone. Two field experiments were conducted to examine the effect of verbenone on the colonization pattern of this beetle. The first experiment tested the combined effect of trans-conophthorin, a non-host bark volatile with known repellent effect, and verbenone on Pinus sylvestris L. (Pinaceae) log piles of two sizes, but failed to protect them against I.sexdentatus attack when these two infochemicals were released at low rates. The results of this experiment suggested an interaction with the associated secondary bark beetle Orthotomicus erosus (Wollaston). A second experiment examined the response of I.sexdentatus and O.erosus to log piles that released verbenone at 0, 2, 10, or 40mgday1. Although I.sexdentatus colonization of Pinus nigra Arnold logs was completely prevented at 40mgday1, O.erosus could be found at all tested verbenone release rates. Besides verbenone, O.erosus colonization density and the height from which logs originated were the variables that best explained I.sexdentatus log colonization pattern. In addition, I.sexdentatus and O.erosus were rarely recorded colonizing the same log, and niche breadth analyses suggested that they excluded each other. The role of verbenone in the colonization process and its potential use in the prevention of population buildups of damaging bark beetles such as I.sexdentatus are discussed.