Applied Chemical Ecology of Spruce Beetle in Western North America

Spruce beetle (Dendroctonus rufipennis (Kirby)) is a major cause of spruce (Picea spp.) mortality in western North America. We synthesized the literature on the chemical ecology of spruce beetle, focusing on efforts to reduce host tree losses. This literature dates back to the mid-20th century and focuses on spruce beetle populations in Alaska, U.S., western Canada, and the central and southern Rocky Mountains, U.S. Spruce beetle aggregation pheromone components include frontalin (1,5-dimethyl-6,8-dioxabicyclo[3.2.1]octane), seudenol (3-methyl-2-cyclohexen-1-ol), MCOL (1-methyl-2-cyclohexen-1-ol), and verbenene (4-methylene-6,6-dimethylbicyclo[3.1.1]hept-2-ene). The attraction of spruce beetle to one aggregation pheromone component is enhanced by the co-release of other aggregation pheromones and host compounds (e.g., α-pinene). Several baits that attract spruce beetles are commercially available and are used for survey and detection, population suppression, snag creation, and experimental purposes. The antiaggregation pheromone is MCH (3-methyl-2-cyclohexen-1-one), which has been evaluated for reducing colonization of felled spruce since the 1970s. Beginning in the early 2000s, MCH has been evaluated for protecting live, standing spruce from colonization by and mortality attributed to spruce beetle. With a few exceptions, significant reductions in levels of spruce beetle colonization and/or spruce mortality were reported. More recent efforts have combined MCH with other repellents (e.g., nonhost compounds) in hope of increasing levels of tree protection. Today, several formulations of MCH are registered for tree protection purposes in the U.S. and Canada.