Spruce beetle, Dendroctonus rufipennis (Kirby) (Coleoptera: Curculionidae), is the most destructive pest of mature spruce (Picea) in western North America. Recent outbreaks in Alaska and other western US states highlight the need for tools to protect Picea from D. rufipennis. The primary antiaggregation pheromone of D. rufipennis (3-methylcyclohex-2-en-1-one, MCH) and various combinations of potential repellents (1-octen-3-ol, exo-brevicomin, endo-brevicomin, ipsdienol, ipsenol, limonene, and verbenone) were tested for their ability to disrupt the response of D. rufipennis to attractant-baited multiple-funnel traps. Two assays were conducted on the Kenai Peninsula, Alaska, in June and July 2021. All treatments significantly reduced the mean number of D. rufipennis caught compared to the baited control. No other significant differences were observed among treatments. Informed by these and other data, tree protection studies were established in Lutz spruce, Picea x lutzii, on the Kenai Peninsula in 2022 and in Engelmann spruce, Pi. engelmannii, in the Uinta Mountains, Utah, in 2021. All experimental trees were baited with frontalin. Repellent treatments included MCH (SPLAT MCH, ISCA Inc., Riverside, CA, USA) and at least 1 additional repellent combination. In Alaska, all treatments significantly reduced colonization (strip attacks + mass attacks) and mortality of individually treated Pi. x lutzii and all Picea within 11.3-m radius of each treated Pi. x lutzii compared to the control. In Utah, all treatments except for SPLAT MCH + octenol significantly reduced colonization compared to the control. Only SPLAT MCH + Acer kairomone blend (AKB) and SPLAT MCH + octenol reduced Pi. engelmannii mortality compared to the control. SPLAT MCH + AKB and SPLAT MCH + acetophenone and green leaf volatiles (PLUS) were the most effective across both studies. The implications of these and other results to the development of an effective semiochemical repellent for D. rufipennis are discussed.

Of the more than five hundred and fifty species of North American bark beetles (Coleoptera: Curculionidae, Scolytinae), approximately twenty species occasionally cause large amounts of tree mortality in conifer forests. During 2000–2020, trends in bark beetle impacts changed dramatically across North America compared to those observed during the mid- to late 20th century. We review tools and tactics available for bark beetle suppression and prevention and provide an overview of temporal and spatial trends in bark beetle impacts in North American forests during 2000–2020. Higher impacts were observed for several bark beetle species in western North America accompanied by substantial declines in eastern North America driven by large reductions in southern pine beetle (Dendroctonus frontalis) activity in the southeastern United States. Regional differences likely result from a higher species richness of both bark beetles and their hosts in western North America, stronger direct and indirect effects of climate change (warming and drying) on bark beetles in western North America, and differences in forest composition, management history, and other abiotic stressors and disturbances. Compared to the mid- to late 20th century, bark beetles have had increased impacts in western North America and reduced impacts in eastern North America, the latter driven by large reductions in southern pine beetle (Dendroctonus frontalis) activity in the southeastern United States. We review tools and tactics available to foresters and other natural resource managers to reduce the negative impacts of bark beetles on forests. Furthermore, we provide several potential explanations for recent trends in bark beetle impacts between eastern and western North America.

We tested 3-methyl-2-cyclohexen-1-one (MCH) and novel semiochemicals as potential spruce beetle (Dendroctonus rufipennis Kirby) (Coleoptera: Curculionidae, Scolytinae) repellents over multiple years in Utah and Colorado trapping bioassays. MCH is a known spruce beetle repellent and our testing revealed Acer kairomone blend (AKB) and isophorone plus sulcatone as repellents. We subsequently tested these semiochemicals for area and single tree protection to prevent spruce beetle attacks at locations in Utah, Colorado, Wyoming, New Mexico, and Alaska. Individual tree protection trials found MCH-AKB provided significant protection against spruce beetle attacks in the southern Rocky Mountains but not in Alaska. Adding sulcatone or doubling MCH-AKB pouches did not further enhance protection. A degree of protection was extended to spruce at least 10 m distant from the repellents, including in Alaska. Tree diameter was not a significant covariate among treated trees but was positively correlated with the probability of infestation for surrounding spruce. In area protection trials, spruce in control plots were 2.4 times more likely to be in a higher severity attack class compared with spruce in plots treated with MCH-AKB pouches deployed at 30 sets per hectare. Tree diameter had a significant, positive relationship to the probability of infestation. We found MCH-AKB to offer a high degree of protection against beetle attack in Engelmann spruce (Picea engelmannii Parry ex Engelm.) (Pinales: Pinaceae) (Picea engelmannii Parry ex Engelm.) (Pinales: Pinaceae), especially for single tree protection (66% of control trees were strip- or mass-attacked compared with 6% of repellent-treated trees). AKB requires registration and labeling, however, before this economical and environmentally benign semiochemical can be used operationally.

Plant host specificity of prey buprestid beetles was used to estimate the minimum distance of hunting flights by the solitary fossorial wasp, Cerceris fumipennis Say. Plant hosts of the 5 beetle species investigated were each found at less than 200 m of the wasp nesting area. Although these results indicate neither average nor maximal hunting range, they suggest a working hypothesis that foraging in close proximity to the nesting site may be the norm.