Mountain pine beetle, Dendroctonus ponderosae Hopkins, is among the most significant forest insect pests, particularly in lodgepole pine, Pinus contorta Dougl. ex Loud., forests in western North America. We established a network of 125, 0.081-ha circular plots in P. contorta forests in Colorado, Idaho, Montana, Utah, and Wyoming to document tree mortality and stand-level responses to D. ponderosae outbreaks. We found notable reductions in several key metrics but also observed significant variability in per-year (0–71%) and cumulative mortality (2–87%). We used this long-term monitoring dataset and employed generalized linear mixed effects modeling to determine the biophysical drivers of the variation in P. contorta mortality. Models were fitted to the entire (2005–2024) dataset, and to two truncated datasets: outbreak years only (2005–2012) and maximum per year P. contorta mortality per plot. Explanatory variables included tree, plot, and environmental factors (temperature and water availability). Our models highlighted several significant drivers of P. contorta mortality. The most significant and consistent were individual tree dbh and quadratic mean diameter (QMD). Larger individual tree dbh and larger QMD positively influenced the probability of P. contorta mortality. Tree dbh interacted significantly with water availability variables, particularly November-March snowpack. Increased snowpack and greater densities of nonhost tree species decreased mortality. These results suggest that management efforts should account for the frequency of large-diameter P. contorta and that density reduction and/or increasing tree species (nonhost) and structural diversity may provide mitigation strategies for reducing P. contorta mortality attributed to D. ponderosae in the Intermountain West.

DOI: 10.18474/JES24-31 Abstract Bark beetles (Coleoptera: Curculionidae, Scolytinae) cause extensive tree mortality in conifer forests in the western United States. One method to protect conifers from bark beetles involves applications of liquid formulations of insecticides to the tree bole using high-pressure (e.g., >= 2,241 kPa) ground-based sprayers. Several active ingredients and products are effective when properly applied in accordance with the label. Researchers recently have developed more portable methods that inject small quantities of systemic insecticides directly into trees. The purpose of this review is to synthesize information on the efficacy, residual activity, and environmental safety of insecticides commonly used to protect conifers from bark beetles in the western United States so that informed, judicious decisions can be made about the use of these insecticides. This review serves as an update to "Advances in insecticide tools and tactics for protecting conifers from bark beetle attack in the western United States" (Fettig et al. 2013a) and focuses, where applicable, on relevant literature published since 2012.

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.

Rising global temperatures driven by anthropogenic carbon emissions are creating new challenges for food crop agriculture and forest management around the world. Droughts and other severe weather events are becoming more common and more extreme, causing both chronic stress and acute damage in cultivated and natural plant life, whereas warmer temperatures favor outbreaks of plant diseases and insect pests in many situations. At the same time, growing awareness of the health and environmental risks associated with broad-spectrum chemical pesticides has led crop growers and forest managers to seek out more selective, sustainable alternative techniques to mitigate the impact of harmful arthropods. Arthropod repellents have proven an efficacious strategy to reduce these impacts in the field of public health, where they are a key tactic in the suppression of diseases transmitted by hematophagous arthropods, but repellents are comparatively rarely employed to manage pests of agriculture and forestry. This chapter describes several cases in which repellents using beetle semiochemicals antiaggregation pheromones have been developed and evaluated in the field by the authors, successfully reducing tree mortality and/or crop damage induced by coffee berry borer (Hypothenemus hampei Ferrari) in Arabica coffee (Coffea arabica L.); by aggressive Dendroctonus bark beetles in single trees and small stands of North American forest species; and by ambrosia beetles on apple and avocado crops, as well as southeastern forest species.

Spruce beetle, Dendroctonus rufipennis Kirby (Coleoptera: Curculionidae), is a lethal pest of spruce trees in North America. Despite decades of research, a semiochemical repellent that consistently and effectively protects spruce trees remains elusive. We evaluated the efficacy of 3-methyl-2-cyclohexen-1-one (MCH) in a proprietary, volatile compound release technology (SPLAT) alone and with two adjuvants, Acer kairomone blend (AKB) and acetophenone + green leaf volatiles (PLUS) to protect individually treated Picea engelmannii Parry ex. Engelm. (Pinales: Pinaceae), and Pi. engelmannii within 11.3-m radius of the individually treated trees from colonization and mortality attributed to D. rufipennis in western Wyoming. Ninety-one Pi. engelmannii were baited with frontalin and randomly assigned to one of seven treatments (n = 13): 3.5 g of MCH applied as SPLAT MCH (SPLAT3.5), 3.5AKB, 3.5PLUS, 7 g of MCH applied as SPLAT MCH (SPLAT7), 7AKB, 7PLUS, and baited control (bait only). All repellents except SPLAT3.5 and SPLAT7 significantly reduced colonization of individually treated Pi. engelmannii compared to the baited control. 3.5PLUS, 7AKB, and 7PLUS reduced colonization most effectively, and all repellents significantly reduced mortality of individually treated Pi. engelmannii compared to the baited control. All repellents also significantly reduced colonization and mortality of neighboring Pi. engelmannii.

Of the > 6000 species of bark beetles (Coleoptera: Curculionidae, Scolytinae), ~ 25 species cause significant amounts of tree mortality in conifer-dominated forests. Several tactics are available to manage bark beetle infestations and to reduce associated levels of tree mortality. Suppression involves short-term tactics designed to address current infestations by manipulating beetle populations and typically includes the use of sanitation harvests, insecticides, semiochemicals, or a combination of these and other treatments. Prevention is designed to reduce the probability and severity of future infestations by manipulating stand, forest, and/or landscape conditions by reducing the number of susceptible hosts through thinning, prescribed burning, and/or altering age classes and species compositions. In this chapter, we review the ecology and management of bark beetles in conifer-dominated forests in North America and Europe, where they exert their largest impacts, and provide six case studies focused on the effects of altered forest and climatic conditions on bark beetle ecology and management. We conclude that in many forests bark beetle outbreaks have and will continue to be exacerbated by climate change due to shifts in temperature and precipitation that influence bark beetles, their hosts, and community associates. Changes in forest structure and composition by natural processes and management practices have and will continue to be important factors as well. As a result, natural resource managers will be increasingly challenged to manage bark beetle populations, and to facilitate recovery of landscapes impacted by bark beetle outbreaks. In most cases, current management tactics are based on research and development executed in the 20th century and unable to meet the demands imposed by altered forest and climatic conditions without some modification and/or adaptation.

Abstract Spruce beetle, Dendroctonus rufipennis Kirby (Coleoptera: Curculionidae), causes significant mortality of mature spruce, Picea spp. (Pinales: Pinaceae), in western North America. We evaluated the effectiveness of two formulations of bole injections of emamectin benzoate (TREE-äge® G4 and TREE-äge R10; Arborjet, Inc., Woburn, MA) alone and combined with propiconazole (Propizol®; Arborjet, Inc.) for protecting Engelmann spruce, Picea engelmannii Parry ex Engelm., from mortality attributed to colonization by D. rufipennis. Treatments were injected 16–19 July 2017, and levels of Pi. engelmannii mortality were determined for 2018 and 2019. Each experimental tree (n = 30, including an untreated control group) was baited with aggregation pheromone (frontalin) June–September 2018. All surviving treated Pi. engelmannii and a second untreated control group were baited June–September 2019. Both TREE-äge G4 and TREE-äge R10 significantly reduced levels of Pi. engelmannii mortality compared with the untreated control; however, protection was limited to one field season. Protection was increased to two field seasons by combining TREE-äge G4 and TREE-äge R10 with Propizol. The addition of Propizol, a triazole fungicide, likely reduced the progression of blue stain within treated Pi. engelmannii increasing tree health and resistance to D. rufipennis.

Snags (standing dead trees) are important components of forest ecosystems that, among other benefits, provide critical habitat for many species of wildlife, but also represent important safety concerns to firefighters, forest workers, and the public. We identified factors that influence the fall rates of lodgepole pines, Pinus contorta Dougl. ex Loud., killed by bark beetles during a severe regional-scale outbreak of mountain pine beetle, Dendroctonus ponderosae Hopkins, that occurred in 2004-2012. Data were obtained during annual assessments (2010-2019) of a network of 107 0.081-ha circular plots installed in P. contorta forests in Colorado, Idaho, Montana, Utah and Wyoming, U.S. A total of 3789 P. contorta snags were monitored, and in each case we recorded, among other variables, the year the snag was created and the year the snag fell to the forest floor. Among snag age classes (i.e., number of years since tree death), the highest number of snags (1046) were 12 years since death (YSD), and those 13 and 14 YSD exhibited the lowest fall rates to date (<10%) despite being the oldest in our study. Snags 13 and 14 YSD were among the largest in diameter. Snag fall occurred in every snag age class from 1 to 14 YSD, with the greatest proportion of snag fall events occurring 4-8 YSD. By 2019, 24.7% (937) of snags fell to the forest floor. We modeled snag fall using a Cox's proportional-hazards model that included six covariates of interest: elevation (m), slope aspect (categorical, cardinal direction), slope (%), canopy cover (%), snag height (m), and snag height:dbh (m, diameter at 1.37 m in height). Slope aspect had the strongest influence on fall rates. Northern aspects, increased canopy cover, and taller snag heights decreased the probability of snag fall. Conversely, southern aspects and increased height:dbh ratios (i.e., taller, skinner snags) increased the probability of snag fall. The predicted half-life (i.e., the amount of time since death required for 50% of the snag population to fall to the forest floor) was similar to 16 YSD after which the function predicted a linear, similar to 0.04/year decline in snag survival probability 15-30 YSD. The observed longevity of P. contorta snags confers important ecological benefits for some wildlife, and may offer opportunities for extended periods of salvage. However, checking (cracks) rapidly occurred, and many snags 6 YSD and older had at least one check at 1.37 m and 5.5 m in height, which can negatively impact lumber recovery. The relatively slow snag fall rates observed in our study also lengthen concerns regarding hazard trees, human safety, and protection of critical infrastructure. The implications of these and other results to management of P. contorta forests are discussed.

Changes in grain trading between Russian Far Eastern ports and North America in the late 1980s and early 1990s led to introductions of Lymantria dispar asiatica (Vnukovskij), formerly called the Asian gypsy moth (AGM), and the recognition of a new pathway for its transport. Unlike the pathways commonly used and regulated for commodities and for packaging material containing pest organisms, this presented a unique pathway for AGM. Vessels departing from the Russia Far East transiting to ports on the west coast of the United States (US) and Canada (CA) were infested with life stages of AGM and related species. Upon arrival in North America, eggs oviposited on the surfaces of the ships and its cargo hatched with larvae ballooning to vegetation surrounding port areas leading to the potential establishment of AGM populations. A multi layered monitoring and inspection program was developed to mitigate this risk of introduction, initially for Russian Far Eastern ports, and eventually to include specified areas of other Asian countries. In this article, we summarize and review the integral parts of this mitigation program, which include: risk assessments, AGM monitoring in foreign and domestic ports, vessel cleaning and certification by a government Plant Protection Organization (PPO) or its proxy, AGM surveillance, and eradication of introduced AGM in ports and other areas within the United States and Canada.The uniqueness of this program is characterized by its complexity, which involves coordinated efforts of PPOs, the use of various inspection organizations, and the support of ocean transportation industries.

Whitebark pine, Pinus albicaulis Engelm., is a subalpine tree endemic to western North America. This species provides multiple ecosystem services and is suffering widespread mortality from mountain pine beetle, Dendroctonus ponderosae Hopkins. Verbenone is a pheromone produced as D. ponderosae feed, and high air concentrations of verbenone deter D. ponderosae from colonizing trees. Synthetic verbenone has been formulated into products used to prevent D. ponderosae from colonizing trees. We compared the ability of verbenone pouches and SPLAT Verb to protect individuals and small stands of P. albicaulis. With individual trees in Montana, all treated trees survived regardless of verbenone formulation and rate, whereas untreated trees suffered 70 and 90% mortality in 2015 and 2016. In plot experiments in California from 2015 to 2017, and Oregon from 2015 to 2018, verbenone was applied to trees spaced similar to 10 m apart, and survival of small (12.7-23 cm DBH = diameter at 1.37 m height), medium (23.1-33 cm DBH) and large (>33 cm DBH) trees was compared. In California, where >80% of untreated trees survived, pouches increased survival similar to 2 to 3% and SPLAT Verb increased survival similar to 4 to 7% regardless of tree size. In Oregon, verbenone pouches and SPLAT Verb performed similarly on medium and small trees, but large trees had greater survival when treated with SPLAT Verb (similar to 93%) than pouches (similar to 82%). Compared to verbenone pouches, SPLAT Verb appears to better protect P. albicaulis from D. ponderosae.

Bark beetles are keystone species that can alter the structure and function of forested ecosystems, yet the mechanisms underlying host selection and successful colonization remain poorly understood for most species. Comparison of closely related tree species that vary in their susceptibility to bark beetles could provide insights into such mechanisms. Here, we compare physical and chemical characteristics of blue (Picea pungens Engelm.) and Engelmann (Picea engelmannii Parry ex Engelm.) spruce, species rarely (blue) and frequently (Engelmann) selected and colonized by the spruce beetle (Dendroctonus rufipennis Kirby) in the western U.S. At three sites (Utah, U.S.) where these species co-occur, 15 trees of each species were selected and traits important for bark beetle survival and population dynamics were measured and compared (bark and phloem thickness, resin flow, phloem and volatile chemistry, beetle landing and colonization success). There were significant differences in bark and phloem thickness and resin flow between species. Bark was thicker and phloem was thinner in blue spruce than Engelmann spruce whereas resin flow was highly variable but greater in blue spruce. Concentrations of within-phloem terpenes in blue spruce were more than double those for Engelmann spruce. Engelmann spruce foliage emitted greater concentrations of volatiles than blue spruce. Spruce beetles landed at higher rates on baited Engelmann spruce than baited blue spruce, and Engelmann spruce was more likely to be colonized. Collectively, these results suggest that blue spruce is a less suitable host for spruce beetle than Engelmann spruce due to a combination of factors including: thicker bark, thinner phloem, higher resin flow, lower concentrations of volatile terpenes, and higher concentrations of constitutive terpenes in phloem tissue, several which are known to be toxic to spruce beetles.

Mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), is the most important forest insect in western North America. We determined causes and rates of tree mortality and changes in forest structure and composition associated with D. ponderosae outbreaks in the Intermountain West, U.S. during 2004-2019 based on a network of 125 0.081-ha circular plots installed in Colorado, Idaho, Montana, Utah and Wyoming. Incipient populations of D. ponderosae began in 2004; peaked in 2007; and returned to endemic levels in 2011 in Idaho, Montana, Utah and Wyoming. In Colorado, incipient populations began in 2004; peaked in 2009; and returned to endemic levels in 2012. A total of 5107 trees died, 98.6% were lodgepole pine, Pinus contorta Dougl. ex Loud. Fifteen contributing factors were identified, including (in order of importance, highest to lowest) D. ponderosae, unknown causes, pine engraver, Ips pini (Say), wind, breakage and/or adjacent tree fall, Pityogenes knechteli Swaine/Pityopthorus confertus Swaine, suppression, spruce beetle, Dendroctonus rufipennis (Kirby), root disease, western balsam bark beetle, Dryocoetes confusus (Swain), lodgepole pine dwarf mistletoe, Arceuthobium americanum Nutt. ex. Engelm., stem diseases, woodborers, North American porcupine, Erethizon dorsatum (L.), mule deer, Odocoileus hemionus (Rafinesque), and lodgepole pine beetle, Dendroctonus murrayanae Hopkins. Most tree mortality (68.8%) was attributed solely to D. ponderosae, although D. ponderosae also occurred in association with other contributing factors. Overall, significant reductions in mean dbh (by 5.3%), mean quadratic mean diameter (by 8.6%), mean tree height (by 15.9%), mean number of trees (by 40.8%), mean basal area (by 52.9%), and mean stand density index (SDI) (by 51.8%) were observed. Significant reductions in tree density were observed in all diameter classes, except the smallest (midpoint = 10 cm, 5 -cm classes). Significant increases in the mean number of snags (by 1324.7%) were observed, and most snags remain standing (71.3%). Pinus contorta remains the dominant tree species, and while significant increases in the number of subalpine fir, Abies lasiocarpa (Hooker) Nuttall, seedlings and saplings were observed, a long-term shift in tree composition is unlikely. Tree mortality (number of trees killed) was positively correlated with the initial number of live trees, basal area of live trees, SDI, and aspect, but not slope or elevation. The implications of these and other results to recovery and management of P. contorta forests in the Intermountain West are discussed.

Bark beetles are important disturbance agents in coniferous forests, and spruce beetle, Dendroctonus rufipennis (Kirby) (Coleoptera: Curculionidae), is one of the more notable species causing landscape-level tree mortality in western North America. We evaluated the efficacy of bole injections of emamectin benzoate (TREE-age (R); Arborjet Inc., Woburn, MA) alone and combined with propiconazole (Alamo (R); Syngenta Crop Protection Inc., Wilmington, DE) for protecting Engelmann spruce, Picea engelmannii Parry ex Engelmann (Pinales: Pinaceae), from mortality attributed to colonization by D. rufipennis. Two injection periods in 2013 (the spring and fall of the year prior to trees first being challenged by D. rufipennis in 2014) and distributions of injection points (7.6- and 15.2-cm spacings) were evaluated. Tree mortality was monitored over a 3-yr period (2014-2017). Emamectin benzoate injected in spring at a narrow spacing (7.6 cm) was the only effective treatment. Two (but not three) field seasons of protection can be expected with a single injection of this treatment. We discuss the implications of these and other results regarding the use of emamectin benzoate and propiconazole for protecting western conifers from mortality attributed to bark beetles, and provide suggestions for future research. A table summarizing the appropriate timing of treatments in different bark beetle/host systems is provided.

Significant research has been devoted to the development of semiochemical repellents for mountain pine beetleDendroctonus ponderosaeHopkins. Several formulations of the beetle's antiaggregation pheromone verbenone (4,6,6-trimethylbicyclo[3.1.1]hept-3-en-2-one) are registered to protect pine trees and stands. We compared the efficacy of verbenone and Verbenone Plus for protecting individual lodgepole pinePinus contortaDougl. ex Loud. and small stands ofP. contortafrom mortality attributed toD. ponderosae. Verbenone Plus is a blend of semiochemicals [(-)-verbenone, acetophenone, and (E)-2-hexen-1-ol + (Z)-2-hexen-1-ol] originally developed to inhibit aggregation of western pine beetleD. brevicomisLeConte. It is the only effective semiochemical repellent that protects ponderosa pineP. ponderosaDougl. ex Laws. from mortality attributed toD. brevicomis, but has yet to be registered or commercialized. Both verbenone and Verbenone Plus were effective for protecting individualP. contortaand small stands ofP. contortafrom mortality attributed toD. ponderosae. Verbenone alone was as effective as Verbenone Plus. An obstacle to the broader use of semiochemical repellents for the management of bark beetles is the relatively high cost and specificity of the semiochemicals involved. A semiochemical repellent with efficacy across multiple bark beetle species and hosts, such as Verbenone Plus, would be desirable, assuming the additional components are not cost-prohibitive or limit registration.

Bark beetle outbreaks alter forests in many ways including stand structure, fuels and fire behavior, wildlife habitat, and aesthetic value. Less understood are the effects outbreaks have on understory vegetation, despite the importance for overstory succession, nutrient cycling, water quality, soil erosion, and wildlife. Beetle outbreaks also change forests in ways that could promote invasion by nonnative weeds, but this is rarely studied. We assessed changes in cover of understory vegetation and presence/abundance of weeds in lodgepole pine forests in Colorado, Idaho, Montana, Utah and Wyoming, USA following recent mountain pine beetle outbreaks. Incipient beetle populations began in 2004, peaked around 2008, and returned to endemic levels by 2012. Understory vegetation was sampled in 2010, 2012, 2014 and 2018. Total understory cover and cover of shrubs and graminoids remained unchanged, while cover of forbs generally increased. Forb cover was negatively correlated with shrub and canopy cover. Approximately 20% of plots contained weeds and weed abundance increased over time. Presence of weeds was negatively correlated with graminoid cover and positively correlated with tree mortality and snag fall. By 2018, weed abundance was only positively correlated with snag fall. Localized soil disturbance created when snags uproot and fall appears to act as sites of weed invasion and proliferation. Lastly, we provide a global review of the effects of bark beetle outbreaks on understory vegetation which reveals a prevailing short-term increase following outbreaks, but the magnitude of response and cover type affected varies with beetle species/forest type and time since outbreak.

Several formulations of the antiaggregation pheromone verbenone (4,6,6-trimethylbicyclo [3.1.1]hept-3-en-2-one) are registered to protect pine trees and forest stands from mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), but failures in efficacy are not uncommon. In 2011-2013, a novel formulation of (-)-verbenone was developed (SPLAT (R) Verb, 10.0% (-)-verbenone by weight, EPA Reg. No. 80286-20, ISCA Technologies Inc., Riverside, CA, USA) for protecting individual lodgepole pine, Pinus contorta Dougl. ex Loud., and small stands of P. contorta from mortality attributed to D. ponderosae. We evaluated the efficacy of lower doses of SPLAT (R) Verb than previously considered for tree protection on the Beaverhead-Deerlodge National Forest, Montana, USA, 2014-2015. In an individual tree study, D. ponderosae pressure was not sufficient to adequately challenge the treatments as only 56.7% of the untreated controls died. However, if one additional tree in the untreated control had died, all verbenone treatments (30 g, 50 g, and 70 g of SPLAT (R) Verb/tree, and one 7-g verbenone pouch/tree) would have been considered efficacious. In a small-scale stand study, fewer P. contorta were colonized by D. ponderosae on 0.41-ha experimental plots treated with 2.5 kg and 3.5 kg of SPLAT (R) Verb [250 g and 350 g of (-)-verbenone, respectively] and the 7-g verbenone pouch [50 pouches/plot, 350.0 g of (-)-verbenone/plot] compared to the untreated control. No significant difference was observed between 1.5 kg of SPLAT (R) Verb [150 g of (-)-verbenone] and the untreated control. Fewer P. contorta were killed by D. ponderosae on experimental plots treated with 1.5 kg, 2.5 kg and 3.5 kg of SPLAT (R) Verb and the verbenone pouch compared to the untreated control. No other significant differences were observed among treatments. Collectively, these data suggest that lower doses of SPLAT (R) Verb can be used for tree protection than previously considered, and at a substantial cost savings that could make this strategy economically viable for area-wide management of D. ponderosae.

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.