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This article discusses the challenges posed by non-native forest insects and the importance of risk mapping approaches to address this threat. It highlights the impacts of invasive forest insects on forest health, ecosystem services, and the economy. The article emphasizes the importance of pest risk models and maps in assessing the risk posed by invasive pests and guiding management and surveillance strategies. It also presents various modeling methods and tools that have been developed to predict the phenology, climate suitability, and spread of invasive insects. The article concludes by emphasizing the need for engagement with end users and improving outreach and training to ensure the broader uptake of pest forecasting tools and map products. The given text consists of a list of references and citations related to the topic of invasive forest insects and their impact on ecosystems. The references cover various aspects of the issue, including the ecological and economic impacts of invasive insects, the role of climate change in facilitating their spread, and the development of decision support systems for risk assessment and management. The text emphasizes the need for surveillance and early detection of high-consequence pests and pathogens to prevent their establishment and spread. It also highlights the importance of accurate species distribution modeling and phenology forecasting in managing invasive forest pests. [Extracted from the article]

Highlights • Infestations by mountain pine beetle expanded rapidly under prolonged dry spells. • Temperatures above normal occurred simultaneously with high infestation numbers. • Range shifts were associated with local aridity and temperature deviations from normal. Abstract The recent range expansion of the mountain pine beetle, Dendroctonus ponderosae Hopk. (Coleoptera: Curculionidae), into evolutionarily naïve lodgepole and jack pine forests of northwestern Canada has triggered concern that continued eastward expansion through the boreal forest will threaten other pine species native to eastern North America. This unprecedented breach of a historic geoclimatic barrier was precipitated by a "hyperepidemic" west of the Rocky Mountains comprising the largest mountain pine beetle eruption in recorded history. We assessed climate-related latitudinal shifts of pre-outbreak populations of mountain pine beetle in western Canada over a 26-year period preceding the hyperepidemic, as movements of pre-outbreak populations determine, in part, the extent of subsequent outbreaks. We used digitized records of annual aerial overview surveys (1965–1979, 1986–1996) of tree-killing activity, comprising > 122,000 individual infestation polygons, and temperature and aridity data to associate trends in deviations of weather variables from historical averages with latitudinal shifts by the insect. Overall, we found that seasonal and multiyear weather phenomena such as anomalous temperature increases in a stable aridity regime, or vice-versa, and warmer-than-normal winter temperatures explained small but significant variation in northward annual range shifts after factoring out spatial and temporal variation. The numbers of discrete, tree-killing infestations increased rapidly during 1965–1979, and northward range shifts of 300 km in the early 1970s coincided with abnormally dry conditions. Mountain pine beetle populations advanced northward by 391 km from 1965 to 1996. Consistently high infestation levels of the mountain pine beetle occurred simultaneously with above-average temperatures that extended for nearly a decade immediately preceding the hyperepidemic. Climate-associated range shifts can provide gateways to rapid range expansions, and evoke concern with regard to future impacts of other bark beetle species inhabiting regions likely to experience multiyear droughts and/or temperature increases under climate change. [ABSTRACT FROM AUTHOR]

Since the mountain pine beetle (MPB) breached the Rocky Mountains and first appeared in the province of Alberta, Canada, in alarming numbers in the summer of 2005, it has spread eastward across Alberta at an average rate of 80 km/year. In the absence of aggressive control, the beetle will undoubtedly continue to spread eastward. The spread rate is expected to slow as the leading edge invasion front moves further from significant population sources in the dense pine of the Rocky Mountain foothills into the scattered pine of the boreal plains region. However, the realized rate of spread is uncertain, as it will be regulated by a number of factors, some of which are uncertain (e.g. how an insect behaves in a novel environment), inherently unpredictable (e.g. weather), or under human control (e.g. spread control efforts). Whereas previous studies have examined factors affecting spread individually, we present a synthetic framework that models future spread rates as a function of coupled nonlinear recruitment dynamics that arise from the distinct population phases of MPB, and correlated thermal response functions that are characteristic of the influence of climate and climate change on ecosystem processes. We analyzed the model’s behavior under two climatic driving scenarios (drying climate and warming climate) and one forest health scenario (an increase in the ratio of stressed to vigorous trees), with the hypothesis that these scenarios would produce unanticipated outcomes in the severity and timing of beetle outbreaks. Our results showed a classic “tipping-point” model capable of generating sudden, unanticipated behavior, demonstrating that MPB populations may respond very strongly to small changes in climate. The MPB may be the first of many systems to behave in unprecedented ways. The model makes clear that the eastward rate of spread will depend on whether, when, and where the system transitions from the current epidemic state to a new endemic state. However, major uncertainties in the system limit our ability to make robust predictions of spread under natural conditions. The integrating framework presented here provides insight into scientific uncertainties worth targeting for applied research into spread management. In the absence of ability to predict beetle spread, forest management should continue to explore ways of coping with unpredictable disturbances, including adaptive capacity to adjust to transformational ecosystem changes expected under climate change. [ABSTRACT FROM AUTHOR]

The range of many Holarctic forest insects does not comprise the entire range of their hosts, as they are often limited to more southern latitudes by the adverse effects of cold temperatures. Global climate warming has led to the increased potential for forest insects to invade novel habitats of native hosts within the same landmass. The mountain pine beetle (MPB; Dendroctonus ponderosae) has recently expanded into higher‐latitude forests of the principal host, lodgepole pine (Pinus contorta var. latifolia), and the susceptibility of trees is greater in these systems compared to forests in the native range. We assessed the contribution of the induced defensive response of hosts to this elevated susceptibility, and whether these discrepancies are the result of coevolution with host populations within the historic native range of the insect. We challenged trees using paired treatments of a beetle‐attack simulation and a generic defensive response elicitor (methyl jasmonate) to mitigate variability in the induced response among trees within and among populations, from within and outside the historic range of the beetle. We then assessed the production of monoterpene chemicals by the trees in response to treatments using gas chromatography/mass spectrometry. The differential induction of monoterpenes in response to simulated beetle attack relative to the generic elicitor was highest in populations with the highest putative historic exposure to MPB. Elevated susceptibility and invasion potential of the beetle in novel systems is the proximate result of reduced defensive capacity, ultimately arising from a lack of coevolution with the beetle in novel systems. In forested systems with climate‐driven herbivore–host distributional asymmetry, continued warming will potentially exacerbate the impacts of aggressive insect herbivores as they invade defensively naïve host populations. [ABSTRACT FROM AUTHOR]

Eruptive forest insects are highly influential agents of change in forest ecosystems, and their effects have increased with recent climate change. State-dependent life histories contribute significantly to the population dynamics of eruptive forest insect herbivores; however, the proximate mechanisms by which these species shift between states is poorly understood. Laboratory bioassays were conducted using the mountain pine beetle (Dendroctonus ponderosae) to determine the effect of maternal host selection on offspring host preferences, as they apply to population state-dependent behaviors. Female mountain pine beetles exhibited state-dependent preference for artificial host material amended with monoterpenes in the absence of other cues, such that individuals reared in high-density epidemic-state simulations rejected low monoterpene conditions, while low-density endemic-state beetles accepted low monoterpene conditions. State-specific behavior in offspring was dependent on rearing conditions, as a function of maternal host selection, and these effects were observed within one generation. Density-dependent host selection behaviors exhibited by female mountain pine beetle offspring is reinforced by context-dependent maternal effects arising from parental host selection, and in situ exposure to conspecifics. These results demonstrate potential proximate mechanisms that control population dynamics in eruptive forest insects, and will allow for more accurate predictions of continued impact and spread of these species. [ABSTRACT FROM AUTHOR]

The range of mountain pine beetle ( Dendroctonus ponderosae ) has expanded in recent years to include many evolutionarily naïve forests in western Canada. These forests include novel populations of the principal host species, lodgepole pine ( Pinus contorta ), the novel species jack pine ( Pinus banksiana ), and their hybrids ( P. contorta × P. banksiana ). These novel forests are chemically and physically different than native forests, and recent studies have shown beetle reproductive performance is enhanced in these novel habitats. We conducted a field experiment to determine the effect of differing host chemistry, specifically α-pinene content, on secondary attraction by foraging mountain pine beetles. Alpha-pinene is the precursor molecule for the production of trans -verbenol, the main aggregation pheromone for this beetle species. We found that elevated relative concentrations of α-pinene in bolts significantly increased their attractiveness to in situ mountain pine beetles. Seventy-five percent of attacks were found on infested bolts with the most α-pinene relative to other monoterpenes. Other measures of terpene chemistry between bolt types could not explain the pattern of attacks. This result suggests that elevated concentrations of α-pinene could increase the rate of aggregation and attack success by the mountain pine beetle in novel pine forests. Newly invaded hybrid and jack pine in the western boreal forest are reported to contain 3–4 times the relative concentration of α-pinene than lodgepole pines in forests in which the beetle has coevolved. These elevated concentrations may help the mountain pine beetle overcome some of the potential restraints for establishment and spread in the boreal forest, such as low pine volume and connectivity, and continue expanding its range. [ABSTRACT FROM AUTHOR]

Insect outbreaks exert landscape-level influences, yet quantifying the relative contributions of various exogenous and endogenous factors that contribute to their pattern and spread remains elusive. We examine an outbreak of mountain pine beetle covering an 800 thousand ha area on the Chilcotin Plateau of British Columbia, Canada, during the 1970s and early 1980s. We present a model that incorporates the spatial and temporal arrangements of outbreaking insect populations, as well as various climatic factors that influence insect development. Onsets of eruptions of mountain pine beetle demonstrated landscape-level synchrony. On average, the presence of outbreaking populations was highly correlated with outbreaking populations within the nearest 18 km the same year and local populations within 6 km in the previous two years. After incorporating these spatial and temporal dependencies, we found that increasing temperatures contributed to explaining outbreak probabilities during this 15 yr outbreak. During collapse years, landscape-level synchrony declined while local synchrony values remained high, suggesting that in some areas host depletion was contributing to population decline. Model forecasts of outbreak propensity one year in advance at a 12 by 12 km scale provided 80% accuracy over the landscape, and never underestimated the occurrence of locally outbreaking populations. This model provides a flexible approach for linking temperature and insect population dynamics to spatial spread, and complements existing decision support tools for resource managers. [ABSTRACT FROM AUTHOR]

Biome-scale disturbances by eruptive herbivores provide valuable insights into species interactions, ecosystem function, and impacts of global change. We present a conceptual framework using one system as a model, emphasizing interactions across levels of biological hierarchy and spatiotemporal scales. Bark beetles are major natural disturbance agents in western North American forests. However, recent bark beetle population eruptions have exceeded the frequencies, impacts, and ranges documented during the previous 125 years. Extensive host abundance and susceptibility, concentrated beetle density, favorable weather, optimal symbiotic associations, and escape from natural enemies must occur jointly for beetles to surpass a series of thresholds and exert widespread disturbance. Opposing feedbacks determine qualitatively distinct outcomes at junctures at the biochemical through landscape levels. Eruptions occur when key thresholds are surpassed, prior constraints cease to exert influence, and positive feedbacks amplify across scales. These dynamics are bidirectional, as landscape features influence how lower-scale processes are amplified or buffered. Climate change and reduced habitat heterogeneity increase the likelihood that key thresholds will be exceeded, and may cause fundamental regime shifts. Systems in which endogenous feedbacks can dominate after external forces foster the initial breach of thresholds appear particularly sensitive to anthropogenic perturbations. [ABSTRACT FROM AUTHOR]