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Summary Societal impact statement The European spruce bark‐beetle, Ips typographus, is a major pest of Norway spruce across mainland Europe; however, until 2018, it was considered absent from the United Kingdom (UK). The finding of a breeding population of I. typographus in Kent, England, in 2018 and subsequent findings in pheromone traps across the southeast of England, has led to an urgent need to improve understanding of environmental suitability across the UK. Two distinct published phenological models for I. typographus, developed in Sweden and Austria, were adapted for use in the UK and validated against pheromone trap data collected at the original site of infestation and in the surrounding area from 2019 to 2022. Both models captured some, but not all, of the within‐season variation in trap catches. One, the PHENIPS model, more accurately captured early season flight patterns. The climate in the southeast of England is mild enough to facilitate two generations of the beetle, while further north the pest is expected to be univoltine. At high altitude in Scotland, there is insufficient thermal warming within a season for the completion of one annual generation. Phenological modelling does not explain why the pest failed to establish in England prior to 2018 including when a large amount of infested material was imported to sawmills in the 1940s. Under 2 and 3°C global warming scenarios, we might expect to see an increase in potential voltinism across the UK in the next few decades, increasing the risk of large outbreaks of I. typographus were it allowed to establish. In 2018, a breeding population of the European spruce bark‐beetle, Ips typographus, was discovered in woodland in southeast England. Ips typographus is a major forest pest in continental Europe; however, despite previous findings at ports and sawmills, this was the first recorded infestation in the UK. The number of generations per year (voltinism) varies with latitude and altitude. Applying a phenological model, we find that the current climate in southern UK could support two generations, while temperature accumulation in parts of Scotland may be insufficient to support one generation. Global warming will increase voltinism and hence the risk of establishment. [ABSTRACT FROM AUTHOR]

Extreme weather events are increasingly recognized as major stress factors for forest ecosystems, causing both immediate and long-term effects. This study focuses on the impacts experienced by the forests of Valdisotto, Valfurva, and Sondalo (28% of the total area is covered by forests) in Upper Valtellina (Italy) due to the Vaia storm that occurred in October 2018. To define the immediate impacts of Vaia, we assess the economic value of forest ecosystem services (ESs), particularly those provided by timber production and carbon sequestration, pre- and post-Vaia and during the emergency period. We used the market price method to assess the economic values of timber production and carbon sequestration, as these are considered to be marketable goods. Based on data processed from Sentinel-2 satellite images (with a spatial resolution of 10 m), our results show that, despite the reduction in forest area (−2.02%) and timber stock (−2.38%), the economic value of the timber production increased after Vaia due to higher timber prices (i.e., from a total of €124.97 million to €130.72 million). However, considering the whole emergency period (2019–2020), the total losses are equal to €5.10 million for Valdisotto, €0.32 million for Valfurva, and €0.43 million for Sondalo. Instead, an economic loss of 2.88% is experienced for carbon sequestration, with Valdisotto being the more affected municipality (−4.48% of the pre-Vaia economic value). In terms of long-term impacts, we discuss the enhanced impacts due to the spread of the bark beetle Ips typopgraphus. [ABSTRACT FROM AUTHOR]

Forest ecosystems are long-term exposed to dry periods in Europe, which leads to a significant loss of vitality and higher mortality, especially in coniferous forests. Identifying stress in the early stages when measures can be taken to protect the forest and living trees is crucial. Current detection methods are based on field surveys by forest workers or remote sensing methods to cover larger areas, which use changes in spectral reflectance of the forest canopy. In some cases, the attacked trees do not change their appearance, and based on calculations of vegetation indices from remote sensing data, the attack cannot be mapped. We present an innovative methodology based on non-optical analysis, namely identifying a group of volatile compounds and microclimate signs in forest stands that indicate stress factors in forest stands. An attacked tree by a bark beetle produces increased amounts of biogenic volatile organic compounds associated with defense, and the microclimate changes due to interrupted transpiration. In addition, the bark beetle uses the aggregation pheromone to attract more individuals and to attack the tree massively. In this study, we tested three electronic noses (Miniature Bosch sensor device with 25,419 samples, Sensory device for environmental applications with 193 samples, Handheld VOC Detector Tiger with 170 samples) in a freshly infested spruce stand. The measurement was conducted at ground level with the help of a human operator and was repeated six times to verify the detection capability of the electronic noses. To verify the capability of electronic noses to predict tree infestation, we used machine learning Random Forest. The results demonstrated that electronic noses can detect bark beetle infestation start (within 1 week of the first attack). The Miniature Bosch sensor device achieved the highest accuracy with a value of 95%, in distinguishing forest sections that are healthy and infested; the second most accurate electronic nose is the Sensory device for environmental applications, with an accuracy of 89%. Our proposed methodology could be used to detect bark beetle presence. [ABSTRACT FROM AUTHOR]

Several Persian lime trees were found to exhibit dieback and yellowing during monitoring of the intensity of Huanglongbing disease on a 6-year-old commercial Persian lime orchard in San Rafael, Veracruz, Mexico, between August and October 2022. During the examination of the trees, we discovered small holes on the bark of the main stem and lower branches, significant cracking of the bark, and beetles crawling on the surface. Removal of the bark on the crevices showed the presence of larvae and adults plausibly feeding from the inner bark tissue. Phloeonemus interruptus (Coleoptera: Zopheridae) adults were found. Although it is unknown whether P. interruptus will become invasive, this study confirmed that it is associated with Persian lime trees. Thus, this serves as a bellwether to warn of the potential direct damage or transmission of fungi or oomycetes, such as those in the genera Lasiodiplodia and Phytophthora. To the best of our knowledge, this is the first report of the association of Phloeonemus interruptus with Persian lime (Citrus latifolia Tan. Rutaceae) in the central region of Veracruz, Mexico. [ABSTRACT FROM AUTHOR]

The European spruce bark beetle Ips typographus is a widespread pest in Norway spruce-dominated forests in Eurasia. Predicting its phenology and voltinism is crucial to plan forest management measures and to mitigate mass outbreaks. Current phenology models are based on constant temperatures inferred from laboratory experiments; however, insect life cycles under natural conditions are rather driven by diurnal and seasonal temperature fluctuations. Therefore, phenology models based on fluctuating temperatures would reflect field conditions more realistically and might thus improve model predictions. In a laboratory experiment, we investigated the development of I. typographus, applying mean temperatures between 3 and 35 °C and diurnal temperature oscillations of up to ± 15 °C. Subsequently, we calibrated developmental rate models and applied them to climate data, in order to assess the effect of temperature fluctuations on voltinism under field conditions. Our results showed that diurnal temperature oscillations significantly affected developmental rates. Compared to constant temperatures, development was faster at temperature oscillations falling below the lower developmental threshold, and slower at temperature oscillations exceeding the developmental optimum. Furthermore, short exposures to suboptimal temperatures affected I. typographus less than expected from constant conditions. Natural temperature fluctuations thus accelerate development under cool, shaded conditions, whilst slowing it under hot, sun-exposed conditions, thereby ultimately affecting voltinism. Our findings highlight the importance to account for diurnal temperature fluctuations for more accurate predictions of developmental rates of I. typographus in natural thermal environments, and provide the fundament for improving current phenology models to support effective bark beetle management in a warming climate. [ABSTRACT FROM AUTHOR]

Uncrewed Aerial Systems (UAS) offer a versatile solution for monitoring forest ecosystems. This study aimed to develop and assess an individual tree-based methodology using multi-temporal, multispectral UAS images to track changes caused by the European spruce bark beetle (Ips typographus L.). The approach encompassed four key steps: (1) individual tree detection using structure-from-motion point clouds, (2) tree species classification, (3) health classification of spruce trees as healthy, declined, or dead, and (4) change detection, identifying fallen/removed trees and alterations in tree health status. The developed methodology was employed to quantify changes in a bark beetle outbreak area covering 215 hectares in southeastern Finland during 2019–2021. The dataset included two managed and two conserved forest areas. The uncertainty estimation demonstrated the overall accuracies ranging from 0.58 to 0.91 for individual tree detection, 0.84 for species classification, and 0.83–0.96 for health classification, and a F1-score of 0.91 for the fallen or removed tree detection. Maps and statistics were produced, containing information on the health of the spruce trees in the area and information on changes, including trees that died during monitoring and those that fell or were removed from the forest. The results demonstrated successful control of the outbreak in the managed stands, evidenced by moderate tree mortality. Conversely, in the conserved stands, the outbreak resulted in dramatic tree mortality. This method serves stakeholders by enabling large-scale outbreak impact monitoring, facilitating timely risk assessment, and validating bark beetle outbreak management strategies. [ABSTRACT FROM AUTHOR]

The view of insects and their microbiota as a holobiont is increasingly relevant as globalization and climate change aids the spread of pests to new areas. Examples of such pests include bark, ambrosia, and woodborer beetles (BAWBBs hereafter) that are important natural components of forest ecosystem processes, but may also cause substantial damage in native and invasive ranges. Microbiota has been shown to perform various functions for these beetles, but we are only beginning to reveal the complex chemically mediated interactions among the beetle, the host tree and their microbiota. In this review we a) summarize current knowledge about the influence of beetle ecology in the formation of the holobiont, b) how microbial compounds may function as beetle semiochemicals, and/or contribute to nutrient acquisition, defence, and maintenance of the holobiont, c) the influence of external factors that affect the holobiont, and d) pinpoint open questions and suggest potential methods needing attention in order to utilize this knowledge in of management of invasive or outbreaking BAWBBs. [ABSTRACT FROM AUTHOR]

The winter mortality of mountain pine beetle (Dendroctonus ponderosae Hopkins) larvae caused by temperatures below survivable thresholds and sudden decreases in temperature is among the most influential factors limiting population growth. Due to the importance of winter mortality in the demise of mountain pine beetle infestations, a widely used winter mortality model was developed at the Canadian Forest Service and the United States Forest Service. It predicts lethal temperatures and survival probabilities given temperature time series over the winter season. We present a rare and possibly the first peer-reviewed validation of this winter mortality model, wherein we independently tested the model at a new region in Canada by comparing model predictions to the observed lower lethal temperature thresholds and cold-associated mortality. Model predictions were biologically reasonable but slightly biased. Bias was exacerbated by the inaccurate translation of air temperature data from weather stations to temperatures under the bark where larvae develop. The spatial prediction of relative mortality observed across the study area in Banff National Park was poor—likely because the mountainous terrain presents a difficult prediction challenge when under-bark temperatures are not directly observed. Our results will help inform users of model constraints and how to optimize the accuracy of model predictions. [ABSTRACT FROM AUTHOR]

Simple Summary: Simple Summary: Acoustic communication is present in different groups of insects and is used in different contexts during their life cycle. Bark beetles are a group of insects of ecological importance, because they can kill a large number of trees and affect forest succession These insects communicate using chemical signals for long distances, but while on or in the tree, they use acoustic communication to interact between individuals during the colonization of their host trees. A series of sounds have been described for bark beetles, which are produced by specialized anatomical structures under different conditions, such as stress, courtship, and territoriality. In this study, we worked with males of Dendroctonus adjunctus, and we described the stridulatory structures using optical and electron microscopy. In addition, we recorded and characterized the types of calls and their spectral and temporal characteristics under stress conditions, female–male, and male–male interactions. Results showed that the shape of the stridulatory apparatus is like males of other beetle species in the genus, and we identified single– and multi–noted calls with differences in temporal and spectral characteristics under three behavioral contexts. Finally, a new type of withdrawal call was identified in male–male interactions. The acoustic communication system (ACS) in bark beetles has been studied mainly in species of the genera Dendroctonus, Ips and Polygraphus. Specifically, ACS of the roundheaded pine beetle, Dendroctonus adjunctus, has been little studied. In this study, we described the stridulatory apparatus of this beetle using optical and scanning electron microscopy and recorded the call types produced by males in three behavioral contexts: stress, female–male–, and male–male interactions. From the spectrograms and waveforms, call types, as well as temporal (tooth strike, tooth strike rate, and intertooth strike interval) and spectral features (minimum, maximum and dominant frequency), were determined. Males have a functional elytro–tergal stridulatory apparatus—females do not—consisting of a file for the pars stridens and two lobes for the plectrum. Most of spectro–temporal features were statistically different between single– and multi–noted calls and across the three behavioral contexts. In the male–male interaction, a new type of call named "withdrawal" was produced by the male withdrawing or fleeing. Our results suggest that the spectro–temporal features of single– and multiple–noted calls in the three behavioral conditions are specific and different from each other. Yet, the combination of single and multiple calls determines an overall calling pattern characteristic of the tested behaviors and, therefore, is species–specific. [ABSTRACT FROM AUTHOR]

The article analyses the temporalities attributed by tourism-related literature to transitions of the environment of the Bohemian Forest in the second half of the long 19th century, with a special focus on the gales and bark beetle outbreak that occurred in the 1860s and 1870s. The expansion of both individual and organised tourism in the region from the late 1870s aligned with its economic decline, which followed a period of rapid development associated with eliminating the damage caused by the outbreak, an occurrence that severely affected the health of the forest and the inhabitants of the Bohemian Forest region. The article suggests that tourism acted as a resilience strategy, enabling adaptation to socio-economic uncertainties engendered by living in a more-than-human world. In addition to nationalist motives, the perception of nature and its transitions played a key role in the establishment of tourism in the region, which was often characterised by its forests. [ABSTRACT FROM AUTHOR]

Introduction: As a result of climate change and bark beetle outbreaks in forests, extensive salvage, and sanitary cutting have been undertaken in Europe, resulting in many clear-cuts with coarse stumps. The populations of pine weevils (Hylobius abietis and Hylobius pinastri) are steadily increasing. A high abundance of pine weevils feeding on seedlings typically results in significant economic losses and prolongs the forest establishment period. However, information on these species spatial distribution and habitat selection patterns, necessary for assessing their harmfulness and subsequently accurately estimating their threat to reforested areas, is lacking. To determine which factors influence spatial selection patterns and seedling type preference, this study investigated which clear-cut factors increase pine weevil abundance and which seedling types (species and age) are the most preferred. Methods: The experiment was carried out on 20 clear-cuts in the central Czech Republic. We evaluated soil moisture level, average stump distance and diameter, proportion of other conifers, and whether the stumps were mulched. We detected the abundance of pine weevils using pitfall traps. We determined the feeding scar intensity on the first 10 cm of seedling stems on commonly used seedlings for reforestation in central Europe: 1-year-old Scots pine (Pinus sylvestris), European larch (Larix decidua), and 3-year-old Norway spruce (Picea abies), with 1,200 seedlings in total. The individual seedling types alternated in rows. The results were evaluated using generalized linear mixed-effect models (GLMMs). As dependent variables we used total numbers of H. abietis and H. pinastri. The soil moisture level, mulching, proportion of other conifers, average stump diameter, and distance were considered independent variables. Results: We found that Norway spruce was the least attractive to pine weevils. We found a higher abundance of H. abietis females in moist clear-cuts, confirming that dry clear-cuts are less suitable for oviposition. Conclusion: According to our findings, if foresters want to plant coniferous seedlings, it seems that planting older spruce is a better option than planting larch and pine. These findings provide valuable insights for forest management and reforestation strategies, equipping foresters with the knowledge to mitigate the threat of pine weevils and ensure successful forest establishment. [ABSTRACT FROM AUTHOR]

A taxonomically comprehensive perspective on the fungal associates of bark beetles (Coleoptera: Curculionidae: Scolytinae), and powerful molecular tools for detection of these fungi, are imperative to understanding bark beetle impacts on forest ecosystems. The most common filamentous fungi living alongside bark beetles in infested trees are ophiostomatoids (Ascomycota: Ophiostomatales and Microascales), yet an undescribed species of Neonectria (Neonectria sp. nov.; Ascomycota: Hypocreales) was recently identified cohabitating with the alder bark beetle, Alniphagus aspericollis, in red alder, Alnus rubra. The hardwood-infesting alder bark beetle is found throughout the range of its red alder host in the Pacific Coast region of North America and is associated with Neonectria sp. nov. in southwestern British Columbia, Canada. The aim of this study was to describe and name Neonectria sp. nov. and to develop a quantitative PCR (qPCR) assay to enable rapid detection of Neonectria sp. nov. from individual adult alder bark beetles and to define the distribution of the fungus. Neonectria sp. nov. was phylogenetically and morphologically determined to represent a distinct species closely related to N. ditissima and is described herein as Neonectria bordenii sp. nov. Neonectria bordenii was reliably detected from individual wholebeetle DNA extractions using a probe-based qPCR assay targeting multi-copy internal transcribed spacers (ITS) of nuclear ribosomal DNA. The qPCR assay amplified the fungus from 87.8 % (36/41) of individual alder bark beetle samples and was highly sensitive to N. bordenii, with a lower limit of detection of 1 × 10-6 ng/µL of culture DNA (or ~262 genome copies). Application of the qPCR assay developed in this study will expedite future research evaluating N. bordenii as a potential symbiote of the alder bark beetle. [ABSTRACT FROM AUTHOR]

The southern pine beetle, Dendroctonus frontalis Zimmermann is an important mortality agent of Pinus in the eastern United States of America where it commonly shares hosts with the black turpentine beetle, Dendroctonus terebrans (Olivier), which infrequently kills trees. Unlike D. frontalis , which must kill its hosts to become established in the bark and reproduce, D. terebrans can occupy living hosts as a parasite. Olfactory mechanisms whereby D. frontalis initially locates hosts have not been demonstrated, whereas D. terebrans responds strongly to host odors. Because D. terebrans produces frontalin, the primary aggregation pheromone component for D. frontalis, and commonly arrives on hosts prior to D. frontalis , it has been hypothesized that D. terebrans pheromone components can mediate D. frontalis location of suitable, living trees. We assessed this possibility with studies of the semiochemical interactions between D. frontalis and D. terebrans. Coupled gas chromatography-electroantennographic detection analyses indicated that D. terebrans produces nine different olfactory stimulants for D. frontalis, nearly all of them known semiochemicals for D. frontalis. A trapping experiment designed to address the potentially confounding influence of lure contamination confirmed that the D. terebrans pheromone component exo -brevicomin enhances attraction of D. frontalis and thus could be an attractive kairomone. In ambulatory bioassays, male D. frontalis were strongly attracted to odors of frass of solitary female and paired D. terebrans , indicating their attraction to the naturally occurring semiochemicals of D. terebrans. Cues from D. terebrans may influence host and mate-finding success of D. frontalis and, thereby, the latter's virulence. [ABSTRACT FROM AUTHOR]

Eastern larch beetle Dendroctonus simplex LeConte has been outbreaking for the past two decades in the Great Lakes region of North America, impacting approximately 400,000 hectares of eastern larch Larix laricina (tamarack) forest in Minnesota, United States, alone. Range expansions of some Dendroctonus species driven by climate change have occurred across North America as rising temperatures increase climatically suitable habitats across latitudes and elevations. The range of eastern larch beetle is currently sympatric to that of its host, eastern larch, but the insect could, in theory, eventually access ranges of other species of Larix native to North America. We compared host suitability of two potential novel hosts, western larch (Larix occidentalis Nutt.) and subalpine larch (Larix lyalli Parl.) against the beetle’s native host, eastern larch, using a reproductive success experiment conducted in cut bolts of all three species. We measured fertility, maternal gallery length, and offspring size and lipid content as metrics of reproductive success. We found beetles could reproduce in both novel Larix species, with subalpine larch having high levels of success compared to the beetle’s native host, eastern larch. These findings suggest that subalpine larch may be at risk should a range expansion of eastern larch beetle occur.

In this study, hyperspectral data of two geographically distant study areas in Germany were analyzed to find the most effective spectral wavelengths for red-edge-based vegetation indices to differentiate bark beetle-infested Norway spruce into three infestation classes, including green-attack. Considering that the relationship between red-edge position (REP) and reflection shoulder position (RESP) is crucial for the relative quantification of chlorophyll concentration and LAI and their changes due to bark beetle infestation, we tested normalized difference red-edge indices (NDRE) formed from these parameters. Using combinations of 75 spectral bands in the range 685 nm to 850 nm, we analyzed 1187 different NDREs, and two additional vegetation indices, and show that the sorted, normalized Kruskal-Wallis H-value, followed by a frequency analysis of the RESP and REP bands of the 10 % of the highest ranked NDREs is an effective way to identify the global optima of these parameters. The optimal REP and RESP estimated using this approach were determined at 714 nm and 758 nm, respectively. The derived normalized difference red-edge index NDRE758_714 could be successfully applied to both test sites. Moreover, we found that aggregating hyperspectral bands into broader bands – 703 nm to 729 nm for a REP band and 741 nm to 767 nm for a RESP band – did not degrade model accuracy when used in a multispectral NDRE, suggesting that a hyperspectral camera is not required to perform the task. Multinomial logistic regression (MNLR) and random forest (RF) classification models were successfully transferred between the two geographically distant study sites. The predictive accuracies of the models for the test data indicated MNLR to be more robust than the RF. With the MLNR models applied, overall accuracies 77.4 % were achieved in the first study area imaged during the green-attack core period, and 88.2 % in the second study area imaged at the final green-attack stage. Our results contribute to forest health monitoring with imaging spectroscopy data and provide practical recommendations for sensor design with broader bands.

Mountain pine beetle (MPB; Dendroctonus ponderosae Hopkins) is a devastating forest insect pest that has killed millions of hectares of pines in western North America over the past two decades. Like other bark beetles, MPB vectors ophiostomatoid fungal species, some of which are pathogenic to host pine species. The phytopathogenicity of these fungal symbionts has sparked considerable debate regarding their role in facilitating MPB attack success. We tested the hypothesis that MPB ophiostomatoid fungal associates like Grosmannia clavigera (Robinson-Jeffrey and Davidson) Zipfel, de Beer and Wingfield contribute to overwhelming host defenses during MPB mass attack. We compared responses of mature lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) trees growing in natural stands that were mass attacked by MPB with those inoculated with G. clavigera by examining host defense hormones, secondary metabolites, and gene expression profiles. The jasmonate and ethylene signatures of necrotrophic pathogen-triggered response were identified in G. clavigera-inoculated trees, but only the jasmonate signature of a herbivore-triggered response was measured in MPB-attacked trees. Several G. clavigera-induced changes in pine phenolic metabolite profiles and phenolic biosynthesis gene expression patterns were absent in MPB-attacked pines. These findings indicate that ophiostomatoid fungi like G. clavigera are not a major factor in overwhelming host defenses during MPB mass attack. Instead, fungal pathogenicity likely is more important in aiding MPB colonization and development within the host tree. Phenolics appear to play a larger role in the host response to G. clavigera than to MPB, although phenolics may also influence MPB feeding and behavior. [Graphic: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

This study investigates the efficacy of combined treatment strategy, incorporating pheromones for bark beetle I. typographus (IT) and attractant of its natural enemy T. formicarius (TF), along with anti-attractants for IT (containing 1-hexanol, 1-octen-3-ol, 3-octanol, eucalyptol, trans-thujanol, and transconophthorin), to enhance protection methods for Picea abies against biotic disturbances. Two field experiments--trapping experiment and tree protection experiment--were conducted in June 2023 in managed spruce-dominated beetle-affected stands in Czechia. We anticipated higher catches of IT in traps baited with IT pheromone (containing s-ipsdienol, s-cis-verbenol, and 2methyl-3-buten-2-ol) and TF attractant compared to traps using IT pheromone alone, since compounds intrinsic to IT pheromone, namely 2-methyl-3-buten2-ol, ipsenol, and ipsdienol, are integral components of the attractant designed for TF. We hypothesized that application of TF attractant and IT anti-attractant would enhance the treatment's protective properties, assuming that attracted TF would function as a predator, reducing bark beetle population and increasing tree survival rates. Semiochemical composition declared by the producers was verified using gas chromatography-mass spectrometry analysis. In the trapping experiment, EcoTrap-type traps were baited with six combinations of lures and anti-attractant. In the tree protection experiment, 28 mature Norway spruce trees situated at newly created forest edges underwent four treatment types: TF attractant, IT anti-attractant, their combination, and no treatment ("control"). Traps baited solely with TF attractant did not capture either beetle, whereas traps lured with IT pheromone, TF attractant and anti-attractant showed no captures of IT but recorded the highest numbers of TF, suggesting significant potential for combined treatment e_cacy. Surprisingly, tree mortality was observed exclusively among trees treated only with TF attractant and in their vicinity, suggesting unique bark beetles' response to the mixture of predator's attractant and host tree kairomones, a phenomenon that was not previously reported. Application of anti-attractant and TF treatment effectively prevented tree mortality, demonstrating the repellent potential of IT anti-attractant against bark beetles. However, mortality rates showed no significant differences among control trees, those treated with anti-attractants, or those treated with the combination of anti-attractants and TF attractant, underscoring necessity for further research to optimize treatment efficacy. [ABSTRACT FROM AUTHOR]

In recent decades, climatic pressures have altered the forested landscape of Bavaria. Widespread loss of trees has unevenly impacted the entire state, of which 37% is covered by forests (5% more than the national average). In 2018 and 2019—due in large part to drought and subsequent insect infestations—more tree-covered areas were lost in Bavaria than in any other German state. Moreover, the annual crown condition survey of Bavaria has revealed a decreasing trend in tree vitality since 1998. We conducted a systematic literature review regarding the remote sensing of forests in Bavaria. In total, 146 scientific articles were published between 2008 and 2023. While 88 studies took place in the Bavarian Forest National Park, only five publications covered the whole of Bavaria. Outside of the national park, the remaining 2.5 million hectares of forest in Bavaria are understudied. The most commonly studied topics were related to bark beetle infestations (24 papers); however, few papers focused on the drivers of infestations. The majority of studies utilized airborne data, while publications utilizing spaceborne data focused on multispectral; other data types were under-utilized- particularly thermal, lidar, and hyperspectral. We recommend future studies to both spatially broaden investigations to the state or national scale and to increase temporal data acquisitions together with contemporaneous in situ data. Especially in understudied topics regarding forest response to climate, catastrophic disturbances, regrowth and species composition, phenological timing, and in the sector of forest management. The utilization of remote sensing data in the forestry sector and the uptake of scientific results among stakeholders remains a challenge compared to other heavily forested European countries. An integral part of the Bavarian economy and the tourism sector, forests are also vital for climate regulation via atmospheric carbon reduction and land surface cooling. Therefore, forest monitoring remains centrally important to attaining more resilient and productive forests. [ABSTRACT FROM AUTHOR]

The 19 species of Dendroctonus bark beetles native to North America include several of the most significant biotic mortality agents of conifers in this region, and they have impacted millions of hectares of forest in recent decades. Semiochemical attractants play several vital roles in the biology of these insects including host finding, host assessment, and mate finding. They are key to the virulence of these insects, since they mediate the mass attacks that enable killing and reproduction within healthy trees. These attractants consist of combinations of thirteen identified pheromone components in three primary chemical classes and at least ten host-associated compounds dominated by monoterpene hydrocarbons in host defensive resin. Due to their potential for use in pest management technologies, semiochemical attractants for Dendroctonus have received extensive research into their chemical compositions and effects on insect behavior. This paper is intended as a synthesis of this research over the past 60 years as well as a critical examination of approaches to investigation of this topic and interpretation of experimental results. Its purpose is to assist practitioners in formulating suitable attractive lures for use in applications and identify gaps in knowledge of the semiochemistry of Dendroctonus that should be addressed if the practical potential of attractants is to be fully realized. [ABSTRACT FROM AUTHOR]

Fire injury stresses Douglas-fir trees (Pseudotsuga menziesii) that survive a wildfire event, allowing subsequent Douglas-fir beetle (Dendroctonus pseudotsugae) infection to kill trees that may have otherwise survived. This study aimed to determine how fire injury, stand, and tree characteristics drive Douglas-fir beetle host tree selection five years post-fire. We paired 28 adjacent beetle-infected and uninfected stands (infected N = 14) and 140 Douglas-fir trees (infected N = 70) within the 416 Fire burn area in Southwest Colorado. We found no statistically significant differences between infected and uninfected stand characteristics. Individual tree height, DBH, and bark char severity index were significantly higher in infected versus uninfected trees. We created a regression decision tree model to determine the influence of fire injury and tree characteristics on the probability of infection. Trees with a height ≥ 27 m, bark char height < 2.3 m, and DBH < 80 cm had the greatest probability of attack (100%). Trees with a height < 27 m, bark char severity index < 5.5, and DBH < 49 cm had the lowest probability of attack (3.7%). Understanding the influence of fire on Douglas-fir beetle host selection allows land managers to model potential epidemic outbreaks and guide proactive management actions that may reduce beetle outbreak severity or preserve high-value trees not killed by fire. [ABSTRACT FROM AUTHOR]

In Jammu and Kashmir's Govindpora (Ramban) and Salamabad (Baramulla), horticultural nurseries with a majority of Olea europaea subsp. cuspidata (Wall. & G.Don) Cif. plantings were examined for possible bark beetle attacks. These olive tree plantations are infested with a variety of insect pests, but the bark beetle Hylesinus macmahoni (Stebbing, 1909) did significant harm to the olive trees that carry fruit. The beetle attacks and consumes the phloem tissues of the plant during its development, causing the afflicted trees to become weak and eventually die. At both sites, infestations of H. macmahoni were discovered. The cytochrome oxidase subunit I (COI) gene was used to validate the species' diagnosis, and its morphological characteristics were re-described. The species has a polygynous matting system (one male and two females), producing two full and a third partial generation annually in Kashmir. [ABSTRACT FROM AUTHOR]

In 2022, Europe emerged from eight of the hottest years on record, leading to significant spruce mortality across Europe. The particularly dry weather conditions of 2018 triggered an outbreak of bark beetles (Ips typographus), causing the loss of thousands of hectares of Norway spruce stands, including in Wallonia and North-eastern France. A methodology for detecting the health status of spruce was developed based on a dense time series of satellite imagery (Sentinel-2). The time series of satellite images allowed the modelling of the spectral response of healthy spruce forests over the seasons: a decrease in photosynthetic activity of the forest canopy causes deviations from this normal seasonal vegetation index trajectory. These anomalies are caused by a bark beetle attack and are detected automatically. The method leads in the production of an annual spruce health map of Wallonia and Grand-Est. The goal of this paper is to assess the damage caused by bark beetle using the resulting spruce health maps. A second objective was to compare the influence of basic variables on the mortality of spruce trees in these two regions. Lasted 6 years (2017–2022), bark beetle has destroyed 12.2% (23,674 ha) of the spruce area in Wallonia and Grand-Est of France. This study area is composed of three bioclimatic areas: Plains, Ardennes and Vosges, which have not been equally affected by bark beetle attacks. The plains were the most affected, with 50% of spruce forests destroyed, followed by the Ardennes, which lost 11.3% of its spruce stands. The Vosges was the least affected bioclimatic area, with 5.6% of spruce stands lost. For the most problematic sites, Norway spruce forestry should no longer be considered. [ABSTRACT FROM AUTHOR]

Invasions of dendrophagous insects pose major threats to forest ecosystems and to the timber industry. The alien species bark beetle Polygraphus proximus Blandf. of Far Eastern origin has caused Siberian fir dieback in vast areas within several regions of Russia. Rapid spread of the pest and its outbreaks raise the issue of preserving the most important functions, including carbon sequestration, by the damaged forests. In this study, monitoring of carbon pool dynamics was carried out during 2012–2023 on four sample plots showing various degrees of damage in the southern taiga zone of Western Siberia in the Larinsky Landscape Reserve. Dynamics of the forest stands' vitality were reflected in a rapid decline of the number of viable trees and an increase in amounts of deadwood, debris, and soil composition, resulting in a transformation of the natural biological carbon cycle in the native dark coniferous ecosystems. [ABSTRACT FROM AUTHOR]

Forest ecosystems are long-term exposed to dry periods in Europe, which leads to a significant loss of vitality and higher mortality, especially in coniferous forests. Identifying stress in the early stages when measures can be taken to protect the forest and living trees is crucial. Current detection methods are based on field surveys by forest workers or remote sensing methods to cover larger areas, which use changes in spectral reflectance of the forest canopy. In some cases, the attacked trees do not change their appearance, and based on calculations of vegetation indices from remote sensing data, the attack cannot be mapped. We present an innovative methodology based on non-optical analysis, namely identifying a group of volatile compounds and microclimate signs in forest stands that indicate stress factors in forest stands. An attacked tree by a bark beetle produces increased amounts of biogenic volatile organic compounds associated with defense, and the microclimate changes due to interrupted transpiration. In addition, the bark beetle uses the aggregation pheromone to attract more individuals and to attack the tree massively. In this study, we tested three electronic noses (Miniature Bosch sensor device with 25,419 samples, Sensory device for environmental applications with 193 samples, Handheld VOC Detector Tiger with 170 samples) in a freshly infested spruce stand. The measurement was conducted at ground level with the help of a human operator and was repeated six times to verify the detection capability of the electronic noses. To verify the capability of electronic noses to predict tree infestation, we used machine learning Random Forest. The results demonstrated that electronic noses can detect bark beetle infestation start (within 1 week of the first attack). The Miniature Bosch sensor device achieved the highest accuracy with a value of 95%, in distinguishing forest sections that are healthy and infested; the second most accurate electronic nose is the Sensory device for environmental applications, with an accuracy of 89%. Our proposed methodology could be used to detect bark beetle presence.

IntroductionAs a result of climate change and bark beetle outbreaks in forests, extensive salvage, and sanitary cutting have been undertaken in Europe, resulting in many clear-cuts with coarse stumps. The populations of pine weevils (Hylobius abietis and Hylobius pinastri) are steadily increasing. A high abundance of pine weevils feeding on seedlings typically results in significant economic losses and prolongs the forest establishment period. However, information on these species spatial distribution and habitat selection patterns, necessary for assessing their harmfulness and subsequently accurately estimating their threat to reforested areas, is lacking. To determine which factors influence spatial selection patterns and seedling type preference, this study investigated which clear-cut factors increase pine weevil abundance and which seedling types (species and age) are the most preferred.MethodsThe experiment was carried out on 20 clear-cuts in the central Czech Republic. We evaluated soil moisture level, average stump distance and diameter, proportion of other conifers, and whether the stumps were mulched. We detected the abundance of pine weevils using pitfall traps. We determined the feeding scar intensity on the first 10 cm of seedling stems on commonly used seedlings for reforestation in central Europe: 1-year-old Scots pine (Pinus sylvestris), European larch (Larix decidua), and 3-year-old Norway spruce (Picea abies), with 1,200 seedlings in total. The individual seedling types alternated in rows. The results were evaluated using generalized linear mixed-effect models (GLMMs). As dependent variables we used total numbers of H. abietis and H. pinastri. The soil moisture level, mulching, proportion of other conifers, average stump diameter, and distance were considered independent variables.ResultsWe found that Norway spruce was the least attractive to pine weevils. We found a higher abundance of H. abietis females in moist clear-cuts, confirming that dry clear-cuts are less suitable for oviposition.ConclusionAccording to our findings, if foresters want to plant coniferous seedlings, it seems that planting older spruce is a better option than planting larch and pine. These findings provide valuable insights for forest management and reforestation strategies, equipping foresters with the knowledge to mitigate the threat of pine weevils and ensure successful forest establishment.

The article describes the natural background, the origin, the course and the outcome of the dispute between Poland and the European Commission which was going on in the years 2016–2018 regarding the forest management performed in the Białowieża Forest. The dispute took place on two interrelated levels: natural and legal. The main axis of the dispute between the Polish government and the European Commission was the difference of views as to what actions would prove effective in the fight against the latest gradation of the bark beetle, which occurred with exceptional intensity in the Białowieża Forest in 2015, and what actions would be most beneficial in the context of preserving rare species of birds and insects that make up the fauna of the Białowieża Forest. The article presents extensively the arguments raised by both parties to the conflict in the proceedings before the Court of Justice of the European Union, which were initiated by a complaint filed by the European Commission. As a commentary on these arguments, the views expressed in the scientific literature as to the proper reaction in response to a recurrent infestation of the bark beetle, usefulness and efficacy of the active forest management operations questioned by the European Commission, as well as an impact of these operations on the conservation of natural habitats, insects and birds are presented. The legal dimension of the dispute boiled down to the question of what actions in the situation were allowed, required or prohibited under Polish and EU law.

Extreme weather events are increasingly recognized as major stress factors for forest ecosystems, causing both immediate and long-term effects. This study focuses on the impacts experienced by the forests of Valdisotto, Valfurva, and Sondalo (28% of the total area is covered by forests) in Upper Valtellina (Italy) due to the Vaia storm that occurred in October 2018. To define the immediate impacts of Vaia, we assess the economic value of forest ecosystem services (ESs), particularly those provided by timber production and carbon sequestration, pre- and post-Vaia and during the emergency period. We used the market price method to assess the economic values of timber production and carbon sequestration, as these are considered to be marketable goods. Based on data processed from Sentinel-2 satellite images (with a spatial resolution of 10 m), our results show that, despite the reduction in forest area (−2.02%) and timber stock (−2.38%), the economic value of the timber production increased after Vaia due to higher timber prices (i.e., from a total of €124.97 million to €130.72 million). However, considering the whole emergency period (2019–2020), the total losses are equal to €5.10 million for Valdisotto, €0.32 million for Valfurva, and €0.43 million for Sondalo. Instead, an economic loss of 2.88% is experienced for carbon sequestration, with Valdisotto being the more affected municipality (−4.48% of the pre-Vaia economic value). In terms of long-term impacts, we discuss the enhanced impacts due to the spread of the bark beetle Ips typopgraphus.

This study considered the mechanical properties of primary blue-stained sapwood of Norway spruce infested by the bark beetle Ips typographus. Nineteen stems from Stammerberg (ZH, Switzerland) were harvested in three different seasons and after different periods of bark beetle outbreaks. Density, Brinell hardness including elastic recovery after load, and key strength properties were tested on blue-stained wood and non-infected controls. Differences in mechanical properties were analysed according to the stand and storage time of the stems after the bark beetle attack. Spruce harvested at a late stage after the bark beetle attack (2–3 months) showed a clear reduction in impact bending strength, a significant loss in surface elastic recovery after indentation during Brinell hardness test, and a striking number of specimens with brittle fracture behaviour during Three-Point-Bending. Light microscopy and the results of the mechanical tests give clear evidence to suggest that wood-degrading fungi are already active in addition to the sap-staining fungi. Especially after larger outbreaks of bark beetles, it must be assumed that sapwood of Norway spruce does not only show the typical blue stain, but also incipient stages of wood degradation by wood-degrading fungi. [ABSTRACT FROM AUTHOR]

Simple Summary: Symbiotic bacteria play an essential role in the digestion, detoxification, and nutrient supply of bark and ambrosia beetles. They may even promote the invasiveness and adaptability of invasive beetles. However, as a newly invasive pest in China, the diversity and community structure of bacteria associated with Hylurgus ligniperda is still unclear. This hinders our ability to comprehend their invasion mechanism and ecological adaptability. Therefore, this study revealed the differences in the diversity and community composition of associated bacteria in the beetle's elytra, prothorax, and gut. Our findings revealed that the microbial population of the elytra was distinct from that of the prothorax and gut. Additionally, gender disparities existed throughout the bacterial population of elytra. The distribution of associated bacteria in different organs of males and females may indicate that they undertake different ecological functions. This study will help to understand the bacterial communities that may play important roles in Hylurgus ligniperda. Hylurgus ligniperda (Fabricius) (Curculionidae: Scolytinae) is a new invasive pest beetle in China, which colonized the Shandong province, causing devastating damage. Originating in Europe, it has spread to Oceania, Asia, North and South America. Bacterial associates have been frequently reported to play a vital role in strengthening the ecological adaptations of bark and ambrosia beetles. The environmental adaptability of H. ligniperda may be supported by their associated bacteria. Bacterial communities colonizing different body parts of insects may have different functions. However, little is known about the bacteria associated with H. ligniperda and their potential involvement in facilitating the adaptation and invasion of the beetles into new environments. In this study, we employed high-throughput sequencing technology to analyze the bacterial communities associated with male and female adults of H. ligniperda by comparing those colonizing the elytra, prothorax, and gut. Results showed that the bacterial communities of male and female adults were similar, and the elytra samples had the highest bacterial diversity and richness, followed by the gut, while the prothorax had the lowest. The dominant phyla were Proteobacteria, Firmicutes, and Actinobacteriota, while the dominant genera were Serratia, Lactococcus, Rhodococcus, unclassified Enterobacteriaceae, and Gordonia. Among these, Rhodococcus and Gordonia were the specific genera of endobacteria and ectobacteria, respectively. Differences in the distribution of associated bacteria may suggest that they have different ecological functions for H. ligniperda. The results of functional prediction showed that bacteria were enriched in terpenoid backbone biosynthesis, degradation of aromatic compounds, limonene and pinene degradation, neomycin, kanamycin and gentamicin biosynthesis, indicating that they may assist their beetles in synthesizing pheromones, degrading toxic secondary metabolites of host trees, and antagonizing pathogenic fungi. These results help us understand the interaction between H. ligniperda and bacteria and highlight possible contributions to the invasion process. [ABSTRACT FROM AUTHOR]

Decaying wood is an essential element of forest ecosystems and it affects its other components. The aim of our research was to determine the decomposition rate of deadwood in various humidity and thermal conditions in the gaps formed in the montane forest stands. The research was carried out in the Babiogórski National Park. The research plots were marked out in the gaps of the stands, which were formed as a result of bark beetle gradation. Control plots were located in undisturbed stands. The research covered wood of two species -- spruce and beech in the form of cubes with dimensions of 50 mm x 50 mm x 22 mm. Wood samples were placed directly on the soil surface and subjected to laboratory analysis after 36 months. A significant influence of the wood species and the study plot type on the physicochemical properties of the tested wood samples was found. Wood characteristics strongly correlated with soil moisture. A significantly higher mass decline of wood samples was recorded on the reference study plots, which were characterized by more stable moisture conditions. Poorer decomposition of wood in the gaps regardless of the species is related to lower moisture. The wood species covered by the study differed in the decomposition rate. Spruce wood samples were characterized by a significantly higher decomposition rate compared to beech wood samples. Our research has confirmed that disturbances that lead to the formation of gaps have a direct impact on the decomposition process of deadwood. [ABSTRACT FROM AUTHOR]

The Eurasian Spruce Bark Beetle (Ips typographus) (L. 1758) (Coleoptera: Scolytinae) poses a significant threat to Eurasia's Norway spruce (Picea abies) (L.) Karst, forests. Early detection of infested trees is crucial to control beetle outbreaks and allow salvage logging before the next generation emerges. Besides traditional methods, new approaches focus on monitoring volatile organic compounds, mainly monoterpenes, emitted by infested trees. Using analytical chemistry, we studied the distribution of these compounds, particularly α-pinene, around infested trees. In lab trials, we optimized α-pinene detection using dynamic absorption and solid-phase microextraction (SPME), analyzed by gas chromatography with flame ionization detection (GC-FID). We conducted forest trials, revealing varying α-pinene abundance due to changing conditions. However, consistent trends emerged: levels were highest near the infested tree stem and 1.3 m above ground in the first trial and at a 1 m distance from the infested stem in the second. We generated a three-dimensional cloud depicting the distribution of α-pinene around infested trees in their natural habitat. These findings open avenues for detecting bark beetles on a large scale by mapping elevated concentrations of volatile organic compounds emitted by infested trees, potentially leading to alternative pest management methods. Scanning methods, such as electronic sensors combined with remote sensing, hold promise for this application. [ABSTRACT FROM AUTHOR]

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Bohemian Switzerland is a national park in Northern Czechia famous for its sandstone rocks, which were affected by a massive fire in 2022. Specific geomorphology of the region affected the spreading of the fire and complicated its extinguishing. The fire directly or indirectly damaged several geosites in Bohemian Switzerland. The catastrophe brought a possibility of showing the unique connection between geoheritage and present climate change and increasing awareness about the problems. The text is focused on field education of geography, striving to strengthen environmental awareness among students through educating their teachers. The research is based on desk research, field observation and didactic principles application. The causes of the fire were complex, including physical geographical (drought and bark beetle calamity within climate change) and human geographical phenomena (mass tourism and tourist misbehavior, inappropriate forestry practices). The teachers we worked with reached similar conclusions at the end of our course. Our fieldwork educational concept proved viable and was appreciated by them mainly thanks to the incorporation of research-based learning and the absence of unnatural emphasis on climate change. Climate change is a politicized topic, bringing controversies to the classrooms in the peripheral region. The approach we proposed is anchored in inquiry-based methods and touches on the issue indirectly. [ABSTRACT FROM AUTHOR]

Colonization of hosts by bark beetles is generally mediated by aggregation pheromones. Species competing for the same resource can limit interspecific interactions and maintain reproductive isolation by using different pheromones. In the southern United States, 3 sympatric species of Ips breed in pine hosts, each with a different pheromone blend. Ips avulsus (Eichhoff) uses ipsdienol and lanierone; Ips calligraphus (Germar) uses ipsdienol, cis-verbenol, and trans-verbenol; and Ips grandicollis (Eichhoff) uses ipsenol. Different species can also minimize cross-attraction by using different enantiomeric ratios of the same pheromones. Studies on the enantiomeric ratio of ipsdienol used by I. avulsus have come to contradictory conclusions in part because of geographic and seasonal variation. There is growing evidence that semiochemical context, in the form of different co-baits used in trapping experiments, may also play a role in the responses of I. avulsus to enantiomeric ratios of ipsdienol. We conducted a trapping study at 2 locations with traps baited with (+)-ipsdienol or racemic ipsdienol and co-baited with ipsenol, lanierone, or both ipsenol and lanierone. We found context-dependent effects of both lanierone and ipsenol on the response of I. avulsus to ipsdienol. We suggest that responses to different bait and co-bait combinations may have been shaped by different types of interactions such as the absence of conspecifics or a related species, or the presence of beneficial or antagonistic interspecific interactions. [ABSTRACT FROM AUTHOR]

This study investigates the efficacy of combined treatment strategy, incorporating pheromones for bark beetle I. typographus (IT) and attractant of its natural enemy T. formicarius (TF), along with anti-attractants for IT (containing 1-hexanol, 1-octen-3-ol, 3-octanol, eucalyptol, trans-thujanol, and trans-conophthorin), to enhance protection methods for Picea abies against biotic disturbances. Two field experiments—trapping experiment and tree protection experiment—were conducted in June 2023 in managed spruce-dominated beetle-affected stands in Czechia. We anticipated higher catches of IT in traps baited with IT pheromone (containing s-ipsdienol, s-cis-verbenol, and 2-methyl-3-buten-2-ol) and TF attractant compared to traps using IT pheromone alone, since compounds intrinsic to IT pheromone, namely 2-methyl-3-buten-2-ol, ipsenol, and ipsdienol, are integral components of the attractant designed for TF. We hypothesized that application of TF attractant and IT anti-attractant would enhance the treatment's protective properties, assuming that attracted TF would function as a predator, reducing bark beetle population and increasing tree survival rates. Semiochemical composition declared by the producers was verified using gas chromatography-mass spectrometry analysis. In the trapping experiment, EcoTrap-type traps were baited with six combinations of lures and anti-attractant. In the tree protection experiment, 28 mature Norway spruce trees situated at newly created forest edges underwent four treatment types: TF attractant, IT anti-attractant, their combination, and no treatment (“control”). Traps baited solely with TF attractant did not capture either beetle, whereas traps lured with IT pheromone, TF attractant and anti-attractant showed no captures of IT but recorded the highest numbers of TF, suggesting significant potential for combined treatment efficacy. Surprisingly, tree mortality was observed exclusively among trees treated only with TF attractant and in their vicinity, suggesting unique bark beetles' response to the mixture of predator's attractant and host tree kairomones, a phenomenon that was not previously reported. Application of anti-attractant and TF treatment effectively prevented tree mortality, demonstrating the repellent potential of IT anti-attractant against bark beetles. However, mortality rates showed no significant differences among control trees, those treated with anti-attractants, or those treated with the combination of anti-attractants and TF attractant, underscoring necessity for further research to optimize treatment efficacy.

Rapid detection and identification of the extent of spruce bark beetle infestation in the field is a necessity for researchers, forest rangers, and tree protection agencies. This paper presents an innovative solution that uses an autonomous multifunctional probe with embedded artificial intelligence. This approach is based on the real-time object detection method, called “first object, more object” (FOMO), which is adapted to the energy-efficient architecture of the ESP32 microcontroller. Neural network algorithms for fast image processing were trained using data sets from various locations in central Europe, which were heavily affected by the bark beetle calamity. The results of the experimental verification of the deployment of this smart probe in the field demonstrate a high level of precision in the detection and identification of the extent of damage.

Abstract Key message During pest outbreaks, mapping tools play an important role. Participatory projects can provide useful ground data, which have a high accuracy in detecting early-stage infestations and small spots of the European spruce bark beetle Ips typographus. However, satellite approaches are fundamental to clearly estimate infestation occurrence because ground data are spatially biased. Here, we show how a participatory approach involving nonspecialized staff and based on GIS-based app may contribute ground truth data that are fully complementary to satellite data. Context In Europe, bark beetle outbreaks were recently triggered by windstorms and heat waves, with the European spruce bark beetle Ips typographus. as the most important pest species. Huge efforts are needed for continuous mapping and monitoring of affected areas, especially during an incipient large-scale infestation. This is particularly difficult in mountain landscapes because of the rugged topography. Aims In addition to the use of remote sensing techniques, ground surveys are still an important source of data, providing detailed information on the symptoms of the affected trees and the stage of the attacks. Unfortunately, these surveys are extremely time demanding and require intensive field work. We wanted to assess how a participatory approach based on nonspecialized staff may contribute to data collection. Methods Georeferenced outbreak data were collected in the field in the Southern Alps (Italy) using a smartphone application based on ArcGIS platform. The survey was based on a participatory approach on a voluntary basis, involving citizens aware of forest practices. Visual analysis of satellite images was performed monthly to assess the visibility of reported infestations. Using a binomial model, we tested how the type of report (i.e., on-site/off-site), size of spot, stage of infestation, and their interactions affect detectability. In addition, spot occurrences within a study area were mapped for comparison with ground surveillance. Closeness to roads was tested between reported and unreported spots. Results WebGIS platform allowed us to retrieve near real-time information on bark beetle outbreaks and to compare the results with satellite imagery. Using visual analysis of satellite images, we detected only ~ 50% of the spots observed in the field, and detectability decreased dramatically for smaller and early-stage spots. Field observations were mostly concentrated near roads and covered only ~ 10% of the spots detected on satellite images. Conclusion The participatory approach is particularly helpful in mapping early-stage and small infestations, while satellite images are better suited at covering large areas and detect large and advanced-stage spots. The integration of those approaches is promising, and it can greatly improve the overall understanding of bark beetle outbreaks under emergency situations. A greater effort in developing smart applications for ground detection will benefit future monitoring of forest pests.

The acoustic communication system (ACS) in bark beetles has been studied mainly in species of the genera Dendroctonus, Ips and Polygraphus. Specifically, ACS of the roundheaded pine beetle, Dendroctonus adjunctus, has been little studied. In this study, we described the stridulatory apparatus of this beetle using optical and scanning electron microscopy and recorded the call types produced by males in three behavioral contexts: stress, female–male–, and male–male interactions. From the spectrograms and waveforms, call types, as well as temporal (tooth strike, tooth strike rate, and intertooth strike interval) and spectral features (minimum, maximum and dominant frequency), were determined. Males have a functional elytro–tergal stridulatory apparatus—females do not—consisting of a file for the pars stridens and two lobes for the plectrum. Most of spectro–temporal features were statistically different between single– and multi–noted calls and across the three behavioral contexts. In the male–male interaction, a new type of call named “withdrawal” was produced by the male withdrawing or fleeing. Our results suggest that the spectro–temporal features of single– and multiple–noted calls in the three behavioral conditions are specific and different from each other. Yet, the combination of single and multiple calls determines an overall calling pattern characteristic of the tested behaviors and, therefore, is species–specific.

The Mediterranean pine engraver, Orthotomicus erosus (Wollaston) (Col.: Curculionidae: Scolytinae), is a destructive bark beetle in pine forests worldwide. Regarding the recent outbreak of O. erosus in Iran, its flight activity and population density were monitored in four contaminated sites in western Tehran. These four sampling sites included Tabiat Park, Khargush Darreh Forest Park, Chitgar Park behind Bam Riding Club as well as Chitgar Park 9th Aghaghiya Street (western Tehran). Two pheromone traps (ECONEX ORTHOTOMICUS EROSUS 60 DAYS pheromone, Spain) were installed in each sampling site at the height of 2.5 m in the south direction of the pine trees. The number of trapped adults was recorded at 10-day intervals from April 2019 to March 2020. In total, 8514 adults of O. erosus were collected using pheromone traps during the sampling period. The results showed that the adult flight started from April in four sampling sites. The flight periods of adults continued until November in Tabiat Park, Khargush Darreh Forest Park, and Chitgar Park, behind Bam Riding Club. Differently, the last adults were collected in October in Chitgar Park, 9th Aghaghiya Street. In addition, the flight peaks of O. erosus occurred in August in Tabiat Park, Khargush Darreh Forest Park, and Chitgar Park, behind Bam Riding Club. However, the highest number of adults were trapped in July in Chitgar Park, 9th Aghaghiya Street. Based on our results, the number of trapped adults was significantly different in sampling sites. The mean number of trapped adults was the highest (183.25 ± 0.11) in Chitgar Park, 9th Aghaghiya Street and lowest (106.32 ± 0.07) in Tabiat Park during the whole monitoring experiment. These findings on flight activity and population fluctuation of O. erosus in local conditions could be helpful to establish an efficient and successful management program for this destructive pest.

Decaying wood is an essential element of forest ecosystems and it affects its other components. The aim of our research was to determine the decomposition rate of deadwood in various humidity and thermal conditions in the gaps formed in the montane forest stands. The research was carried out in the Babiogórski National Park. The research plots were marked out in the gaps of the stands, which were formed as a result of bark beetle gradation. Control plots were located in undisturbed stands. The research covered wood of two species – spruce and beech in the form of cubes with dimensions of 50 ​mm × ​50 ​mm × ​22 ​mm. Wood samples were placed directly on the soil surface and subjected to laboratory analysis after 36 months. A significant influence of the wood species and the study plot type on the physicochemical properties of the tested wood samples was found. Wood characteristics strongly correlated with soil moisture. A significantly higher mass decline of wood samples was recorded on the reference study plots, which were characterized by more stable moisture conditions. Poorer decomposition of wood in the gaps regardless of the species is related to lower moisture. The wood species covered by the study differed in the decomposition rate. Spruce wood samples were characterized by a significantly higher decomposition rate compared to beech wood samples. Our research has confirmed that disturbances that lead to the formation of gaps have a direct impact on the decomposition process of deadwood.

Discoloration of the sapwood caused by blue-stain fungi on conifer logs during interim storage causes significant loss to the forest industry. The fungal infection is often associated with bark beetle attacks because the spores are transmitted by the beetles. They can also be disseminated by rain-splash and moist air. While there are methods to protect logs from sap-stain in wood yards, this is often not possible in the forest for practical and regulatory reasons. Timing of harvesting and timely transportation are often the only ways to prevent blue-stain. To estimate the urgency of transportation, knowledge of the growth of blue-stain fungi and its dependence on weather conditions is of great interest. The proportion of discolored sapwood on Norway spruce logs was recorded along a time series, together with weather data in two field experiments conducted in spring and summer at two alpine sites in Austria. A predictive model was developed to estimate the proportion of blue-stained sapwood based on the temperature sum to which the logs were exposed. After harvest in March, there was a time lag of 82 and 97 days at the two respective sites, caused by initially low temperatures, before discoloration started. In contrast, sap-stain occurred 14 days after the harvest in June, when warm conditions prevailed from the start. The nonlinear least square regression model can help to estimate a window of opportunity to transport wood before it loses its value and serves as a sub model for lead time estimation within logistic decision support systems.

Key message: During pest outbreaks, mapping tools play an important role. Participatory projects can provide useful ground data, which have a high accuracy in detecting early-stage infestations and small spots of the European spruce bark beetle Ips typographus. However, satellite approaches are fundamental to clearly estimate infestation occurrence because ground data are spatially biased. Here, we show how a participatory approach involving nonspecialized staff and based on GIS-based app may contribute ground truth data that are fully complementary to satellite data. Context: In Europe, bark beetle outbreaks were recently triggered by windstorms and heat waves, with the European spruce bark beetle Ips typographus. as the most important pest species. Huge efforts are needed for continuous mapping and monitoring of affected areas, especially during an incipient large-scale infestation. This is particularly difficult in mountain landscapes because of the rugged topography. Aims: In addition to the use of remote sensing techniques, ground surveys are still an important source of data, providing detailed information on the symptoms of the affected trees and the stage of the attacks. Unfortunately, these surveys are extremely time demanding and require intensive field work. We wanted to assess how a participatory approach based on nonspecialized staff may contribute to data collection. Methods: Georeferenced outbreak data were collected in the field in the Southern Alps (Italy) using a smartphone application based on ArcGIS platform. The survey was based on a participatory approach on a voluntary basis, involving citizens aware of forest practices. Visual analysis of satellite images was performed monthly to assess the visibility of reported infestations. Using a binomial model, we tested how the type of report (i.e., on-site/off-site), size of spot, stage of infestation, and their interactions affect detectability. In addition, spot occurrences within a study area were mapped for comparison with ground surveillance. Closeness to roads was tested between reported and unreported spots. Results: WebGIS platform allowed us to retrieve near real-time information on bark beetle outbreaks and to compare the results with satellite imagery. Using visual analysis of satellite images, we detected only ~ 50% of the spots observed in the field, and detectability decreased dramatically for smaller and early-stage spots. Field observations were mostly concentrated near roads and covered only ~ 10% of the spots detected on satellite images. Conclusion: The participatory approach is particularly helpful in mapping early-stage and small infestations, while satellite images are better suited at covering large areas and detect large and advanced-stage spots. The integration of those approaches is promising, and it can greatly improve the overall understanding of bark beetle outbreaks under emergency situations. A greater effort in developing smart applications for ground detection will benefit future monitoring of forest pests. [ABSTRACT FROM AUTHOR]

The current knowledge of morphology and chaetotaxy of the different developmental stages within the subfamily Scolytinae presents an information deficit that needs to be addressed. Thus, the objective of the present study was to describe, the chaetotaxy and morphology of larvae and pupae, and determine the number of larval instars, the sexual dimorphism in adults, and the development time in Phloeosinus tacubayae. The number of larval instars was determined using traditional morphometry of cephalic capsule and multivariate analysis; description of morphology and chaetotaxy of larvae and pupae, and sexual dimorphism in adults was based on light microscopy and scanning electron microscopy photographs; finally, we quantified development time by mean reviews of 10 gallery systems selected randomly in infested logs, in the laboratory. Morphometric analysis of the cephalic capsule allowed the recognition of 3 different instars. Our results showed that the larvae of P. tacubayae have unique attributes in the body that differentiate them from other genera of the subfamily for example the epicranial suture is not marked, and differentiated from Phloeosinus canadensis , such as a smaller number of setae in the maxillae and without a tergal plate. The pupa had a smaller number of setae on the whole body. The most useful morphological characters to identify a sexual dimorphism in adults were found in the shape and relative position of the seventh and eighth tergites; development time lasted 40 days in total, being the pupal stage the one that took the longest to complete. [ABSTRACT FROM AUTHOR]

Insect and disease outbreaks in forests are biotic disturbances that can profoundly alter ecosystem dynamics. In many parts of the world, these disturbance regimes are intensifying as the climate changes and shifts the distribution of species and biomes. As a result, key forest ecosystem services, such as carbon sequestration, regulation of water flows, wood production, protection of soils, and the conservation of biodiversity, could be increasingly compromised. Despite the relevance of these detrimental effects, there are currently no spatially detailed databases that record insect and disease disturbances on forests at the pan‐European scale. Here, we present the new Database of European Forest Insect and Disease Disturbances (DEFID2). It comprises over 650,000 harmonized georeferenced records, mapped as polygons or points, of insects and disease disturbances that occurred between 1963 and 2021 in European forests. The records currently span eight different countries and were acquired through diverse methods (e.g., ground surveys, remote sensing techniques). The records in DEFID2 are described by a set of qualitative attributes, including severity and patterns of damage symptoms, agents, host tree species, climate‐driven trigger factors, silvicultural practices, and eventual sanitary interventions. They are further complemented with a satellite‐based quantitative characterization of the affected forest areas based on Landsat Normalized Burn Ratio time series, and damage metrics derived from them using the LandTrendr spectral–temporal segmentation algorithm (including onset, duration, magnitude, and rate of the disturbance), and possible interactions with windthrow and wildfire events. The DEFID2 database is a novel resource for many large‐scale applications dealing with biotic disturbances. It offers a unique contribution to design networks of experiments, improve our understanding of ecological processes underlying biotic forest disturbances, monitor their dynamics, and enhance their representation in land‐climate models. Further data sharing is encouraged to extend and improve the DEFID2 database continuously. The database is freely available at https://jeodpp.jrc.ec.europa.eu/ftp/jrc‐opendata/FOREST/DISTURBANCES/DEFID2/. [ABSTRACT FROM AUTHOR]

Recent hot droughts in California resulted in ponderosa pine (Pinus ponderosa) mortality attributed to drought and western pine beetle (WPB, Dendroctonus brevicomis). While drought alone can cause tree death, direct warming effects on WPB are a contributing factor. Research on WPB generation timing (voltinism), however, is lacking.We monitored WPB tree attacks and adult emergence timing at two California sites and developed a degree‐day model from field‐observed data. Historical, contemporary, and future temperatures for several California sites were used with the model to examine trends in WPB voltinism.Field data showed a single summer and an overwinter generation at a northern California site. As summer temperatures increased beyond 1900–1980 averages, the predicted number of full and partial WPB generations by 2021 had increased from ~2 annual (one summer and one overwinter) generations historically to ~2.3 at two northern California sites and from ~2.3 to ~3.2 at two warmer California sites.Historical and contemporary data suggest winter warming was not sufficient for an additional generation overwinter. Instead, increases in generations were driven by summer and fall temperatures.Unconstrained increases in the number of future annual generations will be limited by complex, but not well understood, WPB thermal adaptations. Increased knowledge of temperature‐driven WPB population growth will improve forest vegetation models aimed at predicting ponderosa pine mortality in a changing climate. [ABSTRACT FROM AUTHOR]

The widespread tree mortality caused by the European spruce bark beetle (Ips typographus L.) is a significant concern for Norway spruce-dominated (Picea abies H. Karst) forests in Europe and there is evidence of increases in the affected areas due to climate warming. Effective forest monitoring methods are urgently needed for providing timely data on tree health status for conducting forest management operations that aim to prepare and mitigate the damage caused by the beetle. Unoccupied aircraft systems (UASs) in combination with machine learning image analysis have emerged as a powerful tool for the fast-response monitoring of forest health. This research aims to assess the effectiveness of deep neural networks (DNNs) in identifying bark beetle infestations at the individual tree level from UAS images. The study compares the efficacy of RGB, multispectral (MS), and hyperspectral (HS) imaging, and evaluates various neural network structures for each image type. The findings reveal that MS and HS images perform better than RGB images. A 2D-3D-CNN model trained on HS images proves to be the best for detecting infested trees, with an F1-score of 0.759, while for dead and healthy trees, the F1-scores are 0.880 and 0.928, respectively. The study also demonstrates that the tested classifier networks outperform the state-of-the-art You Only Look Once (YOLO) classifier module, and that an effective analyzer can be implemented by integrating YOLO and the DNN classifier model. The current research provides a foundation for the further exploration of MS and HS imaging in detecting bark beetle disturbances in time, which can play a crucial role in forest management efforts to combat large-scale outbreaks. The study highlights the potential of remote sensing and machine learning in monitoring forest health and mitigating the impacts of biotic stresses. It also offers valuable insights into the effectiveness of DNNs in detecting bark beetle infestations using UAS-based remote sensing technology. [ABSTRACT FROM AUTHOR]

Different regions have different forms of combating bark beetles. Pheromone traps are a biotechnical control method effective against bark beetles that damage forests and cause great losses. In particular, studies conducted on the possible effects of global climate change show that changes in climate can cause mass increases in beetle populations and that this situation may cause serious damage to forests. This study was conducted in 2019 in the forested land within the boundaries of the Akcasu, Beldibi, Davulga, Dorukhan, Sarigol and Tefen Forest Range Districts, which are affiliated with the Devrek Forestry Directorate of Zonguldak Forest Regional Directorate. In this study, ten different stand types were taken into consideration, and the general characteristics of these stand. The measurements made over the months of the experiment were noted, and at the end of the study, the data were evaluated with variance analysis and Duncan's test with SPSS software. Based on this expected potential danger, studies on this subject are of great importance. Even though the subjects of this study (e.g., the factors triggering increases in beetle populations (especially bark beetles), leading to serious destruction in forests, natural enemies, and biological control methods) are critical, an insufficient number of studies have been conducted on these topics. In addition, effective natural enemies should be identified, and methods for rearing them in a laboratory environment should be investigated. Finally, suitable species should be reared and released into nature. It is recommended to diversify and continue the studies on these subjects. [ABSTRACT FROM AUTHOR]

In recent decades, climatic pressures have altered the forested landscape of Bavaria. Widespread loss of trees has unevenly impacted the entire state, of which 37% is covered by forests (5% more than the national average). In 2018 and 2019—due in large part to drought and subsequent insect infestations—more tree-covered areas were lost in Bavaria than in any other German state. Moreover, the annual crown condition survey of Bavaria has revealed a decreasing trend in tree vitality since 1998. We conducted a systematic literature review regarding the remote sensing of forests in Bavaria. In total, 146 scientific articles were published between 2008 and 2023. While 88 studies took place in the Bavarian Forest National Park, only five publications covered the whole of Bavaria. Outside of the national park, the remaining 2.5 million hectares of forest in Bavaria are understudied. The most commonly studied topics were related to bark beetle infestations (24 papers); however, few papers focused on the drivers of infestations. The majority of studies utilized airborne data, while publications utilizing spaceborne data focused on multispectral; other data types were under-utilized- particularly thermal, lidar, and hyperspectral. We recommend future studies to both spatially broaden investigations to the state or national scale and to increase temporal data acquisitions together with contemporaneous in situ data. Especially in understudied topics regarding forest response to climate, catastrophic disturbances, regrowth and species composition, phenological timing, and in the sector of forest management. The utilization of remote sensing data in the forestry sector and the uptake of scientific results among stakeholders remains a challenge compared to other heavily forested European countries. An integral part of the Bavarian economy and the tourism sector, forests are also vital for climate regulation via atmospheric carbon reduction and land surface cooling. Therefore, forest monitoring remains centrally important to attaining more resilient and productive forests.