Mountain forests provide essential ecosystem services, including protection against natural hazards. However, climate change and the predominance of structurally homogeneous Norway spruce stands increase their predisposition to disturbances such as windthrow, bark beetle infestation, and snow breakage. Given limited resources for proactive and reactive forest management, prioritizing silvicultural interventions is crucial. We present a framework for the spatially explicit assessment of forest predisposition to snow breakage, windthrow, and bark beetle infestation at 10 m resolution across regional scales. The approach integrates high-resolution forest structural and site factor attributes primarily derived from nationally available airborne laser scanning (ALS) data. These attributes are weighted using an expert-based model according to their influence on disturbance predisposition. Weighted values are aggregated and classified into four predisposition classes, from low (< 50th) to extreme (> 95th percentile). Validation of local foresters at 142 reference sites showed significant correlations between forester-rated and modeled predisposition for windthrow and bark beetle, but not for snow breakage. New bark beetle infestations were strongly associated with increasing predisposition classes. Forest structural parameters such as forest mixture and spruce share, development stage, and canopy layering were key predictors and could be determined with high accuracy, enabling detailed and accurate predisposition mapping even in steep terrain. Assessing predisposition to snow breakage remains challenging due to the high stochastic variability in the location, characteristics, and amount of snow fall. As the main predictors are derived from nationwide ALS data, the methodology is transferable to other mountain regions. Developed in close collaboration with practitioners, the framework supports operational forest management by improving prioritization of interventions. • Framework for spatially explicit predisposition mapping in mountain forests. • Use of detailed forest structure parameters based on nationwide airborne laser scanning. • High correlation between predisposition mapping and on-site forester assessment. • Increase of detected bark beetle nests with increasing predisposition class. • Support of spatial prioritization of forest management interventions.

Small size imposes constraints on flight due to a reduction in aerodynamic efficiency of small wings. Consequently, miniature insects are often considered to be poor flyers that disperse by drifting in winds. Only few studies have actually measured the active flight of very small insects. The few that did, report surprisingly high flight speeds compared to the size of such small creatures. To test both the limits to flight performance and response to wind, we tracked free-flight within a wind tunnel in a whitefly, a thrips, and a bark beetle. The studied species represent small insects from three different orders (Hemiptera, Thysanoptera and Coleoptera) that underwent independent miniaturization in the course of evolution. Flights were tracked with and without wind and the wind was either horizontal or vertical. From the 3D flight trajectories of the insects, we extracted aerial velocity and manoeuvring performance. The insects did not passively drift downwind and two of the three insects studied displayed distinct upwind flight behaviours. Maximal flight speed was slower than that of larger insects, but faster in terms of body length per second. The manoeuvrability of two out of the three studied species exceeded that of larger animals in terms of flight speed for a minimal turning radius. These findings advocate the inclusion of active flight in small insect dispersal models and suggest that miniaturization may result in improved aerial manoeuvrability.

Forests provide many ecological and economic functions, but they are increasingly exposed to the invasion of various harmful insects. The bark beetle Dendroctonus micans and pine processionary moth Thaumetopoea pityocampa are highly destructive insect pests that kill living trees, leading to significant reductions in forest productivity and widespread tree death. In addition to these, Glyphodes pyloalis is another tree pest that damages mulberries, which are economically important for silk yarn production. In this study, a strain (27b2) from Beauveria bassiana was isolated from the cambium pests D. micans and Ips sexdentatus, which were collected dead from their natural habitat. Then, it was identified by morphological and molecular tests. The isolates of B. bassiana secondary metabolites were extracted from its extracellular medium and mycelium with ethyl acetate and acetone and then the efficacy of crude extracts against insect pests (D. micans adults and larvae), (Glyphodes pyloalis larvae and T. pityocampa larvae) was evaluated at concentrations of 500, 2000, and 5000ppm. Consequently, it was determined that the ethyl acetate and acetone extracts of B. bassiana 27b2 showed a 100% lethal effect on D. micans adults and larvae, while the acetone extract showed a 100% lethal effect on T. pityocampa larvae. The data suggest that the secondary metabolites of isolate 27b2 may be utilized as bio-pesticides for the control of these pests. Also, this is the first study examining the lethal effects of secondary metabolites extracted from B. bassiana on T. pityocampa, and D. micans.

Spatial patterns of bark beetle–induced pine mortality on a Mediterranean island: Implications for forest impact assessment

Quantifying the probability of bark beetle induced damage in central German Norway spruce forests

Comprehensive transcriptomic analysis reveals detoxification gene expansion and adaptive genetic variation in the emerging pest Acanthotomicus suncei.

The mountain pine beetle (MPB) exhibits all the hallmarks of a cross-scale disturbance agent, with nonlinear population dynamics driven by positive density-dependent feedbacks that link fast behavioural processes to slow, landscape-level environmental change. Although this feedback loop typically fuels rapid irruption, it can in principle be reversed through sustained population removal. We document such a reversal in Alberta’s commercial pine forest over 2006–2023. No single causal variable effectively captures the collapse mechanism; instead, collapse reflects a syndrome involving two sets of drivers operating at different spatial scales. Intrinsic density-dependent factors include beetle pressure measured at breast-height on the stem, attacks up the height of the stem, and the density of attacked trees in the surrounding cluster. Extrinsic environmental drivers operating at the landscape scale include winter temperatures, drought, pine volumes, and pine ancestry. Despite several million freshly attacked trees detected annually from 2009 to 2012, outbreak expansion did not occur. We explain why the removal of freshly attacked trees is the most plausible explanation for the observed decoupling between r (seasonal recruitment) and R (interannual expansion), which were uncharacteristically uncorrelated throughout 2006–2019. This decoupling indicates that the positive feedback loop linking brood productivity to landscape-level spread was disrupted during the years when it would normally have been strongest. Cold winters in 2018–2020 contributed to the final collapse, but the decisive factor was the earlier disruption of density-dependent feedback through green-tree removal, which limited population growth and tree mortality from 2010 to 2017 and prevented any rebound after 2020. This case illustrates how cross-scale outbreak collapse can be engineered in systems with strong positive feedbacks, and places MPB within a broader class of species whose persistence depends on remaining above population-viability thresholds set by Allee effects. • MPB brood productivity and outbreak spread were decoupled across 2006–2019. • Population removal broke the positive feedback driving beetle irruption. • Cross-scale collapse occurred despite strong density-dependent recruitment. • Cold winters aided collapse, but feedback disruption was the decisive factor. • Five management stages are identified for suppressing irruptive bark beetle systems.

Stored grains are highly vulnerable to insect pests, which can cause significant post-harvest losses worldwide. The invasive bark beetle Pagiocerus frontalis (Coleoptera: Curculionidae: Scolytinae) poses a major threat to maize and avocado seeds, yet the influence of temperature on its biology and damage potential is poorly understood. Here, we examined the effects of six constant temperatures (13, 17, 21, 25, 29, 33°C) on survival, development, reproduction, and grain damage. Beetles thrived under moderately warm conditions (21, 25 and 29°C), with the highest progeny, grain damage, and weight loss at 25°C, while extreme temperatures (13or33°C) suppressed activity and reproduction. These findings clarify the species' thermal preferences and suggest that controlling storage temperature, either by cooling or heat treatment, could reduce pest-induced losses, providing a sustainable, non-chemical strategy for protecting stored grains. This information can also be incorporated into climate-based predictive models to forecast pest survival, establishment, and potential damage.

Bark beetle–fungus associations are essential for nutrition, detoxification, and host colonisation, but their composition and function vary across developmental stages and environmental contexts. Hence, we characterised the fungal communities associated with two pine-feeding bark beetles, Ips sexdentatus (ISX) and Ips acuminatus (IAC), across developmental stages and compared wild-collected and laboratory-bred populations using ITS2 amplicon sequencing. Both beetle species maintained a stable core mycobiome dominated by Kuraishia, Ogataea, Ophiostoma, Graphilbum, and Cyberlindnera. These taxa have been earlier reported to be associated with nutrient provisioning, detoxification of host secondary metabolites, and chemical signalling. Adult beetles showed species-specific community differences, whereas wild-collected beetles, particularly IAC, harboured higher fungal diversity than laboratory populations, indicating a strong environmental effect. Beetles shared more fungal taxa with control wood than with gallery wood, suggesting possible fungal acquisition during feeding and concurrent restructuring of the wood mycobiome during infestation. Monoterpene bioassays with selected yeast symbionts showed differential growth responses to α-pinene, 3-carene, and terpinolene, and their mixture, with the mixture producing stronger inhibition than individual compounds. These yeast symbionts further displayed selective antagonistic activity in vitro against selected filamentous fungi, including entomopathogenic taxa, along with detectable lytic and digestive enzyme activities. Together, our findings highlight a link between community structure, predicted functions, and observed interaction phenotypes, providing a strong basis for future mechanistic studies of beetle–fungus–conifer interactions.

Abstract Outbreaks of bark beetles in recent years often leave large volumes of dead Norway spruce ( Picea abies L.) standing in the forest up to several years before harvest. This study evaluated how standing storage duration (0–4 years) in two German regions (Sauerland and Harz) influenced the development of rot and blue stain, water absorption and durability. The assessment for percentage coverage of fungi on dead trees showed increasing rot with prolonged standing storage, particularly in the uppermost and lowermost stem sections, whereas blue stain coverage did not increase over time. Microscopy did not indicate the occurrence of blue stain fungi to be correlated with the presence of basidiomycete wood-decay fungi, although some blue stained spruce specimens exhibited higher capillary water uptake (CWU) than non-stained wood, which could theoretically improve water availability for decay fungi. However, no significant difference was detected between the CWU of blue stained and non-blue stained groups overall. Durability and decay rate did not differ among trees of investigated standing stored durations in a durability test following EN 113-2 (2021). These results indicated that the blue staining of Norway spruce wood, while affecting water absorption, did not independently elevate the risk of basidiomycete decay. However, the longer the standing storage, the more likely for increased opportunities for mechanical damage, moisture ingress, and subsequent decay.

Defining the invasion boundaries of a non-native bark beetle, Ips amitinus

Forest disturbances are increasingly understood as social-ecological phenomena involving diverse actors. Here, we focused on one of the Europe's largest recent disturbances-the drought-triggered bark beetle outbreak in Central Europe (2017-2022). Based on a survey of 165 respondents, we examined perceived disturbance drivers, response actions, and the alignment between them as an indicator of a value-action gap that is often present in social-ecological and governance systems. Climatic and forest structure-related factors were identified as the dominant drivers, aligning with current scientific understanding, whereas socio-economic and management constraints were perceived as less influential. Reported responses reflected awareness of climate-change risks and involved workforce training, adaptive change in species composition, and water-retention measures. Cause-action alignment was observed in nearly half of respondents, particularly among managers and legal entities. We found a relatively sound understanding of disturbance causes and corresponding responses, likely shaped by recent experience with anunprecedented disturbance impact.

Ips typographus is the most important pest of Norway spruce (Picea abies), responsible for large-scale outbreaks in Central Europe that have led to extensive mortality of spruce stands. Control strategies rely primarily on timely sanitary felling, while other methods, including tree injection, play only a supplementary role. In 2022 and 2023, the efficacy of tree injection with emamectin benzoate was evaluated on Norway spruce. At each of 10 study sites, five trees were injected with 4 mL of 4.5% solution per hole drilled and five control trees were selected. All trees were baited with a pheromone lure to attract I. typographus. Following infestation, trees were debarked at seven sections distributed along the length of the main trunk to record the number and lengths of maternal and larval galleries. While the number of maternal galleries did not significantly differ between treated and control trees, the number of larval galleries was significantly lower in injected trees, suggesting that larvae of I. typographus are more sensitive to the insecticide than adults. Additionally, both maternal and larval galleries were significantly shorter in treated trees compared to control trees. The lengths of galleries, both maternal and larval, decreased progressively toward the top of the tree starting from the third section. The findings of this study suggest that emamectin benzoate injections could be a valuable tool for suppressing the development of I. typographus in Norway spruce. Injected trees can be a more environmentally friendly alternative method to insecticide-treated trap trees. However, further research is required to optimize application protocols and evaluate their long-term efficacy. © 2026 Society of Chemical Industry.

The tight coupling between drought and insect attack threatens trees in a warmer world. Trees with differing levels of hydraulic safety and efficiency likely have different susceptibilities to insect attack, but how the hydraulic architecture of woody tissues moderates the relationship between drought and insects remains unknown at the species scale. Here, we test how hydraulic safety and efficiency, derived from anatomical and isotopic measurements of the stem xylem, coordinate to regulate growth and survival of whitebark pines in the Rocky Mountains, USA. We assess intraspecific and ontogenetic variability in xylem hydraulic traits by comparing trees that survived or were killed during a mountain pine beetle outbreak. At the individual tree scale, we found synergies between safety and efficiency: at the time of the outbreak, trees with higher cell-wall reinforcement and wood density (safety) also had higher average theoretical hydraulic conductivity and carbon-use efficiency (efficiency), and this was associated with higher growth, carbon storage and survival. At the annual timescale, however, we found tradeoffs between safety and efficiency: higher safety was associated with lower efficiency for seven of nine pairwise comparisons. Yet, years that optimized both safety and efficiency showed the most tree growth and carbon storage. The xylem hydraulic traits underlying tree growth and survival were not stationary over time, but prominent differences at the time of the outbreak suggest that both higher hydraulic safety and efficiency were positively associated with resistance against bark beetles. The importance of hydraulic traits to tree survival suggests that tree responses to increasing herbivory will depend on tree responses to climate warming and hydrological changes.

Despite many years of research, it remains challenging to determine why some trees survive bark beetle attacks while others do not. Current theory suggests that survival is predicated by interactions between tree defense systems and climatic drivers, but such interactions are poorly resolved at the scale of individual trees. Using a widespread conifer species (Engelmann spruce, Picea engelmannii) and a lethal phloem-feeding herbivore (North American spruce bark beetle, Dendroctonus rufipennis) as a study system, we characterized tree responses to mass attack across five populations representing a climate gradient in a field experiment. Over the course of a growing season, we measured variation in monoterpene concentrations in the phloem of 100 trees, half of which were challenged with mass attack using pheromone baits. Study trees were visited two years after baiting to record survival, and match survival to constitutive and induced monoterpenes. Our results revealed that regional climate correlated with constitutive, pre-attack concentration of monoterpenes in spruce phloem: a 1 kPa increase in vapor pressure deficit correlated with a doubling of monoterpene concentration. Higher constitutive phloem monoterpene concentrations predicted tree survival: a one-fold increase in concentration was associated with a three-fold increase in the odds of survival. Regional climate did not significantly affect the magnitude of induced response; however, early induction of monoterpenes in phloem distal to attack sites was associated with an average of twofold increase in survival odds, suggesting rapidity of monoterpene induction is a key resistance trait. These findings extend our understanding of climate-defense relationships in this system and indicate that Engelmann spruce tree populations in warmer and drier sites may have traits associated with higher constitutive resistance.

Broadleaf-feeding bark beetles remain far less studied than conifer-infesting species, particularly with respect to their semiochemical orientation and host selection. Here, we investigated the responses of the beech bark beetle Taphrorychus bicolor to host- and non-host-derived volatile organic compounds (VOCs) using field trapping experiments and electrophysiological analyses conducted in the Voděradské bučiny National Nature Reserve (Central Bohemia, Czechia). Pheromone-baited traps were supplemented with plant material from the host Fagus sylvatica or the non-host species Picea abies and Taxus baccata , and relative trap catches and male proportions were evaluated using generalized linear mixed-effects models. Traps baited with pheromone alone captured the highest number of T. bicolor (122,342 individuals), whereas the addition of P. abies branches significantly reduced trap catches and resulted in the lowest proportion of males (14%) among all treatments, suggesting a potential repellent effect of spruce-derived cues. Branches of F. sylvatica and T. baccata did not significantly affect beetle captures compared with the pheromone-only control, indicating the absence of an attractive effect of host-derived volatiles under the experimental conditions used. VOCs emitted by host beech and non-host spruce were collected using dynamic headspace sampling and analyzed by GC–EAD and GC × GC–TOF–MS. Antennal responses in beech samples were elicited by eucalyptol, γ-terpinene, and terpinolene, whereas in spruce samples two unidentified compounds elicited antennal responses, with host identity explaining 41.2% of the variation in antennal response profiles (R 2 = 0.412, p &amp;lt; 0.001). No antennal responses were detected to abundant monoterpenes in either VOC blend. This study provides the first evidence of differential antennal responses to host- and non-host-derived VOCs in T. bicolor , together with behavioral evidence of a potential repellent effect of non-host volatiles, with implications for mixed forest management strategies aimed at reducing bark beetle pressure on beech stands under ongoing climate change.

Histiogaster arborsignis Woodring, 1963 (Acari: Acaridae) is a fungivorous acarid mite whose phoretic deutonymphs commonly disperse on wood-boring insects. Although the mite has been reported from Ips typographus in Germany, its occurrence in Central Europe has been poorly documented. Here, we report the first confirmed record of H. arborsignis associated with the Eurasian spruce bark beetle I. typographus in the Czech Republic and provide new evidence of its ecological roles within bark beetle gallery systems. Deutonymphs carried abundant adherent fungal propagules and transferred viable spores to PDA medium, from which the entomopathogenic fungus Beauveria bassiana (Balsamo-Crivelli, 1835) Vuillemin, 1912 was isolated and identified using multilocus DNA barcoding (ITS, TEF1-α, RPB1). The taxonomic identity of the mite was confirmed by morphology and COI sequencing. Laboratory observations showed that deutonymphs successfully moulted to adults in the presence of fungal colonies and interacted closely with mycelium, indicating the use of fungi as a developmental and nutritional resource. Feeding trials further revealed that adults actively attacked and consumed larvae and pupae of I. typographus within 24 hours, leaving only chitinised remains. Together, these results demonstrate that H. arborsignis is not merely a passive phoretic associate of I. typographus, but a multifunctional component of the bark beetle–mite–fungus system, acting simultaneously as a disperser on adult beetles, a carrier of viable entomopathogenic fungal propagules, and an opportunistic predator of susceptible beetle developmental stages. This newly documented association and regional range extension highlight the need to incorporate acarid mites into ecological and applied frameworks of bark beetle dynamics in European spruce forests.

International timber trade has accelerated the global spread of the invasive red-haired pine bark beetle H. ligniperda, posing persistent challenges to phytosanitary inspection and border biosecurity. Rapid isothermal amplification assays are increasingly deployed in frontline quarantine settings to support timely regulatory decisions. However, their performance under the heterogeneous biological backgrounds typical of traded timber remains insufficiently evaluated, particularly with respect to the practical implications of low-level false-positive signals. We re-evaluated a previously reported isothermal assay for H. ligniperda using conditions that simulate timber transport and routine customs workflows. Fifty non-target arthropod species (predominantly insects), selected from quarantine interception records, were included to represent taxa likely to co-occur in operational contexts. Material from Lema decempunctata consistently generated weak but reproducible amplification signals across replicates. Sanger sequencing excluded contamination, confirming low-level non-target amplification in complex biological matrices. Although the signals were faint, ambiguous results in quarantine settings may trigger shipment detention, confirmatory laboratory testing, or temporary trade restrictions, thereby increasing inspection workload, delaying clearance, and generating avoidable compliance costs. These findings indicate that trade-mediated species assemblages can compromise assay performance beyond expectations derived from conventional taxonomy-based specificity testing. To reduce interpretive uncertainty and associated regulatory burden, we propose a tiered diagnostic workflow combining rapid on-site isothermal screening with specificity-oriented SYBR Green qPCR confirmation. This strategy enhances diagnostic reliability while preserving operational efficiency in applied biosecurity surveillance.

ABSTRACT Capsule The landscape mosaic and increased heterogeneity resulting from a severe forest disturbance (windstorm followed by bark beetle outbreak) in Northern Italy increased suitable habitat for the European Nightjar, primarily due to the newly established shrub cover. Aims In 2024, we investigated the occupancy pattern of the European Nightjar in a forest area in Trentino (Italy) damaged by the Vaia windstorm in 2018 and by a subsequent bark beetle infestation (mainly the Eight-toothed Spruce Bark Beetle Ips typographus). Methods We conducted point count surveys at 52 points across the 200 ha study area, encompassing a range of different types of environments, including intact forest, pre-existing clearings and windthrows caused by the Vaia storm. Results We found a positive effect of shrub coverage on European Nightjar occupancy probability, while other storm-related features, e.g. roots and bare ground, had a positive (yet weak) influence. European Nightjars seemed to benefit from the mosaic of landscape features and increased environmental heterogeneity that have emerged in this post-windstorm forest area, which was previously dominated by closed-canopy conifer trees. Conclusions Future management of the study area and similar sites should consider the ecological opportunities arising from disturbance, and the importance of preserving part of the new clearings with dead wood legacies, in order to build a more resilient and biodiverse forest ecosystem.

Abstract The abundance of forest pest insects such as bark beetles is commonly assessed using pheromone traps emptied at regular intervals. While providing a rough estimate of infestation risk, trap‐based monitoring programmes come with multiple drawbacks, for example notable costs as well as limitations regarding the resolution, timeliness and area‐wide availability of data. Swarming models can overcome these drawbacks—however, such models rely on accurate swarming data. To this aim, we developed a novel automatic pheromone trapping system and applied it to assess swarming intensity of three tree‐killing bark beetle species, that is Ips typographus , Pityogenes chalcographus and Pityokteines curvidens . The recorded data on swarming and related climatic parameters, covering multiple sites and years along an elevation gradient in Southwest Germany, were subsequently used to calibrate predictive swarming models. Temperature was identified as the most significant driver of swarming intensity across all three bark beetle species, showing a strong alignment with established developmental rate curves. Additional factors influencing swarming patterns included global radiation, day of year, study site and pheromone release. The automatic traps deliver highly accurate real‐time data, enabling timely and area‐wide predictions, which can be directly integrated into digital risk assessment tools. Synthesis and applications . Automated trap data help bark beetle management to act more timely and targeted, thereby facilitating an effective mitigation of outbreaks. Moreover, the immediate data transmission makes regular manual trap collections unnecessary. While swarming models cannot quantify absolute trap catches without site‐ and trap‐specific calibration, they provide robust predictions for relative swarming intensity at the stand scale. Integrated into dynamic risk models, they can be seen as the next step towards a digitalization of pest monitoring and are likely to complement or even replace conventional monitoring programmes in the future.