Entomologist Jiri Hulcr and science journalist Marc Abrahamsoffer a funny and informative introduction to the bark beetle, one of theworld's most maligned, misunderstood, and fascinating insects.
Early detection of bark- and wood-boring beetles is critical to support the eradication of recently established populations in novel regions. Flight intercept traps baited with semiochemical lures ...are essential for surveillance and population monitoring of introduced insects. We present laboratory and field data to test potential improvements in trap sensitivity to detect Hylastes ater (Paykull), Hylurgus ligniperda (Fabricius) (Coleoptera:Scolytinae), and Arhopalus ferus (Mulsant) (Coleoptera:Cerambycidae). We evaluated the effects of type and permeability of plastic material on release rates of host-plant volatiles and the addition of the pheromone racemic E-fuscumol on beetle species catch within an exotic Pinus radiata (D. Don) plantation forest. We trapped 228,278 H. ligniperda, 91 H. ater, and 2,504 A. ferus over two experiments. Our results show strong attraction of H. ligniperda to host-plant volatiles with a positive relationship between increased release rates and trap catch. H. ater follows this trend, with attraction to ethanol and (-)-beta-pinene. H. ligniperda was more strongly attracted to host volatiles than H. ater, the average ratio between baited and unbaited traps being 51.25:1 and 3.75:1, respectively for each species. There was no effect of host-plant volatiles or release rate on A. ferus catch, but a weak attraction by A. ferus to racemic E-fuscumol. Overall, we demonstrate speciesspecific differences in Coleoptera attraction to host-plant volatile release rates and semiochemical blends. Results demonstrate mechanisms to improve trap catch of H. ligniperda and H. ater. Racemic E-fuscumol shows some promise for A. ferus, but further investigation is required to determine whether chirality affects attraction. Key words: lure, release-rate, fuscumol, wood borer, bark beetle
•The Czech Republic has become an epicentre of bark beetle outbreaks in Europe.•We identified the transition from wind- to drought-driven outbreak dynamics.•The outbreak triggered a cascade of social ...impacts restricting management operations.•Effective responses require fundamental changes in the regional forest-based sector.
Outbreaks of tree-killing insects are intensifying globally, affecting economies, human well-being, and driving ecosystem transitions. The Czech Republic has recently become Europe’s epicenter of the outbreak of spruce bark beetle Ips typographus, the most aggressive species in Eurasia. We investigated a countrywide outbreak dynamic during the period 2003–2019, with a special focus on the period 2017–2019 when the outbreak reached an unprecedented intensity. In order to identify main outbreak drivers, we investigated annual time series of the volume of trees killed by bark beetles in the Czech districts (n = 77), and a suite of climatic and forest structure-related predictors using Generalized Additive Models. Finally, we reviewed a large body of public materials to understand broader social, ecological, and economic implications of the outbreak.
We found that bark beetles were damaging 0.2–1.4% of Norway spruce growing stock annually across the Czech Republic in the period 2003–2016. This level increased to 3.1–5.4% in 2017–2019, causing the total depletion of spruce in some regions. The long-term bark beetle dynamics (2003–2019) was driven by the combination of wind disturbance and climatic drivers, represented in our study by annual temperature anomaly and Standardized Precipitation-Evapotranspiration Index. However, the effect of wind was diminished during the period 2017–2019, whereas the effect of drought dominated. Our findings thus suggest a transition from wind- to drought-driven bark beetle dynamics.
The outbreak and subsequent large-scale salvaging and wood transportation affected quality of life of people in a broad vicinity of outbreak areas. Extensive management actions aggravated some of the notorious conflicts between forest management and nature conservation, and highlighted the poor harmonization of respective policies. A decrease in timber price, an excessive workload, and other cascading effects caused severe revenue loss, requiring state interventions amounting to ca 260 million EUR in 2018–2019.
We suggest that increasing frequency of climate extremes in combination with the unfavorable forest structure pushed Central European spruce forests to the margin of their ecological space and unfolded large-scale forest transformations. Effective responses will require fundamental structural changes in the regional forest-based sector, particularly aiming at increased social and ecological resilience.
Ips sexdentatus, also known as the six-toothed spruce bark beetle, is a species that primarily colonizes spruce trees (Pinaceae) across Eurasia. While not yet recorded outside of its native range, it ...was listed the 2023 Priority Pest List designed by USDA’s Animal and Plant Health Inspection Service and has a high invasion potential to the North American continent.
Polyphosphates (PolyP), i.e. phosphate polymers, are commonly found in pure cultures of various microorganisms. Although they have been the subject of intensive microbiological research in the past, ...they have never been directly studied in species-rich soil microbial communities. So far, there are only few studies indirectly suggesting that soil microorganisms build up PolyP as a storage for phosphorus (P), and use them when soil P availability decreases. We attempted to provide direct evidence for PolyP presence in soil microorganisms, and test if the PolyP can be detected in the soil microbial biomass P pool applying the standard chloroform-fumigation extraction method. Twelve different soil samples were collected along the gradient of forest recovery after the bark beetle outbreak in the catchments of two adjacent glacier lakes (Plešné and Čertovo, Bohemian forest, Czech Republic). The presence of PolyP in the samples was assessed by staining in a manipulative experiment designed to deplete any PolyP present. Carbon (C), nitrogen (N), and P in the microbial biomass were estimated by the chloroform-fumigation extraction method and soil slurries of fresh samples stained by the Neisser method. The soils were then mixed with sterile sand and supplemented with growth medium without P. The rate of growth of microbial biomass was estimated from oxygen consumption during one week incubation at dark. After one week, the microbial biomass C, N, and the P were estimated again and samples stained. The combination of the incubation experiment and staining proved that the soil microorganisms in the collected samples contained PolyP and that PolyP were used to achieve maximum growth rate under P-limited conditions. The C to N to P ratio increased significantly over one week of incubation reflecting the changing PolyP content. To further confirm that the fumigation extraction method is sensitive to PolyP content, manufactured PolyP was added to all soils at different steps of the fumigation extraction method, and its recovery was estimated. Recovery ranged from 80 to 100%. Abiotic depolymerisation at acidic conditions required for the correct quantification of P-PO
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using molybdenum-blue method was very likely responsible for half of the recovery, the remaining being enzymatic depolymerisation. We conclude that PolyP are ubiquitous in soils and affect microbial biomass P estimation. The high recovery rate of PolyP around 90% implies that presence of PolyP can cause a significant overestimation of the microbial biomass P when typical correction factor 0.4 is used.
•48.9% of trees died.•Pinus ponderosa exhibited the highest levels of mortality (89.6%), with 39.4% of plots losing all P. ponderosa.•Mortality of P. ponderosa was highest at the lowest elevations, ...concentrated in large trees, and attributed mostly to Dendroctonus brevicomis.•Tree regeneration was dominated by Calocedrus decurrens and Quercus spp., representing a potential shift in composition from forests dominated by P. ponderosa.•Tree mortality was positively correlated with tree density and slope.
Much of California, U.S. experienced a severe drought in 2012–2015 inciting a large tree mortality event in the central and southern Sierra Nevada. We assessed causal agents and rates of tree mortality, and short-term impacts to forest structure and composition based on a network of 11.3-m fixed-radius plots installed within three elevation bands on the Eldorado, Stanislaus, Sierra and Sequoia National Forests (914–1219, 1219–1524 and 1524–1829 m on the Eldorado, Stanislaus, Sierra; 1219–1524, 1524–1829, and 1829–2134 m on the Sequoia), where tree mortality was most severe. About 48.9% of trees died between 2014 and 2017. Tree mortality ranged from 46.1 ± 3.3% on the Eldorado National Forest to 58.7 ± 3.7% on the Sierra National Forest. Significantly higher levels of tree mortality occurred in the low elevation band (60.4 ± 3.0%) compared to the high elevation band (46.1 ± 2.9%). Ponderosa pine, Pinus ponderosa Dougl. ex Laws., exhibited the highest levels of tree mortality (89.6%), with 39.4% of plots losing all P. ponderosa. Mortality of P. ponderosa was highest at the lowest elevations, concentrated in larger-diameter trees, and attributed primarily to colonization by western pine beetle, Dendroctonus brevicomis LeConte. About 89% of P. ponderosa in the three largest diameter classes were killed, representing loss of an important structural component of these forests with implications to wildlife species of conservation concern. Sugar pine, P. lambertiana Dougl., exhibited the second highest levels of tree mortality (48.1%). Mortality of P. lambertiana was concentrated in the mid-diameter classes and attributed primarily to colonization by mountain pine beetle, D. ponderosae Hopkins. White fir, Abies concolor (Gord. & Glend.) Lindl. ex Hildebr., and incense cedar, Calocedrus decurrens (Torr.) Florin, exhibited 26.3% and 23.2% mortality, respectively. Only one Quercus died. Tree mortality (numbers of trees killed) was positively correlated with tree density and slope. A time lag was observed between the occurrence of drought and the majority of tree mortality. Tree regeneration (seedlings and saplings) was dominated by C. decurrens and Quercus spp., representing a potential long-term shift in composition from forests that were dominated by P. ponderosa. About 22.2% of plots contained plant species considered invasive, including cheatgrass, Bromus tectorum L., ripgut brome, Bromus diandrus Roth, bull thistle, Cirsium vulgare (Savi) Ten., and yellow star-thistle, Centaura solstitalis L. The implications of these and other results to recovery and management of drought-impacted forests in the central and southern Sierra Nevada are discussed.
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.
•Synchronous western balsam bark beetle (WBBB) outbreaks in British Columbia caused widespread mortality to subalpine fir between 1998 and 2019.•P(WBBB) was positively related to volume of fir within ...8 km and within a 1 km2 pixel.•A longer growing season, increased degree day accumulation, and drought increased the probability of WBBB outbreak.•Irruptive populations did not appear to exhibit landscape scale spread.•Over the last 20 years, WBBB has moved northward and upward as a result of an increased growing season and increased degree day accumulation at high latitudes and elevations.
Warming temperatures and drought are leading to unprecedented irruptions of forest insects worldwide. Altered climatic regimes have the potential to allow native forest insects to express novel behaviors and expand in latitude and elevation beyond their hypothesized thermal tolerances. Yet, disentangling the drivers of novel behaviors and range expansions is difficult due to cross-scalar interactions that dictate forest insect population dynamics. We investigated the irruptive dynamics of western balsam bark beetle (Dryocoetes confusus Swaine), which undergoes intermittent, long-lasting, but low-severity outbreaks in subalpine fir (Abies lasiocarpa Hook) forests. We compiled data from 1998 to 2019 across British Columbia, Canada, at 1 and 16 km2 resolutions to describe the spatiotemporal structure of beetle outbreaks, predict the landscape susceptibility to outbreaks, explain when outbreaks occur based on bioclimatic drivers, explore whether beetle populations exhibit self-driving growth, and determine whether the extent of outbreaks has increased. Overall, we found that outbreaks occur in discrete clusters and are synchronous at distances of 10–25 km. Further, we found that landscape susceptibility to beetle outbreaks was best explained by latitude*elevation (i.e., the product of latitude m and elevation m Z-standardized) and volume of fir (m3/ha; >17.5 cm size class; >100 yrs.) both within 8 km and each pixel. Meanwhile, a longer growing season, increased growing degree day accumulation, and drought best explained when outbreaks occurred. Further, we did not find evidence to suggest that beetle populations exhibit self-driving population growth. Finally, we found that the extent of beetle outbreaks has increased over the last 20 years and that increases in landscape susceptibility primarily occurred at higher latitude*elevations and were best explained by an increase in the mean growing season and degree day accumulation. In other words, abnormally warm temperatures have facilitated a northward and upward expansion of western balsam bark beetle. Collectively, these results serve as the first quantification of the spatiotemporal dynamics of this understudied insect and support previous modeling efforts to investigate the multi-scale drivers of western balsam bark beetle outbreaks. We propose that future work should identify specific supercooling points, the relationship between temperature and development rate, and how the relatively high within-stand variability in age and size class of subalpine fir affect the irruptive dynamics of this understudied bark beetle.
