Search Results (105)

Dendroctonus armandi is a major primary pest of Chinese white pine in the Qinling–Bashan forest region. By feeding on the phloem and vectoring symbiotic fungi that cause blue stain in the sapwood, it drives rapid decline and mortality of host trees. As a key wood-boring forest insect, its outbreaks are closely linked to adaptive strategies in energy metabolism. Adipokinetic hormone (AKH) is a highly conserved insect neuropeptide and plays a major role in regulating energy metabolism. This study aimed to determine how the AKH gene regulates energy use in D. armandi under different stress conditions. We cloned the DaAKH gene and its receptor gene, DaAKHR, from D. armandi. DaAKH and DaAKHR showed the highest expression in emerged adults and the lowest levels in pupae. In larvae and in adult males and females, DaAKH transcripts were predominantly expressed in the head, whereas DaAKHR was enriched in the fat body. Under starvation and cold stress, DaAKH and DaAKHR expression were significantly upregulated; under heat stress, expression first increased and then decreased. Across stress treatments, RNAi significantly downregulated DaAKH and DaAKHR expression in D. armandi. Under starvation, RNAi reduced mortality, lowered lipid metabolism, and led to lipid accumulation, thereby mitigating premature energy depletion and starvation-induced death. By contrast, under heat and cold stress, RNAi significantly increased mortality, significantly reduced triglyceride and glycogen consumption, and suppressed metabolism. These results indicate that DaAKH and DaAKHR regulate energy allocation under starvation stress and help maintain adaptive capacity under temperature stress in D. armandi. By tuning energy metabolism, DaAKH and DaAKHR help resist environmental stress and maintain reproduction and population size. This study advances understanding of the physiological responses and molecular mechanisms of D. armandi under stress conditions and provides a new avenue for metabolism-targeted control. Full article

Background: Dendroctonus armandi, an oligophagous beetle primarily infesting Pinus armandii, is geographically restricted and persistent in central China, causing significant ecological and economic losses. However, the intrinsic factors driving its continuous occurrence remain unclear. We examined the genetic variation patterns across the species’ range to explore its phylogeographic structure. Methods: We analyzed mitochondrial DNA sequence (mtDNA) data to assess population genetic structure and estimate the divergence times of distinct lineages. Results: Phylogenetic analysis identified four haplogroups corresponding to the Minshan (MSM), Qinling (QLM), Micang (MCM), and Ta-pa (TPM) Mountains. Demographic analyses revealed that QLM and TPM haplogroups have undergone population expansion events. Divergence time estimates indicated four lineages diverged during the Late Pleistocene. Notably, D. armandi may have followed two horizontal and one vertical independent colonization routes. The first route extended from MSM into QLM and then spread eastward along the QLM; the second route progressed from MSM into MCM and continued eastward into TPM; and the third route migrated southward from QLM into TPM. Conclusions: Climate oscillations, geographical isolation, and the patchy distribution of host trees collectively shaped the phylogeographic patterns of D. armandi. These findings elucidate the evolution and adaptability of D. armandi in mountainous environments. Full article

To elucidate the effect of cold stress on Dendroctonus valens larvae, a study was conducted under controlled laboratory conditions to examine the physiological and biochemical mechanisms associated with cold stress, coupled with transcriptome sequencing. Physiological and biochemical assessments indicated stable water content in larvae during cold stress initiation, with triglycerides and fats serving as primary energy reserves that decreased over cold stress progression. Glycogen and trehalose were identified as energy sources for larval energy metabolism, with their levels increasing as cold stress duration extended. Superoxide dismutase (SOD) activity exhibited an initial decline followed by an increase, while peroxidase (POD) activity initially rose before decreasing over induction time, and catalase (CAT) activity decreased during cold stress induction. Transcriptome sequencing at various time points revealed 4630 upregulated and 1554 downregulated genes, predominantly involved in metabolic pathways such as carbohydrate, amino acid, and lipid metabolism. Quantitative polymerase chain reaction (qPCR) results validated the transcriptome data accuracy. This investigation delineated the physiological, biochemical, and transcriptome alterations during cold stress, offering a theoretical framework for the rational prediction of Dendroctonus valens outbreaks. Full article

Bark beetles depend on detoxifying enzymes to counteract the defensive terpenoids produced by host trees. Insect ABC transporters play a critical role in the detoxification of insecticides and plant secondary metabolites. However, the specific functions of ABC genes in the metabolism of host allelochemicals remain unclear in D. armandi. In this study, we observed that verapamil significantly enhanced the mortality of host allelochemicals in beetles, indicating that ABC transporter genes are involved in the metabolism of monoterpenes by D. armandi. We then sequenced and characterized the full-length cDNAs of three ABCH subfamily genes (DaABCH1–DaABCH3) from D. armandi. Spatiotemporal expression profiling revealed that all three genes were upregulated during developmental transitions (egg to larva and pupa to adult) and tissue-specific enrichment in detoxification-related organs (Malpighian tubules, fat body, and midgut). Additionally, DaABCH3 expression was detected in the hindgut and brain. Furthermore, DaABCH1 and DaABCH2 were significantly induced by treatment with α-pinene and limonene, whereas DaABCH3 was induced by β-pinene and limonene. Importantly, silencing DaABCH1 significantly increased mortality in adults fumigated with α-pinene and limonene. These results strongly suggest that DaABCH1 acts as a key regulator modulating D. armandi’s sensitivity to host plant allelochemicals. This finding provides a conceptual basis for developing novel control strategies against this economically significant forest pest. Full article

Fungi and bacteria associated with bark beetles can facilitate successful tree colonization, and, in some cases, these fungi act as pathogens of trees. The red turpentine beetle (RTB, Dendroctonus valens) is a bark beetle native to North America that colonizes stressed pines, rarely killing healthy trees. The fungal communities associated with RTB adults, larval galleries, and control tree phloem from red pine (Pinus resinosa) and white pine (P. strobus) forests in the Great Lakes region of the United States were characterized using both culture-independent and culture-dependent methods. Similarly, the bacterial communities associated with RTB adults in the same region were characterized using a culture-independent method. There were significant differences between the adult beetle fungal communities and the tree-based fungal communities. Culture-independent sequencing of RTB adults showed high abundances of the fungal order Filobasidiales (red pine: 28.71% relative abundance, white pine: 6.91% relative abundance), as well as the bacterial orders Enterobacterales (red pine: 53.72%, white pine: 22.15%) and Pseudomonadales (red pine: 15.86%, white pine: 12.91%). In contrast, we isolated high amounts of fungi in the orders Pleosporales (red pine: 21.79%, white pine: 15.90%) and Eurotiales (red pine: 15.38%, white pine: 16.51%) from the adult beetles by culturing. Culture-independent sequencing of beetle galleries yielded high abundances of fungi in the orders Helotiales (red pine: 22.23%, white pine: 23.21%), whereas culture-based isolation from the same galleries yielded high amounts of Eurotiales (red pine: 17.91%, white pine: 17.91%), Hypocreales (red pine: 16.42%, white pine: 16.42%), and Ophiostomatales (red pine: 23.39%, white pine: 23.39%). This contrasts with the culture-independent method, where, likely due to limitations in the sequencing method, the Ophiostomatales accounted for only around 2% of the fungi from RTB galleries in both pine species. We observed a high species-level diversity of Ophiostomatales associated with RTB, isolating 14 species from the Great Lakes region. Leptographium terebrantis, a species that has been described in association with RTB throughout the United States, was the most common species (e.g., >35% of the Ophiostomatales relative abundance in red pine environments and >14% of the Ophiostomatales relative abundance in the white pine environment). This study enhances our understanding of RTB-associated fungi and bacteria in the beetle’s native range at both the community and species levels. Full article

Dendroctonus armandi is a native bark beetle that infests healthy Pinus armandii Franch. in western China. The complex symbiotic relationships with diverse microbes are critical to hosts for survival and outbreak dynamics. Understanding the potential functions and assembly metabolisms of these symbiotic microbes to host colonization are therefore crucial. Metagenomic analysis revealed that gut microbial communities differed from cuticular ones significantly. The cuticle exhibited greater fungal diversity, while the gut supported a significantly higher bacterial diversity. Our findings indicated that gut unclassified Burkholderiales, Escherichia, Bacteroides and Prevotella may play a crucial role in degrading terpenes, phenols and polysaccharides rather than cuticular microbes. Stochastic processes appeared to be served as the primary drivers shaping the core microbial community structures. Cuticular dominant and functional microbial community assemblies except for Escherichia may be primarily driven by stochasticity to adapt the unstable habitats. The direct comparison of gut and cuticular microbiomes may provide valuable insights into the specific functions of symbiotic microbes, and offer critical molecular data for broader understanding of symbiotic relationship between bark beetles and microbes. Full article

Tree phenotypes vary because of genotype–climate interactions, and this variation influences host selection by tree-killing bark beetles. As climate-driven bark beetle outbreaks intensify, identifying phenotypic traits that best predict resistance or susceptibility is critical. We examined genetic variation, secondary chemistry, growth rates, and climate sensitivity in interior ponderosa pine (Pinus ponderosa var. scopulorum Engelm.) at two sites in the Black Hills—Devils Tower National Monument (DETO), Wyoming, and Wind Cave National Park (WICA), South Dakota—experiencing low-moderate levels of mountain pine beetle (Dendroctonus ponderosae Hopkins) activity. Genetic structure differed between sites. At DETO, large and small trees formed a single genetic cluster, whereas at WICA, two clusters emerged, one consisting of large trees and another comprising both small and large trees. The concentrations of some terpenes also differed between sites. Compared to beetle-killed trees, surviving trees exhibited distinct lifelong growth patterns and greater sensitivity to climate. Notably, surviving trees showed significant correlations of growth with climate variables, while beetle-killed trees were relatively insensitive. Long-term responsiveness of growth to climate was a stronger predictor of tree susceptibility to beetles than responses in years just before attacks occurred. These findings suggest trees with lower sensitivity to climate may be more vulnerable to beetle attack under changing climatic conditions. Full article

Background/Objectives: Within their host trees, mountain pine beetles (MPBs, Dendroctonus ponderosae) interact with many fungal species, each releasing a unique profile of volatile organic compounds (VOCs). The FVOCs released by the two primary symbionts of MPBs, Grosmannia clavigera and Ophiostoma montium, have been found to enhance MPB attraction in the field and laboratory studies. Opportunistic, saprophytic fungal species, such as Aspergillus sp. and Trichoderma atroviride, are also common in MPB galleries and can negatively impact MPB fitness. However, little is known about the FVOCs produced by these fungal species and how they may impact MPB feeding and attraction. Methods: To address this knowledge gap, we characterized the FVOC profile of T. atroviride, and performed bioassays to test the effects of its FVOCs on MPB attraction and feeding activity. Results: Our chemical analysis revealed several FVOCs from T. atroviride known to inhibit the growth of competing fungal species and impact subcortical-beetle attraction. Conclusions: From those FVOCs, we recommended four compounds—2-pentanone, 2-heptanone, 2-pentanol, and phenylethyl alcohol—for use in future field tests as anti-attraction lures for MPBs. In bioassays, we also observed strong MPB repellency from FVOCs released by T. atroviride, as well as the mild effects of FVOCs on MPB feeding activity. Our findings highlight the potential for these FVOCs to be utilized in the development of more effective MPB anti-attractant lures, which are crucial for the monitoring and management of low-density MPB populations. Full article

Spruce beetle (Dendroctonus rufipennis (Kirby)) is a major cause of spruce (Picea spp.) mortality in western North America. We synthesized the literature on the chemical ecology of spruce beetle, focusing on efforts to reduce host tree losses. This literature dates back to the mid-20th century and focuses on spruce beetle populations in Alaska, U.S., western Canada, and the central and southern Rocky Mountains, U.S. Spruce beetle aggregation pheromone components include frontalin (1,5-dimethyl-6,8-dioxabicyclo[3.2.1]octane), seudenol (3-methyl-2-cyclohexen-1-ol), MCOL (1-methyl-2-cyclohexen-1-ol), and verbenene (4-methylene-6,6-dimethylbicyclo[3.1.1]hept-2-ene). The attraction of spruce beetle to one aggregation pheromone component is enhanced by the co-release of other aggregation pheromones and host compounds (e.g., α-pinene). Several baits that attract spruce beetles are commercially available and are used for survey and detection, population suppression, snag creation, and experimental purposes. The antiaggregation pheromone is MCH (3-methyl-2-cyclohexen-1-one), which has been evaluated for reducing colonization of felled spruce since the 1970s. Beginning in the early 2000s, MCH has been evaluated for protecting live, standing spruce from colonization by and mortality attributed to spruce beetle. With a few exceptions, significant reductions in levels of spruce beetle colonization and/or spruce mortality were reported. More recent efforts have combined MCH with other repellents (e.g., nonhost compounds) in hope of increasing levels of tree protection. Today, several formulations of MCH are registered for tree protection purposes in the U.S. and Canada. Full article

The mountain pine beetle Dendroctonus ponderosae (Curculionidae: Scolytinae) (MPB) is one component of an intensively studied co-evolved insect–host system. We investigated the spatial genetic structure of the MPB within its historic and recent geographic range expansion as it relates to host use in western North America using 13 pre-selected microsatellite loci. Analysis of molecular variation (AMOVA) indicates that genetic structure is not correlated with the host tree species and therefore does not support the hypothesis of the formation of a host race within this species. STRUCTURE analysis delineates four main clusters in western North America: (1) northern: northern British Columbia/northern Alberta; (2) central: southern British Columbia/southern Alberta/Washington/Idaho/Montana; (3) southwestern: Oregon/California/Nevada; and (4) southeastern: Utah/Wyoming/Arizona/Colorado/South Dakota. Heterozygosity, allelic richness, and the number of private alleles are greatest in the Southwest cluster. This cluster correlates with one of the three refugia hypothesized from a recent analysis of neo-Y haplotypes and represents an important reservoir of MPBs’ genetic diversity. Full article

Wildfire activity in the western U.S. has highlighted the importance of effective management to address this growing threat. The Lookout Mountain Thinning and Fuels Reduction Study (LMS) is an operational-scale, long-term study of the effects of forest restoration and fuel reduction treatments in ponderosa pine (Pinus ponderosa Dougl. ex Laws.) and mixed-conifer forests in central Oregon, U.S. The broad objectives of the LMS are to examine the effectiveness and longevity of treatments on wildfire risk and to assess the collateral effects. Treatments include four levels of overstory thinning followed by mastication of the understory vegetation and prescribed burning. Stands were thinned to residual densities of 50, 75, or 100% of the upper management zone (UMZ), which accounts for site differences as reflected by stand density relationships for specific plant communities. A fourth treatment combines the 75 UMZ with small gaps (~0.1 ha) to facilitate regeneration (75 UMZ + Gaps). A fifth treatment comprises an untreated control (UC). We examined the causes and levels of tree mortality that occurred 2–9 years after treatments. A total of 391,292 trees was inventoried, of which 2.3% (9084) died. Higher levels of tree mortality (all causes) occurred on the UC (7.1 ± 1.9%, mean ± SEM) than on the 50 UMZ (0.7 ± 0.1%). Mortality was attributed to several bark beetle species (Coleoptera: Curculionidae) (4002 trees), unknown factors (2682 trees), wind (1958 trees), suppression (327 trees), snow breakage (61 trees), prescribed fire (19 trees), western gall rust (15 trees), cankers (8 trees), mechanical damage (5 trees), dwarf mistletoe (4 trees), and woodborers (3 trees). Among bark beetles, tree mortality was attributed to western pine beetle (Dendroctonus brevicomis LeConte) (1631 trees), fir engraver (Scolytus ventralis LeConte) (1580 trees), mountain pine beetle (Dendroctonus ponderosae Hopkins) (526 trees), engraver beetles (Ips spp.) (169 trees), hemlock engraver (Scolytus tsugae (Swaine)) (77 trees), and Pityogenes spp. (19 trees). Higher levels of bark beetle-caused tree mortality occurred on the UC (2.9 ± 0.7%) than on the 50 UMZ (0.3 ± 0.1%) which, in general, was the relationship observed for individual bark beetle species. Higher levels of tree mortality were attributed to wind on the 100 UMZ (1.0 ± 0.2%) and UC (1.2 ± 1.5%) than on the 50 UMZ (0.2 ± 0.02%) and 75 UMZ (0.4 ± 0.1%). Higher levels of tree mortality were attributed to suppression on the UC (0.5 ± 0.3%) than on the 50 UMZ (0.003 ± 0.002%) and 75 UMZ + Gaps (0.0 ± 0.0%). Significant positive correlations were observed between measures of stand density and levels of tree mortality for most causal agents. Tree size (diameter at 1.37 m) frequently had a significant effect on tree mortality, but relationships varied by causal agent. The forest restoration and fuels reduction treatments implemented on the LMS increased resistance to multiple disturbances. The implications of these and other results to the management of fire-adapted forests are discussed. Full article

The pine bark beetle is a devastating forest pest, causing significant forest losses worldwide, including 25% of pine forests in Honduras. This study focuses on Dendroctonus frontalis and Ips spp., which have affected four of the seven native pine species in Honduras: Pinus oocarpa, P. caribaea, P. maximinoi, and P. tecunumanii. Artificial intelligence (AI) is an essential tool for developing susceptibility models. However, gaps remain in the evaluation and comparison of these algorithms when modeling susceptibility to bark beetle outbreaks in tropical conifer forests using Google Earth Engine (GEE). The objective of this study was to compare the effectiveness of three algorithms—random forest (RF), gradient boosting (GB), and maximum entropy (ME)—in constructing susceptibility models for pine bark beetles. Data from 5601 pest occurrence sites (2019–2023), 4000 absence samples, and a set of environmental covariates were used, with 70% for training and 30% for validation. Accuracies above 92% were obtained for RF and GB, and 85% for ME, along with robustness in the area under the curve (AUC) of up to 0.98. The models revealed seasonal variations in pest susceptibility. Overall, RF and GB outperformed ME, highlighting their effectiveness for implementation as adaptive approaches in a more effective forest monitoring system. Full article

Bark beetle-associated bacteria from the sub-boreal and boreal forests of northern Canada represent a largely unexplored source of bioactive natural products. This study aims to investigate the chemical potential of bacteria isolated from Dendroctonus ponderosae, Dendroctonus rufipennis, Dendroctonus pseudotsugae, and Ips perturbatus by focusing on nitrogen-containing secondary metabolites. Genomic analyses of the bacterial isolates identified diverse biosynthetic gene clusters (BGCs), including nonribosomal peptides (NRPs), NRPS-PKS hybrids, and ribosomally synthesized and post-translationally modified peptides (RiPPs), many of which exhibit low sequence homology, suggesting potential for novel bioactive compounds. Nitrogen-15 NMR spectroscopy was employed to detect nitrogen-containing functional groups in crude extracts, revealing distinct signals for amides, amines, and nitrogen heterocycles. The combination of BGC predictions and NMR data highlighted the genetic and chemical diversity of these bacteria and underscored the potential for discovering novel nitrogen-rich metabolites. These findings provide a foundation for further exploration of bioactive natural products with pharmaceutical and agrochemical applications and potential to contribute to the understanding of the chemical ecology of bark beetle–microbe interactions in northern ecosystems. Full article

Foresters and natural resource managers are increasingly exploring opportunities for the early detection of emerging forest health concerns. One of these emerging concerns is the eastern larch beetle (ELB, Dendroctonus simplex LeConte), a native insect of tamarack (Larix laricina (Du Roi) K., Koch). Historically, the ELB attacked only dead or dying trees, but with climate change, it is now becoming a damaging disturbance agent that affects healthy trees as well. This shift creates a need to evaluate the methods used to detect and quantify the impacted areas. In northern Wisconsin, USA, 50 tamarack stands or aerial detection polygons were surveyed in the field during the 2023 growing season to explore different detection tools for ELBs. We visited 20 polygons identified by aerial sketch map surveys as having ELB mortality, 20 tamarack stands identified by the Astrape satellite imagery algorithm as disturbed, and 10 randomly selected stands from the Wisconsin forest inventory database (WisFIRs) for landscape-level context. For each of the detection methods and the Random stands, information on species composition, mortality, signs of ELB, invasive species, and water presence was quantified. ELBs were common across the landscape, but were not always associated with high levels of mortality. While overstory tree mortality was frequently observed in both aerial sketch map surveys and Astrape, it was not always linked to tamarack mortality. Current methods of detection may need to be re-evaluated in this environment. Tamarack stands in northern Wisconsin were highly heterogeneous in species, which is likely contributing to the difficulties in identifying both tamarack mortality and tamarack mortality specifically caused by ELBs across the two detection methods. Given the evolving impacts of climate change and the shifting dynamics between forests and insects, it is essential to evaluate and innovate detection methods to manage these ecosystems effectively. Full article

The red turpentine beetle Dendroctonus valens is an invasive forest pest that has been rapidly spreading northward since its introduction in China. Some ophiostomatalean associates of D. valens are essential contributing factors for this beetle to become an aggressive pine killer in China. In this study, a survey was conducted in a new invasive area of this beetle’s habitat in Liaoning Province. A total of 126 ophiostomatalean fungal associates of D. valens were isolated. Based on the combination of morphological characteristics and phylogeny, these isolates were identified as Ceratocystiopsis jianpingensis sp. nov., along with two new records, Leptographium terebrantis and Ophiostoma gilletteae. Ophiostoma gilletteae was the dominant species, with an isolation rate of 85.7%. The results of this study show that more shared ophiostomatalean fungi are associated with D. valens in China and North America, and accumulate resources for the development of fungal associate-mediated bark beetle management strategies. Full article