G-Protein Coupled Receptor Gpr-1 Is Important for the Growth and Nutritional Metabolism of an Invasive Bark Beetle Symbiont Fungi Leptographium procerum.

Leptographium procerum has been demonstrated to play important roles in the invasive success of red turpentine beetle (RTB), one of the most destructive invasive pests in China. Our previous studies found that bacterial volatile ammonia plays an important role in the maintenance of the RTB-L. procerum invasive complex. In this study, we found a GPCR gene Gpr-1 that was a response to ammonia but not involved in the ammonia-induced carbohydrate metabolism. Deletion of Gpr-1 significantly inhibited the growth and pathogenicity but thickened the cell wall of L. procerum, resulting in more resistance to cell wall-perturbing agents. Further analyses suggested that Gpr-1 deletion caused growth defects that might be due to the dysregulation of the amino acid and lipid metabolisms. The thicker cell wall in the ΔGpr-1 mutant was induced through the cell wall remodeling process. Our results indicated that Gpr-1 is essential for the growth of L. procerum by regulating the nutritional metabolism, which can be further explored for potential applications in the management of RTB.

The essential role of arginine biosynthetic genes in lunate conidia formation, conidiation, mycelial growth, and virulence of nematophagous fungus, Esteya vermicola CBS115803.

BACKGROUND: The pinewood nematode (Bursaphelenchus xylophilus) causes severe damage to pine trees. The nematophagous fungus, Esteya vermicola, exhibits considerable promise in the biological control of Bursaphelenchus xylophilus due to its infectivity. Notably, the lunate conidia produced by E. vermicola can infect Bursaphelenchus xylophilus. In the study, we aim to investigate the genes involved in the formation of the lunate conidia of E. vermicola CBS115803. RESULTS: Esteya vermicola CBS115803 yielded 95% lunate conidia on the complete medium (CM) and 86% bacilloid conidia on the minimal medium (MM). Transcriptomic analysis of conidia from both media revealed a significant enrichment of differentially expressed genes in the pathway related to 'cellular amino acid biosynthesis and metabolism'. Functional assessment showed that the knockout of two arginine biosynthesis genes (EV232 and EV289) resulted in defects in conidia germination, mycelial growth, lunate conidia formation, and virulence of E. vermicola CBS115803 in Bursaphelenchus xylophilus. Remarkably, the addition of arginine to the MM improved mycelial growth, conidiation and lunate conidia formation in the mutants and notably increased conidia yield and the lunate conidia ratio in the wild-type E. vermicola CBS115803. CONCLUSION: This investigation confirms the essential role of two arginine biosynthesis genes in lunate conidia formation in E. vermicola CBS115803. The findings also suggest that the supplementation of arginine to the culture medium can enhance the lunate conidia yield. These insights contribute significantly to the application of E. vermicola CBS115803 in managing Bursaphelenchus xylophilus infections. © 2023 Society of Chemical Industry.

Transcriptomic analysis of the fungus Graphilbum sp. in response to the pine wood nematode.

Graphilbum species are important blue stain fungi associated with pine trees and are widely distributed throughout Asia, Australia, and North Africa. Pine wood nematode (PWN) primarily feed on ophiostomatoid fungi such as Graphilbum sp. in wood, the population of PWNs was increased, and incomplete organelle structures were observed in Graphilbum sp. hyphal cells following exposure to PWNs. In this study, we showed that Rho and Ras were involved in the MAPK pathway, SNARE binding and small GTPase-mediated signal transduction, and their expression was upregulated in the treatment group. However, the expression of the Rab7 involved in MAPK and small GTPase-mediated signal pathway was downregulated in the treatment group. Thus, further research is needed to study the MAPK pathway and related Ras and Rho genes in Graphilbum sp. associated with the PWN population. Overall, transcriptomic analysis clarified the basic mechanisms of mycelial growth in Graphilbum sp. fungus used as a food source by PWNs.

Nutritional Profile and Ecological Interactions of Yeast Symbionts Associated with North American Spruce Beetle (Dendroctonus rufipennis).

To better understand functional ecology of bark beetle-microbial symbioses, we characterized yeast associates of North American spruce beetle (Dendroctous rufipennis Kirby) across populations. Seven yeast species were detected; Wickerhamomyces canadensis (Wickerham) Kurtzman et al. (Sachharomycetales: Saccharomycetaceae) was the most common (74% of isolates) and found in all populations. Isolates of W. canadensis were subsequently tested for competitive interactions with symbiotic (Leptographium abietinum, = Grosmannia abietina) and pathogenic (Beauvaria bassiana) filamentous fungi, and isolates were nutritionally profiled (protein and P content). Exposure to yeast headspace emissions had isolate-dependent effects on colony growth of symbiotic and pathogenic fungi; most isolates of W. canadensis slightly inhibited growth rates of symbiotic (L. abietinum, mean effect: - 4%) and entomopathogenic (B. bassiana, mean effect: - 6%) fungi. However, overall variation was high (range: - 35.4 to + 88.6%) and some yeasts enhanced growth of filamentous fungi whereas others were consistently inhibitory. The volatile 2-phenylethanol was produced by W. canadensis and synthetic 2-phenylethanol reduced growth rates of both L. abietinum and B. bassiana by 36% on average. Mean protein and P content of Wickerhamomyces canadensis cultures were 0.8% and 7.2%, respectively, but isolates varied in nutritional content and protein content was similar to that of host tree phloem. We conclude that W. canadensis is a primary yeast symbiont of D. rufipennis in the Rocky Mountains and emits volatiles that can affect growth of associated microbes. Wickerhamomyces canadensis isolates vary substantially in limiting nutrients (protein and P), but concentrations are less than reported for the symbiotic filamentous fungus L. abietinum.

The cytochrome P450s of Leptographium qinlingensis: Gene characteristics, phylogeny, and expression in response to terpenoids.

Leptographium qinlingensis is one of the major fungal associates of the Chinese white pine beetle (Dendroctonus armandi) and is an active participant in the large-scale death of Pinus armandi. Beetles and associated fungi have evolved efficient systems for overcoming the toxicity of host defense chemicals, which consist of a multitude of monoterpenes and diterpenes. As fungal cytochromes (CYPs) can detoxify and degrade various xenobiotic compounds, we identified 11 CYPs from L. qinlingensis to analyze their potential function in detoxifying or degrading host chemical defense. These 11 CYPs of L. qinlingensis belong to 6 clans and cluster into 3 clades, clade 2, clade 8 and clade 10, based on their phylogenetic relationships. Moreover, we also analyzed the transcript levels of CYPs following treatment with terpenes or expression in mycelia grown on terpenoids as a carbon source. The results in this paper showed that several CYPs were upregulated after treatment with terpenes or growth on terpenoids as the only carbon source. Our research provides some insight into the function of CYPs from bark beetle symbiotic fungi in the detoxification of pine defense compounds or their relationships with the utilization of terpenoids.

The compact mitogenome of Ceratocystiopsis pallidobrunnea.

Ceratocystiopsis is a fungal genus that has been assigned to the Ophiostomatales, fungi known for their association with various bark beetles and other arthropods. The mitochondrial genome of Ceratocystiopsis pallidobrunnea has been characterized and compared with other members of the genus Ceratocystiopsis and Ophiostomatales. At 29 022 bp, the mitogenome of C. pallidobrunnea is the smallest reported so far for this genus. Gene arrangement was observed to be conserved for this group of fungi, and mitogenome variation appears to be mostly due to the absence and presence of introns. The long-term goal is to apply mitogenomes to resolve taxonomic issues within the Ophiostomatales and within the various genera that comprise the Ophiostomataceae.

Molecular basis of cycloheximide resistance in the Ophiostomatales revealed.

Resistance to the antibiotic Cycloheximide has been reported for a number of fungal taxa. In particular, some yeasts are known to be highly resistant to this antibiotic. Early research showed that this resulted from a transition mutation in one of the 60S ribosomal protein genes. In addition to the yeasts, most genera and species in the Ophiostomatales are highly resistant to this antibiotic, which is widely used to selectively isolate these fungi. Whole-genome sequences are now available for numerous members of the Ophiostomatales providing an opportunity to determine whether the mechanism of resistance in these fungi is the same as that reported for yeast genera such as Kluyveromyces. We examined all the available genomes for the Ophiostomatales and discovered that a transition mutation in the gene coding for ribosomal protein eL42, which results in the substitution of the amino acid Proline to Glutamine, likely confers resistance to this antibiotic. This change across all genera in the Ophiostomatales suggests that the mutation arose early in the evolution of these fungi.

First Look Into the Ambrosia Beetle-Fungus Symbiosis Present in Commercial Avocado Orchards in Michoacán, Mexico.

Most beetle-fungus symbioses do not represent a threat to agricultural and natural ecosystems; however, a few beetles are able to inoculate healthy hosts with disease-causing fungal symbionts. Here, we report the putative nutritional symbionts associated with five native species of ambrosia beetles colonizing commercial avocado trees in four locations in Michoacán. Knowing which beetles are present in the commercial orchards and the surrounding areas, as well as their fungal associates, is imperative for developing a realistic risk assessment and an effective monitoring system that allows for timely management actions. Phylogenetic analysis revealed five potentially new, previously undescribed species of Raffaelea, and three known species (R. arxi, R. brunnea, R. fusca). The genus Raffaelea was recovered from all the beetle species and across the different locations. Raffaelea lauricola (RL), which causes a deadly vascular fungal disease known as laurel wilt (LW) in Lauraceae species, including avocado, was not recovered. This study points to the imminent danger of native ambrosia beetles spreading RL if the pathogen is introduced to Mexico's avocado orchards or natural areas given that these beetles are associated with Raffaelea species and that lateral transfer of RL among ambrosia beetles in Florida suggests that the likelihood of this phenomenon increases when partners are phylogenetically close. Therefore, this study provides important information about the potential vectors of RL in Mexico and other avocado producing regions. Confirming beetle-fungal identities in these areas is especially important given the serious threat laurel wilt disease represents to the avocado industry in Mexico.

Phylogenetic and phylogenomic analyses reveal two new genera and three new species of ophiostomatalean fungi from termite fungus combs.

The Ophiostomatales (Ascomycota) accommodates more than 300 species characterized by similar morphological adaptations to arthropod dispersal. Most species in this order are wood-inhabiting fungi associated with bark or ambrosia beetles. However, a smaller group of species occur in other niches such as in soil and Protea infructescences. Recent surveys of Termitomyces fungus gardens (fungus combs) of fungus-growing termites led to the discovery of characteristic ophiostomatalean-like fruiting structures. In this study, these ophiostomatalean-like fungi were identified using morphological characteristics, conventional molecular markers, and whole genome sequencing. In addition, the influence of the extracts derived from various parts of Termitomyces combs on the growth of these fungi in culture was considered. Based on phylogenomic analyses, two new genera (Intubia and Chrysosphaeria) were introduced to accommodate these ophiostomatalean species. Phylogenetic analyses revealed that the isolates resided in three well-supported lineages, and these were described as three new species (Intubia macrotermitinarum, I. oerlemansii, and Chrysosphaeria jan-nelii). Culture-based studies showed that these species do not depend on the Termitomyces comb material for growth.

Termite Presence and Feeding on Loblolly Pine Wood Differs Among Four Root-Infecting Bluestain (ophiostomatoid) Fungal Species.

Bark beetles and root weevils can impact forests through tree death on landscape scales. Recently, subterranean termites have been linked to these beetles via the presence of bluestain fungi (Ascomycota: Ophiostomataceae), which are vectored to trees by beetles. However, only a small subset of bluestain species have been examined. Here, we tested whether termite-bluestain association patterns in the field reflect termite feeding preference in laboratory choice trials. We documented the presence of four bluestain fungi (Leptographium procerum (W.B. Kendr.), L. terebrantis (Barras & Perry), Grosmannia huntii (Rob.-Jeffr.), and G. alacris (T.A. Duong, Z.W. de Beer & M.J. Wingf.) in the roots of 2,350 loblolly pine trees in the southeastern United States and whether termites were present or absent on these roots and paired this with laboratory choice feeding trials. Termites were found 2.5-fold on tree roots with at least one bluestain fungus present than tree roots without bluestain fungi. Although termites in this study and others were associated with L. procerum, L. terebrantis, and marginally G. huntii, termites only showed preferential feeding on wood inoculated with G. huntii in laboratory trials. This suggests that increased termite presence on wood with bluestain fungi may be driven by factors other than increased wood palatability. Termites could thus disproportionately affect wood turnover rates for specific pools (e.g., bark beetle and root weevil attacked trees) and in some cases (e.g., G. huntii) accelerate wood decomposition. This study supports the growing evidence that the association between subterranean termites and bluestain fungi is spatially and taxonomically widespread.

Production of complementary defense metabolites reflects a co-evolutionary arms race between a host plant and a mutualistic bark beetle-fungal complex.

Intra-specific variation in conifers has been extensively studied with respect to defense against herbivores and pathogens. While studies have shown the ability of individual or specific mixtures of compounds to influence insects and microbes, research testing biologically relevant mixtures of defense compounds reflecting intra-specific variation amongst tree populations to enemy complexes is needed. We characterized the variations in lodgepole pine monoterpenes from a progeny trial in western Canada and grouped trees in four clusters using their monoterpene profiles. We then selected 11 representative families across four clusters and amended their entire monoterpene profiles (with the exception of ß-phellandrene) in media to determine how representative families affect the performance of the mountain pine beetle or its fungal symbiont. We placed adult beetles or inoculated fungus on the amended media and measured beetle performance and fungal growth as a proxy to host suitability. We found that different clusters or families differentially influenced beetle or fungal responses. However, monoterpene profiles of trees suitable to the beetle or the fungus were dissimilar. These outcomes reflect a co-evolutionary arms-race between the host and the bark beetle-fungus complex, which has resulted in the production of complementary defense metabolites among different pine populations to enhance tree survival.

Ophiostomatalean fungi associated with wood boring beetles in South Africa including two new species.

Ambrosia beetles are small wood inhabiting members of the Curculionidae that have evolved obligate symbioses with fungi. The fungal symbionts concentrate nutrients from within infested trees into a usable form for their beetle partners, which then utilize the fungi as their primary source of nutrition. Ambrosia beetle species associate with one or more primary symbiotic fungal species, but they also vector auxiliary symbionts, which may provide the beetle with developmental or ecological advantages. In this study we isolated and identified ophiostomatalean fungi associated with ambrosia beetles occurring in a native forest area in South Africa. Using a modified Bambara beetle trap, living ambrosia beetle specimens were collected and their fungal symbionts isolated. Four beetle species, three Scolytinae and one Bostrichidae, were collected. Five species of ophiostomatalean fungi were isolated from the beetles and were identified using both morphological characters and DNA sequence data. One of these species, Raffaelea sulphurea, was recorded from South Africa for the first time and two novel species were described as Ceratocystiopsis lunata sp. nov. and Raffaelea promiscua sp. nov.

Interspecific variation in spruce constitutive and induced defenses in response to a bark beetle-fungal symbiont provides insight into traits associated with resistance.

Differences in defensive traits of tree species may predict why some conifers are susceptible to bark beetle-fungal complexes and others are not. A symbiotic fungus (Leptographium abietinum (Peck) M.J. Wingf.) associated with the tree-killing bark beetle (Dendroctonus rufipennis Kirby) is phytopathogenic to host trees and may hasten tree decline during colonization by beetles, but defense responses of mature trees to the fungus have not been experimentally examined. To test the hypothesis that interspecific variation in spruce resistance is explained by defense traits we compared constitutive (bark thickness and constitutive resin ducts) and induced defenses (resin flow, monoterpene composition, concentration, phloem lesion formation and traumatic resin ducts) between two sympatric spruces: Engelmann spruce (Picea engelmannii Parry ex Engelm.-a susceptible host) and blue spruce (Picea pungens Engelm.-a resistant host) in response to fungal inoculation. Four central findings emerged: (i) blue spruce has thicker outer bark and thinner phloem than Engelmann spruce, which may restrict fungal access to phloem and result in less beetle-available resource overall; (ii) both spruce species induce monoterpenes in response to inoculation but blue spruce has higher constitutive monoterpene levels, induces monoterpenes more rapidly, and induces higher concentrations over a period of time consistent with spruce beetle attack duration; (iii) Engelmann and blue spruce differed in the monoterpenes they upregulated in response to fungal inoculation: blue spruce upregulated α-pinene, terpinolene and γ-terpinene, but Engelmann spruce upregulated 3-carene and linalool; and (iv) blue spruce has a higher frequency of constitutive resin ducts and produces more traumatic resin ducts in annual growth increments than Engelmann spruce, though Engelmann spruce produces more resin following aseptic wounding or fungal inoculation. These findings suggest that higher constitutive resin duct densities and monoterpene concentrations, as well as the ability to rapidly induce specific monoterpenes in response to L. abietinum inoculation, are phenotypic traits associated with hosts resistant to spruce beetle colonization.

Mutualistic Ophiostomatoid Fungi Equally Benefit from Both a Bark Beetle Pheromone and Host Tree Volatiles as Nutrient Sources.

Interactions between mutualistic bark beetles and ophiostomatoid fungi have received considerable attention in recent years. Studies have shown how volatile organic compounds emitted from mutualist fungi affect the behaviors of several bark beetle species. However, we currently lack sufficient knowledge regarding whether bark beetle pheromones can influence mutualist fungi. Here, we measured growth and biomass of two mutualistic fungi of the mountain pine beetle in response to headspace of a beetle pheromone (trans-verbenol), a blend of host tree volatiles, the combination of both, or control (no volatile source) in vitro experiments consisting of a nitrogen-based medium. The surface area and ergosterol content of the mycelia were used as surrogates for fungal growth and biomass respectively. We found that both growth and biomass of Grosmannia clavigera and Ophiostoma montium were greater in medium exposed to any type of volatile sources than the control. While growth and ergosterol content of G. clavigera were highest in the combination treatment, there were no differences in growth or biomass among the types of volatiles introduced for O. montium. These results suggest that both mutualistic fungi can utilize both bark beetle pheromone and host tree volatiles as nutrient sources. Overall, these results support the on-going studies on the role of volatile organic compounds mediating mutualistic bark beetle-fungi interactions.

Sap flow, xylem anatomy and photosynthetic variables of three Persea species in response to laurel wilt.

Laurel wilt, a lethal vascular wilt disease caused by the fungus Raffaelea lauricola, affects several tree species in the Lauraceae, including three Persea species. The susceptibility to laurel wilt of two forest tree species native to the southern USA, Persea borbonia and Persea palustris, [(Raf.) Sarg.] and avocado, Persea americana (Mill.) cv Waldin, was examined and related to tree physiology and xylem anatomy. Net CO2 assimilation (A), stomatal conductance (gs), leaf chlorophyll index (LCI), leaf chlorophyll fluorescence (Fv/Fm), xylem sap flow, theoretical stem hydraulic conductivity (Kh) and xylem vessel anatomy were assessed in trees of each species that were inoculated with R. lauricola and in control trees. Laurel wilt caused a reduction in A, gs, LCI, Fv/Fm and blockage of xylem vessels by tyloses formation that negatively impacted Kh and sap flow in all Persea species. However, disease susceptibility as indicated by canopy wilting and sapwood discoloration was less pronounced in P. americana cv Waldin than in the two forest species. Xylem vessel diameter was significantly smaller in P. borbonia and P. palustris than in P. americana cv Waldin. Differences in laurel wilt susceptibility among species appear to be influenced by physiological and anatomical tree responses.

Effect of culture conditions on conidia production and enhancement of environmental stress resistance of Esteya vermicola in solid-state fermentation.

AIMS: Esteya vermicola is an endoparasitic fungus producing lunate conidia, which kill pine wood nematode (PWN), and PWN could cause pine wilt disease (PWD). The aims of this study were to increase production and confirm the resistance (temperature and UV irradiation) of lunate conidia, and further determine the effective concentrations of conidia infecting PWN. METHODS AND RESULTS: In this study, rice was used as a carrier to absorb conidial suspension to propagate conidia. The optimal conditions for lunate conidia production were 25°C temperature, 9 days of culture time, 2 : 1 rice/distilled water ratio and 10% inoculum size. The germination rate of E. vermicola cultured on potato dextrose agar was influenced by UV irradiation, similar to growth on rice. Esteya vermicola cultured on rice under heat stress might be more suitable for application in the field. The concentration (1 × 108 conidia per ml) to kill PWN had the highest infectivity among the four conidia concentrations tested after 3 days of inoculation. CONCLUSIONS: This study showed a rice substrate-supported high-quality conidia production and the optimal infectivity concentration of E. vermicola. SIGNIFICANCE AND IMPACT OF THE STUDY: These results provide the necessary process of an economical and efficient biological control strategy against PWD.

New compounds from Japanese oak wilt disease-associated fungus Raffaelea quercivora.

Two new compounds, a new lactone, quercilactone A (1), and (17R)-hydroxynafuredin (5), as well as five known compounds, scytalone (2), 3S,4R-hydoxy-scytalone (3), nafuredin (4), (+)-(3R,5R)-3-hydroxy-5-decanolide (6) and 3-ethyl-4-hydroxy-6-methyl-2H-pyran-2-one (7), were isolated from Raffaelea quercivora, a fungus that causes Japanese oak wilt disease. The structures of these compounds were determined by 1D and 2D NMR spectroscopic analyses. The absolute configuration at C-17 of 5 was determined to be R by the modified Mosher's method. Compounds 1, 2, and 7 exhibited weak phytotoxic activity in lettuce seedlings at a concentration of 100 µg mL-1.

Rapid Detection of Raffaelea lauricola Directly from Host Plant and Beetle Vector Tissues Using Loop-Mediated Isothermal Amplification.

Since its introduction in 2002, laurel wilt disease has devastated indigenous lauraceous species in the southeastern United States. The causal agent is a fungal pathogen, Raffaelea lauricola, which, after being introduced into the xylem of trees by its vector beetle, Xyleborus glabratus, results in a fatal vascular wilt. Rapid detection and accurate diagnosis of infections is paramount to the successful implementation of disease management strategies. Current management operations to prevent the spread of laurel wilt disease are largely delayed by time-consuming laboratory procedures to confirm the diagnosis. In order to greatly speed up the operations, we developed a loop-mediated isothermal amplification (LAMP) species-specific assay that targets the ß-tubulin gene region of R. lauricola, and allows for the rapid detection of the pathogen directly from host plant and beetle tissues. The assay is capable of amplifying as little as 0.5 pg of fungal DNA and as few as 50 conidia. The assay is also capable of detecting R. lauricola directly from wood tissue of artificially inoculated redbay saplings as early as 10 and 12 days postinoculation, when testing high-quality and crude DNA extracts, respectively. Finally, crude DNA extracts of individual adult female X. glabratus beetles were assayed and the pathogen was detected from all specimens. This assay greatly reduces the time required to confirm a laurel wilt diagnosis and, because LAMP technology is well suited to provide point-of-care testing, it has the potential to expedite and facilitate implementation of management operations in response to disease outbreaks.

Genomic and transcriptomic insights into Raffaelea lauricola pathogenesis.

BACKGROUND: Laurel wilt caused by Raffaelea lauricola is a lethal vascular disease of North American members of the Lauraceae plant family. This fungus and its primary ambrosia beetle vector Xyleborus glabratus originated from Asia; however, there is no report of laurel wilt causing widespread mortality on native Lauraceae trees in Asia. To gain insight into why R. lauricola is a tree-killing plant pathogen in North America, we generated and compared high quality draft genome assemblies of R. lauricola and its closely related non-pathogenic species R. aguacate. RESULTS: Relative to R. aguacate, the R. lauricola genome uniquely encodes several small-secreted proteins that are associated with virulence in other pathogens and is enriched in secondary metabolite biosynthetic clusters, particularly polyketide synthase (PKS), non-ribosomal peptide synthetase (NRPS) and PKS-NRPS anchored gene clusters. The two species also exhibit significant differences in secreted proteins including CAZymes that are associated with polysaccharide binding including the chitin binding CBM50 (LysM) domain. Transcriptomic comparisons of inoculated redbay trees and in vitro-grown fungal cultures further revealed a number of secreted protein genes, secondary metabolite clusters and alternative sulfur uptake and assimilation pathways that are coordinately up-regulated during infection. CONCLUSIONS: Through these comparative analyses we have identified potential adaptations of R. lauricola that may enable it to colonize and cause disease on susceptible hosts. How these adaptations have interacted with co-evolved hosts in Asia, where little to no disease occurs, and non-co-evolved hosts in North America, where lethal wilt occurs, requires additional functional analysis of genes and pathways.

An invasive beetle-fungus complex is maintained by fungal nutritional-compensation mediated by bacterial volatiles.

Mutualisms between symbiotic microbes and animals have been well documented, and nutritional relationships provide the foundation for maintaining beneficial associations. The well-studied mutualism between bark beetles and their fungi has become a classic model system in the study of symbioses. Despite the nutritional competition between bark beetles and beneficial fungi in the same niche due to poor nutritional feeding substrates, bark beetles still maintain mutualistic associations with beneficial fungi over time. The mechanism behind this phenomenon, however, remains largely unknown. Here, we demonstrated the bark beetle Dendroctonus valens LeConte relies on the symbiotic bacterial volatile ammonia, as a nitrogen source, to regulate carbohydrate metabolism of its mutualistic fungus Leptographium procerum to alleviate nutritional competition, thereby maintaining the stability of the bark beetle-fungus mutualism. Ammonia significantly reduces competition of L. procerum for carbon resources for D. valens larval growth and increases fungal growth. Using stable isotope analysis, we show the fungus breakdown of phloem starch into D-glucose by switching on amylase genes only in the presence of ammonia. Deletion of amylase genes interferes with the conversion of starch to glucose. The acceleration of carbohydrate consumption and the conversion of starch into glucose benefit this invasive beetle-fungus complex. The nutrient consumption-compensation strategy mediated by tripartite beetle-fungus-bacterium aids the maintenance of this invasive mutualism under limited nutritional conditions, exacerbating its invasiveness with this competitive nutritional edge.