Search

The longleaf pine Pinus palustris Miller (Pinales: Pinaceae) ecosystem once covered as many as 37 million hectares across the southeastern United States. Through fire suppression, development, and conversion to other plantation pines, this coverage has dwindled to fewer than 2 million hectares. A recent focus on the restoration of this ecosystem has revealed its complex and biologically diverse nature. Arthropods of the longleaf pine ecosystem are incredibly numerous and diverse—functionally and taxonomically. To provide clarity on what is known about the species and their functional roles in longleaf pine forests, we thoroughly searched the literature and found nearly 500 references. In the end, we tabulated 51 orders 477 families, 1,949 genera, and 3,032 arthropod species as having been stated in the scientific literature to occur in longleaf pine ecosystems. The body of research we drew from is rich and varied but far from comprehensive. Most work deals with land management objective associated taxa such as pests of pine, pests of—and food for—wildlife (red-cockaded woodpecker, northern bobwhite quail, gopher tortoise, pocket gopher, etc.), and pollinators of the diverse plant understory associated with longleaf pine. We explored the complex role frequent fire (critical in longleaf pine management) plays in determining the arthropod community in longleaf pine, including its importance to rare and threatened species. We examined known patterns of abundance and occurrence of key functional groups of longleaf pine-associated arthropods. Finally, we identified some critical gaps in knowledge and provide suggestions for future research into this incredibly diverse ecosystem.

Longleaf pine (Pinus palustris Mill.) savannas and woodlands are known for providing numerous ecosystem services such as promoting biodiversity, reducing risk of wildfire and insect outbreaks, and increasing water yields. In these open pine systems, there is also interest in managing carbon (C) in ways that do not diminish other ecosystem services. Additionally, there may be management strategies for accomplishing these same objectives in plantations and degraded stands that developed from natural regeneration. For example, C accumulation in live trees and C storage in harvested wood products could be increased by extending rotations and converting plantations to multi-aged stands. Belowground C storage could be enhanced by incorporating pyrogenic C into the mineral soil before planting longleaf pines in clearcut areas, but this may be contrary to findings that indicate that minimizing soil disturbance is important for long-term soil C storage. We suggest examining approaches to reduce total ecosystem C emissions that include using targeted browsing or grazing with domesticated livestock to supplement prescribed burning, thereby reducing C emissions from burning. The mastication of woody vegetation followed by a program of frequent prescribed burning could be used to reduce the risk of substantial C emissions from wildfires and to restore function to savannas and woodlands with hardwood encroachment and altered fire regimes. Many of these approaches need to be validated with field studies or model simulations. There is also a need to improve the estimates of dead wood C stocks and C storage in harvested wood products. Finally, eddy covariance techniques have improved our understanding of how disturbances influence longleaf pine C dynamics over multiple time scales. However, there is a need to determine the degree to which different silvicultural approaches, especially those for adapting ecosystems to climate change, influence C accumulation. Overall, our review suggests that there are numerous opportunities for research on C dynamics in longleaf pine ecosystems, and these systems are likely well-positioned to accomplish C objectives while offering other ecosystem services.

Eye gnats (mainly Liohippelates pusio and Liohippelates collusor) are pest species that have been the subject of considerable research and extension activity in the United States since the 1930s. They cause considerable discomfort and stress—and may transmit pathogens—to humans and animals. We reviewed the abundant literature on biological, ecological, and management aspects of Liohippelates eye gnats. Eye gnat biology and life cycles have been well studied in agricultural systems. However, their ecology, roles in trophic cascades, and functions in natural ecosystems, particularly forests, are not well documented. Additionally, there remain opportunities to improve traps, repellents, deterrents, and controls for eye gnats. The substantial and substantive early work on these insects provides a strong foundation for future investigations and extension.

The ectosymbiotic community associated with bark and ambrosia beetles is diverse and speciose and adapted for life within tree tissues. This community—composed of fungi, bacteria, viruses, nematodes, and mites—interacts with beetle hosts in a variety of ways. Interactions are often not simple or clearly understood, and are rather context-dependent, shifting with changing environments. Ectosymbionts also interact with the tree and with natural enemies and competitors of beetle hosts within trees. In this chapter, we describe the effects of changing climate, especially elevated temperatures, on the composition and interactions of the ectosymbiotic community associated with bark and ambrosia beetles. We address (1) how changes in climate can differentially affect growth and reproduction of ectosymbiotic species, (2) how climate can drive changes in tree condition, increasing or decreasing secondary defenses, phloem nutrients, and moisture and affecting ectosymbionts associated with beetles, and (3) how climate change affects interactions among ectosymbionts, beetles, and trees.

Catastrophic wind disturbances under climatic changes are causing major economic impacts and ecological changes that can persist for decades. Bark beetle (Coleoptera: Curculionidae) population and community dynamics are often linked to such wind disturbances at several spatial and temporal scales ranging from damage to individual trees to large-scale windthrow that may prompt multiyear outbreaks on the landscape scale. In this chapter, we discuss how catastrophic wind disturbances and ensuing biological legacies enhance bark beetle populations, particularly in the context of climatic changes. The high level of variability at the tree, stand, and landscape levels created by windstorms generally has positive consequences for eruptive bark beetle species, particularly in Europe. Poststorm timber salvaging to alleviate pest burdens may push biotic elements, especially those dependent on coarse woody debris and forest gaps, into different successional pathways. Climate change is undoubtedly influencing the interactions between these two major disturbance agents by increasing their intensity and severity levels and altering landscape characteristics with feedback loops. In the Anthropocene, predictive modeling of network interactions between multiple abiotic and biotic disturbances and stressors will be critical for effective mitigation, forest restoration, and sustainable forestry practices in a rapidly changing world.

Ecosystem process models can be used to predict forest response to disturbances at a range of scales. Selection of the spatial class of model should depend on the scale of the research or management question, and model type should depend on the ecosystem attributes of interest. In some cases, multiple classes of models could be used to address a single research question, with evaluations at each scale having potential benefits and drawbacks. This study examines two classes of models relative to how fire return intervals impact carbon and species dynamics in a southeastern U.S. pineland. A model that can be run as a global class model (ED) and a landscape class model (LANDIS‐II) were parameterized with species inventory data from an experimental Pinus Palustris (longleaf pine) forest in southwest Georgia, and simulations were calibrated with literature values, then validated with eddy‐covariance data from the study site. A variety of fire scenarios that included prescribed fire with a 2‐yr return interval, fire exclusion, and three wildfire scenarios (20‐, 50‐, and 100‐yr return intervals) were used for model runs. Results were compared and evaluated with regard to ecosystem carbon and species dynamics. Both models illustrated that prescribed fire provided the greatest carbon sequestration potential and most stable aboveground biomass through time when compared to the wildfire scenarios. The fire exclusion scenario for LANDIS‐II was the only scenario where prescribed fire did not provide the greatest carbon sequestration potential. However, fire exclusion on the order of centuries was a condition of this outcome and the occurrence of such long fire‐free periods is considered unrealistic in this fire‐prone landscape. Differences between models were primarily the result of the underlying characteristics of each model class, namely the spatial resolution and number of species included. In the end, two vastly different scale models supported the conclusion that high frequency prescribed fire in southeastern U.S. pinelands stabilizes carbon and maintains species composition in an ecosystem that is a known ecological hotspot.

Southern pine forests are important fiber and wood sources, and critical to local, regional, and national economies in the United States. Recently, certain areas of southern pine forests, especially those dominated by loblolly pine (Pinus taeda), have been reported to exhibit abnormally high levels of tree dieback and mortality. However, causal agents either have not been well defined or are controversial in their impacts on tree health. We assessed various abiotic (e.g., slope, aspect, soil characteristics) and biotic (e.g., tree species, stand characteristics, presence of root fungi) factors in 37 healthy (asymptomatic) and unhealthy (symptomatic) sites to elucidate specific factors affecting loblolly pine health in Alabama and Georgia. Soil nutrient content did not differ statistically between healthy and unhealthy sites, but manganese contents were slightly greater, and nitrogen and carbon contents were slightly lower in healthy sites. Unhealthy sites did have a higher silt content than did healthy sites. Pine stems and basal area were greater on unhealthy than on healthy sites, whereas opposite trends were observed for the incidence of stem cankers and mechanical damage. An increased incidence of the root fungal pathogen Heterobasidion irregulare, the causal agent of Heterobasidion root disease, was found on unhealthy sites, but incidence of Leptographium spp. did not differ between the two site types. Thus, soil attributes, stand structure, and management history seem to be the most critical factors affecting loblolly pine health, at least at the local level. Further, some of these factors may be improved through appropriate silvicultural techniques, emphasizing the importance of silviculture in maintaining pine health throughout the southern region.

The primary goal of invasive species management is to eliminate or reduce populations of invasive species. Although management efforts are often motivated by broader goals such as to reduce the negative impacts of invasive species on ecosystems and society, there has been little assessment of the consistency between population-based (e.g., removing invaders) and broader goals (e.g., recovery of ecological systems) for invasive species management. To address this, we conducted a comprehensive review of studies (N = 151) that removed invasive species and assessed ecological recovery over time. We found positive or mixed outcomes in most cases, but 31% of the time ecological recovery did not occur or there were negative ecological outcomes, such as increases in non-target invasive species. Ecological recovery was more likely in areas with relatively little anthropogenic disturbance and few other invaders, and for the recovery of animal populations and communities compared to plant communities and ecosystem processes. Elements of management protocols, such as whether invaders were eradicated (completely removed) versus aggressively suppressed (≥90% removed), did not affect the likelihood of ecological recovery. Our findings highlight the importance of considering broader goals and unintended outcomes when designing and implementing invasive species management programs.

Freshly lifted seedlings and 21-year-old trees of loblolly pine were wound-inoculated with Leptographium species recovered from the soil and/or roots of trees with loblolly decline symptoms in central Alabama. Seedlings inoculated with L. procerum in the greenhouse produced significantly fewer root initials and a smaller root mass than control seedlings. Vertical lesions produced in seedlings by L. serpens and L. terebrantis were significantly longer than in controls. Lesions produced in mature trees by L. serpens and L. lundbergii were significantly longer than in controls. Of the fungi tested, L. serpens, L. terebrantis, and L. lundbergii were the most aggressive and may pose the greatest threat to loblolly pines.

We assessed awareness and perceptions of forest landowners and managers in the southeastern United States regarding their stand health especially under the context of the southern pine decline (SPD) phenomenon. E-mail and paper surveys were sent to 4,670 forest landowners and managers in Florida, Georgia, and South Carolina with an overall response rate of 28%. About half (51%) of respondents reported having healthy and symptom-free pine stands, and only 11% reported elevated levels of dying pine or pine mortality within the last year. Few (30%) respondents were aware of SPD. Insects, disease, and drought were perceived as the most important threats to pine health. Respondents usually used material from state agencies, professional speakers, or research publications for information regarding pine stand management. Data indicate a favorable outlook for pine health in the southeastern United States, as landowners were engaged and willing to use recognized management prescriptions.

We contend that traditional approaches to forest conservation and management will be inadequate given the predicted scale of social-economic and biophysical changes in the 21st century. New approaches, focused on anticipating and guiding ecological responses to change, are urgently needed to ensure the full value of forest ecosystem services for future generations. These approaches acknowledge that change is inevitable and sometimes irreversible, and that maintenance of ecosystem services depends in part on novel ecosystems, i.e., species combinations with no analog in the past. We propose that ecological responses be evaluated at landscape or regional scales using risk-based approaches to incorporate uncertainty into forest management efforts with subsequent goals for management based on Achievable Future Conditions (AFC). AFCs defined at a landscape or regional scale incorporate advancements in ecosystem management, including adaptive approaches, resilience, and desired future conditions into the context of the Anthropocene. Inherently forward looking, ACFs encompass mitigation and adaptation options to respond to scenarios of projected future biophysical, social-economic, and policy conditions which distribute risk and provide diversity of response to uncertainty. The engagement of science-management-public partnerships is critical to our risk-based approach for defining AFCs. Robust monitoring programs of forest management actions are also crucial to address uncertainty regarding species distributions and ecosystem processes. Development of regional indicators of response will also be essential to evaluate outcomes of management strategies. Our conceptual framework provides a starting point to move toward AFCs for forest management, illustrated with examples from fire and water management in the Southeastern United States. Our model is adaptive, incorporating evaluation and modification as new information becomes available and as social–ecological dynamics change. It expands on established principles of ecosystem management and best management practices (BMPs) and incorporates scenarios of future conditions. It also highlights the potential limits of existing institutional structures for defining AFCs and achieving them. In an uncertain future of rapid change and abrupt, unforeseen transitions, adjustments in management approaches will be necessary and some actions will fail. However, it is increasingly evident that the greatest risk is posed by continuing to implement strategies inconsistent with current understanding of our novel future.

The southeastern United States is among the most productive forested areas in the world. Four endemic southern pine species – loblolly, longleaf, shortleaf, and slash – contribute significantly to the economic and ecological values in the region. A recently described phenomenon known as Southern Pine Decline (SPD) has been reported as having widespread impact in the southern pine region, particularly on loblolly pine. Root-feeding weevils and their associated fungi have been suggested as causal agents, even though literature and empirical research suggests that they are secondary insects colonizing weakened trees. Further, no published information exists about whether their associated fungi can cause mortality of mature trees in the southeastern U.S. Since there are significant management implications for pine health, we reviewed and critically examined the SPD phenomena on the southern landscape. Our regional analyses of USDA Forest Inventory and Analysis data show no discernable patterns related to pine growth or mortality, especially as related to topographic factors. There are no large-scale patterns related to pine mortality suggesting multiple interacting factors impacting tree health at stand-level. As such, the hypothesis that SPD is a regionally important decline syndrome and labeling declining southern pine stands as SPD is not supported. Instead, we discuss many abiotic (soil types, climate) and biotic (insects, pathogens, genetics) factors that may be interacting with each other and affecting southern pine health. Finally, we suggest management recommendations for landowners with pine health issues.

Conifers possess a suite of physiochemical defenses that protect their subcortical tissues from bark beetle - fungal complexes. These defenses include rapid induction of terpenoids and phenolics at the site of attack. Studies of the distribution, induction, and bioactivity of conifer terpenoids have focused heavily on monoterpenes. We assessed induction of diterpene acids in white spruce (Picea glauca) and red pine (Pinus resinosa) to fungal associates of two bark beetles, and the responses of four spruce beetle (Dendroctonus rufipennis)-associated fungi to three diterpene acids. Constitutive phloem contents differed between species, in that red pine had extremely low concentrations of diterpene acids, whereas white spruce had substantial constitutive levels. Induction differed quantitatively. Both red pine and white spruce exhibited marked increases, but red pine underwent greater increases and achieved higher concentrations than white spruce. Induction also differed qualitatively in that red pine showed lower diversity and fewer compositional changes during induction than white spruce. In red pine,fungal inoculation accompanying wounding elicited greater increases than wounding alone, but in white spruce total concentrations were higher following wounding alone. Spruce beetle fungal symbiont growth varied among species and compounds. Some diterpenes elicited both stimulatory and inhibitory effects on fungi, depending on concentration. All four fungi exhibited higher tolerances compared to those associated with pine bark beetles in previous studies. Variation in tolerances to, and potentially metabolism of, diterpene acids by symbionts may reflect differences in constitutive levels between spruce and pine, and partially explain differences in concentrations achieved during induction.

The southern pine beetle (SPB) is a major disturbance in pine forests throughout the range of southern yellow pines, and is a significant influence on forests throughout several Central Hardwood Region (CHR) ecoregions. At endemic levels, SPB colonizes individual stressed or lightning-struck trees, acting as a natural thinning agent. During outbreaks, tree mortality from SPB may impact CHR forests by indirectly converting stands to other species types, or changing the stand age and structure. Southern pine beetle can also create disturbance in stands by causing mortality in large clusters of pine trees or by hastening the succession from pine-hardwood forests to late-successional forest by killing single or groups of overstory pine trees. Populations are cyclical and have traditionally impacted CHR forests every 7–25 years, depending on location. The most significant outbreaks in this region in the past 65 years occurred 1974–1976 and 1997–2003, with the most recent impacting more than 405,000 ha, and caused an estimated economic loss of more than $1 billion across six states. In this chapter we examine the spatial extent and frequency of SPB outbreaks in the CHR. We also discuss the severity of disturbance caused by SPB to forests in this region over the past 65 years; how this disturbance has altered the resultant forests; and the potential impacts of changes in climate and anthropogenic effects on preventing infestations and reducing levels of tree mortality attributed to SPB.

Insect fungus gardens consist of a community of interacting microorganisms that can have either beneficial or detrimental effects to the farmers. In contrast to fungus-farming ants and termites, the fungal communities of ambrosia beetles and the effects of particular fungal species on the farmers are largely unknown. Here, we used a laboratory rearing technique for studying the filamentous fungal garden community of the ambrosia beetle, Xyleborinus saxesenii, which cultivates fungi in tunnels excavated within dead trees. Raffaelea sulfurea and Fusicolla acetilerea were transmitted in spore-carrying organs by gallery founding females and established first in new gardens. Raffaelea sulfurea had positive effects on egg-laying and larval numbers. Over time, four other fungal species emerged in the gardens. Prevalence of one of them, Paecilomyces variotii, correlated negatively with larval numbers and can be harmful to adults by forming biofilms on their bodies. It also comprised the main portion of garden material removed from galleries by adults. Our data suggest that two mutualistic, several commensalistic and one to two pathogenic filamentous fungi are associated with X. saxesenii. Fungal diversity in gardens of ambrosia beetles appears to be much lower than that in gardens of fungus-culturing ants, which seems to result from essential differences in substrates and behaviours.

The Sirex noctilio (woodwasp)–Amylostereum areolatum (fungus) complex has caused substantial losses to pine industries in its introduced range. The nematode Deladenus siricidicola that parasitizes S. noctilio and feeds on A. areolatum is widely used as a biological control agent for S. noctilio, but not with consistent success. This variable success could be due to factors that influence the feeding and reproductive ability of the nematode on A. areolatum. We test two main hypotheses that emerge from this prediction. First, we compared the survival of D. siricidicola on the South African field strain and the Australian laboratory strain of A. areolatum, to examine a possible incompatibility between nematode and fungal strain. Second, we examined the competitive interactions of these two A. areolatum strains with two common sapstain fungi, Diplodia pinea and Ophiostoma ips, that occur in S. noctilio infested trees in South Africa. The effect of water potential on the outcome of these fungal interactions was also considered. The data showed that D. siricidicola survives at comparable levels on the two A. areolatum strains. Water potential of the media significantly influenced growth of the fungi and their ability to capture host resource in competitive interactions. D. pinea competed increasingly better against A. areolatum with decreasing water potential. The results suggest that competitive interactions between A. areolatum and sapstain fungi could negatively influence the success of D. siricidicola, especially under conditions of lowered water potential.

Ophiostomatoid fungi are important components within the highly damaging insect-fungal complexes attacking trees in North America. This group includes the disease agents responsible for Dutch elm disease and laurel wilt, as well as a number of associates of tree-killing bark beetles. While systemic fungicides have been applied against ophiostomatoids in certain fungus-host systems, the breadth of their utility and their management implications for a wide array of fungus and host species remain uncertain. To evaluate the impact of commercially available fungicides against the bluestaining fungus Ophiostoma minus, an associate of the southern pine beetle, researchers conducted two experiments with loblolly pines (Pinus taeda; mean dbh 14.2 and 18.5 cm, respectively) in central Louisiana, U.S. The first experiment screened three fungicides (Alamo®, Arbotect® 20-S, and PHOSPHO-jet) for their systemic impacts on O. minus, and the second further evaluated the best performing product (Alamo) alone and in combination with Arbotect 20-S. In all cases, loblolly pines were stem-injected basally and challenged with inoculations of cultured O. minus at time periods ranging from 28 days to 738 days post-treatment. In both experiments, treatment of loblolly pines with Alamo produced the smallest lesion areas, indicating that this treatment was the most effective for limiting the within-tree growth of O. minus. This effect was still present more than two years post-treatment. The study authors conclude that Alamo is the most effective product of those evaluated for prophylactic treatment against O. minus, and suggest that evidence is building for the effectiveness of this product generally against ophiostomatoid fungi.

Body reserves may determine the reproductive output of animals, depending on their resource allocation strategy. In insects, an accumulation of reserves for reproduction is often obtained before dispersal by pre-emergence (or maturation) feeding. This has been assumed to be an important cause of delayed dispersal from the natal nest in scolytine beetles. In the cooperatively breeding ambrosia beetles, this is of special interest because in this group delayed dispersal could serve two alternative purposes: “selfish” maturation feeding or “altruistic” alloparental care. To distinguish between these two possibilities, we have experimentally studied the effect of delayed dispersal on future reproductive output in the xyleborine ambrosia beetle Xyleborus affinis. Females experimentally induced to disperse and delayed dispersing females did not differ in their body condition at dispersal and in their founding success afterwards, which indicates that females disperse independently of condition, and staying adult females are fully mature and would be able to breed. However, induced dispersers produced more offspring than delayed dispersers within a test period of 40 days. This suggests that delayed dispersal comes at a cost to females, which may result primarily from alloparental care and leads to a reduced reproductive output. Alternatively, females might have reproduced prior to dispersal. This is unlikely, however, for the majority of dispersing females because of the small numbers of offspring present in the gallery when females dispersed, suggesting that mainly the foundress had reproduced. In addition, “gallery of origin” was a strong predictor of the reproductive success of females, which may reflect variation in the microbial complex transmitted vertically from the natal nest to the daughter colony, or variation of genetic quality. These results have important implications for the understanding of proximate mechanisms selecting for philopatry and alloparental care in highly social ambrosia beetles and other cooperatively breeding arthropods.

Recent studies have revealed several examples of intimate associations between insects and Actinobacteria, including the Southern Pine Beetle Dendroctonus frontalis and the Spruce Beetle Dendroctonus rufipennis. Here, we surveyed Streptomyces Actinobacteria co-occurring with 10 species of Dendroctonus bark beetles across the United States, using both phylogenetic and community ecology approaches. From these 10 species, and 19 other scolytine beetles that occur in the same trees, we obtained 154 Streptomyces-like isolates and generated 16S sequences from 134 of those. Confirmed 16S sequences of Streptomyces were binned into 36 distinct strains using a threshold of 0.2% sequence divergence. The 16S rDNA phylogeny of all isolates does not correlate with the distribution of strains among beetle species, localities, or parts of the beetles or their galleries. However, we identified three Streptomyces strains occurring repeatedly on Dendroctonus beetles and in their galleries. Identity of these isolates was corroborated using a house-keeping gene sequence (efTu). These strains are not confined to a certain species of beetle, locality, or part of the beetle or their galleries. However, their role as residents in the woodboring insect niche is supported by the repeated association of their 16S and efTu from across the continent, and also having been reported in studies of other subcortical insects.

In this study, the production of extracellular enzymes by fungi associated with southern pine beetle was investigated for the first time. Cellulase and polyphenol oxidase production were analyzed for three beetle associated fungi. Only the mutualistic symbiont Entomocorticium sp. A was found to produce cellulases and polyphenol oxidase. In time course analyses of cellulase production in batch cultures, Entomocorticium sp. A showed maximum activity of 0.109 U/ml and 0.141 U/ml for total cellulase and endoglucanase activity respectively. Polyphenol oxidase production was simultaneous with fungal growth. Characterization of polyphenol oxidase by activity staining suggests that the enzyme is a tyrosinase/catechol oxidase. Enzyme assays in the presence of polyphenol oxidase inhibitors support the results of the activity staining.

Forest landscape models simulate forest change through time using spatially referenced data across a broad spatial scale (i.e. landscape scale) generally larger than a single forest stand. Spatial interactions between forest stands are a key component of such models. These models can incorporate other spatio-temporal processes such as natural disturbances (e.g. wildfires, hurricanes, outbreaks of native and exotic invasive pests and diseases) and human influences (e.g. harvesting and commercial thinning, planting, fire suppression). The models are increasingly used as tools for studying forest management, ecological assessment, restoration planning, and climate change. In this paper, we define forest landscape models and discuss development, components, and types of the models. We also review commonly used methods and approaches of modeling forest landscapes, their application, and their strengths and weaknesses. New developments in computer sciences, geographic information systems (GIS), remote sensing technologies, decision-support systems, and geo-spatial statistics have provided opportunities for developing a new generation of forest landscape models that are increasingly valuable for ecological research, restoration planning and resource management.

Bark beetles are associated with diverse assemblages of microorganisms, many of which affect their interactions with host plants and natural enemies. We tested how bacterial associates of three bark beetles with various types of host relationships affect growth and reproduction of their symbiotic fungi. Fungi were exposed to volatiles from bacteria in an arena that imposed physical separation but shared airspace. We also exposed fungi to vapors of the host compound, α-pinene, and to combinations of bacterial volatiles and α-pinene. Bacterial volatiles commonly stimulated growth of Leptographium procerum (W.B. Kendr.) M.J. Wingf. and Grosmannia clavigera (Rob.-Jeffr. & R.W. Davidson) Zipfel, Z.W. de Beer & Wingf., which are symbiotic fungi of Dendroctonus valens LeConte and Dendroctonus ponderosae Hopkins, respectively. They less commonly stimulated growth of Ophiostoma ips (Rumbold) Nannf., which is associated with Ips grandicollis Eichhoff. Some bacteria inhibited L. procerum, Ophiostoma montium (Rumbold) von Arx (another associate of D. ponderosae), and O. ips. Bacteria greatly stimulated spore production of symbionts of D. valens and D. ponderosae. α-Pinene strongly affected some of these relationships, causing amplification, reduction, or reversal of the interactions among the bacteria and fungi. Our results show that some bacteria associated with bark beetles directly affect fungal symbionts and interact with tree chemistry to affect fungal growth and sporulation. The strongest effects were induced by bacteria associated with beetles adapted to attacking living trees with vigorous defenses, and on fungal reproductive structures.

The spruce beetle, Dendroctonus rufipennis, is an eruptive forest pest of significant economic and ecological importance. D. rufipennis has symbiotic associations with a number of microorganisms, especially the ophiostomatoid fungus Leptographium abietinum. The nature of this interaction is only partially understood. Additionally, mite and nematode associates can mediate bark beetle-fungal interactions, but this has not yet been studied for spruce beetles. In this study, we found eight mite species associated with spruce beetles: Tarsonemus ips, T. endophloeus, Histiogaster arborsignis, Dendrolaelaps quadrisetus, Proctolaelaps hytricoides, Trichouropoda alascae, T. n. sp. nr dalarenaensis, and Urobovella n. sp 767. The most prevalent species was H. arborsignis. In addition, 75% of beetles examined carried nematodes, with six species represented. These included a new species of Parasitorhabditis, Ektaphelenchus obtusus, Bursaphelenchus n. sp. 727, Aphelenchoides n. sp., Panagrolaimus sp., and Mykoletzkya ruminis. H. arborsignis showed strong feeding and oviposition preferences for L. abietinum among four fungal species tested in laboratory assays. Information on our attempts to culture the various nematode species collected from D. rufipennis is also provided. Bursaphelenchus were cultured from D. rufipennis nematangia plated on agar containing L. abietinum but not sterile agar. Thus, L. abietinum plays an important role in these gallery communities, affecting the tree-killing bark beetle, its phoretic mites, and nematodes. These data add to our understanding of bark beetle-microorganism interactions.

Resin flow is the primary means of natural defense against southern pine beetle (Dendroctonus frontalis Zimm.), the most important insect pest of Pinus spp. in the southern United States. As a result, factors affecting resin flow are of interest to researchers and forest managers. We examined the influence of fertilization, artificial wounding and fungal inoculation on resin flow in 6- and 12-year-old stands of loblolly pine (Pinus taeda L.) and determined the extent of that influence within and above the wounded stem area and through time. Fertilization increased constitutive resin flow, but only the younger trees sustained increased resin flow after wounding and inoculation treatments. An induced resin flow response occurred between 1 and 30 days after wounding and inoculation treatments. Wounding with inoculation resulted in greater resin flow than wounding alone, but increasing amounts of inoculum did not increase resin flow. Increased resin flow (relative to controls) lasted for at least 90 days after wounding and inoculation. This increase appeared to be limited to the area of treatment, at least in younger trees. The long-lasting effects of fungal inoculation on resin flow, as well as the response to fertilization, suggest that acquired resistance through induced resin flow aids in decreasing susceptibility of loblolly pine to southern pine beetle.

The southern pine beetle (Dendroctonus frontalis Zimmermann) kills all pines within its range and is among the most important forest pest species in the US. Using a specialized mycangium surrounded by gland cells in the pronotum, adult females culture, transport, and inoculate two fungi into beetle galleries during oviposition. These fungal symbionts, to varying degrees, exclude antagonistic fungi and provide nutrients to larvae. However, the mechanisms (e.g. secreted antibiotic chemicals or nutrients, proteins or pathways) by which this relationship is maintained are not known. Here we present the first global and differential proteome profile of the southern pine beetle pronotum. Two-dimensional polyacrylamide electrophoresis, tandem mass spectrometry, and database searches revealed that the majority of pronotal proteins were related to energy-yielding metabolism, contractile apparati, cell structure, and defence. The identified proteins provide important insights into the molecular and biochemical processes of, and candidates for functional genomics to understand mycangia and pronotum functions in, the southern pine beetle.

The forests of southeastern North America are influenced by a variety of disturbances including fire and insect outbreaks. In this paper, we discuss the role of disturbances in structuring forest landscapes with particular emphasis placed on the reciprocal interaction between forest structure and outbreaks of the southern pine beetle (Dendroctonus frontalis Zimmermann). We highlight work in which we are currently involved to illustrate the importance and utility of using spatially explicit forest modeling as a tool for understanding forest–insect interactions and its potential role in determining management strategies.

The reciprocal interaction of landscape structure and ecological processes is a cornerstone of modern landscape ecology. We use a simulation model to show how landscape structure and herbivory interact to influence outbreaks of southern pine beetle (Dendroctonus frontalis Zimmermann) in a landscape representative of the southern Appalachian Mountains, USA. We use LANDIS and its biological disturbance agent module to simulate the effects of landscape composition (proportion of landscape in host area) and host aggregation on the size and severity of insect outbreaks and the persistence of the host species, Table Mountain Pine (Pinus pungens Lamb.). We find that landscape composition is less important in the modeled landscapes than host aggregation in structuring the severity of insect outbreaks. Also, simulated southern pine beetle outbreaks over time tend to decrease the aggregation of host species on the landscape by fragmenting large patches into smaller ones, thereby reducing the severity of future outbreaks. Persistence of Table Mountain pine decreases throughout all simulations regardless of landscape structure. The results of this study indicate that when considering alternative restoration strategies for insect-affected landscapes, it is necessary to consider the patterns of hosts on the landscape as well as the landscape composition.

We used LANDIS, a model of forest disturbance and succession, to simulate successional dynamics of forests in the southern Appalachian Mountains. The simulated environments are based on the Great Smoky Mountains landscapes studied by Whittaker. We focused on the consequences of two contrasting disturbance regimes—fire exclusion versus frequent burning—for the Yellow pine (Pinus L., subgenus Diploxylon Koehne) and oak (Quercus L.) forests that occupy dry mountain slopes and ridgetops. These ecosystems are a conservation priority, and declines in their abundance have stimulated considerable interest in the use of fire for ecosystem restoration. Under fire exclusion, the abundance of Yellow pines is projected to decrease, even on the driest sites (ridgetops, south- and west-facing slopes). Hardwoods and White pine (P. strobus L.) replace the Yellow pines. In contrast, frequent burning promotes high levels of Table Mountain pine (P. pungens Lamb.) and Pitch pine (P. rigida Mill.) on the driest sites and reduces the abundance of less fire-tolerant species. Our simulations also imply that fire maintains open woodland conditions, rather than closed-canopy forest. For oaks, fire exclusion is beneficial on the driest sites because it permits oaks to replace the pines. On moister sites (north- and east-facing slopes), however, fire exclusion leads to a diverse mix of oaks and other species, whereas frequent burning favors Chestnut oak (Q. montana Willd.) and White oak (Q. alba L.) dominance. Our results suggest that reintroducing fire may help restore decadent pine and oak stands in the southern Appalachian Mountains.

The relative abundance and nature of associations between symbiotic species can be affected by abiotic conditions with consequences for population dynamics. We investigated the effects of temperature on the community of mites and fungi associated with the southern pine beetle, Dendroctonus frontalis , an important pest of pine forests in the southern United States. First, we determined whether the growth rates of mutualistic and antagonistic fungi associated with D. frontalis differed in their responses to temperature. Second, we tested the effects of temperature on the abundance of, and interactions among, fungi, mites and beetles within D. frontalis -infested trees. Fungi differed in their growth responses to temperature, resulting in changes in fungal-beetle associations. Mite species associated with D. frontalis also differed in their responses to temperature, resulting in different mite communities associated with bark beetle progeny. The effects of temperature on beetle reproduction could not be ass...

Question: Can fire be used to maintain Yellow pine (Pinus subgenus Diploxylon) stands disturbed by periodic outbreaks of southern pine beetle? Location: Southern Appalachian Mountains, USA. Methods: We used LANDIS to model vegetation disturbance and succession on four grids representative of xeric landscapes in the southern Appalachians. Forest dynamics of each landscape were simulated under three disturbance scenarios: southern pine beetle, fire, and southern pine beetle and fire, as well as a no disturbance scenario. We compared trends in the abundance of pine and hardwood functional types as well as individual species. Results: Yellow pine abundance and open woodland conditions were best maintained by a combination of fire and southern pine beetle disturbance on both low elevation sites as well as mid-elevation ridges & peaks. On mid-elevation SE-W facing slopes, pine woodlands were best maintained by fire alone. Conclusions: Our simulations suggest that fire can help maintain open pine woodlands in stands affected by southern pine beetle outbreaks.

Insects are major components of forest ecosystems, representing most of the biological diversity and affecting virtually all processes and uses. In the USA, bark beetles (Coleoptera: Curculionidae, Scolytinae) heavily influence the structure and function of these ecosystems by regulating certain aspects of primary production, nutrient cycling, ecological succession and the size, distribution and abundance of forest trees. The purpose of this report is to review tree and stand factors associated with bark beetle infestations and analyze the effectiveness of vegetation management practices for mitigating the negative impacts of bark beetles on forest ecosystems. We describe the current state of our knowledge and identify gaps for making informed decisions on proposed silvicultural treatments. This review draws from examination of 498 scientific publications (many of which are cited herein) on this and related topics. # 2006 Elsevier B.V. All rights reserved.

A vast community of organisms occurs on and within bark beetles and bark beetle-infested trees. The large diversity of symbiotic species covers a breadth of functional roles that are often redundant or substitutable. Symbiotic associations can be facultative or obligatory, and vary from antagonistic to mutualistic depending on the context at which the interactions occurs. Most symbiotic organisms are phoretic, and thus are transferred from tree to tree by bark beetles or other arthropods. Symbionts influence bark beetle communication, reproduction, nutrition and population dynamics, as well as tri-trophic interactions, competition among species, and host-tree utilization by bark beetles. Taxa considered symbiotic with bark beetles include fungi, bacteria, viruses, algae, mites, protozoa, and nematodes, among others. Interactions among symbionts are often mediated by host plant chemistry, abiotic factors such as temperature, or other phoretic organisms. Some of the symbionts, such as fungi, amplify our view of bark beetles as pests, as they may be tree pathogens or influence the coloration and texture of wood or plant products. However, some symbionts may also provide a solution to bark beetle population outbreaks and range expansion, as some symbiotic species are harmful to bark beetles and could be used as biological control agents.

We report the Þrst study of gut-associated bacteria of bark beetles using both culture- dependent and culture-independent methods. These insects are major pests of pine trees but also contribute to important ecological functions such as nutrient cycling. We found members of the - and -Proteobacteria and Firmicutes in larvae of the southern pine beetle, Dendroctonus frontalis Zimmermann. Sequences from three larval guts were grouped into one to three operational taxonomic units (OTUs) at 3% difference among sequences. Communities in adult southern pine beetle guts consisted solely of members of the -Proteobacteria. These could be grouped into three to Þve OTUs at 3% difference between sequences. These gut communities have relatively low species richness, which may resect the specialization needed to exploit a nutrient-poor food source, colonize a chemically complex habitat, and maintain consistent associations with mutualistic fungi. However, there is considerable variation in gut microbiota composition among individual insects, suggesting the need for additional studies on sources of variation and potential substitutability among species performing similar functions.

Colonisation of host trees by an endophytic herbivore, the spruce beetle, Dendroctonus rufipennis , is accompanied by invasion of its galleries by a number of fungal species. Four of these associated species were identified as Leptographium abietinum , Aspergillus fumigatus , Aspergillus nomius , and Trichoderma harzianum . 2. Trichoderma and Aspergillus significantly reduced spruce beetle survival and reproduction in controlled assays. 3. A previously undescribed behaviour was observed, in which spruce beetle adults exuded oral secretions, especially within fungus-pervaded galleries. 4. These oral secretions inhibited the growth of fungi except A. nomius , and disrupted the morphology of the latter. Administration of these secretions indicated a dose- dependent inhibitory effect. 5. Oral secretions cultured on microbiological media yielded substantial bacterial growth. 6. Filter-sterilised secretions failed to inhibit fungal growth, evidence that the bacteria are responsible for the antifungal activity. 7. Nine bacterial isolates belonging to the Actinobacteria, Firmicutes, Gammapro- teobacteria, and Betaproteobacteria taxa were obtained from the secretions. 8. Bacterial isolates showed species-specific inhibitory activity against the four fungi antagonistic to spruce beetle. The bacterium with the strongest fungal inhibition activity was the actinomycete Micrococcus luteus . 9. The production of bark beetle secretions containing bacteria that inhibit fungal growth is a novel finding. This suggests an additional level of complexity to ecological associations among bark beetles, conifers, and microorganisms, and an important adaptation for colonising subcortical tissue.

Ophiostoma ips is a common fungal associate of various conifer-infesting bark beetles in their native ranges and has been introduced into non-native pine plantations in the Southern Hemisphere. In this study, we used 10 microsatellite markers to investigate the population biology of O. ips in native (Cuba, France, Morocco and USA) and non-native (Australia, Chile and South Africa) areas to characterize host specificity, reproductive behaviour, and the potential origin as well as patterns of spread of the fungus and its insect vectors. The markers resolved a total of 41 alleles and 75 haplotypes. Higher genetic diversity was found in the native populations than in the introduced populations. Based on the origin of the insect vectors, the populations of O. ips in Australia would be expected to reflect a North American origin, and those in Chile and South Africa to reflect a European origin. However, most alleles observed in the native European population were also found in the native North American population; only the allele frequencies among the populations varied. This admixture made it impossible to confirm the origin of the introduced Southern Hemisphere (SH) populations of O. ips . There was also no evidence for specificity of the fungus to particular bark beetle vectors or hosts. Although O. ips is thought to be mainly selffertilizing, evidence for recombination was found in the four native populations surveyed. The higher genetic diversity in the North American than in the European population suggests that North America could be the possible source region of O. ips.