Effects of Mycangial Fungi and Host Tree Species on Progeny Survival and Emergence of Dendroctonus ponderosae (Coleoptera: Scolytidae)

ArticleinEnvironmental Entomology 27(6):1393-1401 · December 1998with 41 Reads
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Abstract
Dendroctonus jeffreyi Hopkins and its sibling species, D. ponderosae Hopkins, are bark beetles associated with symbiotic fungi disseminated in maxillary mycangia. Although both D. jeffreyi and D. ponderosae are associated with the fungus Ophiostoma clavigerum (Robinson-Jeffrey & Davidson), D. ponderosae is also associated with a 2nd fungus, Ophiostoma montium (Rumbold von Arx). Adult D. jeffreyi and D. ponderosae that carried O. clavigerum (isolated from D. jeffreyi), O. clavigerum (isolated from D. ponderosae), O. montium, or were fungus-free, were reared in the laboratory and introduced into bolts of Pinus contorta Douglas ex Louden and Pinus jeffreyi Greville & Balfour, hosts of D. ponderosae and D. jeffreyi, respectively, to test for effects of the fungi on progeny survival and ability to use different host tree species. Dendroctonus ponderosae associated with O. clavigerum (isolated from D. jeffreyi) and D. ponderosae associated with O. montium produced brood in both P. contorta and P. jeffreyi. The average weight of female progeny was not significantly affected by fungal or tree species. However, the production of progeny adults was significantly higher, and emergence significantly earlier, for D. ponderosae associated with O. clavigerum (isolated from D. jeffreyi) and developing in P. contorta than for D. ponderosae developing with O. montium in P. contorta. No brood was produced by D. jeffreyi or by fungus-free D. ponderosae. Larval galleries were shortest in the O. clavigerum/P. contorta treatment, whereas the longest larval galleries were produced in the O. montium/P. jeffreyi treatment. Both host tree species and fungus have an effect on the ability of progeny to successfully develop.

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    A recent accumulation of studies has demonstrated that nongenetic, maternally transmitted factors are often critical to the health and development of offspring and can therefore play a role in ecological and evolutionary processes. In particular, microorganisms such as bacteria have been championed as heritable, symbiotic partners capable of conferring fitness benefits to their hosts. At the same time, parents may also pass various nonmicrobial organisms to their offspring, yet the roles of such organisms in shaping the developmental environment of their hosts remain largely unexplored. Here, we show that the nematode Diplogastrellus monhysteroides is transgenerationally inherited and sexually transmitted by the dung beetle Onthophagus taurus. By manipulating artificial chambers in which beetle offspring develop, we demonstrate that the presence of D. monhysteroides nematodes enhances the growth of beetle offspring, empirically challenging the paradigm that nematodes are merely commensal or even detrimental to their insect hosts. Finally, our research presents a compelling mechanism whereby the nematodes influence the health of beetle larvae: D. monhysteroides nematodes engineer the bacterial and fungal communities that also inhabit the beetle developmental chambers, including specific taxa known to be involved in biomass degradation, possibly allowing larval beetles better access to their otherwise recalcitrant, plant-based diet. Thus, our findings illustrate that nongenetic inheritance can include intermediately sized organisms that live and proliferate in close association with, and in certain cases enhance, the development of their hosts’ offspring.
  • Article
    Full-text available
    Mountain pine beetle, Dendroctonus ponderosae Hopkins, is a primary agent of forest disturbance in western North America. Episodic outbreaks occur at the convergence of favorable forest age and size class structure and climate patterns. Recent outbreaks have exceeded the historic range of variability of D. ponderosae-caused tree mortality affecting ecosystem goods and services at broad spatial scales. At the same time, significant advances have occurred in our understanding of the chemical ecology of D. ponderosae and in the development of semiochemical-based tools and tactics to protect trees from mortality attributed to D. ponderosae. We synthesize related information relevant to the ecology and management of D. ponderosae and identify factors limiting the effectiveness and utility of semiochemical treatments, areas of continuing research and fields for which further work is needed.
  • Article
    Full-text available
    Over 18 million ha of forests have been destroyed in the past decade in Canada by the mountain pine beetle (MPB) and its fungal symbionts. Understanding their population dynamics is critical to improving modeling of beetle epidemics and providing potential clues to predict population expansion. Leptographium longiclavatum and Grosmannia clavigera are fungal symbionts of MPB that aid the beetle to colonize and kill their pine hosts. We investigated the genetic structure and demographic expansion of L. longiclavatum in populations established within the historic distribution range and in the newly colonized regions. We identified three genetic clusters/populations that coincide with independent geographic locations. The genetic profiles of the recently established populations in northern British Columbia (BC) and Alberta suggest that they originated from central and southern BC. Approximate Bayesian Computation supports the scenario that this recent expansion represents an admixture of individuals originating from BC and the Rocky Mountains. Highly significant correlations were found among genetic distance matrices of L. longiclavatum, G. clavigera, and MPB. This highlights the concordance of demographic processes in these interacting organisms sharing a highly specialized niche and supports the hypothesis of long-term multipartite beetle-fungus co-evolutionary history and mutualistic relationships.
  • Article
    The inflorescences and infructescences of African Protea trees provide habitat for a large diversity of Sporothrix species. Here we describe two additional members, Sporothrix nsini sp. nov. and Sporothrix smangaliso sp. nov., that are associated with the infructescences of various Protea species from grasslands and savannas in the KwaZulu-Natal, North-West, Gauteng and Mpumalanga provinces of South Africa. Their description raises the number of described Protea-associated Sporothrix species to twelve. S. smangaliso sp. nov. is distantly related to other Protea-associated species and, in phylogenies using multiple markers (ITS, beta-tubulin and calmodulin), groups with taxa such as Sporothrix bragantina from Brazil and Sporothrix curviconia from the Ivory Coast. S. nsini sp. nov. resolved as sister to a clade containing four other Protea-associated species within the Sporothrix stenoceras complex. S. nsini sp. nov. was collected from within the same infructescences of Protea caffra that also contained the closely related S. africana and S. protearum. This highlights the need to study and understand the factors that influence host selection and speciation of Sporothrix in this atypical niche.
  • Article
    During host‐breadth expansion, phytophagous insects incur risk from potentially deleterious novel host environments at the same time as potentially securing a potential escape in space or time from competing species.Bark beetles reproduce under the bark of stems and branches of mature, stressed or moribund trees, and may suffer high mortality from plant defences and inter‐ and intraspecific competition.An epidemic of mountain pine beetle (Dendroctonus ponderosae Hopkins) in western Canada has extended to over 18.1 million hectares of lodgepole pine (Pinus contorta Douglas ex. Loudon) forests.In some areas, mountain pine beetles have been found to reproduce within interior hybrid spruces [Picea glauca (Moench) Voss × engelmannii Parry ex. Engelmann], a normally rare occurrence.Using mountain pine beetles reared from naturally‐infested interior hybrid spruce and lodgepole pine hosts, we examined the effect of female natal species and colonized host species on the ability to attract mates and reproduce within spruce and pine logs deployed as a choice assay in a field setting. Additionally, we examined whether the arrival and reproduction of competitors such as pine engravers (Ips spp.) was associated with reduced brood production.Females reared from pine and spruce exhibited similar reproductive potentials. Recruitment and establishment of ovipositional galleries, larval galleries and pupal chambers were similar in the typical and novel hosts.Reproduction by mountain pine beetles in spruce, although successful, was significantly lower than in pine. This reduction occurred despite spruce logs being almost entirely free of competing secondary beetles.
  • Conference Paper
    When mountain pine beetles (Coleoptera: Curculionidae) attempt to colonize healthy hosts, trees respond by accumulating high concentrations of defensive chemicals at the point of attack. These compounds consist largely of monoterpenes and diterpene resin acids that inhibit both beetles and their symbiotic fungi. We evaluated whether bacteria associated with the mountain pine beetle degrade these terpenoids, thus potentially assisting in host colonization. We found that some bacteria grew in terpene-amended media and, with some bacteria, terpenes were degraded. Additionally, we detected genes involved in degradation of both mono- and diterpenes from bacteria associated with beetles and their galleries. These results suggest that beetle-associated bacteria may be important contributors to the ability of bark beetles to survive in, and kill trees.
  • Article
    Ambrosia beetles subsist on fungal symbionts that they carry to, and cultivate in, their natal galleries. These symbionts are usually saprobes, but some are phytopathogens. Very few ambrosial symbioses have been studied closely, and little is known about roles that phytopathogenic symbionts play in the life cycles of these beetles. One of the latter symbionts, Raffaelea lauricola, causes laurel wilt of avocado, Persea americana, but its original ambrosia beetle partner, Xyleborus glabratus, plays an uncertain role in this pathosystem. We examined the response of a putative, alternative vector of R. lauricola, Xyleborus bispinatus, to artificial diets of R. lauricola and other ambrosia fungi. Newly eclosed, unfertilized females of X. bispinatus were reared in no-choice assays on one of five different symbionts or no symbiont. Xyleborus bispinatus developed successfully on R. lauricola, R. arxii, R. subalba and R. subfusca, all of which had been previously recovered from field-collected females of X. bispinatus. However, no development was observed in the absence of a symbiont or on another symbiont, Ambrosiella roeperi, recovered from another ambrosia beetle, Xylosandrus crassiusculus. In the no-choice assays, mycangia of foundress females of X. bispinatus harbored significant colony-forming units of, and natal galleries that they produced were colonized with, the respective Raffaelea symbionts; with each of these fungi, reproduction, fecundity and survival of the beetle were positively impacted. However, no fungus was recovered from, and reproduction did not occur on, the A. roeperi and no symbiont diets. These results highlight the flexible nature of the ambrosial symbiosis, which for X. bispinatus includes a fungus with which it has no evolutionary history. Although the “primary” symbiont of the neotropical X. bispinatus is unclear, it is not the Asian R. lauricola.
  • Article
    Full-text available
    Separating symbioses from incidental associations is a major obstacle in symbiosis research. In this survey of fungi associated with Asian bark and ambrosia beetles, we used quantitative culture and DNA barcode identification to characterize fungal communities associated with co-infesting beetle species in pines (Pinus) of China and Vietnam. To quantitatively discern likely symbioses from coincidental associations, we used multivariate analysis and multilevel pattern analysis (a type of indicator species analysis). Nearly half of the variation in fungal community composition in beetle galleries and on beetle bodies was explained by beetle species. We inferred a spectrum of ecological strategies among beetle-associated fungi: from generalist multispecies associates to highly specialized single-host symbionts that were consistently dominant within the mycangia of their hosts. Statistically significant fungal associates of ambrosia beetles were typically only found with one beetle species. In contrast, bark beetle-associated fungi were often associated with multiple beetle species. Ambrosia beetles and their galleries were frequently colonized by low-prevalence ambrosia fungi, suggesting that facultative ambrosial associations are commonplace, and ecological mechanisms such as specialization and competition may be important in these dynamic associations. The approach used here could effectively delimit symbiotic interactions in any system where symbioses are obscured by frequent incidental associations. It has multiple advantages including (1) powerful statistical tests for non-random associations among potential symbionts, (2) simultaneous evaluation of multiple co-occurring host and symbiont associations, and (3) identifying symbionts that are significantly associated with multiple host species.
  • Article
    Full-text available
    Ecology of the Mountain Pine Beetle Dendroctonus ponderosae (Coleoptera: Scolytidae) and Its Associated Microorganisms: For a Risk Assessment of Its Invasion into Japan. Etsuko SHODA-KAGAYA,(1'*) Akira UEDA,(2) Hayato MASUYA(3) and Natsumi KANZAKI(1) (1)Forestry and Forest Products Research Institute; 1 Matsunosato, Tsukuba, Ibaraki 305-8687, Japan. (2)Kyushu Research Center, Forestry and Forest Products Research Institute; 4-11-16 Kurokami, Chuo, Kumamoto, Kumamoto 860-0862, Japan. (3)Tohoku Research Center, Forestry and Forest Products Research Institute; 92-25 Nabeyashiki, Shimokuriyagawa, Morioka, Iwate 020-0123, Japan.
  • Article
    Morphology, mitochondrial DNA (mtDNA) restriction fragment polymorphisms (RFLPs) and nuclear DNA (nDNA) fingerprinting were used to clarify relationships among the morphologically similar Ophiostoma and Leptographium species associated with mycangia of three Dendroctonus bark beetles (Ophiostoma clavigerum associated with both D. ponderosae and D. jeffreyi, and L. pyrinum associated with D. adjunctus), as well as a closely related nonmycangial bark beetle associate (L. terebrantis). Most isolates of O. clavigerum form long (40–70 μm), septate conidia, while all isolates of L. terebrantis and L. pyrinum form conidia less than 17.0 μm in length. The conidia of L. pyrinum are pyriform, with truncate bases, while the conidia of the other species form only slightly truncate bases. Conidial masses of L. terebrantis are creamy yellow, while the conidial masses of the other species are white. Nuclear DNA fingerprints resulting from probing PstI restrictions with the oligonucleotide probe (CAC)5 and HaeIII and MspI restrictions of mtDNA, exhibited three major clusters. In the dendrogram developed from mtDNA RFLPs, the L. pyrinum isolates formed one cluster, while the majority of O. clavigerum isolates, including all D. jeffreyi isolates, formed another. A third cluster was composed of all L. terebrantis isolates, as well as several O. clavigerum isolates from D. ponderosae. The inclusion of some O. clavigerum isolates in the L. terebrantis cluster suggests that horizontal transfer of mtDNA has occurred among these fungi. The nDNA dendrogram also exhibited three clusters, and most isolates of L. pyrinum, L. terebrantis and O. clavigerum grouped separately; however, one isolate of O. clavigerum grouped with the L. terebrantis isolates, while one isolate of L. terebrantis grouped with O. clavigerum. No genetic markers were found that distinguished between O. clavigerum associated with D. ponderosae and O. clavigerum associated with D. jeffreyi. Ophiostoma clavigerum might be a recently diverged morphological variant of L. terebrantis, with special adaptations for grazing by young adults of D. jeffreyi and D. ponderosae. The anamorph of O. clavigerum, Graphiocladiella clavigerum, is transferred to Leptographium.
  • Article
    The pine weevil (Hylobius abietis, Coleoptera: Curculionidae) is an important pest of conifer seedlings in Europe. Despite its economic importance, little is known about the composition of its gut microbial community and the role it plays in mediating the weevil's ability to utilize conifers as a food source. Here, we characterized the gut bacterial communities of different populations of H. abietis across Europe and compared them to those of other beetles that occupy similar ecological niches. We demonstrate that the microbial community of H. abietis is similar at higher taxonomic levels (family and genus) across locations in Europe, with Wolbachia as the dominant microbe, followed by Enterobacteria and Firmicutes. Despite this similarity, we observed consistent differences between countries and locations, but not sexes. Our meta-analysis demonstrates that the gut bacterial community of the pine weevil is very similar to that of bark beetles that also exploit conifers as a food source. The Enterobacteriaceae symbionts of both host taxa are especially closely related phylogenetically. Conversely, the microbiota of H. abietis is distinct from that of closely related weevils feeding on non-conifer food sources, suggesting that the microbial community of the pine weevil is determined by the environment and may be relevant to host ecology. Furthermore, several H. abietis-associated members of the Enterobacteriaceae family are known to contain genes involved in terpenoid degradation. As such, we hypothesize that the gut microbial community is important for the utilization of conifer seedlings as a food source, either through the detoxification of plant secondary metabolites or supplementation of essential nutrients. This article is protected by copyright. All rights reserved.
  • Article
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    The Chinese white pine beetle is arguably the most destructive forest insect in the Qinling Mountains in Northern China. Little is known about the structure of the fungal communities associated with Dendroctonus armandi, even though this wood-boring insect plays important roles in ecosystem and biological invasion processes that result in huge economic losses in pine forests. The aim of this study was to investigate the fungal community structure present in the galleries and guts of D. armandi at different developmental stages using PCR-denaturing gradient gel electrophoresis (DGGE). Analysis of PCR-amplified 18S rRNA gene fragments of fungi from the guts of D. armandi revealed fungal communities of low complexity that differed according to the developmental stage. Yeast of the genus Candida and the filamentous fungi Ophiostoma predominated in D. armandi and its galleries. In particular, Candida accounted for 56% of the fungal community in the pupal stage. Characterizing the evolution and content of the intestinal microbial community structure in D. armandi may facilitate the development of new pest control strategies.
  • Article
    Stored resources in trees reflect physiological and environmental variables and affect life history traits, including growth, reproduction, resistance to abiotic stress, and defense. However, less attention has been paid to the fact that stored resources also determine tissue nutritional quality and may have direct consequences for the success of herbivores and pathogens. Here, we investigated whether stored resources differed between two hosts of the mountain pine beetle (Dendroctonus ponderosae Hopkins, 1902): lodgepole pine (Pinus contorta Douglas ex. Loudon), a common host, and whitebark pine (Pinus albicaulis Engelmann), a more naive host that grows at higher altitudes. Phloem and sapwood were sampled in small- and large-diameter trees at two elevations, and nitrogen, phosphorus, nonstructural carbohydrates, and lipids were measured. We found that concentrations of stored resources increased with elevation and tree diameter for both species and that whitebark pine had thicker phloem than lodgepole pine. Overall, stored resources were higher in whitebark pine such that small-diameter whitebark pine trees often had resource concentrations higher than large-diameter lodgepole pines. These results suggest that whitebark pine is of higher nutritional quality than lodgepole pine, which could have implications for the current expansion of mountain pine beetles into higher altitude and latitude forests in response to climate warming. © 2014, National Research Council of Canada. All rights reserved.
  • Article
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    Bark beetles are associated with diverse communities of symbionts. Although fungi have received significant attention, we know little about how bacteria, and in particular their interactions with fungi, affect bark beetle reproduction. We tested how interactions between four bacterial associates, and two symbiotic and two opportunistic fungi affect performance of mountain pine beetles (Dendroctonus ponderosae) in host tissue. We compared beetle performance in phloem of its historical host, lodgepole pine (Pinus contorta), and its novel host recently accessed through warming climate, jack pine (Pinus banksiana). Overall, beetles produced more larvae, and established longer ovipositional and larval galleries in tissue predominantly colonized by the symbiotic fungi, Grosmannia clavigera or Ophiostoma montium than by the opportunistic colonizer Aspergillus and to a lesser extent, Trichoderma. This occurred in both historical and naïve hosts. Impacts of bacteria on beetle reproduction depended on particular fungus-bacterium combinations and host species. Some bacteria, e.g., Pseudomonas sp. D4-22 and Hy4T4 in P. contorta and Pseudomonas sp. Hy4T4 and Stenotrophomonas in P. banksiana, reduced antagonistic effects by Aspergillus and Trichoderma resulting in more larvae and longer ovipositional and larval galleries. These effects were not selective, as bacteria also reduced beneficial effects by symbionts in both host species. Interestingly, Bacillus enhanced antagonistic effects by Aspergillus in both hosts. These results demonstrate that bacteria influence brood development of bark beetles in host tissue. They also suggest that climate-driven range expansion of D. ponderosae through the boreal forest will not be significantly constrained by requirements of, or interactions among, its microbial associates.
  • Article
    A novel “rearing-tube” method was developed and used to investigate the performance of mountain pine beetle (MPB), Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae: Scolytinae), with its three main ophiostomatalean fungal symbionts, Grosmannia clavigera (Robinson-Jeffrey and Davidson) Zipfel, de Beer, and Wingfield (Ophiostomataceae), Ophiostoma montium (Rumbold) von Arx (Ophiostomataceae), and Leptographium longiclavatum Lee, Kim, and Breuil (Ophiostomataceae). Transparent glass tubes filled with sterile ground jack pine ( Pinus banksiana Lambert; Pinaceae) phloem and sapwood (9:1 ratio) were used to rear MPB from egg to adult with each fungus under controlled environmental conditions. Mountain pine beetle mortality was higher and development longer in fungus-free controls compared to fungal treatments. Among fungal treatments, insects developed faster, constructed shorter larval galleries, and had fewer supernumerary instars with L. longiclavatum. Insect survival was not affected by fungal treatments. Hyphal extension through the rearing medium was fastest for L. longiclavatum . Phloem nitrogen was reduced significantly by the presence of L. longiclavatum. Results support the hypothesis that ophiostomatalean symbionts provide benefits to MPB. The rearing-tube method is useful to tease apart confounding interspecific interactions between bark beetles and symbiotic fungus species.
  • Chapter
    In this chapter we provide an overview of the many different defense strategies of conifers against insect pests and fungal pathogens. Much of this chapter deals with the economically and ecologically important species of pine (Pinus spp.) and spruce (Picea spp.). We highlight the anatomical and chemical defenses as well as their biochemical, molecular, and genomic underpinnings.
  • Article
    Recent outbreaks of forest insects have been directly linked to climate change-induced warming and drought, but effects of tree stored resources on insects have received less attention. We asked whether tree stored resources changed following mountain pine beetle (Dendroctonus ponderosae Hopkins) attack and whether they affected beetle development. We compared initial concentrations of stored resources in the sapwood of whitebark pine (Pinus albicaulis Engelmann) and lodgepole pine (Pinus contorta Douglas ex. Louden) with resource concentrations one year later, in trees that were naturally attacked by beetles and trees that remained unattacked. Beetles did not select host trees based on sapwood resources—there were no consistent a priori differences between attacked versus unattacked trees—but concentrations of nonstructural carbohydrate (NSC), lipids, and phosphorus declined in attacked trees, relative to initial concentrations and unattacked trees. Whitebark pine experienced greater resource declines than lodgepole pine; however, sapwood resources were not correlated with beetle success in either species. Experimental manipulation confirmed that the negative effect of beetles on sapwood and phloem NSC was not due to girdling. Instead, changes in sapwood resources were related to the percentage of sapwood with fungal blue-stain. Overall, mountain pine beetle attack affected sapwood resources, but sapwood resources did not contribute directly to beetle success; instead, sapwood resources may support colonization by beetle-vectored fungi that potentially accelerate tree mortality. Closer attention to stored resource dynamics will improve our understanding of the interaction between mountain pine beetles, fungi, and host trees, an issue that is relevant to our understanding of insect range expansion under climate change.
  • Article
    Full-text available
    Bark beetles carry a number of associated organisms that are transferred to the host tree upon attack that are thought to play a role in tree decline. To assess the pathogenicity to western white pine (WWP; Pinus monticola) of fungi carried by the mountain pine beetle (MPB; Dendroctonus ponderosae), and to evaluate the potential for systemic prophylactic treatments for reducing fungal impacts, experiments were conducted with WWP seedlings to meet three objectives: 1) evaluate pathogenicity of two MPB-associated blue-stain fungi; 2) evaluate phytotoxicity of tree injection products; 3) evaluate the anti-fungal activity of tree injection products, in vitro and in vivo, toward the associated blue-staining fungi. To evaluate pathogenicity, seedlings were inoculated with Grosmannia clavigera or Leptographium longiclavatum, common fungal associates of MPB. Seedling mortality at four months after inoculation was 50% with L. longiclavatum and 90% with G. clavigera, both significantly higher than controls and thereby demonstrating pathogenicity. Phytotoxic effects of TREE-äge®, Alamo®, and Arbotect® were evaluated by stem injection; no phytotoxic effects were observed. Anti-fungal properties of the same three products were evaluated in vitro against G. clavigera, where Alamo was most active. Co-inoculation of G. clavigera and L. longiclavatum into seedlings after a stem injection of Alamo showed significantly less mortality and lesion formation than either species alone. Results support the hypothesis that MPB blue-stain associates, particularly G. clavigera, promote death of WWP when attacked by MPB. These findings suggest that the administration of a fungicide with insecticide for tree protection against bark beetles may be advantageous.
  • Article
    Haplodiploidy is a highly unusual genetic system that has arisen at least 17 times in animals of varying lifestyles, but most of these haplodiploid lineages remain relatively poorly known. In particular, the ecological and genetic circumstances under which haplodiploidy originates have been difficult to resolve. A recent molecular-phylogenetic study has resolved the phylogenetic position of the haplodiploid clade of scolytine beetles as the sister group of the genusDryocoetes . Haplodiploid bark beetles are remarkable in that the entire clade of over 1300 species are apparently extreme (sib-mating) inbreeders, most of which cultivate fungi for food while some attack phloem, twigs or seeds. Here we present a much more detailed molecular-phylogenetic study of this clade. Using partial sequences of elongation factor 1-alpha and the mitochondrial small ribosomal subunit (12S), we reconstructed the phylogeny for 48 taxa within the haplodiploid clade, as well as two species of the diplodiploid sister genus Dryocoetes. Results indicate that the genus Ozopemon is the basal lineage of the haplodiploid clade. Since Ozopemon, Dryocoetes, and other outgroups are phloem-feeding, this strongly suggest that haplodiploidy and inbreeding evolved in a phloem feeding ancestor. Following the divergence ofOzopemon there is a series of extremely short internodes near the base of the clade, suggesting a very rapid rate of diversification in early Miocene (based on fossil evidence and sequence divergence). Among the many substrates for breeding and food resources utilized within this species-rich clade, the cultivation of yeast-like ambrosia fungi in tunnels deep into the wood predominates (nearly 90% of the species). The number of transitions to feeding on such fungi was few, possibly only one, and is perhaps an irreversible transition. The habit of feeding on fungi cultured in xylem makes it possible for the beetles to use a great variety of plant taxa. This extreme resource generalism, in conjunction with the colonization advantage conferred by haplodiploidy and inbreeding, may have promoted the rapid diversification of this clade.
  • Article
    Considerable intraspecific variation was found in the monoterpene composition of the wood oleoresin of Pinus coulteri, P. contorta, P. washoensis, and P. jeffreyi. This paper reports data based on the analysis of 20 to 128 trees per species; except for P. contorta, sampling covered a large portion of the range of each species. In general, there were no distinctive geographical variations, but all except P. jeffreyi had appreciable local variation: P. coulteri in α-pinene, β-phellandrene, and myrcene; P. washoensis in β-pinene, 3-carene, and myrcene; P. contorta in β-phellandrene, 3-carene, and β-pinene. Measurable or trace amounts of sabinene were found in all species except P. washoensis. One unknown compound, tentatively identified as α-thujene, was found in P. washoensis and P. contorta. Another unknown compound, tentatively identified as terpinolene, was found in all species; it varied in quantity in direct proportion to the amount of 3-carene. P. jeffreyi monoterpene consisted of 88 to 99 percent heptane, with measurable or trace amounts of several other monoterpenes.
  • Article
    Full-text available
    The effect of 100 ppm cycloheximide on the linear growth of 53 species of Ceratocystis sensu amplo and related fungi was determined on malt extract agar at 25 C. Generally, only those species with Chalara-like anamorphs (Ceratocystis sensu stricto) were inhibited by 100 ppm cycloheximide. Growth of other Ceratocystis species (Ophiostoma sensu von Arx), Europhium spp., and related anamorphs was generally unaffected by cycloheximide.
  • Article
    The sapwood and heartwood of ponderosa pine (Pinus ponderosa) and Jeffrey pine (P. jeffreyi) have been examined for monoterpenes, fatty and resin acids. The composition of the fatty and resin acids is comparable in each species. The principal qualitative differences between these two species is the presence of the hydrocarbons n-heptane, n-nonane, and n-undecane in the steam volatiles from Jeffrey pine and their apparent absence in ponderosa pine.
  • Article
    Dendroctonus jeffreyi andD. ponderosae are morphologically similar sympatric species of pine bark beetles over portions of their geographic ranges; however,D. jeffreyi is monophagous onP. jeffreyi whileD. ponderosae is highly polyphagous. Both species carry a species of mycangial fungi that are also very similar in appearance. Growth of the two mycangial fungi and of the fungusLeptographium terebrantis (associated with the polyphagous and non-tree-killingDendroctonus valens) in the presence of oleoresin constituents of host and nonhost conifers was tested by placing individual chemicals on agar growth medium and by growing the cultures in saturated atmospheres of the chemicals. The fungus associated withD. jeffreyi showed greater tolerance for chemical constituents placed on the growth medium than the other two fungi, and growth after three days was enhanced by heptane, the dominant constituent ofP. jeffreyi oleoresin. Growth of all three species of fungi was reduced by the resin constituents when the chemicals were presented as saturated atmospheres. The results suggest that the influence of the tree on growth of the symbiotic fungi of the bark beetles during the initial attack process may be different than after colonization by the beetles is complete. The difference in the responses of the apparently related species of mycangial fungi may provide some new insight into the evolutionary history of these beetle/mycangial fungus/host tree systems.
  • Article
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    Growth of the three major fungal associates of Dendroctonusfrontalis Zimmermann in Pinus taeda L. phloem was evaluated with respect to development of the wound-induced lesion following artificial inoculations. Ophiostomaminus (Hedge.) H. & P. Syd. and Ceratocystiopsisranaculosus Perry et Bridges were isolated from apparently healthy phloem 2 cm outside the margin of the visible wound-induced lesion up to 28 days after inoculation. Ophiostomaminus was isolated more often than C. ranaculosus from outside the lesion, and both fungi were isolated less often from outside the lesion with increasing time after inoculation. SJB 122 was never isolated from outside the wound-induced lesion. All fungi were isolated more often adjacent to the inoculation site than at the lesion margin or outside the lesion, and these differences were generally greater with increasing time after inoculation. Following combined inoculations, O. minus inhibited the growth of both mycangial fungi, while C. ranaculosus appeared to inhibit the growth of SJB 122. Inoculations with heat-killed O. minus and C. ranaculosus and two nonpine plant pathogens, Ceratocystisfagacearum (Bretz) Hunt and Hypoxylonatropunctatum (Schw. ex Fr.) Cke., failed to provide strong evidence of chemical elicitors that may stimulate lesion formation in the absence of living fungi capable of growing in the host tissues. Ophiostomaminus grew at least 1.5 cm into the sapwood after 26 days, while C. ranaculosus grew less than 0.5 cm into the sapwood during the same period of time.
  • Article
    Phloem of loblolly and shortleaf pine trees attacked by the southern pine beetle, Dendroctonus frontalis Zimmerman, exhibited a characteristic drying followed by rehydration. Trees With initially higher phloem moistures retained relatively higher levels during drying following attack. Limited population estimates suggested that brood survival was lower in trees with high moisture. In the laboratory, rearing bolts which were waxed to maintain higher phloem moisture had lower beetle survival than unwaxed bolts. High phloem moisture was associated with the formation of long larval mines, instead of feeding chambers, which in turn led to lowered survival. Emergence of the survivors was positively correlated with phloem moisture, suggesting that high moisture was beneficial to larvae and pupae in the outer bark.
  • Article
    Two mycangial fungi, Ceratocystis nigracarpa Davidson and an unidentified basidiomycete, were isolated from the walls of pupal chambers made by Dendroctollus brevicomis LeConte, along with another fungus, Ceratocystis minor Hedge, which is closely associated with the beetle but not found in thc mycangium. Beetles eclosing to the adult stage under axenic conditions had empty mycangia, whereas those eclosing within the pupal chambers acquired spores of both mycangial fungi. Beetles emerging from standing trees had only spores in their mycangia. However, beetles responding to pheromone-baited trees had mycangia filled with spores and mycalia, as did ovipositing females removed from under the bark of newly colonized ponderosa pine. Thus, there is an 8- to 10-day delay between the time beetles emerge and the time the fungi grow and completely fill the mycangium. Beetles apparently do not colonize trees during this time, which suggests that there is a lag between emergence of new adult females and responsiveness to pheromone.
  • Article
    Development time and observed mortality of Dendroctonus frontalis Zimm. in relation to changes in host-tree condition were studied in east Texas during the summer of 1977. Four indices of host condition were monitored: bark, phloem, and xylem moisture and twig xylem water potential. Successful attack initiated predictable patterns of drying and rehydration in the phloem and xylem, and increasingly negative water potentials at the branch tips. These patterns were described mathematically and correlated to beetle development time. Eggs and 1st stage larvae were not affected by changes in phloem moisture in individual trees. However, development of 2nd- and 3rd-stage larvae was slowed when phloem moisture stayed above ca. 170% oven dry weight prior to those stages. Development of 2nd- and 3rd-stage larvae was also slowed in trees exhibiting large decreases in phloem moisture during those stages. Larval mortality was greater than mortality to other life stages. Concurrently, changes in phloem moisture were greatest when larvae were developing. Bark moisture remained at ca. 30% oven dry weight throughout beetle development. Development of 4th stage larvae and pupae was slower in trees with high average bark moisture during those stages.
  • Article
    Full-text available
    Scolytid bark beetles that colonize living conifers are frequently associated with specific fungi that are carried in specialized structures or on the body surface. These fungi are introduced into the tree during the attack process. The continuing association suggests that there is mutual benefit to the fitness of both beetles and fungi. The fungal species may benefit from the association with the beetles by transport to new host trees. Beetle species may benefit from the association with fungi by feeding on the fungi, or by the fungi contributing to the death of the host trees through mycelial penetration of host tissue, toxin release, interactions with preformed and induced conifer defenses, or the combined action of both beetles and fungi during colonization. Extensive research has been directed towards characterizing the interactions of beetle-fungal complexes with live host conifers and determining the ecological advantages for maintaining the associations. However, differences among systems and how species interact under different population and environmental conditions make it difficult to generalize about the importance of the separate biological components in successful host colonization.
  • Article
    A mycangium containing blue-stain fungi and yeasts is located in the cardo of the maxilla of the mountain pine bettle, Dendroctonus ponderosae Hopk. Symbiosis between one or more of the microorganisms and the insect is indicated.