Pine Bark Beetle Research Articles

Climate change may already threaten Scots pine stands in the Swiss Alps

Large numbers of Scots pine are dying in the dry inner-alpine valleys of the European Alps; in Switzerland, locally almost half the Scots pine (Pinus sylvestris L.) population has died since 1995. As Switzerland’s temperature has increased at more than twice the global average in the 20th century and as most of this increase has occurred during the last 20 years, we investigated possible relationships between the dying Scots pine and climatic parameters. We centred our studies in the upper Rhone valley. Our results show that the strong climatic warming that has occurred in recent years may well be the indirect cause of the mortality observed in these forests. Tree mortality was highest following the dry and hot year 1998, and tree defoliation, an indicator of tree vitality, showed a strong correlation with the previous year’s precipitation. While precipitation showed no clear significant trend over time, the number of warm days (mean>20 °C, maximum>25 °C) and potential evapotranspiration have significantly increased over the last 20 years. Higher temperatures favour pine wood nematodes and bark beetles, both of which are found at the study site, and increasing drought stress reduces tree resistance against pathogens. As these forests have in part protective functions, there is a need to better understand the mortality through interdisciplinary research and also to find means to change the species composition in order to establish tree species that are better able to withstand warmer temperatures.

Characterisation of Ophiostoma species associated with pine bark beetles from Mexico, including O. pulvinisporum sp. nov.

Bark beetles (Coleoptera: Scolytidae) are common vectors of Ophiostoma species. These fungi include primary tree pathogens and important sapstain agents. In Mexico, Ips calligraphus and Dendroctonus mexicanus occur on many species of pine. Pinus maximinoi and P. pseudostrobus are the hosts of both species of insects. Little research has been done on ophiostomatoid fungi associated with pine bark beetles in Mexico. We recently obtained specimens of these bark beetles and their galleries from Mexico. The aim of the study was to isolate and identify Ophiostoma species associated with the two beetle species. In total, six ophiostomatoid species were found to be associated with them. These included Ceratocystiopsis minuta, Ophiostoma pluriannulatum, an O. galeiformis-like species, two unidentified Sporothrix spp., as well as a new species similar to O. adjuncti, O. ips, and O. montium, that we name as O. pulvinisporum sp. nov.

Coordinated gene expression for pheromone biosynthesis in the pine engraver beetle, Ips pini (Coleoptera: Scolytidae).

In several pine bark beetle species, phloem feeding induces aggregation pheromone production to coordinate a mass attack on the host tree. Male pine engraver beetles, Ips pini (Say) (Coleoptera: Scolytidae), produce the monoterpenoid pheromone component ipsdienol de novo via the mevalonate pathway in the anterior midgut upon feeding. To understand how pheromone production is regulated in this tissue, we used quantitative real-time PCR to examine feeding-induced changes in gene expression of seven mevalonate pathway genes: acetoacetyl-coenzyme A thiolase, 3-hydroxy-3-methylglutaryl coenzyme A synthase, 3-hydroxy-3-methylglutaryl coenzyme A reductase, mevalonate 5-diphosphate decarboxylase, isopentenyl-diphosphate isomerase, geranyl-diphosphate synthase (GPPS), and farnesyl-diphosphate synthase (FPPS). In males, expression of all these genes significantly increased upon feeding. In females, the expression of the early mevalonate pathway genes (up to and including the isomerase) increased significantly, but the expression of the later genes (GPPS and FPPS) was unaffected or decreased upon feeding. Thus, feeding coordinately regulates expression of the mevalonate pathway genes necessary for pheromone biosynthesis in male, but not female, midguts. Furthermore, basal mRNA levels were 5- to 41-fold more abundant in male midguts compared to female midguts. This is the first report of coordinated regulation of mevalonate pathway genes in an invertebrate model consistent with their sex-specific role in de novo pheromone biosynthesis.

Forests and forest protection in Cyprus

Cyprus, an island located in the eastern Mediterranean Basin, was heavily forested prior to human settlement. Human influence since about 6000 BC has significantly changed the area and composition of the island's forests. Approximately 40% of the Island is presently occupied by forest, maquis and garigue vegetation. The dominant tree species in Cyprus' forests is Pinus brutia, which has been planted extensively on abandoned agricultural lands and areas burned by wildfire. P. brutia forests are subject to periodic wildfire episodes. In addition, young plantations are subject to defoliation by the pine processionary caterpillar, Thaumetopoea pityocampa (Lepidoptera: Pityocampidae), and older forests are subject to attack by several species of bark beetles (Coleoptera: Scolytidae). A policy of extensive planting of pines will, most likely, result in continued problems with wildfire, pine processionary caterpillar and bark beetles in the foreseeable future. Long-term measures to effectively manage these problems include examination of opportunities to plant alternative tree species and to manage the vegetation to increase the diversity of the Island's wildland ecosystems. Key words: Cyprus, forest protection, pine processionary caterpillar, bark beetles, wildfire

Interactions between Orthotomicus erosus (Woll.) (Col., Scolytidae) and the Argentine ant Linepithema humile (Mayr) (Hym., Formicidae)

Interactions occurring between Orthotomicus erosus, an economically important pine bark beetle in Portugal, and the aggressive Argentine ant Linepithema humile were investigated. Tri-trophic “experimental enclosures” consisting of Pinus pinaster logs, O. erosus adults and L. humile workers were set up in the field and in the laboratory. Interactions between ants and scolytids were observed and quantified in terms of the bark beetle’s success in colonizing the logs. The presence of L. humile did not influence the ability of O. erosus to colonize the logs, apparently due to the difficulties met by the ants in handling the bark beetles and to their inability to injure them. Thus, although abundant in many pine stands in Portugal and in spite of its aggressiveness, L. humile does not seem to affect populations of O. erosus.

Comparison of gene representation in midguts from two phytophagous insects, Bombyx mori and Ips pini, using expressed sequence tags

Midgut proteins may provide new molecular targets for insect control. This could be particularly important for some pests, such as pine bark beetles, which are difficult to control by conventional methods. Expressed sequence tags (ESTs) provide information about the activity of a particular tissue, and, in the case of pest insects, may quickly identify potential targets. We present here an EST project representing 574 tentative unique genes (TUGs) expressed in the midgut of the male pine engraver beetle, Ips pini. This tissue uses the mevalonate pathway to produce the monoterpenoid pheromone component, ipsdienol, de novo in response to juvenile hormone (JH) III. Comparison of our ESTs with those previously isolated from larval silkmoth ( Bombyx mori) midguts revealed interesting similarities and differences in gene representation that correlate with the conserved and divergent functions of these two tissues. For example, seven mevalonate pathway genes were represented in the I. pini ESTs, while none were found from B. mori. This type of comparison may assist the identification of species-specific targets for future pest control strategies.

Taxonomic re-evaluation of three related species of Graphium, based on morphology, ecology and phylogeny

Two fungi associated with bark beetles, Graphium pseudormiticum (described in 1994) and Rhexographium fimbriisporum (described in 1995), have two micromorphological characters in common. Both species produce conidia with conspicuous basal frills, and the conidia align in chains, despite being produced in slime. The association of G. pseudormiticum with the pine bark beetle, Orthotomicus erosus, and the association of R. fimbriisporum with the spruce bark beetle, Ips typographus, suggest ecological differences between the two fungal species. Analyses of micromorphology and phylogenetic analyses of aligned 18S and ITS sequences suggest that these two species are congeneric and should be classified in Graphium but that they represent distinct species. A collection of strains tentatively identified as Graphium spp., isolated from Ips typographus on Picea abies, Ips cembrae on Larix decidua and Tomicus minor on Pinus sylvestris in Austria share the same unusual basal conidial frills and conidial chains. Isolates from spruce were identified as G. fimbriisporum and those from pine as G. pseudormiticum. The strains from Ips cembrae on Larix decidua, distinguished by the reddish color of their colonies, microscopic structures and molecular characteristics, are described as the new species Graphium laricis sp. nov., and the close relationship of this species with the other two species is confirmed.

Taxonomic Re-Evaluation of Three Related Species of Graphium, Based on Morphology, Ecology and Phylogeny

Two fungi associated with bark beetles, Graphium pseudormiticum (described in 1994) and Rhexographium fimbriisporum (described in 1995), have two micromorphological characters in common. Both species produce conidia with conspicuous basal frills, and the conidia align in chains, despite being produced in slime. The association of G. pseudormiticum with the pine bark beetle, Orthotomicus erosus, and the association of R. fimbriisporum with the spruce bark beetle, Ips typographus, suggest ecological differences between the two fungal species. Analyses of micromorphology and phylogenetic analyses of aligned 18S and ITS sequences suggest that these two species are congeneric and should be classified in Graphium but that they represent distinct species. A collection of strains tentatively identified as Graphium spp., isolated from Ips typographus on Picea abies, Ips cembrae on Larix decidua and Tomicus minor on Pinus sylvestris in Austria share the same unusual basal conidial frills and conidial chains. Isolates from spruce were identified as G. fimbriisporum and those from pine as G. pseudormiticum. The strains from Ips cembrae on Larix decidua, distinguished by the reddish color of their colonies, microscopic structures and molecular characteristics, are described as the new species Graphium laricis sp. nov., and the close relationship of this species with the other two species is confirmed.

A novel sex-specific and inducible monoterpene synthase activity associated with a pine bark beetle, the pine engraver, Ips pini.

Ecological interactions of conifers and coniferophagous bark beetles are determined in part by terpenoids (isoprenoids), which are major defense metabolites of conifer oleoresin. Curiously, similar compounds are important aggregation pheromones of conifer-attacking bark beetles. Terpene synthases are responsible for generating the enormous variety of terpenoid carbon skeletons found in nature. These catalysts convert short-chain prenyl diphosphates to a diverse assortment of hemiterpene, monoterpene, sesquiterpene, and diterpene natural products. While terpene synthases have frequently been characterized from plant and microbial sources, they have not yet been described in animals. Here we report the discovery of a monoterpene synthase activity in an insect, the pine engraver, Ips pini (Say) (Coleoptera: Scolytidae). Cell-free assays of I. pini revealed that geranyl diphosphate (GDP) is converted to the acyclic monoterpene myrcene in whole-body extracts from males, but not females. Furthermore, the monoterpene synthase activity in males can be induced by prior treatment with juvenile hormone III (JH III) or by feeding on phloem from the host trees, Jeffrey pine (Pinus jeffreyi Grev. & Balf.) or red pine (Pinus resinosa Ait.). The sex-specificity and endocrine induction of this activity argue for its involvement in the biosynthesis of monoterpenoid pheromones mediated by enzymes from insect tissue. This discovery is the first example of a monoterpene synthase in the Metazoa and evokes exciting new questions about the origin, evolution, and occurrence of terpene synthases.

Structure and juvenile hormone-mediated regulation of the HMG-CoA reductase gene from the Jeffrey pine beetle, Dendroctonus jeffreyi

In several pine bark beetle species, juvenile hormone (JH) III regulated 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-R) gene expression has an important role in monoterpenoid pheromone production in males. We investigated the structure and regulated expression of the HMG-R gene ( HMG-R) in the Jeffrey pine beetle, Dendroctonus jeffreyi. cDNA and genomic sequences were recovered using a combination of library screening and PCR. The transcribed portion of the gene spans 9.8 kb and is interrupted by 13 introns. When compared to vertebrate HMG-Rs, the distribution of intron sites suggests a functional role for those in the 5′ untranslated region and membrane anchor domains. Northern blots show that topically applied JH III stimulates HMG-R expression up to 30-fold in male D. jeffreyi, compared to untreated insects, in both a dose- and time-dependent manner. There was no increase in expression levels in similarly treated female insects. The expression pattern is consistent with the production of monoterpenoid pheromone components in male D. jeffreyi, and suggests the utility of the system as a new tool for studying the mechanism of JH action.

Association of wildfire with tree health and numbers of pine bark beetles, reproduction weevils and their associates in Florida

Wildfires burned over 200,000 ha of forest lands in Florida from April to July 1998. This unique disturbance event provided a valuable opportunity to study the interactions of summer wildfires with the activity of pine feeding insects and their associates in the southeastern United States. We compared tree mortality with abundance of bark and ambrosia beetles, reproduction weevils and wood borers relative to fire severity. Over 27% of residual live trees in stands that experienced high fire severity died between October 1998 and May 1999. An additional 2–3% of trees that initially survived the fire died during the second year compared to <1% mortality in unburned stands. One year after the fire, more than 75% of the trees surviving in high fire severity stands had roots infected with one or more species of Leptographium and/or Graphium spp. and nearly 60% of the sampled roots were infected. No such fungi were recovered from roots of trees in unburned stands. Significantly, more root weevils, Hylobius pales and Pachylobius picovorus, were captured in unbaited pitfalls in the moderate and high fire severity stands than in the controls. Mean trap catches of Ips grandicollis, Dendroctonus terebrans and Hylastes salebrosus, three common bark beetles that feed on phloem tissue of pines, were lower in Lindgren traps in the fire-damaged areas than in the control stands. In contrast, catches of the ambrosia beetles, Xyleborus spp. and Monarthrum mali, were higher in burned stands than in control stands. The generalist predator, Temnochila virescens (Coleoptera: Trogositidae), showed a strong positive relationship between abundance and fire severity, while the flat bark beetle, Silvanus sp. (Coleoptera: Sylvanidae), exhibited the reverse trend. Our results show that most tree mortality occurred within 1 year of the fire. Ips or Dendroctonus bark beetle populations did not build up in dead and weakened trees and attack healthy trees in nearby areas. The prevalence of Leptographium spp. in roots may be a symptom of, or result in, weakened trees that may affect the trees’ susceptibility to bark beetles in the future.

Methyl jasmonate induces traumatic resin ducts, terpenoid resin biosynthesis, and terpenoid accumulation in developing xylem of Norway spruce stems.

Norway spruce (Picea abies L. Karst) produces an oleoresin characterized by a diverse array of terpenoids, monoterpenoids, sesquiterpenoids, and diterpene resin acids that can protect conifers against potential herbivores and pathogens. Oleoresin accumulates constitutively in resin ducts in the cortex and phloem (bark) of Norway spruce stems. De novo formation of traumatic resin ducts (TDs) is observed in the developing secondary xylem (wood) after insect attack, fungal elicitation, and mechanical wounding. Here, we characterize the methyl jasmonate-induced formation of TDs in Norway spruce by microscopy, chemical analyses of resin composition, and assays of terpenoid biosynthetic enzymes. The response involves tissue-specific differentiation of TDs, terpenoid accumulation, and induction of enzyme activities of both prenyltransferases and terpene synthases in the developing xylem, a tissue that constitutively lacks axial resin ducts in spruce. The induction of a complex defense response in Norway spruce by methyl jasmonate application provides new avenues to evaluate the role of resin defenses for protection of conifers against destructive pests such as white pine weevils (Pissodes strobi), bark beetles (Coleoptera, Scolytidae), and insect-associated tree pathogens.

The invasion of Pinus radiata seedlings by sapstain fungi, following attack by the Black Pine Bark Beetle, Hylastes ater (Coleoptera: Scolytidae)

The relationship between sub-lethal Pinus radiata seedling attack by the Black Pine Bark Beetle, Hylastes ater, and subsequent invasion by sapstain fungi were investigated. Results show that seedlings attacked by H. ater were more likely to be infected by species of sapstain fungi. In addition, the likelihood of invasion increased with increasing severity of H. ater attack. Fifty percent of severely attacked seedlings were infected by one or more species of sapstain fungi. In total, six species of sapstain fungi were isolated from seedlings. Ophiostoma huntii was the most common species isolated from seedlings. H. ater was found to vector one species of sapstain fungi, although other sapstain species have been found to be associated with H. ater in other studies. Further research is required to fully determine the role of H. ater as a vector of sapstain fungi in New Zealand.

Morphological and genetic identification of the three pine pests of the genus Tomicus (Coleoptera, Scolytidae) in Europe

Abstract Morphological characters were elaborated and part of the mitochondrial COI gene was sequenced in order to facilitate the determination of the three European pine bark beetles Tomicus piniperda, T. destruens and T. minor. The sequence information also provided the first information on the phylogenetic and phylogeographical relationships of these species. Three hair rows were found on the antennal club of T. destruens between the second and third suture. Tomicus piniperda had only one row. Three different hair types were detected on the elytra – two hair types were found on T. piniperda, whereas the third hair type was only detected on the elytra of T. destruens. The COI region (445 bp) revealed high sequence divergence among T. destruens, T. piniperda and T. minor. The three species proved to be monophyletic species with 16.98–19.23% sequence divergence. A phylogenetic approach placed T. minor and T. destruens as sister taxa, which contradicts the morphological findings. European populations of T. piniperda shared two haplotypes, indicating a homogenous distribution of the genotypes. In the American populations only one of these European haplotypes was found. The Greek, Italian and Spanish T. destruens populations revealed three population‐specific haplotypes, indicating restricted gene flow. Species‐specific primers were designed to allow a rapid and definitive determination of the two sibling Tomicus species by PCR.

Evaluation of Multiple-Funnel and Slot Traps for Collection of Southern Pine Bark Beetles and Predators

Pheromone-baited traps are frequently used for research or in monitoring populations of bark beetles such as the southern pine beetle, Dendroctonus frontalis Zimmermann, and Ips spp. which are important pests of southern pines. We compared the effectiveness of two commercially available trap designs, the multiple-funnel trap and the slot trap, for collection of D. frontalis, three species of Ips, and two of their common predators. Slot traps captured greater numbers of bark beetles while multiple-funnel traps captured more predators. Multiple-funnel traps were judged to be easier to transport and check in the field. This study indicates that slot traps are preferable for monitoring southern bark beetles with the least disruption to natural enemy populations, while multiple-funnel traps are better for monitoring bark beetle/predator ratios. Due to ease of checking and handling, multiple-funnel traps are preferable for uses that involve large numbers of traps, long-distance manual hauling, or frequent relocation of traps.

Incomplete barriers to mitochondrial gene flow between pheromone races of the North American pine engraver,Ips pini(Say) (Coleoptera, Scolytidae)

The pine engraver Ips pini (Say) is known to include three pheromone races, but gene flow between these races has not been investigated. We used maternally inherited mitochondrial DNA (mtDNA) variation to infer gene flow between 22 widely distributed North American populations of I. pini for a total of 217 individuals, based on 354 bp of the cytochrome oxidase I gene. Gene flow was estimated cladistically as migrants per generation (Nm) and as haplotype variation between populations (Nst). Three distinct mtDNA haplotype lineages, generally corresponding to eastern (I), Rocky Mountain (II) and western (III) regions of North America, were resolved with a total of 34 distinct I. pini haplotypes. The distributions of these lineages were largely congruent with the geographical ranges of the 'New York', 'California' and 'Idaho–Montana' pheromone races. Only individuals with lineage I mtDNA were observed among eastern populations, whereas individuals with lineage II or III mtDNA predominated among western populations. Gene flow (Nm and Nst) was generally moderate between all populations. However, the presence of lineage I mtDNA on the eastern side of western North America and the absence of lineage II and III mtDNA in eastern North America suggest directional gene flow from east to west. These results indicate that female-controlled assortative mating among pheromone races may disrupt gene flow between conspecifics, reflecting incomplete pre-mating barriers.

Mineral nutrition, resin flow and phloem phytochemistry in loblolly pine.

Southern pine beetles and associated pathogenic fungi represent the largest biotic threat to pine forests in the southeastern USA. The two primary defensive mechanisms of the tree to the beetle-fungal complex are the primary oleoresin flow and the concentrations of preformed and induced secondary compounds. We compared oleoresin flow and concentrations of phloem nutrients, soluble sugars, starch, total phenolics and proanthocyanidins in Pinus taeda L. trees in fertilized and control plots in the Sandhills region of North Carolina. Four blocks of 10 trees per treatment were sampled on five dates from May to November 1995. Phloem nitrogen and potassium concentrations were elevated in trees on fertilized plots, whereas phloem calcium concentrations were decreased. Fertilization significantly enhanced (10-20%) concentrations of phloem phenolics and proanthocyanidins. In contrast, phloem soluble sugars and starch concentrations were up to 30% lower in fertilized trees than in control trees. Increased phenolic concentrations and lower nonstructural carbohydrates should correlate with reduced tissue palatability and decreased pathogen susceptibility in fertilized trees; however, resin flows were significantly lower (30-100%) in fertilized trees compared with control trees, which may facilitate pine bark beetle establishment. Furthermore, fertilization-induced increases in phloem nitrogen concentration may be more important than tissue carbohydrate or phenolic content in determining tissue palatability.

Loblolly pine responds to mechanical wounding with increased resin flow

The oleoresin produced by many conifers has a deleterious effect on numerous associated herbivores, including bark beetles (Coleoptera: Scolytidae), and may have evolved as a plant defense mechanism. Three experiments with juvenile loblolly pine (Pinus taeda L.) used mechanical wounding to drain resin reserves and assess the effects of prior bark wounding on subsequent resin flow up to 7 days post-treatment. Resin flow returned to pre-treatment values within 2 days after wounding began and, in nearly every tree in each experiment, continued to increase on subsequent days. On average, resin flow reached double the pre-treatment values (mean ± SE: 2.10 ± 0.10 vs. 1.13 ± 0.10 g/3 h and 2.28 ± 0.09 vs. 0.90 ± 0.09 g/3 h for wounded vs. pre-treatment in experiments 1 and 2, respectively). Considering its timing and magnitude, this previously undescribed response may be important in modulating interactions between pine trees and bark beetles. In addition, resin flow following treatment was greater in trees in larger crown size classes (thinned &gt; edge of stand = unthinned in experiment 1; edge of stand &gt; thinned &gt; unthinned in experiment 2). This may help explain why trees in thinned stands are less susceptible to southern pine beetle (Dendroctonus frontalis Zimm.) infestation than trees in unthinned stands.

Loblolly pine responds to mechanical wounding with increased resin flow

The oleoresin produced by many conifers has a deleterious effect on numerous associated herbivores, including bark beetles (Coleoptera: Scolytidae), and may have evolved as a plant defense mechanism. Three experiments with juvenile loblolly pine (Pinus taeda L.) used mechanical wounding to drain resin reserves and assess the effects of prior bark wounding on subsequent resin flow up to 7 days post-treatment. Resin flow returned to pre-treatment values within 2 days after wounding began and, in nearly every tree in each experiment, continued to increase on subsequent days. On average, resin flow reached double the pre-treatment values (mean ± SE: 2.10 ± 0.10 vs. 1.13 ± 0.10 g/3 h and 2.28 ± 0.09 vs. 0.90 ± 0.09 g/3 h for wounded vs. pre-treatment in experiments 1 and 2, respectively). Considering its timing and magnitude, this previously undescribed response may be important in modulating interactions between pine trees and bark beetles. In addition, resin flow following treatment was greater in trees in larger crown size classes (thinned > edge of stand = unthinned in experiment 1; edge of stand > thinned > unthinned in experiment 2). This may help explain why trees in thinned stands are less susceptible to southern pine beetle (Dendroctonus frontalis Zimm.) infestation than trees in unthinned stands.

SUSCEPTIBILITY OF IPS CALLIGRAPHUS (GERMAR) AND DENDROCTONUS FRONTALIS ZIMMERMANN (COLEOPTERA: SCOLYTIDAE) TO COLEOPTERAN-ACTIVE BACILLUS THURINGIENSIS, A BACILLUS METABOLITE, AND AVERMECTIN B1

AbstractA simple, reliable feeding bioassay was developed for screening certain biorational insecticides with potential use against pine bark beetles. Adult Ips calligraphus and Dendroctonus frontalis were fed freeze-dried phloem fortified with Avermectin B1, Bacillus thuringiensis with known coleopteran activity, or a bacterial metabolite (R003). Avermectin B1 was toxic to adult I. calligraphus by 4 days at an LC50 of 0.36 μg AI/g of diet. R003 was active against both beetle species, yielding 85–100% mortality after 10 days exposure to a concentration of 360 μg/g of diet. No B. thuringiensis product was toxic at a discriminating concentration of 200 μg of spore/crystal preparation per gram of diet. Beetle mortality on untreated diet remained &lt;10% over the 4–10 days duration of feeding trials. Unadulterated, lyophilized phloem diet did not spoil during bioassays, provided that tanned beetles were taken for bioassays before they emerged from their natal host bolts. Microbial products with scolytid activity, such as Avermectin B1 and R003, could have future value for limiting bark beetle infestations of individual trees or small stands in urban or ecologically sensitive forests. Innovative strategies for delivery would have to be developed, however, to circumvent the cryptic habits of these phloeophagous beetles.