Mountain Pine Beetle Dendroctonus Ponderosae Research Articles

Few chemoreceptor genes in the ambrosia beetle Trypodendron lineatum may reflect its specialized ecology

BackgroundChemoreception is crucial for insect fitness, underlying for instance food-, host-, and mate finding. Chemicals in the environment are detected by receptors from three divergent gene families: odorant receptors (ORs), gustatory receptors (GRs), and ionotropic receptors (IRs). However, how the chemoreceptor gene families evolve in parallel with ecological specializations remains poorly understood, especially in the order Coleoptera. Hence, we sequenced the genome and annotated the chemoreceptor genes of the specialised ambrosia beetle Trypodendron lineatum (Coleoptera, Curculionidae, Scolytinae) and compared its chemoreceptor gene repertoires with those of other scolytines with different ecological adaptations, as well as a polyphagous cerambycid species.ResultsWe identified 67 ORs, 38 GRs, and 44 IRs in T. lineatum (‘Tlin’). Across gene families, T. lineatum has fewer chemoreceptors compared to related scolytines, the coffee berry borer Hypothenemus hampei and the mountain pine beetle Dendroctonus ponderosae, and clearly fewer receptors than the polyphagous cerambycid Anoplophora glabripennis. The comparatively low number of chemoreceptors is largely explained by the scarcity of large receptor lineage radiations, especially among the bitter taste GRs and the ‘divergent’ IRs, and the absence of alternatively spliced GR genes. Only one non-fructose sugar receptor was found, suggesting several sugar receptors have been lost. Also, we found no orthologue in the ‘GR215 clade’, which is widely conserved across Coleoptera. Two TlinORs are orthologous to ORs that are functionally conserved across curculionids, responding to 2-phenylethanol (2-PE) and green leaf volatiles (GLVs), respectively.ConclusionsTrypodendron lineatum reproduces inside the xylem of decaying conifers where it feeds on its obligate fungal mutualist Phialophoropsis ferruginea. Like previous studies, our results suggest that stenophagy correlates with small chemoreceptor numbers in wood-boring beetles; indeed, the few GRs may be due to its restricted fungal diet. The presence of TlinORs orthologous to those detecting 2-PE and GLVs in other species suggests these compounds are important for T. lineatum. Future functional studies should test this prediction, and chemoreceptor annotations should be conducted on additional ambrosia beetle species to investigate whether few chemoreceptors is a general trait in this specialized group of beetles.

Chromosome-level genome assembly and population genomic analyses provide insights into adaptive evolution of the red turpentine beetle, Dendroctonus valens

BackgroundBiological invasions are responsible for substantial environmental and economic losses. The red turpentine beetle (RTB), Dendroctonus valens LeConte, is an important invasive bark beetle from North America that has caused substantial tree mortality in China. The lack of a high-quality reference genome seriously limits deciphering the extent to which genetic adaptions resulted in a secondary pest becoming so destructive in its invaded area.ResultsHere, we present a 322.41 Mb chromosome-scale reference genome of RTB, of which 98% of assembled sequences are anchored onto fourteen linkage groups including the X chromosome with a N50 size of 24.36 Mb, which is significantly greater than other Coleoptera species. Repetitive sequences make up 45.22% of the genome, which is higher than four other Coleoptera species, i.e., Mountain pine beetle Dendroctonus ponderosae, red flour beetle Tribolium castaneum, blister beetle Hycleus cichorii, and Colorado potato beetle Leptinotarsa decemlineata. We identify rapidly expanded gene families and positively selected genes in RTB, which may be responsible for its rapid environmental adaptation. Population genetic structure of RTB was revealed by genome resequencing of geographic populations in native and invaded regions, suggesting substantial divergence of the North American population and illustrates the possible invasion and spread route in China. Selective sweep analysis highlighted the enhanced ability of Chinese populations in environmental adaptation.ConclusionsOverall, our high-quality reference genome represents an important resource for genomics study of invasive bark beetles, which will facilitate the functional study and decipher mechanism underlying invasion success of RTB by integrating the Pinus tabuliformis genome.

Scientific response to intensifying bark beetle outbreaks in Europe and North America

Tree-killing bark beetles are globally the most destructive forest pests and their impacts have increased in recent decades. Such an increase has been consistently reported from Europe and North America, and it is, with high confidence, driven by climate change. We investigated how the scientific community in both continents responded to this situation by conducting a comprehensive search of the Scopus database from 1970 to 2020. Studies that investigated interactions between climate change and two prominent bark beetles in Europe and North America, the European spruce bark beetle Ips typographus (ESBB) and the mountain pine beetle Dendroctonus ponderosae (MPB), were identified. We used several hierarchical search criteria, starting from general aspects of pest – climate change interactions, to studies with clear implications for management and policies.We found that authors investigating the two bark beetle species mentioned climate change in publications beginning in 1998, and have constituted 8.9 and 13.8 % of all studies on ESBB (N = 987) and MPB (N = 1479) recorded in Scopus. However, only part of these studies addressed climate change as a fundamental or integral part of their research design (59.1 % in ESBB and 38.7 % in MPB). We identified 30 studies on ESBB and 50 studies on MPB which informed efforts towards improving bark beetle management strategies to address climate change-affected ecosystem dynamics. Publications on both insects consistently highlighted the importance of vegetation management aiming to reduce the risk and severity of outbreaks and prevent large-scale population expansion. Only a minor portion of studies placed their findings into the context of relevant policies and legislation, and this connection was particularly lacking in studies on MPB.We conclude that research on bark beetle management under climate change has received inadequate attention and it lags behind observed and foreseen global-scale impacts. We suggest that focused and applied research with clear management implications is needed to develop new climate-adapted and evidence-based management strategies.

De novo transcriptome analysis and identification of reproduction control genes from the red palm weevil Rhynchophorus ferrugineus.

Recent attacks by the red palm weevil, Rhynchophorus ferrugineus (Olivier), have become a severe problem for palm species. In present work, fat body transcriptome of adult female red palm weevil was analyzed, focusing on the identification of reproduction control genes. Transcriptome study was completed by means of next-generation sequencing (NGS) using Illumina Hiseq 2000 sequencing system. A total of 105,938,182 raw reads, 102,645,544 clean reads, and 9,238,098,960 clean nucleotides with a guanine–cytosine content of 40.31%, were produced. The processed transcriptome data resulted in 43,789 unique transcripts (with mean lengths of 1,172 bp). It was found that 20% of total unique transcripts shared up to 80%–100% sequence identity with homologous species, mainly the mountain pine beetle Dendroctonus ponderosae (59.9%) and red flour beetle Tribolium castaneum (26.9%). Nearly 25 annotated genes were predicted to be involved in red palm weevil reproduction, including five vitellogenin (Vg) transcripts. Among the five Vg gene transcripts, one was highly expressed compared with the other four (FPKM values of 1.963, 1.471, 1.028, and 1.017, respectively), and the five Vg gene transcripts were designated as RfVg, RfVg-equivalent1, RfVg-equivalent2, RfVg-equivalent3, and RfVg-equivalent4, respectively. The high expression level of RfVg verified by RT-polymerase chain reaction analysis suggested that RfVg is the primary functional Vg gene in red palm weevil. A high similarity of RfVg with other Coleopterans was also reflected in a phylogenetic tree, where RfVg was placed within the clade of the order Coleoptera. Awareness of the major genes that play critical roles in reproduction and proliferation of red palm weevil is valuable to understand their reproduction mechanism at a molecular level. In addition, for future molecular studies, the NGS dataset obtained will be useful and will promote the exploration of biotech-based control strategies against red palm weevil, a primary pest of palm trees.

Efficacy of verbenone and a blend of verbenone and nonhost volatiles for protecting lodgepole pine from mountain pine beetle (Coleoptera: Curculionidae)

Abstract Significant research has been devoted to the development of semiochemical repellents for mountain pine beetle Dendroctonus ponderosae Hopkins. Several formulations of the beetle's antiaggregation pheromone verbenone (4,6,6‐trimethylbicyclo[3.1.1]hept‐3‐en‐2‐one) are registered to protect pine trees and stands. We compared the efficacy of verbenone and Verbenone Plus for protecting individual lodgepole pine Pinus contorta Dougl. ex Loud. and small stands of P. contorta from mortality attributed to D. ponderosae. Verbenone Plus is a blend of semiochemicals [(−)‐verbenone, acetophenone, and (E)‐2‐hexen‐1‐ol + (Z)‐2‐hexen‐1‐ol] originally developed to inhibit aggregation of western pine beetle D. brevicomis LeConte. It is the only effective semiochemical repellent that protects ponderosa pine P. ponderosa Dougl. ex Laws. from mortality attributed to D. brevicomis, but has yet to be registered or commercialized. Both verbenone and Verbenone Plus were effective for protecting individual P. contorta and small stands of P. contorta from mortality attributed to D. ponderosae. Verbenone alone was as effective as Verbenone Plus. An obstacle to the broader use of semiochemical repellents for the management of bark beetles is the relatively high cost and specificity of the semiochemicals involved. A semiochemical repellent with efficacy across multiple bark beetle species and hosts, such as Verbenone Plus, would be desirable, assuming the additional components are not cost‐prohibitive or limit registration.

Energy use by the mountain pine beetle (Coleoptera: Curculionidae: Scolytinae) for dispersal by flight

AbstractThe mountain pine beetle Dendroctonus ponderosae Hopkins is a major native pest of Pinus Linnaeus (Pinaceae) in western North America. Host colonization by the mountain pine beetle is associated with an obligatory dispersal phase, during which beetles fly in search of a suitable host. Mountain pine beetles use stored energy from feeding in the natal habitat to power flight before host colonization and brood production. Lipids fuel mountain pine beetle flight, although it is not known whether other energy sources are also used during flight. In the present study, we compare the level of energy substrates, proteins, carbohydrates and lipids of individual mountain pine beetles flown on flight mills with unflown control beetles. We use a colorimetric method to measure the entire metabolite content of each individual beetle. The present study reveals that mountain pine beetles are composed of more protein and lipid than carbohydrate. Both female and male mountain pine beetles use lipids and carbohydrates as energy sources during flight. There is variation between sexes, however, in the energy substrates used for flight. Male mountain pine beetles use protein, in addition to lipids and carbohydrates, to fuel flight, whereas protein content is not different between flown and control females.

Predators and competitors of the mountain pine beetle Dendroctonus ponderosae (Coleoptera: Curculionidae) in stands of changing forest composition associated with elevation

Abstract The mountain pine beetle Dendroctonus ponderosae (Coleoptera: Curculionidae) is an irruptive tree‐killing bark beetle native to pine stands in western North America. The primary hosts are lodgepole and ponderosa pines. Recent rising temperatures, however, have allowed these beetles to survive at higher elevations more commonly than in the past, thus threatening whitebark pine, a keystone species of high elevation ecosystems and a highly susceptible host. The extent to which risk in whitebark pine stands may be mitigated by predators or competitors is unknown. We compared the communities of coleopteran predators and competitors of D. ponderosae in sites of varying elevation and species composition in Montana and Wyoming, U.S.A. Sites were selected for low to moderate levels of tree mortality, where the potential of natural enemies to prevent D. ponderosae from transitioning into outbreaks would be most relevant. Insect populations were evaluated using unbaited flight‐intercept panel traps and pheromone‐baited multiple funnel traps. Only the predatory beetle species Thanasimus undatulus (Coleoptera: Cleridae) was captured in these non‐outbreak stands. Based on the pheromone‐baited traps, predator load was higher at low‐elevation stands dominated by lodgepole pine than high‐elevation stands dominated by whitebark pine. Phloeophagous insects were more prevalent in the mid‐ and higher‐elevation sites, although most of the species captured would not likely compete substantially for resources with D. ponderosae. We also observed differences in species assemblages between the Montana and Wyoming sites, as well as differing utilities of baited and unbaited traps at low versus moderate tree mortality levels.

Phoretic Symbionts of the Mountain Pine Beetle (Dendroctonus ponderosae Hopkins)

During its life cycle, the tree-killing mountain pine beetle Dendroctonus ponderosae Hopkins interacts with phoretic organisms such as mites, nematodes, fungi, and bacteria. The types of associations these organisms establish with the mountain pine beetle (MPB) vary from mutualistic to antagonistic. The most studied of these interactions are those between beetle and fungi. The least studied are interactions with bacteria, but these have received increased attention recently. Nematodes remain little studied. We reviewed the significant literature pertaining to MPB phoronts. A number of potentially important interactions and contributions resulting from associations between MPB and its phoronts are discussed. A wealth of literature exists on this topic, yet many questions remain unanswered, and the effects of some phoronts on population levels remain unexplored.

A GIS-based risk rating of forest insect outbreaks using aerial overview surveys and the local Moran's I statistic

The objective of this study is to provide an approach for assessing the short-term risk of mountain pine beetle Dendroctonus ponderosae Hopkins (Coleoptera: Scolytidae) attack over large forested areas based on the spatial-temporal behavior of beetle spread. This is accomplished by integrating GIS, aerial overview surveys, and local indicators of spatial association (LISA) in order to measure the spatial relationships of mountain pine beetle impacts from one year to the next. Specifically, we implement a LISA method called the bivariate local Moran's Ii to estimate the risk of mountain pine beetle attack across the pine distribution of British Columbia, Canada. The bivariate local Moran's Ii provides a means for classifying locations into separate qualitative risk categories that describe insect population dynamics from one year to the next, revealing where mountain pine beetle populations are most likely to increase, stay constant, or decline. The accuracy of the model's prediction of qualitative risk was higher in initial years and lower in later years of the study, ranging from 91% in 2002 to 72% in 2006. The risk rating can be continually updated by utilizing annual overview surveys, thus ensuring that risk prediction remains relatively high in the short-term. Such information can equip forest managers with the ability to allocate mitigation resources for responding to insect epidemics over very large areas.

Insect outbreaks increase populations and facilitate reproduction in a cavity‐dependent songbird, the Mountain Chickadee Poecile gambeli

Large‐scale insect outbreaks, typical of temperate ecosystems, may increase food availability and influence species interactions in insectivorous bird communities. We assessed how population densities of a secondary cavity nester, the Mountain Chickadee Poecile gambeli, varied with densities of avian cavity excavators, potential competitors and nest predators, during two large‐scale insect outbreaks of Western Spruce Budworm Choristoneura occidentalis and Mountain Pine Beetle Dendroctonus ponderosae. At the regional level, Mountain Chickadee densities doubled with increases in budworm and beetle availability, then declined with decreases in beetle availability, despite high budworm supply. At the site level, densities of excavators were the best predictor of site‐level variation in Chickadee densities in the following year. During and after the beetle outbreak, Mountain Chickadees used more cavities excavated by Red‐breasted Nuthatches Sitta canadensis and Downy Woodpeckers Picoides pubescens, both of which are bark insectivores that increased in densities concomitantly with the beetle outbreak and whose foraging activities may have facilitated the Mountain Chickadees' access to bark beetles. Thus, Mountain Chickadees showed a numerical response to the food pulse at the regional level, but a functional response to the pulse of nesting cavities at the site level. Plasticity in resource selection and heterospecific attraction may allow Mountain Chickadees to respond to resource pulses in highly variable environments.

The role of vision in the host orientation behaviour of Hylobius warreni

Visual stimuli, often in combination with olfactory stimuli, are frequently important components of host selection by forest‐dwelling phytophagous insects. Warren root collar weevil Hylobius warreni Wood (Coleoptera: Curculionidae) is a native insect in western Canada, where larvae feed primarily on lodgepole pine Pinus contorta and can girdle and kill young trees. This weevil is an emerging problem in areas heavily impacted by mountain pine beetle Dendroctonus ponderosae Hopkins. No olfactory attractants have been identified for this insect, making monitoring and management difficult. Thus, we investigated the role of vision in the host‐finding behaviour of Warren root collar weevil in the absence of known olfactory cues. We conducted three experiments in field enclosure plots aiming to characterize aspects of host‐finding behaviour by adult Warren root collar weevil. We found that both male and female weevils were readily attracted to vertical plastic silhouettes in the shape of a trunk, crown or tree at distances of less than 4 m. This pattern of attraction persisted over 2 years in two slightly different study designs. Blinding the insects removed their ability to orient to these silhouettes, indicating that host‐finding behaviour has a strong visual component. The use of different colour trunks and crowns (black, white and green) did not change the patterns of attraction of the insects to the silhouettes. Exploiting visual attraction in this walking insect may present a new management tool in forest protection strategies.

Climate change could alter the distribution of mountain pine beetle outbreaks in western Canada

Climate change can markedly impact biology, population ecology, and spatial patterns of eruptive insects due to the direct influence of temperature on insect development and population success. The mountain pine beetle Dendroctonus ponderosae (Coleoptera: Curculionidae), is a landscape‐altering insect that infests forests of North America. Abundant availability of host trees due to altered disturbance regimes has facilitated an unprecedented, landscape‐wide outbreak of this pest in British Columbia and Alberta, Canada, during the past decade. A previous outbreak in the 1980s, in central British Columbia, collapsed due to host depletion and extreme cold weather events. Despite the importance of such extreme weather events and other temperature‐related signals in modulating an outbreak, few landscape‐level models have studied the associations of extreme cold events with outbreak occurrences. We studied the individual associations of several biologically‐relevant cold temperature variables, and other temperature/degree‐day terms, with outbreak occurrences in a spatial‐temporal logistic regression model using data from the current outbreak. Timing, frequency, and duration of cold snaps had a severe negative association with occurrence of an outbreak in a given area. Large drops in temperature (>10°C) or extreme winter minimum temperatures reduced the outbreak probability. We then used the model to apply eight different climate change scenarios to the peak year of the current outbreak. Our scenarios involved combinations of increasing annual temperature and different variances about this trend. Our goal was to examine how spatial outbreak pattern would have changed in the face of changing thermal regime if the underlying outbreak behaviour remained consistent. We demonstrate that increases in mean temperature by 1°C to 4°C profoundly increased the risk of outbreaks with effects first being manifested at higher elevations and then at increasing latitudes. However, increasing the variance associated with a mean temperature increase did not change the overall trend in outbreak potential.

Climate change and range expansion of an aggressive bark beetle: evidence of higher beetle reproduction in naïve host tree populations

Summary 1. Hosts may evolve defences that make them less susceptible and suitable to herbivores impacting their fitness. Due to climate change‐driven range expansion, herbivores are encountering naïve host populations with increasing frequency. 2. Aggressive bark beetles are among the most important agents of disturbance in coniferous forest ecosystems. The presence of bark beetle outbreaks in areas with a historically unsuitable climate, in part a consequence of climate change, provided an opportunity to assess the hypothesis that the mountain pine beetle Dendroctonus ponderosae has higher reproductive success in lodgepole pine Pinus contorta trees growing in areas that have not previously experienced frequent outbreaks. 3. We felled and sampled mountain pine beetle‐killed trees from historically climatically suitable and unsuitable areas, i.e. areas with and without a historical probability of frequent outbreaks. Reproductive success was determined from a total of 166 trees from 14 stands. 4. Brood productivity was significantly affected by climatic suitability class, such that mean brood production per female increased as historical climatic suitability decreased. 5. Synthesis and applications. The current study demonstrates that the mountain pine beetle has higher reproductive success in areas where its host trees have not experienced frequent beetle epidemics, which includes much of the current outbreak area in north central British Columbia. This increased productivity of mountain pine beetle is likely to have been a key reason for the rapid population buildup that resulted in unprecedented host tree mortality over huge areas in western Canada. The outbreak thus provides an example of how climate change‐driven range expansion of native forest insects can have potentially disastrous consequences. Since an increased reproductive success is likely to accelerate the progression of outbreaks, it is particularly critical to manage forests for the maintenance of a mosaic of species and age classes at the landscape level in areas where host tree populations are naïve to eruptive herbivores.

Target-specific PCR primers can detect and differentiate ophiostomatoid fungi from microbial communities associated with the mountain pine beetle Dendroctonus ponderosae

The aim of this study was to develop DNA probes that could identify the major fungal species associated with mountain pine beetles (MPB). The beetles are closely associated with fungal species that include ophiostomatoid fungi that can be difficult to differentiate morphologically. The most frequently isolated associates are the pine pathogens Grosmannia clavigera and Leptographium longiclavatum, the less pathogenic Ophiostoma montium, and an undescribed Ceratocystiopsis species ( Cop. sp.). Because growing, isolating and extracting DNA from fungi vectored by MPB can be time and labour intensive, we designed three rDNA primer sets that specifically amplify short rDNA amplicons from O. montium, Cop. sp. and the pine Leptographium clade. We also designed two primer sets on a gene of unknown function that can differentiate G. clavigera and L. longiclavatum. We tested the primers on 76 fungal isolates that included MPB associates. The primers reliably identified their targets from DNA obtained from pure fungal cultures, pulverized beetles, beetle galleries, and tree phloem inoculated with G. clavigera. The primers will facilitate large-scale work on the ecology of the MPB-fungal-lodgepole pine ecosystem, as well as phytosanitary/quarantine sample screening.

Management response to one insect pest may increase vulnerability to another

Summary 1. Large-scale insect outbreaks provide an ideal system to examine the cascade of ecological effects of disturbance regimes across forested landscapes. A major outbreak of the mountain pine beetle Dendroctonus ponderosae continues to exert landscape-level mortality across forests of lodgepole pine Pinus contorta var. latifolia. in western Canada. This outbreak, exacerbated in part by fire suppression and climate change, has affected more than 14 million ha of merchantable forest. Salvage and reforestation efforts are currently underway at landscape-level scales. An emerging concern is the migration of Warren root collar weevil Hylobius warreni from stands with a reduced host pool, i.e. those with a high per cent of mature, dead lodgepole pine, into young, replanted stands, resulting in significant levels of mortality to juvenile trees. 2. The impact of Warren root collar weevil in stands of young trees (9–11 years of age) replanted after salvage harvesting was examined in nine cutblocks (areas delineated for commercial timber harvest, c. 1 km in diameter). All cutblocks, sampled across the central interior of British Columbia, were located next to unsalvaged, mature stands. 3. Field data and aerial surveys revealed higher tree mortality from Warren root collar weevils along cutblock perimeters adjacent to unsalvaged, mature stands. Mortality decreased with increasing distance from the edge of the cutblocks. Additional mortality along these gradients was associated with increasing per cent of pine in the mature stand; more-so if the pine was dead. Moreover, the gradient of mortality became more pronounced with time as mountain pine beetle had attacked the adjacent mature stands. Weevils attacked the largest trees within the replanted cutblocks. 4. These gradients of tree mortality suggest migration of Warren root collar weevils from unsalvaged mature stands into adjacent replanted forests most probably in search of food. 5. Synthesis and applications. This study demonstrates how a management response to a large insect outbreak, itself mediated by anthropogenic factors, can predispose reforested stands to additional, unanticipated threats from other insects. Reforestation strategies following outbreaks of mountain pine beetle may need to include harvesting larger salvage blocks to minimize edge effects and reduce mortality from Warren root collar weevils. Moreover, the inclusion of deciduous non-host tree stock in planting mixes might reduce insect movement and limit tree mortality because of Warren root collar weevils.

Intrinsic and extrinsic determinants of mountain pine beetle population growth

Abstract1 Mountain pine beetleDendroctonus ponderosaepopulations have large, economically significant outbreaks. Density dependence and environmental variability are expected to have important effects on their dynamics. We analysed time series data from an outbreak in the 1930s to determine the relative importance of population density and environmental variability on local population growth rates.2 Resource depletion occurred rapidly at the scale of 0.4 ha and population growth rates were strongly density dependent. Annual environmental changes did not have detectable effects on population growth rates, leading to the conclusion that intrinsic processes influenced local population density more than extrinsic factors during this outbreak.3 Our calculated value ofrmax(1.16) does not suggest intrinsically cyclic population dynamics. Our estimate ofrmaxand density dependence will be useful in developing applied models of mountain pine beetle outbreaks, and the subsequent evaluation of management strategies.

The enemy of my enemy is still my enemy: competitors add to predator load of a tree‐killing bark beetle

Abstract1 The mountain pine beetle Dendroctonus ponderosae is a major tree‐killing bark beetle in North America. We evaluated how the subsequent arrival of a competing bark beetle Ips pini influences the arrival of predators and their impact on both species.2 The predators Temnochila chlorodia and Enoclerus sphegeus were strongly attracted to pheromones of D. ponderosae. By contrast, Enoclerus lecontei was mostly attracted to I. pini pheromones. The host compound myrcene synergized attraction of both D. ponderosae and E. sphegeus to the pheromone of D. ponderosae. However, it inhibited attraction of both I. pini and E. lecontei to I. pini’s pheromone.3 Dendroctonus ponderosae were more attracted to trees than logs treated with its pheromones, whereas I. pini were more attracted to logs than trees treated with its pheromones. Some 78% of T. chlorodia were captured at hosts baited with D. ponderosae pheromones, whereas 83% of E. lecontei were captured at hosts baited with I. pini pheromones. We characterized the sequence of arrival to live trees baited with pheromones of D. ponderosae as: D. ponderosae, T. chlorodia, E. sphegeus, I. pini, E. lecontei.4 Various combinations of I. pini and predators were added to logs colonized by D. ponderosae in the above sequence of arrival observed in live trees baited with D. ponderosae aggregation pheromones. Ips pini reduced D. ponderosae adult brood production. However, the combination of I. pini and E. lecontei did not raise D. ponderosae brood production above that observed with only I. pini present. Similarly, the combination of I. pini and T. chlorodia did not reduce D. ponderosae brood production below that observed with I. pini alone. By contrast, the combination of I. pini, T. chlorodia and E. lecontei caused more brood loss to D. ponderosae than I. pini alone.5 Enoclerus lecontei did not reduce brood production by T. chlorodia, whereas T. chlorodia substantially reduced brood production by E. lecontei.6 Secondary bark beetles that exploit the resource created by primary tree‐killing species exert negative effects through both competition and increased predator load. Implications to the population dynamics, ecology and evolution of tree‐killing bark beetles are discussed.

Risk rating for mountain pine beetle infestation of lodgepole pine forests over large areas with ordinal regression modelling

The mountain pine beetle Dendroctonus ponderosae Hopkins is endemic to lodgepole pine, Pinus contorta var. latifolia Engelmann, forests in western Canada. However, the current beetle epidemic in this area highlights the challenges faced by forest managers tasked with prioritizing stands for mitigation activities such as salvage harvesting and direct control methods. In western Canada, the operational risk rating system for mountain pine beetle is based on biological knowledge gained from a rich legacy of stand-scale field studies. Due to the large spatial (millions of hectares affected) and temporal (over 10 years) extents of the current epidemic, new research into large-area mountain pine beetle processes has revealed further insights into the landscape-scale characteristics of beetle infested forests. In this paper, we evaluated the potential for this new knowledge to augment an established system for rating the short-term risk of tree mortality in a stand due to mountain pine beetle. New variables explored for utility in risk rating include direct shortwave radiation, site index, diameter at breast height, the temporal trends in local beetle populations, Biogeoclimatic Ecosystem Classification and beetle–host interaction variables. Proportional odds ordinal regression was used to develop a model for the Vanderhoof Forest District in west-central British Columbia. Prediction on independent data was assessed with the area under the receiver operator curve (AUC), indicating good discriminatory power (AUC = 0.84) for predicting levels of mountain pine beetle-caused pine mortality.

Bleaching treatments for blue-stained lodgepole pine affected by the mountain pine beetle Dendroctonus ponderosae

Over 400 million m3 of standing lodgepole pine timber in the forests of British Columbia, Canada, is affected by the mountain pine beetle and associated ophiostomatoid fungi that stain the sapwood of infected pine trees a blue-grey color (Lee et al. 2005). Such staining is undesirable in appearance grade wood products and some grades of structural timber, and a simple method of removing the stain or reducing its severity is required. This study screened a range of bleaching agents to determine which ones were most effective at removing the blue stain and then optimised treatment parameters for the most efficient bleaching agent (sodium hypochlorite).

Landscape‐scale genetic variation in a forest outbreak species, the mountain pine beetle (Dendroctonus ponderosae)

The mountain pine beetle Dendroctonus ponderosae is a native species currently experiencing large-scale outbreaks in western North American pine forests. We sought to describe the pattern of genetic variation across the range of this species, to determine whether there were detectable genetic differences between D. ponderosae occupying different host trees in common localities, and to determine whether there was molecular evidence for a past demographic expansion. Using a combination of amplified fragment length polymorphism (AFLP) and mitochondrial sequencing analyses, we found evidence of genetic structuring among populations that followed a broad isolation-by-distance pattern. Our results suggest that the geographical pattern of gene flow follows the core distribution of the principal D. ponderosae host species, around rather than across the Great Basin and Mojave Deserts. Patterns of haplotype diversity and divergence were consistent with a range-wide population expansion. This signal was particularly pronounced in the northern part of the species' range, where outbreak activity is currently increasing. Using AFLP markers, we were unable to detect significant differences among groups of insects sampled from different host trees in common locations. Incidentally, we found that a large proportion of the polymorphic AFLP markers were gender-specific, occurring only in males. While we did not include these markers in our analyses, this finding warrants further investigation.