Reducing spruce beetle Dendroctonus rufipennis (Kirby) (Coleoptera: Curculionidae) emergence for hibernation in central British Columbia by felling infested trees

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Successful colonization, reproduction, and new generation emergence in live interior hybrid spruce Picea engelmannii×glauca by mountain pine beetle Dendroctonus ponderosae

1 Although mountain pine beetle Dendroctonus ponderosae Hopkins are able to utilize most available Pinus spp. as hosts, successful colonization and reproduction in other hosts within the Pinaceae is rare.
2 We observed successful reproduction of mountain pine beetle and emergence of new generation adults from interior hybrid spruce Picea engelmannii × glauca and compared a number of parameters related to colonization and reproductive success in spruce with nearby lodgepole pine Pinus contorta infested by mountain pine beetle.
3 The results obtained indicate that reduced competition in spruce allowed mountain pine beetle parents that survived the colonization process to produce more offspring per pair than in more heavily-infested nearby pine.
4 We also conducted an experiment in which 20 spruce and 20 lodgepole pines were baited with the aggregation pheromone of mountain pine beetle. Nineteen pines (95%) and eight spruce (40%) were attacked by mountain pine beetle, with eight (40%) and three (15%) mass-attacked, respectively.
5 Successful attacks on nonhost trees during extreme epidemics may be one mechanism by which host shifts and subsequent speciation events have occurred in Dendroctonus spp. bark beetles.     

Nesting Ecology of Boreal Forest Birds Following a Massive Outbreak of Spruce Beetles

Abstract: We studied breeding dark-eyed juncos (Junco hyemalis), yellow-rumped warblers (Dendroica coronata), and spruce-nesting birds from 1997 to 1998 among forests with different levels of spruce (Picea spp.) mortality following an outbreak of spruce beetles (Dendroctonus rufipennis) in Alaska, USA. We identified species using live and beetle-killed spruce for nest sites and monitored nests to determine how the outbreak influenced avian habitat selection and reproduction. We tested predictions that 1) nesting success of ground-nesting juncos would increase with spruce mortality due to proliferation of understory vegetation available to conceal nests from predators, 2) nesting success of canopy-nesting warblers would decrease with spruce mortality due to fewer live spruce in which to conceal nests, and 3) both species would alter nest-site selection in response to disturbance. Juncos did not benefit from changes in understory vegetation; nesting success in highly disturbed stands (46%) was comparable to that in undisturbed habitats throughout their range. In stands with low spruce mortality, nesting success of juncos was low (5%) and corresponded with high densities of red squirrels (Tamiasciurus hudsonicus). Yellow-rumped warblers nested exclusively in spruce, but success did not vary with spruce mortality. As disturbance increased, nesting warblers switched from selecting forest patches with high densities of live white spruce (Picea glauca) to patches with beetle-killed spruce. Warblers also placed nests in large-diameter live or beetle-killed spruce, depending on which was more abundant in the stand, with no differences in nesting success. Five of the 12 other species of spruce-nesting birds also used beetle-killed spruce as nest sites. Because beetle-killed spruce can remain standing for >50 years, even highly disturbed stands provide an important breeding resource for boreal forest birds. We recommend that boreal forest managers preserve uncut blocks of infested forest within managed forest landscapes and practice partial harvest of beetle-killed spruce rather than commercial clear-cutting of infested stands in order to sustain breeding bird populations until natural reforestation occurs. Because breeding densities do not always reflect fitness, assessing impacts of a massive natural disturbance should include measuring impacts of changes in vegetation on both reproductive success and predator-prey dynamics.     

Comparison of naturally and synthetically baited spruce beetle trapping systems in the central Rocky Mountains

We compared naturally baited trapping systems to synthetically baited funnel traps and fallen trap trees for suppressing preoutbreak spruce beetle, Dendroctonus rufipennis Kirby, populations. Lures for the traps were fresh spruce (Picea spp.) bolts or bark sections, augmented by adding female spruce beetles to create secondary attraction. In 2003, we compared a naturally baited system ("bolt trap") with fallen trap trees and with synthetically baited funnel traps. Trap performance was evaluated by comparing total beetle captures and spillover of attacks into nearby host trees. Overall, the trap systems did not significantly differ in spruce beetle captures, although bolt traps caught 6 to 7 times more beetles than funnel traps during the first 4 wk of testing. Funnel traps with synthetic lures had significantly more spillover than either trap trees or bolt traps. The study was repeated in 2004 with modifications including an enhanced blend synthetic lure. Again, trap captures were generally similar among naturally and synthetically baited traps, but naturally baited traps had significantly less spillover. Although relatively labor-intensive, the bolt trap could be used to suppress preoutbreak beetle populations, especially when spillover is undesirable. Our work provides additional avenues for management of spruce beetles and suggests that currently used synthetic lures can be improved.     

SHORT-TERM DEMOGRAPHIC RESPONSE OF THE RED-BACKED VOLE TO SPRUCE BEETLE INFESTATIONS IN ALASKA

Abstract: How small mammals are affected by habitat changes caused by forest insect epidemics is largely unknown. Our objective was to determine the influence of spruce beetle (Dendroctonus rufipennis) epidemics on the dynamics of northern red-backed vole (Clethrionomys rutilus) populations approximately 10 years post-infestation. We conducted a mark-recapture study on northern red-backed voles for 2 field seasons in the Copper River Basin, Alaska, USA, where recent beetle infestations were widespread. Using the robust sampling design, we produced estimates of vole abundance, survival, and recruitment in 3 locations that varied in their degree of beetle-induced spruce mortality. Vole abundance inversely related to the level of spruce mortality. Vole recruitment showed a larger contribution from both immigration and in situ reproduction in the low infestation site than in the medium and heavy infestation sites. No differences in vole survival were detectable across the 3 locations with varied beetle-induced spruce mortality levels. Measured vole food resources and protective vegetative cover did not vary greatly across infestation levels. Abundance and recruitment parameters indicate a negative change induced by spruce beetle infestations. However, the effect of beetles was not large enough to cause the variation in vole survival. Spruce mortality levels may need to be over 50% before greatly influencing the habitat and the demographics of northern red-backed voles.     

A predictive framework to assess spatio‐temporal variability of infestations by the European spruce bark beetle

Natural disturbances are key factors for the development of forest ecosystems. In forests of central Europe and Scandinavia, the European spruce bark beetle Ips typographus is the most devastating biotic disturbance agent in Norway spruce Picea abies, but our understanding of the factors determining its spatio‐temporal dynamics is still quite limited. To quantify the drivers of bark beetle dynamics, we analyzed a survey dataset with annual resolution that covers 17 yr and 469 forest districts (10 860 km² of forest area) all over Switzerland. We used Poisson log‐normal models in a Bayesian framework to analyze the spatio‐temporal dynamics of bark beetle infestation spots at the forest district level. Bark beetle infestations increased with increasing heat sum (> 8.3°C), volume of standing Norway spruce stock, and the number of infestation spots of the previous year. Precipitation tended to slightly affect the risk of bark beetle infestations. Two major storm events further increased the spatio‐temporal variability of bark beetle infestations. Spruce abundance, storm damage and temperature are known to be important factors influencing the population dynamics of the European spruce bark beetle. Our study is the first to quantify the combined effects of spruce abundance and heat sum, whereby the heat sum turned out to be the most important and consistent predictor. Because our study area encompasses large ecological and climatological gradients, our model is likely to be applicable to Norway spruce forests in other regions of central Europe and Scandinavia.     

What explains landscape patterns of tree mortality caused by bark beetle outbreaks in Greater Yellowstone?

Aim Bark beetle outbreaks have recently affected extensive areas of western North American forests, and factors explaining landscape patterns of tree mortality are poorly understood. The objective of this study was to determine the relative importance of stand structure, topography, soil characteristics, landscape context (the characteristics of the landscape surrounding the focal stand) and beetle pressure (the abundance of local beetle population eruptions around the focal stand a few years before the outbreak) to explain landscape patterns of tree mortality during outbreaks of three species: the mountain pine beetle, which attacks lodgepole pine and whitebark pine; the spruce beetle, which feeds on Engelmann spruce; and the Douglas‐fir beetle, which attacks Douglas‐fir. A second objective was to identify common variables that explain tree mortality among beetle–tree host pairings during outbreaks. Location Greater Yellowstone ecosystem, Wyoming, USA. Methods We used field surveys to quantify stand structure, soil characteristics and topography at the plot level in susceptible stands of each forest type showing different severities of infestation (0–98% mortality; n= 129 plots). We then used forest cover and beetle infestation maps derived from remote sensing to develop landscape context and beetle pressure metrics at different spatial scales. Plot‐level and landscape‐level variables were used to explain outbreak severity. Results Engelmann spruce and Douglas‐fir mortality were best predicted using landscape‐level variables alone. Lodgepole pine mortality was best predicted by both landscape‐level and plot‐level variables. Whitebark pine mortality was best – although poorly – predicted by plot‐level variables. Models including landscape context and beetle pressure were much better at predicting outbreak severity than models that only included plot‐level measures, except for whitebark pine. Main conclusions Landscape‐level variables, particularly beetle pressure, were the most consistent predictors of subsequent outbreak severity within susceptible stands of all four host species. These results may help forest managers identify vulnerable locations during ongoing outbreaks.     

Fungal associates of the tree-killing bark beetle,Ips typographus,vary in virulence,ability to degrade conifer phenolics and influence bark beetle tunneling behavior

The bark beetle Ips typographus carries numerous fungi that could be assisting the beetle in colonizing live Norway spruce (Picea abies) trees. Phenolic defenses in spruce phloem are degraded by the beetle's major tree-killing fungus Endoconidiophora polonica, but it is unknown if other beetle associates can also catabolize these compounds. We compared the ability of five fungi commonly associated with I. typographus to degrade phenolic compounds in Norway spruce phloem. Grosmannia penicillata and Grosmannia europhioides were able to degrade stilbenes and flavonoids faster than E. polonica and grow on minimal growth medium with spruce bark constituents as the only nutrients. Furthermore, beetles avoided medium amended with phenolics but marginally preferred medium colonized by fungi. Taken together our results show that different bark beetle-associated fungi have complementary roles in degrading host metabolites and thus might improve this insect's persistence in well defended host tissues.     

Sub-cortical Coleoptera in dead pines and spruces: is primeval species composition maintained in managed forests?

The sub-cortical beetle fauna of dead Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) trunks was compared in primeval forests and managed forests in central Finland. The numbers of both individuals and species were higher in the managed forest in spite of the smaller trunk surface area examined. The proportion of rare species was higher in the primeval forest. Although most species occurred both in primeval and managed forests, there were striking differences in the abundance relations: there was only one species (Pytho depressus) in common among the ten most abundant species. The proportion of bark beetles (Scolytidae) was more than 50% in the managed forests, and less than 5% in the primeval forests. The number of species per site was associated with observation date, occurrence of snails and trunk position (standing or lying) in the primeval forest, and with trunk diameter in the managed forests. The occurrence of rare beetle species in dead conifer trunks was related to man's effects on the forest. Although many sub-cortical species can live in managed forests, the fauna differs drastically from that of primeval forests.     

Plant Community Composition as a Predictor of Regional Soil Carbon Storage in Alaskan Boreal Black Spruce Ecosystems

The boreal forest is the largest terrestrial biome in North America and holds a large portion of the world’s reactive soil carbon. Therefore, understanding soil carbon accumulation on a landscape or regional scale across the boreal forest is useful for predicting future soil carbon storage. Here, we examined the relationship between floristic composition and ecosystem parameters, such as soil carbon pools, the carbon-to-nitrogen (C/N) ratio of live black spruce needles, and normalized basal area increment (NBAI) of trees in black spruce communities, the most widespread forest type in the boreal forest of Alaska. Variability in ecosystem properties among black spruce stands was as large as that which had previously been documented among all forest types in the central interior of Alaska; we found an eightfold range in NBAI and fivefold range in mineral soil carbon and nitrogen pools. Acidic black spruce communities had significantly more carbon in the organic soil horizon than did nonacidic black spruce communities, but did not differ in any other measured ecosystem parameter. We explained 48% of the variation in total soil carbon with a combination of plant community indices and abiotic and biotic factors. Plant community composition was at least as effective as any single environmental factor or stand characteristic in predicting soil C pools in Alaskan black spruce ecosystems. We conclude that among the community properties analyzed, the presence of key groups of species, overall species composition, and diversity of certain functional types, especially Sphagnum moss species, are important predictors of soil carbon sequestration in the black spruce forest type.     

Characteristics of treeline plant communities in Alaska

The treeline in Alaska is usually mapped as the limit of white spruce Picea glauca (Moench) Voss along the south slope of the Brooks Range and in western Alaska and as the limit of Sitka spruce Picea sitchensis (Bong.) Carr. on Kodiak Island and in the Alaska Peninsula. In some localities black spruce Picea mariana (Mill.) B.S.P. and paper birch Betula papyrifera Marsh. form components of the treeline community with white spruce. Of special interest are the groves of balsam poplar Populus balsamifera L. occurring on the north slope of the Brooks Range and to the west and southwest of the spruce treeline. There is some question as to whether trees survived in unglaciated portions of Alaska during the last glacial period. Spruce trees became prevalent about 10000 yr ago and may still be expanding to their climatic limits. In some areas of Alaska the treeline was more expanded during the Hypsithermal period than it is at present, but in other regions evidence for such an expansion is lacking. Treeline in some areas seems to have been stable for the last several centuries, but is has been expanding rapidly for the last 40 yr in central and western Alaska and for a longer period on Kodiak Island.     

Past attacks influence host selection by the solitary bark beetle Dendroctonus micans

1. A spatio‐temporal study of host selection and local spread of a solitary bark beetle attacking live spruce Dendroctonus micans (Kugelann) was carried out using a combination of standard statistical methods, geostatistical analyses, and modelling. The study was based on data from three plots (150–300 trees, 0.3–1 ha) from 1978 to 1993. All trees were mapped and successful and abortive bark‐beetle attacks on each tree were counted annually. Because the attacked trees usually survived, temporal attack patterns as well as spatial patterns could be analysed. 2. The distribution of successful insect attacks on the trees was slightly aggregative, indicating some degree of choice rather than totally random establishment. 3. The level of yearly individual attacks per tree was very stable, suggesting that D. micans usually leave the host in which they develop. 4. The attacked trees were distributed randomly in the plots; at the study's spatial scale, the insects dispersed freely throughout the plot (no spatial dependence). 5. On the other hand, time dependence was strong; some trees were attacked repeatedly while others were left untouched. 6. Among a choice of scenarios (random attack, fixed variability in individual host susceptibility, induced host susceptibility following random attack), the best fit was obtained with the model involving induced individual host susceptibility. This type of relation to the host tree contrasts strongly with patterns generally described in host–plant relationships (including gregarious, tree‐killing bark beetles), where local herbivore damage results in induced resistance. 7. These results suggest that the first attacks in a new stand are made at random, that all or most of the beetles emerging from a tree disperse and resample the stand, and that they settle preferentially on trees that were colonised successfully by previous generations.     

The bark beetle Pityogenes chalcographus (L.) (Scolytidae) in living trees: reproductive success, tree mortality and interaction with Ips typographus

Abstract:  Tree-killing ability of Pityogenes chalcographus was experimentally investigated by baiting living spruce Picea abies with synthetic aggregation pheromone, thereby exposing them to beetle attack. Reproductive success was estimated by rearing beetles from stem sections taken from killed trees. The presence of Ips typographus on several killed trees allowed a comparison of reproductive success in the presence and absence of this species. Furthermore, the possibility that breeding material colonized by P. chalcographus may induce subsequent attacks by I. typographus on nearby trees was also studied. The tree killing ability of P. chalcographus was low as only 8% of the baited trees, attacked by P. chalcographus alone, were killed. Tree death was strongly related to the presence of I. typographus , which is in line with the association with aggressive wood-living fungi in this species. The reproductive success was low, with on average less than one daughter beetle produced per mother beetle. The success was significantly higher in trees also inhabited by I. typographus . Tree-parts colonized by P. chalcographus induced almost no attacks by I. typographus on nearby trees.     

Phylogeography of spruce beetles (Dendroctonus rufipennis Kirby) (Curculionidae: Scolytinae) in North America

Tree-feeding insects that are widespread in north temperate regions are excellent models for studying how past glaciations have impacted differentiation and speciation. We used mitochondrial DNA (mtDNA) sequences and allele frequencies at nine microsatellite loci to examine genetic population structure across the current range of the spruce beetle (Dendroctonus rufipennis), an economically important insect in North America. Two major haplotype groups occur across northern North America, from Newfoundland to Alaska, on white spruce (Picea glauca), and a third distinctive haplotype group occurs throughout the Rocky Mountains on Engelmann spruce (Picea engelmannii). The two mtDNA lineages found in northern populations are 3-4% divergent from each other and from the lineages found in the Rocky Mountains. Analyses of microsatellite data also suggest the existence of major population groupings associated with different geographical regions. In the Pacific Northwest, concordant contact zones for genetically distinct populations of spruce beetles and their principal hosts appear to reflect recent secondary contact. Although we could detect no evidence of historical mtDNA gene flow between allopatric population groups, patterns of variation in the Pacific Northwest suggest recent hybridization and introgression. Together with the pollen record for spruce, they also suggest that beetles have spread from at least three glacial refugia. A minimum estimate of divergence time between the Rocky Mountain and northern populations was 1.7 Myr (million years), presumably reflecting the combined effects of isolation during multiple glacial cycles.     

Performance of the tree‐killing bark beetles Ips typographus and Pityogenes chalcographus in non‐indigenous lodgepole pine and their historical host Norway spruce

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Induced terpene accumulation in Norway spruce inhibits bark beetle colonization in a dose-dependent manner

Background

Tree-killing bark beetles (Coleoptera, Scolytinae) are among the most economically and ecologically important forest pests in the northern hemisphere. Induction of terpenoid-based oleoresin has long been considered important in conifer defense against bark beetles, but it has been difficult to demonstrate a direct correlation between terpene levels and resistance to bark beetle colonization.

Methods

To test for inhibitory effects of induced terpenes on colonization by the spruce bark beetle Ips typographus (L.) we inoculated 20 mature Norway spruce Picea abies (L.) Karsten trees with a virulent fungus associated with the beetle, Ceratocystis polonica (Siem.) C. Moreau, and investigated induced terpene levels and beetle colonization in the bark.

Results

Fungal inoculation induced very strong and highly variable terpene accumulation 35 days after inoculation. Trees with high induced terpene levels (n = 7) had only 4.9% as many beetle attacks (5.1 vs. 103.5 attacks m⁻²) and 2.6% as much gallery length (0.029 m m⁻² vs. 1.11 m m⁻²) as trees with low terpene levels (n = 6). There was a highly significant rank correlation between terpene levels at day 35 and beetle colonization in individual trees. The relationship between induced terpene levels and beetle colonization was not linear but thresholded: above a low threshold concentration of ∼100 mg terpene g⁻¹ dry phloem trees suffered only moderate beetle colonization, and above a high threshold of ∼200 mg terpene g⁻¹ dry phloem trees were virtually unattacked.

Conclusion/Significance

This is the first study demonstrating a dose-dependent relationship between induced terpenes and tree resistance to bark beetle colonization under field conditions, indicating that terpene induction may be instrumental in tree resistance. This knowledge could be useful for developing management strategies that decrease the impact of tree-killing bark beetles.     

Tree killing by Ips typographus (Coleoptera: Scolytidae) at stand edges with and without colonized felled spruce trees

Abstract 1 To maintain biodiversity in managed spruce forests in Sweden more wind‐felled trees must be retained. However, there is concern among forest owners that this may result in higher tree mortality caused by the spruce bark beetle, Ips typographus (L.) (Col. Scolytidae). 2 To simulate wind‐felled trees, living spruce trees were cut at spruce stand edges bordering fresh clear‐cuttings. Treatments comprised edges with zero, one or five cut trees colonized by I. typographus. Edges with naturally wind‐felled trees colonized by I. typographus were also included in the analyses. 3 During the two following summers, the number of trees killed by I. typographus did not differ between edges with and without felled trees, or between edges with one or five felled trees. 4 Within edges with felled trees, there were more killed trees close to the felled trees than at other parts of the edges. Thus, felled trees provided focal points for attacks within edges. 5 It is concluded that small numbers of wind‐felled trees colonized by I. typographus may be left near spruce stand edges without increasing the risk of beetle‐induced tree mortality.     

Elution rate and spacing of antiaggregation pheromone dispensers for protecting live trees from Dendroctonus pseudotsugae (Coleoptera: Scolytidae)

The antiaggregation pheromone 3-methylcyclohex-2-en-1-one (MCH) is highly effective in preventing the infestation of high-risk trees by Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins. A large portion of the cost of an MCH treatment is related to the time applicators spend walking through an area dispersing the formulated pheromone. Application of fewer MCH dispensers eluting at a higher rate than those currently registered for operational use could potentially reduce treatment costs. Two higher elution rates, 6 and 18 mg/d per dispenser, were compared with the current standard of 2 mg/d per dispenser and an untreated control on 1-ha circular plots. Dispensers were spaced 5,15, and 44 m apart around the plot perimeters eluting 2, 6, and 18 mg/d, respectively. The nominal dose of MCH was 144 mg/ha/d on all plots. Percentages of Douglas-fir trees > or = 20 cm diameter at breast height mass attacked by Douglas-fir beetle were significantly lower on plots treated with dispensers eluting 2 and 6 mg/d and spaced 5 and 15 m apart, respectively, compared with the untreated control. Infestation rate on plots treated with dispensers eluting 18 mg/d and spaced 44 m apart was not significantly different from the control. Douglas-fir beetle abundance and host tree availability were similar on all plots. These results indicate that MCH dispensers eluting 6 mg/d (three times the current standard rate) and spaced 15 m apart (three times existing standard distance) can effectively prevent Douglas-fir beetle infestations.     

Host and non-host odour signals governing host selection by the pine shoot beetle, Tomicus piniperda and the spruce bark beetle, Hylurgops palliatus (Col., Scolytidae)

Abstract:  Tomicus piniperda and Hylurgops palliatus colonize susceptible host trees by responding to host-specific odour signals as well as by avoiding volatiles emanating from non-host conifers. In the field, the pine shoot beetle, T. piniperda , responded in high numbers to natural odour sources provided by their host tree, Pinus sylvestris , while the non-host conifers Larix decidua , Picea abies , or Pseudotsuga menziesii were significantly less attractive. In contrast, the spruce bark beetle, Hylurgops palliatus , preferentially responded to its main host, P. abies . Furthermore, T. piniperda attacks on P. sylvestris bolts decreased in presence of bark and wood particles from the non-host P. abies , whereas particles from P. menziesii appeared not to affect T. piniperda attacks. Apparently, tree-specific volatiles act at close range as specific signals that lead to the successful discrimination and colonization of the respective host tree species.     

Biotic disturbance in expanding subarctic forests along the eastern coast of Hudson Bay

* The past and present occurrence of insect disturbance on white spruce (Picea glauca) trees was evaluated at their northern range limit on the eastern coast of Hudson Bay, and its effects on tree growth and population dynamics studied. * Three sites were sampled along an altitudinal gradient. Ring-width chronologies and stem analysis were used to evaluate tree growth. The occurrence of holes in the bark, of resin pockets and blue-stain fungi, and ring-width evidence for growth releases were used to assess the impact of bark beetle. * The white spruce population was established at these sites in the 17th century. Since their establishment, the spruce trees have developed a tree growth form, except at the uppermost site, where severe growth suppression occurred in the 19th century. Bark beetle and blue-stain fungi occurred with different timing and intensity. Their highest occurrence, associated with high mortality rates, was at the lowest site in the late 20th century. In the uppermost sites, biotic disturbance has occurred since the 18th century, associated with evidence for mechanical disturbance. * The simultaneous arrival of white spruce in the area resulted in a synchronous onset of spruce beetle activity driven by tree ageing. Unfavourable climatic conditions affected tree growth severely in the most exposed sites.