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Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins (DFB), is the most damaging insect pest of Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, in western North America. Individual high-value trees and stands can be protected during DFB outbreaks using the beetle's anti-aggregation pheromone, 3-methylcyclohex-2-en-1-one (MCH), which is available in several commercial formulations. However, other methylcyclohexanones similar in molecular structure to MCH have been shown to repel bees from agricultural areas. In forest systems, wild bees (Hymenoptera: Apiformes) provide essential pollination services to many forb and shrub species. Therefore, it is important to determine whether resident wild bee communities are affected in forests treated with MCH. To address this, the bee community was sampled within experimental sites located in Idaho and Montana, USA in 2016. At both sites, there was no significant difference in overall bee abundance, species richness, or diversity between MCH-treated plots and untreated control plots. Overall, these results indicate that treatment of Douglas-fir with MCH does not negatively impact the resident wild bee community.

The Douglas-fir beetle (Dendroctonus pseudotsugae Hopkins) (Coleoptera: Curculionidae) antiaggregation pheromone, 3-methylcyclohex-2-en-1-one (MCH), has been used since 2000 to protect high-value trees and stands throughout western North America. Operational treatments involve placing individual releasers on a 12 m × 12 m grid throughout the area to be protected. In this study, six widely spaced trap lines were established with aggregation attractant–baited traps located 1, 3, 9, 27, and 81 m from a location where an operational MCH release device was alternately either present or absent, and changes in catches caused by the MCH device were assessed at all distances. Trap catches were suppressed by about 70% at one and three metres, by 50% at nine metres, by 30% at 27 m, and not at all at 81 m. Inhibition by the MCH device varied with distance (m) from the source according to the function 0.79 − 0.092x0.51 (R2 = 0.986). Decline of attractant inhibition with distance from the MCH device was much less steep than would have been expected if catch inhibition had varied directly with the average airborne concentration of MCH.

This paper reviews the literature on the identification of 3-methylcyclohex-2-en-1-one (MCH) as the antiaggregation pheromone of the Douglas-fir beetle (Dendroctonus pseudotsugae Hopkins) (Coleoptera: Curculionidae) and the development of successful management applications using the pheromone. Previously unpublished data from two studies on novel uses of MCH are included. The successful development of antiaggregation pheromone-based treatments for the Douglas-fir beetle is discussed in relation to efforts to develop similar treatments for other bark beetle species, and opportunities for future research on MCH and the Douglas-fir beetle are suggested.

The status of wild bees has received increased interest following recent estimates of large-scale declines in their abundances across the United States. However, basic information is limited regarding the factors affecting wild bee communities in temperate coniferous forest ecosystems. To assess the early responses of bees to bark beetle disturbance, we sampled the bee community of a Douglas-fir, Pseudotsuga menziesii (Mirb.), forest in western Idaho, United States during a Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins (Coleoptera: Curculionidae), outbreak beginning in summer 2016. We resampled the area in summer 2018 following reductions in forest canopy cover resulting from mortality of dominant and codominant Douglas-fir. Overall, results from rarefaction analyses indicated significant increases in bee diversity (Shannon’s H) in 2018 compared to 2016. Results from ANOVA also showed significant increases in bee abundance and diversity in 2018 compared to 2016. Poisson regression analyses revealed percent tree mortality from Douglas-fir beetle was positively correlated with increases in total bee abundance and species richness, where community response variables displayed a cubic trend with percent tree mortality. Percent reduction in canopy cover from 2016 to 2018 was also correlated with bee species richness and diversity. These findings suggest that wild bee communities may benefit from changes in forest structure following bark beetle outbreaks.

Outbreaks of conifer bark beetles in Europe and North America have increased in scale and severity in recent decades. In this study, we identify existing fossil records containing bark beetle remains from the end of the Last Glacial Maximum (~14,000 cal. yr BP) to present day using the online databases Neotoma and BugsCEP and literature searches, and compare these data with modern distribution data of selected tree-killing species. Modern-day observational data from the Global Biodiversity Information Facility (GBIF) database was used to map recorded distributions from AD 1750 to present day. A total of 53 fossil sites containing bark beetle remains, from both geological and archeological sites, were found during our searches. Fossil sites were fewer in Europe ( n = 21) than North America ( n = 32). In Europe, 29% of the samples in which remains were found were younger than 1000 cal. yr BP, while in North America, remains were mainly identified from late Glacial (~14,000–11,500 cal. yr BP) sites. In total, the fossil records contained only 8 of 20 species we consider important tree-killing bark beetles in Europe and North America based on their impacts during the last 100 years. In Europe, Ips sexdentatus was absent from the fossil record. In North America, Dendroctonus adjunctus, Dendroctonus frontalis, Dendroctonus jeffreyi, Dendroctonus pseudotsugae, Dryocoetes confusus, Ips calligraphus, Ips confusus, Ips grandicollis, Ips lecontei, Ips paraconfusus, and Scolytus ventralis were absent. Overall, preserved remains of tree-killing bark beetles are rare in the fossil record. However, by retrieving bulk material from new and existing sites and combining data from identified bark beetle remains with pollen, charcoal, tree rings, and geochemistry, the occurrence and dominance of bark beetles, their outbreaks, and other disturbance events can be reconstructed.

Douglas-fir dominated forests are an integral part of the Pacific Northwest. In the Cedar River Municipal Watershed, Washington, these forests provide erosion control and ecosystem buffering for the Cedar River system that supplies high-quality drinking water to the Seattle area. Mortality of Douglas-fir in the watershed has been increasing in recent years. The Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins, as well as fungal pathogens, are key agents of mortality in Douglas-fir dominated forests, but their contributions to the current rates of mortality are unknown. We modeled D. pseudotsugae phenology in western Washington and estimated peak flight of overwintering adults at 344.5 cumulative degree-days (base temperature threshold = 4.3°C). We extended the results from the phenology model when assuming a 1.7°C increase in temperature and estimated that D. pseudotsugae adult flight could be advanced by 21–27 d. We also conducted a field study over 2 yr to quantify the individual and interacting roles of D. pseudotsugae, root rot pathogens, and other abiotic and biotic variables as drivers of Douglas-fir mortality. Study sites with recent high rates of mortality of Douglas-fir (>30%) were generally in lower elevation stands and affected by both D. pseudotsugae and root rot pathogens. Attacks by D. pseudotsugae in 1 yr were significantly associated with the presence of root rot mycelia in the following year, but not vice versa. The development of a D. pseudotsugae phenology model for the region and the identification of variables associated with Douglas-fir mortality facilitates the development of management strategies.

The Douglas-fir beetle (Dendroctonus pseudotsugae Hopkins) occasionally colonizes western larch [Larix occidentalis Nutt. (Pinales: Pinaceae)] growing in close proximity to its primary host, Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco (Pinales: Pinaceae)], but brood have never been found to survive in live western larch. Western larch produces the monoterpene 3-carene in higher concentrations than Douglas-fir. In this study, the toxicity and repellency of 3-carene to Douglas-fir beetle was evaluated in a series of laboratory and field tests. In a laboratory bioassay, 3-carene was one of the most toxic monoterpenes to Douglas-fir beetles among those tested. In a field trial, addition of 3-carene to multiple-funnel traps baited with frontalin (the primary component of Douglas-fir beetle aggregation pheromone) or frontalin and α-pinene significantly reduced the number of Douglas-fir beetles collected. In another field study, live western larch, felled western larch, live Douglas-fir, felled Douglas-fir, and live Douglas-fir surrounded by 3-carene releasers were baited with Douglas-fir beetle aggregation pheromones. There were significantly fewer Douglas-fir beetle entrance holes and egg galleries excavated on both live western larch and live Douglas-fir surrounded by 3-carene compared with live Douglas-fir. Most egg galleries excavated in live western larch were heavily impregnated with resin and no eggs hatched. There were no significant differences in egg galleries excavated or eggs hatched between felled western larch and felled Douglas-fir. Collectively, these data support the hypothesis that 3-carene slows the colonization process in live western larch allowing more time for host trees to respond to a colonization attempt and a higher likelihood of successfully resisting infestation.

Voucher specimens (109) of bee species associated with MS Thesis: Interactions between wild bee communities and Douglas-fir beetle (Dendroctonus pseudotsugae) populations in Douglas-fir (Pseudotsuga menziezii) forests of the Intermountain West

Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, trees and stands can be protected from Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins (DFB)-caused mortality by application of synthetic formulations of the beetle’s antiaggregation pheromone, 3-methylcyclohex-2-en-1-one (MCH). A biodegradable formulation of MCH, SPLAT MCH, was developed and evaluated for protecting individual Douglas-fir trees and small stands from colonization and mortality by DFB. In an individual-tree experiment in Idaho, both MCH bubble capsules and SPLAT MCH significantly reduced the proportion of treated trees colonized and killed by DFB compared to untreated controls. SPLAT MCH was as effective as MCH bubble capsules for protecting individual trees. Both MCH bubble capsules and SPLAT MCH significantly reduced the proportion of trees colonized and killed by DFB within 0.04-ha circular plots surrounding each treated tree compared to untreated controls. In 0.41 ha stands in New Mexico, both MCH bubble capsules and SPLAT MCH significantly reduced the proportion of trees colonized and killed by DFB compared to untreated controls, again with no differences observed between MCH treatments. In a similar stand level trial in Idaho, neither MCH treatment significantly reduced the proportion of trees colonized by DFB, and only MCH bubble capsules significantly reduced levels of tree mortality compared to untreated controls, but no significant difference was observed between SPLAT MCH and MCH bubble capsules. Overall, the results indicate that SPLAT MCH is as effective as MCH bubble capsules for protecting individual trees and small stands of Douglas-fir from DFB-caused mortality.

Climate change is altering the frequency and severity of forest disturbances such as wildfires and bark beetle outbreaks, thereby increasing the potential for sequential disturbances to interact. Interactions can amplify or dampen disturbances, yet the direction and magnitude of future disturbance interactions are difficult to anticipate because underlying mechanisms remain poorly understood. We tested how variability in postfire forest development affects future susceptibility to bark beetle outbreaks, focusing on mountain pine beetle (Dendroctonus ponderosae) and Douglas-fir beetle (Dendroctonus pseudotsugae) in forests regenerating from the large high-severity fires that affected Yellowstone National Park in Wyoming in 1988. We combined extensive field data on postfire tree regeneration with a well-tested simulation model to assess susceptibility to bark beetle outbreaks over 130 y of stand development. Despite originating from the same fire event, among-stand variation in forest structure was very high and remained considerable for over a century. Thus, simulated emergence of stands susceptible to bark beetles was not temporally synchronized but was protracted by several decades, compared with stand development from spatially homogeneous regeneration. Furthermore, because of fire-mediated variability in forest structure, the habitat connectivity required to support broad-scale outbreaks and amplifying cross-scale feedbacks did not develop until well into the second century after the initial burn. We conclude that variability in tree regeneration after disturbance can dampen and delay future disturbance by breaking spatiotemporal synchrony on the landscape. This highlights the importance of fostering landscape variability in the context of ecosystem management given changing disturbance regimes.

Current recommendations for applying the antiaggregation pheromone 3-methylcyclohex-2-en-1-one (MCH) to protect live trees from Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins, infestation are to space individual passive releasers (MCH bubble capsules) on a 12- by 12-m grid throughout areas to be protected. Previous field studies and a theoretical study using a puff dispersion model to predict pheromone concentrations have shown that releasers emitting higher rates of MCH spaced farther apart may be as effective as the established standard treatment. During 2012 and 2013, we tested higher release rates of MCH at correspondingly wider spacings to keep the total amount of MCH released per unit area equal in all treatments. In 2012 near Challis, ID, treatments included the established standard release rate and spacing, four and six times the standard release rate at correspondingly wider spacings, and an untreated control. In 2013 near Ketchum, ID, treatments included the established standard release rate and spacing, five and seven times the standard release rate at correspondingly wider spacings, and an untreated control. Results from both years indicated that all MCH treatments were equally effective in reducing Douglas-fir beetle infestation. Using higher release rate formulations at wider spacings will reduce labor costs of installing MCH treatments, and, in cases where it is necessary, retrieving the releasers as well. In addition to reducing labor costs, the revised treatment protocol may increase the feasibility of treating areas that currently may not be possible due to treatment costs.

Mass attack by tree-killing bark beetles (Curculionidae: Scolytinae) brings about large chemical changes in host trees that can have important ecological consequences. For example, mountain pine beetle (Dendroctonus ponderosae Hopkins) attack increases emission of terpenes by lodgepole pine (Pinus contorta Dougl. ex Loud.), affecting foliage flammability with consequences for wildfires. In this study, we measured chemical changes to Douglas-fir (Pseudotsuga menziesii var. glauca (Mirb.) Franco) foliage in response to attack by Douglas-fir beetles (Dendroctonus pseudotsugae Hopkins) as trees die and crowns transitioned from green/healthy, to green-infested (year of attack), to yellow (year after attack), and red (2 yr after attack). We found large differences in volatile and within-needle terpene concentrations among crown classes and variation across a growing season. In general, emissions and concentrations of total and individual terpenes were greater for yellow and red needles than green needles. Douglas-fir beetle attack increased emissions and concentrations of terpene compounds linked to increased tree flammability in other conifer species and compounds known to attract beetles (e.g., [Formula: see text]-pinene, camphene, and D-limonene). There was little relationship between air temperature or within-needle concentrations of terpenes and emission of terpenes, suggesting that passive emission of terpenes (e.g., from dead foliage) does not fully explain changes in volatile emissions. The potential physiological causes and ecological consequences of these bark beetle-associated chemical changes are discussed.

An outbreak of the Douglas-fir tussock moth, Orgyia pseudotsugata McDunnough, occurred in the South Platte River drainage on the Pike-San Isabel National Forest in the Colorado Front Range attacking Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco. Stocking levels, species composition, and tree size in heavily and lightly defoliated stands were similar. Douglas-fir tussock moth defoliation resulted in significant Douglas-fir mortality in the heavily defoliated stands, leading to a change in dominance to ponderosa pine, Pinus ponderosa Lawson. Douglas-fir beetle, Dendroctonus pseudotsuqae Hopkins, populations increased following the defoliation event but caused less mortality, and did not differ between heavily and lightly defoliated stands. Douglas-fir tussock moth-related mortality was greatest in trees less than 15 cm dbh (diameter at 1.4 m above the ground) that grew in suppressed and intermediate canopy positions. Douglas-fir beetle-related mortality was greatest in trees larger than 15 cm dbh that grew in the dominant and co-dominant crown positions. Although both insects utilize Douglas-fir as its primary host, stand response to infestation is different. The extensive outbreak of the Douglas-fir tussock moth followed by Douglas-fir beetle activity may be associated with a legacy of increased host type growing in overstocked conditions as a result of fire exclusion.

Understanding how disturbances interact to shape ecosystems is a key challenge in ecology. In forests of western North America, the degree to which recent bark beetle outbreaks and subsequent fires may be linked (e.g., outbreak severity affects fire severity) and/ or whether these two disturbances produce compound effects on postfire succession is of widespread interest. These interactions remain unresolved, largely because field data from actual wildfires following beetle outbreaks are lacking. We studied the 2008 Gunbarrel Fire, which burned 27 200 ha in Douglas-fir (Pseudotsuga menziesii ) forests that experienced a bark beetle outbreak 4-13 years prefire (''gray stage,'' after trees have died and needles have dropped), to determine whether outbreak severity influenced subsequent fire severity and postfire tree regeneration. In 85 sample plots we recorded prefire stand structure and outbreak severity; multiple measures of canopy and forest-floor fire severity; and postfire tree seedling density. Prefire outbreak severity was not related to any measure of fire severity except for mean bole scorch, which declined slightly with increasing outbreak severity. Instead, fire severity varied with topography and burning conditions (proxy for weather at time of fire). Postfire Douglas-fir regeneration was low, with tree seedlings absent in 65% of plots. Tree seedlings were abundant in plots of low fire severity that also had experienced low outbreak severity (mean ¼ 1690 seedlings/ha), suggesting a dual filter on tree regeneration. Although bark beetles and fire collectively reduced live basal area to ,5% and increased snag density to .2000% of pre-outbreak levels, the lack of relationship between beetle outbreak and fire severity suggests that these disturbances were not linked. Nonetheless, effects on postfire tree regeneration suggest compound disturbance interactions that contribute to the structural heterogeneity characteristic of mid/lower montane forests.

An instantaneous puff dispersion model was used to assess concentration fields of the Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins, antiaggregation pheromone, 3-methylcyclohex-2-en-1-one (MCH), within a 1-ha circular plot. Several combinations of MCH release rate and releaser spacing were modeled to theoretically analyze optimal deployment strategies. The combinations of MCH release rate and releaser spacing used in the modeling exercise were based on results of previous field studies of treatment efficacy. Analyses of model results suggest that a release rate up to six times the initial standard, at a correspondingly wider spacing to keep the total amount of pheromone dispersed per unit area constant, may be effective at preventing Douglas-fir beetle infestation. The model outputs also provide a visual representation of pheromone dispersion patterns that can occur after deployment of release devices in the field. These results will help researchers and practitioners design more effective deployment strategies.

Douglas-fir beetle (Dendroctonus pseudotsugae Hopkins) (DFB) causes considerable mortality to Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) in western North American forests. We evaluated the use of semiochemical-baited multiple-funnel traps for the protection of small, high-value stands of trees, such as those occurring in campgrounds, rest areas, and small parks when Douglas-fir mortality caused by populations of DFB were at levels of concern to land managers. At two sites in western Montana in 2004, three treated plots were surrounded by three trapping stations arranged in an equilateral triangle (200 m per triangle side). Similar, untreated plots were used for comparison. More than 2 million DFB were trapped and removed from treated plots during 2004, but this trapping did not protect Douglas-fir at either site. Conversely, the ratio of infested to living trees increased substantially due to trapping at one of the sites. Placing semiochemical lures adjacent to stands of susceptible trees...

Dendroctonus pseudotsugae Hopkins infests Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, throughout the distribution of that tree species from British Columbia to northern Mexico. The subspecies Dendroctonus pseudotsugae barragani Furniss was described from the mountains of Chihuahua, Sierra Madre Occidental, Mexico, whereas the nominal subspecies, Dendroctonus pseudotsugae pseudotsugae Hopkins, occurs north of Mexico. The description of D. p. barragani was based on the only known Mexican population at that time. More recently, new populations of this beetle have been discovered at 13 additional localities in Chihuahua, Durango, Coahuila, and Nuevo Leon, Mexico. To test whether these additional populations support the existence of two subspecies, we performed a taxonomic reassessment combining molecular markers (cytochrome oxidase I), morphological characters used in the original description, and newly described morphological characters. Phylogenetic analysis of 89 haplotypes confirms that the Mexican populations are distinct from the sampled populations in the United States and Canada. Morphological analysis indicates that intraspecific variation is greater than previously considered within Mexican populations. However, at least seven characters on the head, pronotum, and elytra (including three previously undescribed characters of frons sculpture) consistently discriminate among Canada—U.S. and Mexico populations. The extension of the known distribution of this beetle in Mexico and verification of its subspecific status will aid in the management and conservation of Pseudotsuga in Mexico.

High attack density resulted in lower dry weight and fat content of most developmental stages of the Douglas-fir beetle Dendroctonus pseudotsugae Hopk., but did not seem to significantly affect the weight and fat content of young adults during their period of subcortical feeding; probably because they normally form feeding aggregations. Lower temperature increased the effect of competition on size and fat content by causing longer larval mines and greater interaction between members of adjacent broods. The temperature regime during brood development of the Douglas-fir beetle affected the accumulation and retention of lipids. Fat content declined during early adult life at all temperatures tested, but the greatest decrease occurred at a constant temperature. The decline in fat content during early adult life and the previously established correlation between fat content and behavior is discussed in relation to different scolytid life histories. Zusammenfassung Uber einige Faktoren, welche die Grose, den Fettgehalt und das Verhalten einer Borkenkafer-Art beeinflussen Eine hohe Befallsdichte fuhrte zum Absinken des Trockengewichts und Fettgehalts der meisten Entwicklungsstadien des Borkenkafers Dendroctonus pseudotsugae Hopk. Das Gewicht und der Fettgehalt junger Imagines wahrend der Zeit ihres Frases unter der Rinde schien davon jedoch nicht beeinflust, vielleicht weil die Borkenkafer normalerweise Frasgesellschaften bilden. Niedere Temperaturen steigerten den Affekt der Konkurrenz auf Korpergrose und Fettgehalt, indem sie zur Anlage langerer Larvengange und zu verstarkten Interaktionen zwischen den Larven benachbarter Bruten fuhrte. Wahrend der Larvenentwicklung werden die Fette akkumuliert und zuruckgehalten. Der Fettgehalt der jungen Borkenkafer-Imagines sank bei allen Untersuchungen, insbesondere bei konstanten Temperaturen. Der Fettabbau wahrend der ersten Zeit des Imagmallebens und die Korrelationen zwischen Fettgehalt und Verhaltensweise werden im Hinblick auf die verschiedenartige Lebensweise von Borkenkafern erortert.

In field experiments synthetic seudenol (3-methyl-2-cyclohexen-1-ol), a female-produced pheromone, strongly increased the response of Douglas-fir beetles to DouglureR (combination of frontalin and host terpenes). The addition of ethanol also increased the attractiveness, and the 2 alcohols in combination enhanced the effectiveness of Douglure by severalfold. Zusammenfassung Synergistische Wirkungen von Ethylalkohol auf die pheromon-bedingte Aggregation von Dendroctonus pseudotsugae (Col., Scolytidae) Bei Freilandexperimenten wurde die Reaktion des Borkenkafers D. pseudotsugae auf das Pheromon DouglureR (eine Kombination von Frontalin und Wirtspflanzenterpenen) bei Kombination mit dem von den Borkenkafer-Weibchen Produzierten Pheromon Seudenol (3-methyl-2-cyclohexen-1-ol) erheblich verstarkt. Auch die Hinzufugung von Ethanol steigerte die Attraktivitat, beide Alkohole zusammen erhohten die Anlockwirkung von Douglure um ein Mehrfaches.

The identity of a reported Dendroctonus pseudotsugae attractant, 3-methyl-2-cyclohexen-1-ol (MCH-ol), was confirmed by GLC/MS analysis of volatiles collected over live attractive female. In bioassay with previously known attractants, MCH-ol synergistically evoked male arrestment and stridulation in the laboraotry and high attraction predominantly of males in the field. Verbenone was similarly identified and was synergistically active to a lesser degree. The known double effect of the antiaggragetive pheromone 3-methyl-2-cyclohexen-1-one (MCH) was confirmed, at it repressed response to the attractants at high concentration but at very low concentration it increased response to MCH-ol and frontalin. The highest field response occurred to these three components together. Comparative GLC of feces and volatiles from pairs supports the belief that fecal release of MCH with the other attractants is quantitatively less than the release stimulated by the presence of the male and/or its sonic signal. Zusammenfassung Weitere Komponenten des Aggregations-Pheromons von Dendroctonus pseudotsugae (Col., Scolyt.) Aus den Duftstoffen lebender Kafer von Dendroctonus pseudotsugae wurde 3-methyl-2-cyclohexen-1-ol (MCH-ol) gewonnen und seine Identitat chromatographisch sowie auch massenspektrometrisch bestatigt. In Laborversuchen bewirkte MCH-ol, in Verbindung mit den schon bekannten Pheromonen, eine stark zunehmende Anlockung sowie Stridulation der Mannchen. Auch in Freilandversuchen lockte dieses Pheromon die fliegenden Borkenkafer, vor allem die Mannchen, stark an. Als weiteres Pheromon wurde Verbenone aus den lebenden Borkenkafern gewonnen, doch war es synergistisch weniger aktiv. Die bekannte Doppelwirkung des antiaggregativen Pheromons 3-methyl-2-cyclohexen-1-one (MCH) wurde bestatigt: eine hohere Konzentration des MCH blockierte die Anlockung an die attraktiven Stoffe ganzlich, wahrend es in sehr geringer Konzentration die Anlockung an Frontalin und MCH-ol erheblich vergroserte. Die groste Anlockung wurde im Felde erzielt, wenn die drei Pheromone zusammen angeboten wurden. Vergleichende chromatographische Untersuchungen des Borkenkaferfrasses, des Kotes und der Duftstoffe zeigten, das die Freisetzung von MCH aus Borkenkaferkot quantitativ bedeutend geringer ist als die Freigabe, die durch die Anwesenheit des Mannchens und seine Stridulation stimuliert wird.

The relationship between high fat content and dispersive behavior reported for the Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins, holds true for Ips paraconfusus Lanier. Laboratory investigation revealed that the overwintered generation contained a significantly smaller proportion of responsive individuals than the spring generation. The nonresponsive individuals of both the overwintered and subsequent spring generation were found to have a markedly higher fat content than responsive individuals. It was also determined that the overwintered non-responders contained significantly more fat than their spring generation counterparts. Examination of adults for nemic-infection revealed considerable variation in the level of infection, but the non-responders were generally less heavily parasitized than the responders. Zusammenfassung Zur interzyklischen Variabilitat des Fettgehalts und des Verhaltens bei Ips paraconfusus Lanier Die von Dendroctonus pseudotsugae beschriebenen Bezeichnungen zwischen dem Fettgehalt und dem Ausbreitungsverhalten treffen auch fur Ips paraconfusus zu. Laboruntersuchungen zeigten, das die uberwinternde Generation einen signifikant kleineren Anteil an (im Olfaktometer auf mannliche Pheromone) reagierenden Individuen enthalt als die Fruhjahrs-generation. Die nicht reagierenden Individuen beider Generationen besasen einen hoheren Fettgehalt als die reagierenden, wobei wieder unter den nicht reagierenden die Uberwinterer mehr Fett besasen als die Angehorigen der Fruhjahrsgeneration. Eine Untersuchung auf Nematoden-Befall ergab, das die nicht reagierenden allgemein weniger parasitiert waren als die reagierenden.

Four treatments (control, burn-only, thin-only, and thin-and-burn) were evaluated for their effects on bark beetle-caused mortality in both the short-term (one to four years) and the long-term (seven years) in mixed-conifer forests in western Montana, USA. In addition to assessing bark beetle responses to these treatments, we also measured natural enemy landing rates and resin flow of ponderosa pine (Pinus ponderosa) the season fire treatments were implemented. All bark beetles were present at low population levels (non-outbreak) for the duration of the study. Post-treatment mortality of trees due to bark beetles was lowest in the thin-only and control units and highest in the units receiving burns. Three tree-killing bark beetle species responded positively to fire treatments: Douglas-fir beetle (Dendroctonus pseudotsugae), pine engraver (Ips pini), and western pine beetle (Dendroctonus brevicomis). Red turpentine beetle (Dendroctonus valens) responded positively to fire treatments, but never caused mortality. Three fire damage variables tested (height of crown scorch, percent circumference of the tree bole scorched, or degree of ground char) were significant factors in predicting beetle attack on trees. Douglas-fir beetle and pine engraver responded rapidly to increased availability of resources (fire-damaged trees); however, successful attacks dropped rapidly once these resources were depleted. Movement to green trees by pine engraver was not observed in plots receiving fire treatments, or in thinned plots where slash supported substantial reproduction by this beetle. The fourth tree-killing beetle present at the site, the mountain pine beetle, did not exhibit responses to any treatment. Natural enemies generally arrived at trees the same time as host bark beetles. However, the landing rates of only one, Medetera spp., was affected by treatment. This predator responded positively to thinning treatments. This insect was present in very high numbers indicating a regulatory effect on beetles, at least in the short-term, in thinned stands. Resin flow decreased from June to August. However, resin flow was significantly higher in trees in August than in June in fire treatments. Increased flow in burned trees later in the season did not affect beetle attack success. Overall, responses by beetles to treatments were short-term and limited to fire-damaged trees. Expansions into green trees did not occur. This lack of spread was likely due to a combination of high tree vigor in residual stands and low background populations of bark beetles.

Genetic structure of phytophagous insects has been widely studied, however, relative influence of the effect of geographic isolation, the host plant or both has been subject of considerable debate. Several studies carried out on bark beetles in the genus Dendroctonus evaluated these factors; nonetheless, recent evidence has shown that genetic structuring is a more complex process. Our goal was to examine the effect of geographic isolation on genetic structure of the Douglas-fir beetle Dendroctonus pseudotsugae. We used mtDNA cytochrome oxidase I (COI) sequences and RAPD markers. One hundred-seventy-two individuals were obtained from 17 populations, for which we analyzed 60 haplotypes (among 172 sequences of COI gene, 550 bp long) and 232 RAPD markers (7 primers). Analyses of molecular variance (AMOVA and SAMOVA), F-statistics and linear regressions suggest that the genetic structure of D. pseudotsugae is strongly influenced by geographic distance. We found that D. pseudotsugae has high intra- and inter-population genetic variation compared with several other bark beetles. Genetic differences among populations based on COI and RAPD markers were correlated with geographic distance. The observed genetic differences between northern (Canada-USA) and southern (Mexico) populations on Pseudotsuga menziesii var. glauca confirm that these two sets of populations correspond to previously assigned subspecies.

We tested methylcyclohexenone (MCH), an anti-aggregation pheromone for the Douglas-fir beetle (Dendroctonus pseudotsugae), for protection of Douglas-fir (Pseudotsuga menziesii) stands by applying MCH-releasing polymer flakes by helicopter twice during summer 2006 to five 4.05-ha plots in the State of Washington, USA. Five similar plots served as untreated controls. We assessed D. pseudotsugae flight into study plots using baited pheromone traps, and tallied D. pseudotsugae attack rates on all P. menziesii trees in 2005 and 2006. We also measured stand basal area and incorporated that as an explanatory variable in the analysis. Significantly fewer D. pseudotsugae were trapped in treated plots than in control plots, and significantly fewer P. menziesii trees were attacked in treated plots than in control plots. The attack rate in untreated stands was nearly 10 times that of treated plots, and stands with higher basal area were significantly more likely to be attacked by D. pseudotsugae than were stands of lower basal area. Attack rates in 2006 and 2005 were significantly correlated, regardless of treatment.

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) were monitored for 4 years following three wildfires. Logis- tic regression analyses were used to develop models predicting the probability of attack by Douglas-fir beetle (Dendroc- tonus pseudotsugae Hopkins, 1905) and the probability of Douglas-fir mortality within 4 years following fire. Percent crown volume scorched (crown scorch), cambium injury, diameter at breast height (DBH), and stand density index for Douglas-fir were most important for predicting Douglas-fir beetle attacks. A nonlinear relationship between crown scorch and cambium injury was observed, suggesting that beetles did not preferentially attack trees with both maximum crown scorch and cambium injury, but rather at some intermediate level. Beetles were attracted to trees with high levels of crown scorch, but not cambium injury, 1 and 2 years following fire. Crown scorch, cambium injury, DBH, and presence/absence of beetle attack were the most important variables for predicting postfire Douglas-fir mortality. As DBH increased, the pre- dicted probability of mortality decreased for unattacked trees but increased for attacked trees. Field sampling suggested that ocular estimates of bark char may not be a reliable predictor of cambium injury. Our results emphasize the important role of Douglas-fir beetle in tree mortality patterns following fire, and the models offer improved prediction of Douglas-fir mortality for use in areas with or without Douglas-fir beetle populations. Resume´ : Des douglas de Menzies (Pseudotsuga menziesii (Mirb.) Franco) ont etesuivis pendant 4 ans a la suite de trois incendies de foret. Des analyses de regression logistique ont eteutilisees pour elaborer des modeles de prediction de la probabilited'une attaque du dendroctone du douglas (Dendroctonus pseudotsugae Hopkins, 1905) et de la probabiliteque le douglas de Menzies meure dans les quatre annees suivant un feu. Le volume de cime roussi, les dommages au cambium, le diametre ahauteur de poitrine (DHP) et l'indice de densitedu peuplement de douglas de Menzies etaient les variables les plus importantes pour predire les attaques du dendroctone. Une relation non lineaire entre le roussissement de la cime et les dommages au cambium a eteobservee, ce qui signifie que les dendroctones n'attaquent pas de preference les arbres qui ont ala fois le maximum de dommages a la cime et au cambium mais plutot un niveau intermediaire quel- conque. Les dendroctones etaient attires par les arbres avec un degreelevede roussissement de la cime mais sans dom- mages au cambium, un et 2 ans apres un feu. Le roussissement de la cime, les dommages au cambium, le DHP et la presence ou l'absence d'attaques du dendroctone etaient les variables les plus importantes pour predire la probabiliteque le douglas de Menzies meure apres un feu. La probabiliteestimee de mortalitediminuait avec l'augmentation du DHP chez les arbres qui n'avaient pas eteattaques alors que la probabilitequ'un arbre meure augmentait avec l'augmentation du DHP chez les arbres qui avaient eteattaques. Des echantillons preleves sur le terrain indiquent que l'estimation oculaire d'une couche superficielle d'ecorce carbonisee pourrait ne pas etre un predicteur fiable de dommages au cambium. Nos re´- sultats font ressortir l'importance du role que joue le dendroctone du douglas dans les patrons de mortaliteapres un feu et les modeles offrent de meilleures predictions de la mortalitedu douglas de Menzies dans les zones avec ou sans popula- tions de dendroctone. (Traduit par la Redaction)

Increased wildfire activity and recent bark beetle outbreaks in the western United States have increased the potential for interactions between disturbance types to influence forest characteristics. However, the effects of interactions between bark beetle outbreaks and subsequent wildfires on forest succession remain poorly understood. We collected data in dry mixed conifer forests across Idaho and western Montana to test whether vegetation responses differ between sites experiencing single and repeated disturbances. We compared tree seedling density and age, surface fuel loading, and stand structure characteristics in stands that experienced either high severity wildfire, large‐scale tree mortality from bark beetles, or stands that experienced high bark beetle mortality followed by severe wildfire within 3–8 years of attack. Tree seedling density was 300–400% higher in gray bark beetle‐affected stands than burned sites, but there was no evidence that a beetle and wildfire interaction affected seedling densities. The age distribution of Douglas‐fir and grand fir seedlings in stands with repeated disturbances differed from those that only experienced wildfire, suggesting that seed availability varies between these stands. Though both bark beetle outbreaks and wildfires resulted in the death of numerous large trees and surface woody fuel loads 100–200% greater than control sites, the creation of large snags and higher fuel loads across the landscape may have ecological benefits. Compounding effects of bark beetle activity and wildfires were not observed in surface fuel loadings or stand densities. Overall, the effects of high severity wildfire drove post‐disturbance fuel complexes and succession whereas the effects of Dendroctonus pseudotsugae and Dendroctonus brevicomis outbreaks before wildfires resulted in minimal post‐wildfire differences. We conclude that although seedling age structure is responsive to bark beetle and fire interactions, in terms of fuel complexes and tree densities these disturbances are non‐additive and compounding effects on forest trajectory of dry mixed conifer forests of the northern Rockies were not supported.

There has been a long-standing pre-occupation with how phytophagous insects use olfactory cues to discriminate hosts from non-hosts. Foragers, however, should use whatever cues are accurate and easily assessed, including visual cues. 2. It was hypothesised that three bark beetles, the mountain pine beetle (MPB), Dendroctonus ponderosae Hopkins, the Douglas-fir beetle (DFB), D. pseudotsugae Hopkins, and the western balsam bark beetle (WBBB), Dryocoetes confusus Swaine, integrate visual and olfactory information to avoid non-host angiosperms (e.g. paper birch, trembling aspen), that differ in visual and semiochemical profile from their respective host conifers (lodgepole pine, Douglas-fir, interior fir), and tested this hypothesis in a series of field trapping experiments. 3. All three species avoided attractant-baited, white (non-host simulating) multiple- funnel traps, and preferred attractant-baited black (host-simulating) traps. In experiments combining white, non-host traps with non-host angiosperm volatiles, bark beetles were repelled by these stimuli in an additive or redundant manner, confirming that these species could integrate visual and olfactory information to avoid non-host angiosperms while flying. 4. When antiaggregation pheromones were released from white traps, the DFB and MPB were repelled in an additive-redundant manner, suggesting that beetles can integrate diverse and potentially anomalous stimuli. 5. The MPB demonstrated the most consistent visual preferences, suggesting that it may be more of a 'visual specialist' than the DFB or WBBB, for which visual responses may be more contingent on olfactory inputs.

1 Synthetic blends of bole and foliage volatiles of four sympatric species of conifers were released from pheromone-baited multiple-funnel traps to determine if three species of tree-killing bark beetles (Coleoptera: Scolytidae): (i) exhibited primary attraction to volatiles of their hosts and (ii) discriminated among volatiles of four sympatric species of host and nonhost conifers. 2 Bole and foliage volatiles from Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, increased the attraction of coastal and interior Douglas-fir beetles, Dendroctonus pseudotsugae Hopkins, to pheromone-baited traps. Primary attraction to bole volatiles was observed in interior D. pseudotsugae. Beetles were significantly less attracted to the pheromone bait when it was combined with volatiles of lodgepole pine, Pinus contorta var. latifolia Engelm. or interior fir, Abies lasiocarpa × bifolia. 3 The monoterpene myrcene synergized attraction of mountain pine beetles, Dendroctonus ponderosae Hopkins, to their aggregation pheromones, but there was no evidence of primary attraction to host volatiles or discrimination among volatiles from the four conifers. 4 There was significant primary attraction of the spruce beetle, Dendroctonus rufipennis Kirby, to bole and foliage volatiles of interior spruce, Picea engelmannii × glauca, but beetles did not discriminate among volatiles of four sympatric conifers when they were combined with pheromone baits. 5 Our results indicate that host volatiles act as kairomones to aid pioneer Douglas-fir beetles and spruce beetles in host location by primary attraction, and that their role as synergists to aggregation pheromones is significant. For the mountain pine beetle, we conclude that random landing and close range acceptance or rejection of potential hosts would occur in the absence of aggregation pheromones emanating from a tree under attack.

Host selection in tree-killing bark beetles (Coleoptera: Scolytidae) is mediated by a complex of semiochemical cues. Using gas chromatographic-electroantennographic detection (GC-EAD) and GC-mass spectrometric analyses, we conducted a comparative study of the electrophysiological responses of four species of tree-killing bark beetles, the Douglas-fir beetle, Dendroctonus pseudotsugae, Hopkins, the mountain pine beetle, D. ponderosae Hopkins, the spruce beetle, D. rufipennis Kirby, and the western balsam bark beetle, Dryocoetes confusus Swaine, to volatiles captured by aeration of 1) bole and foliage of four sympatric species of conifers, Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, lodgepole pine, Pinus contorta var. latifolia Engelm., interior spruce, Picea engelmannii x glauca, and interior fir, Abies lasiocarpa x bifolia, and 2) con- and heterospecific beetles at three stages of attack. We identified 13 monoterpenes in the conifers and nine compounds in the volatiles of beetles that elicited antennal responses. There was no qualitative difference in the terpene constitution of the four species of conifers and very little difference across beetle species in their antennal response to compounds from conifers or beetles. The lack of species-specific major or minor components in conifers suggests that beetles would need to detect differences in the ratios of different compounds in conifers to discriminate among them. Attraction to hosts and avoidance of nonhost conifers may be accentuated by perception of compounds emitted by con- and heterospecific beetles, respectively. The 22 compounds identified are candidate semiochemicals with potential behavioural roles in host location and discrimination.

Nine compounds identified from captured volatiles of the Douglas-fir beetle, Dendroctonus pseudotsugae, the mountain pine beetle, D. ponderosae, and the spruce beetle, D. rufipennis, that elicited antennal responses in males and females of one or more of these species were tested in the field to determine behavioural activity. 1-Octen-3-ol, found in the volatiles of females of all three species decreased the response of male and female coastal and male interior D. pseudotsugae and both sexes of D. ponderosae to their aggregation pheromones. Acetophenone, identified in the volatiles of females of all three species, significantly decreased the response of interior female D. pseudotsugae. trans-Verbenol, a potent aggregation pheromone of D. ponderosae, decreased the response of both sexes of D. pseudotsugae, while 3-methyl-2-cyclohexen-1- one (MCH), the antiaggregation pheromone of D. pseudotsugae and D. rufipennis decreased the response of both sexes of D. ponderosae. While it has been demonstrated that semiochemical mediated interspecific communication occurs among bark beetles infesting the same host, this study demonstrates that beetles can perceive signals emitted by heterospecifics attacking nonhosts and can potentially use them to avoid attacking the wrong species of conifer.