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We investigated geographic variation in the semiochemistry of major disturbance agents of western North American pine forests, Dendroctonus brevicomis Le Conte and Dendroctonus barberi Hopkins (Coleoptera: Curculionidae: Scolytinae), species separated by the Great Basin in the USA that until recently were synonymous. At 15 sites in the western USA and northern Mexico, beetle populations were examined to determine (1) pheromone production by solitary, mining females, (2) male electroantennogram amplitudes in response to known semiochemicals for the genus, or (3) relative attractiveness of two female-produced pheromone components (endo- and exo-brevicomin) and two host odors (alpha-pinene and myrcene) to beetles in the field. Compared to female beetles collected east of the Great Basin (D. barberi), western females (D. brevicomis) produced a consistently higher proportion of, and male antenna were correspondingly more sensitive to, the exo- than the endo-isomer of brevicomin. With the exception of one sampling location (where no preference was observed), beetles west of the Great Basin were more attracted to exo- than endo- brevicomin trap lures, whereas eastern beetles displayed the reverse preference. In contrast, there was not a consistent difference between these populations regarding relative attraction or olfactory response to myrcene or alpha-pinene, although some geographic variability was evident. These data show that the semiochemical systems of D. brevicomis and D. barberi have diverged and corroborate genetic and morphological evidence that they are distinct, allopatric species.

Tetropium fuscum (Fabricius) (Coleoptera: Cerambycidae), a phloem-feeding and wood-boring beetle introduced from Eurasia, attacks spruce in eastern Canada alongside its native congener Tetropium cinnamopterum Kirby. We reared phloem- and wood-feeding insects (and their predators) from bolts of red and Norway spruce (Picea rubens and Picea abies) in Nova Scotia, comparing insect communities between bolts with added eggs of T. fuscum or T. cinnamopterum and bolts without added Tetropium (controls). We tested for impacts of each Tetropium on insect community structure (Simpson's diversity, richness, and evenness). We also asked whether, consistent with Darwin's Naturalization Hypothesis, Tetropium spp. would have greater impacts on emergence of its closer relatives (which might be most likely to compete and/or share natural enemies). Addition of Tetropium eggs (either species) to bolts lowered insect diversity in both host trees. Both richness and evenness components of diversity were always lower in +Tetropium treatments, although different components reached statistical significance in different Tetropium species × host combinations. Addition of Tetropium spp. significantly reduced emergence of some species: Evodinus monticola (Randall) (Coleoptera: Cerambycidae) was reduced by T. fuscum on both hosts and by T. cinnamopterum on Norway spruce; Hylobius congener Dalla Torre, Schenkling, and Marshall was reduced by T. fuscum on red spruce; and Xylophagus sp. (Diptera: Xylophagidae) was reduced by T. cinnamopterum on Norway spruce. However, there was no relationship between Tetropium's impact on a community member and their phylogenetic relatedness, and the overall impacts of Tetropium presence were not very different between T. fuscum and T. cinnamopterum., (© The Author(s) 2017. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

We examined the native community of insects interacting with an invasive species, Tetropium fuscum (F.) (Coleoptera: Cerambycidae), in its new range to explore reasons for the invader's relatively slow spread. Tetropium fuscum is a European spruce borer established in Nova Scotia since at least 1990, but it has spread only about 125 km from its site of introduction. We compared the densities of Tetropium spp., their known parasitoids, and the community of wood-boring insects at sites located within the invasion zone in Nova Scotia versus well outside this zone, in New Brunswick, Canada. Using red spruce trees stressed by girdling or felling, we tested whether: 1) T. fuscum had altered the native wood-boring community; 2) T. fuscum displaced a native congener, Tetropium cinnamopterum (Kirby); and 3) parasitism rates of Tetropium spp. differed between the invaded and noninvaded zones. Both Tetropium spp. and their parasitoid wasps emerged exclusively from felled trees as opposed to girdled trees. We found no difference in community diversity inside versus outside the invasion zone. The combined densities of both Tetropium spp. and their overall parasitism rates also did not differ between zones, but T. cinnamopterum density was significantly greater outside the invasion zone, suggesting T. fuscum may displace the native congener where they are sympatric. Our results suggest that the native and invasive Tetropium spp. act as a single functional species in the invasion zone. We speculate that natural control agents (predators, parasitoids, and competitors) might be limiting the rate of spread of T. fuscum., (© Her Majesty the Queen in Right of Canada 2016. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

We compared pheromone production and response for populations of western pine beetle, Dendroctonus brevicomis LeConte, from sites in northern Arizona and northern California. Volatiles were collected from individuals of both sexes that had mined as a pair in a Pinus ponderosa log for 1 d, and they were subsequently analyzed by gas chromatography coupled to mass-spectrometry. Principal component analysis of quantities of Dendroctonus pheromone components indicated strong site-associated clustering of blend composition for females but not males. Much of the clustering in females evidently was due to differences in the production of endo- and exo-brevicomin, which occurred in average ratios of 0.1:1 and 19:1 for populations in the California and Arizona sites, respectively. In the California site, exo- was better than endo-brevicomin in enhancing trap catches of both sexes to lures containing the host-tree odor α-pinene and the male-produced aggregation pheromone component frontalin. In an identical test in the Arizona site, endo- was a better adjuvant than exo-brevicomin for male attraction, whereas females did not show a significant preference. At neither location were the isomers antagonistic to one another in activity. Thus, one aggregation pheromone has apparently diverged between these populations, concurrent with published evidence that D. brevicomis on either side of the Great Basin are genetically distinct and are possibly different species. Furthermore, production of and response to the isomers of brevicomin by flying Dendroctonus frontalis Zimmermann in the Arizona site were similar to those of sympatric D. brevicomis. This interspecific signal overlap is likely sustainable since joint species mass-attacks may assist both species in overcoming host defenses, thereby increasing host availability.

It is well understood that forces from multiple trophic levels simultaneously influence herbivore performance, but how the relative strength of these forces vary over space and time is less clear. We evaluated seasonal variation in the impact of bottom-up forces (host condition), top-down forces (natural enemies), and competition on the performance of an exotic wood borer. Tetropium fuscum (F.) (Coleoptera: Cerambycidae) eggs that were either protected or exposed were placed on healthy and stressed red spruce, Picea rubens Sargent, trees at three different times during the natural T. fuscum flight period. We also measured the length of necrotic lesions (i.e., an induced hypersensitive response) that developed in response to attacking T. fuscum. As predicted, T. fuscum performance was usually greater, and induced host defenses lower, on stressed than on healthy trees, but the impact of host condition on T. fuscum performance varied seasonally. Timing of attack was critical, influencing the strength of bottom-up forces and consequently all measures of T. fuscum performance. Survival was reduced when T. fuscum attacked too early (late-May) or too late (late-June), which may result in stabilizing selection for attack time in this species. Parasitism and competition were generally negligible during this study. Our results suggest that timing of attack is critical for this wood borer and that temporal variation in the impact of top-down and bottom-up forces should be considered in other systems.

Tetropium fuscum (F.) attacks weakened Norway spruce, Picea abies (L.) Karst., in its native Europe and may colonize healthy spruce in Nova Scotia, Canada. We used manipulative field experiments to evaluate: 1) the development of T. fuscum on apparently healthy red spruce (Picea rubens Sarg.) in Nova Scotia; 2) the influence of red spruce physiological condition (healthy, girdled or cut) on T. fuscum performance; and 3) the impact of natural enemies and competitors on T. fuscum performance when developing on trees of varying condition. Tetropium fuscum successfully developed on healthy red spruce. Survival was higher on healthy than on girdled or cut trees when larvae were exposed to natural enemies and competitors. The benefits of reduced competition and parasitism on healthy trees appeared to compensate for any reductions in nutritional quality, increase in host resistance, or both. In contrast, when T. fuscum were protected from natural enemies, apparent survival was highest on girdled trees. Tetropium fuscum development took longer on healthy than on cut or girdled trees, and emerged adults were largest on healthy trees. The disparities in adult sizes among the three treatments may mean that healthy trees are more nutritious. Alternatively, the differences may indicate that a greater amount of time was spent feeding in healthy than in girdled or cut trees. Tree condition appears to have a direct impact on the success of T. fuscum, influencing survival, development time, and adult size, and may mediate the impact of natural enemies and competitors, further affecting T. fuscum performance.

We studied the host selection behavior and feeding preference of the emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae). A. planipennis is an exotic forest insect pest native to Asia that was discovered in North America in 2002 and is causing widespread mortality of ash trees (Fraxinus spp.) in southeast Michigan and surrounding states. We compared host selection and feeding behavior on different species of ash including Manchurian ash (F. mandshurica Rupr.), green ash (F. pennsylvanica Marsh), white ash (F. americana L.), black ash (F. nigra Marsh), blue ash (F. quadrangulata Michx.), and European ash (F. excelsior L). Manchurian ash is native to Asia, whereas the other species (native to North America or Europe) represent novel hosts for A. planipennis. Beetles distributed themselves more frequently and fed to a greater extent on green, black, and white ash compared with blue, European, and Manchurian ash. Although beetles consumed every ash species offered to them, Manchurian ash and blue ash were least preferred in feeding bioassays. When we analyzed the volatile content of intact and girdled ash for quantitative variation in 11 compounds that elicited antennal activity, we found that the overall volatile profiles of the six ash species differed significantly in their relative amounts of antennally active compounds. Green ash has lower relative amounts of volatiles compared with Manchurian ash, which might render it more attractive and less resistant to A. planipennis. Lower tolerance and resistance of green ash might make it more susceptible to mortality compared with Manchurian ash, which coevolved with the beetle in its native range. Repellent odors, potential antifeedants, and genes for resistance in Manchurian ash could be explored for methods to manage A. planipennis populations.

The superiority of the host monoterpene myrcene as a synergist for trans-verbenol and exo-brevicomin, aggregation pheromone components of the mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), suggests that the ancestral host of the mountain pine beetle is a pine rich in myrcene. A field trapping experiment in British Columbia testing reconstituted bole oleoresin of whitebark pine, Pinus albicaulis Engelmann, composed of mainly myrcene (20.7%), terpinolene (6.8%), and 3-carene (61.9%) showed it to be a better pheromone synergist than reconstituted bole oleoresin of lodgepole pine, Pinus contorta variety latifolia Engelmann, which contained only 2.7, 1.0, and 6.0%, respectively, of the above-mentioned three compounds. In the same experiment myrcene alone was the best synergist. In subsequent experiments, testing myrcene, terpinolene and 3-carene alone and in all possible binary and ternary combinations, a 50:50 blend of myrcene and terpinolene released at the same rate as either compound alone generally resulted in trap catches approximately 3 times higher than with myrcene as a synergist. This result held as long as the terpinolene was free of contaminants, and the traps were in the open, well away from potential interference of semiochemicals emitted by newly attacked trees. 3-Carene seemed to be inert or slightly inhibitory. No single monoterpene tested alone or in binary or ternary combination in the absence of pheromones was attractive. There was no effect of doubling or tripling the release rate of myrcene or terpinolene. In five of nine experiments, adding terpinolene to myrcene caused a significant increase in the percentage of female mountain pine beetles captured. Among host pines, the presence of highly synergistic monoterpenes at various levels in combination with other monoterpenes that are apparently either inert or inhibitory could account for different degrees of pheromone synergism, and thus host preference. The highly synergistic effect of combining myrcene plus terpinolene with the mountain pine beetle aggregation pheromone components opens up the potential for suppression of populations through semiochemical-based mass trapping.

Previous research indicated that the aggregation pheromone of the southern pine beetle, Dendroctonus frontalis, is produced only by females, the sex that initiates attacks. We provide evidence indicating that secondarily arriving males augment mass aggregation by releasing the attractive synergist (+)-endo-brevicomin. Healthy pines artificially infested with both sexes of D. frontalis were significantly more attractive to conspecifics than trees infested solely with females. Coupled gas chromatography-electroantennographic detection (GC-EAD) analyses of volatiles isolated from male beetles revealed substantially greater olfactory sensitivity by D. frontalis to endo-brevicomin than to any other component. The threshold of detection of both sexes for (+)-endo-brevicomin was four orders of magnitude lower than for its antipode and at least one order of magnitude lower than for either enantiomer of frontalin, the major female-produced aggregation pheromone component. Pairing with a female in a gallery stimulated individual male beetles to produce hundreds of nanograms of (+)-endo-brevicomin. (+)-endo-Brevicomin was detected in a small percentage of female D. frontalis, whereas (-)-endo-brevicomin was never detected in either sex. In field trapping bioassays, we confirmed that (+)-endo-brevicomin is a potent synergist for attractive combinations of frontalin and pine turpentine. However, (+)-endo-brevicomin failed to attract D. frontalis either when presented alone or in combination with turpentine. We postulate that mass colonization of host trees by D. frontalis is mediated by distinct semiochemicals from both sexes rather than females alone. Our discovery of a key aggregation pheromone component in such an apparently well-studied species implies that the pheromone models of other bark beetles could benefit from systematic reexamination using newer technologies. Additionally, baits fortified with (+)-endo-brevicomin may enhance pest management strategies that exploit attractants for D. frontalis.

Timing of arrival at a resource often determines an individual's reproductive success. Tree-killing bark beetles can reproduce in healthy trees by attacking in adequate numbers to overcome host defences that could otherwise be lethal. This process is mediated by aggregation and antiaggregation pheromones. Beetles that arrive early in such a "mass attack" must contend with undiminished tree defences, and produce enough pheromones to attract more beetles, but have a head start on gallery construction and egg-laying. Beetles that arrive late may be impeded by competition and diminishing availability of phloem, but should experience fewer costs associated with pheromone production and battling tree defences. We investigated relationships between timing of arrival, body size, pheromone production and fitness in the southern pine beetle, Dendroctonus frontalis. In field experiments, we captured beetles that arrived early (pioneers) and late on slash pine trees, Pinus elliottii, and measured pheromone amounts in their hindguts. We marked gallery entrances of beetles as they landed on a tree and measured their reproductive success after the attack terminated. We found no difference in body size or pheromone amounts between early and late arrivers. Most beetles arrived at the middle of the attack sequence, and excavated longer galleries per day than early arrivers. The number of offspring produced per day by beetles that established galleries midway through mass attack was higher than those that arrived early or very late in the sequence. Our results suggest that beetles do not exhibit adaptive phenotypic plasticity in pre-landing pheromone production, depending on the extent of previous colonisation of a host. Rather, it appears that stabilising selection favours beetles that attack in the middle of the sequence, and contributes to attack synchrony. Synchronous attack on trees is essential before population booms characteristic of tree-killing bark beetles can occur in nature.

Aim: The concept of "island disharmony" has been widely applied to describe the systematic over‐ and under‐representation of taxa on islands compared to mainland regions. Here, we explore an extension of that concept to biological invasions. We compare biogeographical patterns in native and non‐native beetle (Coleoptera) assemblages from around the world to test whether beetle invasions represent a random sample of species or whether some families are more prone to invade than others. Location: Global. Methods: Numbers of non‐native beetle species established in ten regions worldwide were compared with the land area of each region. The distribution of species among families was compared with the distribution among families for all species native to the same region and with the distribution among families for the global pool of all known beetle species. Ordination analysis was used to characterize differences among native and non‐native assemblages based upon the distribution of species among families. Results: We report a total of 1,967 non‐native beetle species across all ten regions, and a classic log–log relationship between numbers of species per region and land area though relationships are generally stronger for native assemblages. Some families (e.g., Dermestidae and Bostrichidae) are over‐represented and others (e.g., Carabidae, Scarabaeidae and Buprestidae) are under‐represented in non‐native assemblages. The distribution of species among families is generally similar among native assemblages with greatest similarities among nearby regions. In contrast, non‐native species assemblages are more similar to each other than to native species assemblages. Main conclusions: Certain families are over‐represented, and others are under‐represented in non‐native beetle assemblages compared to native assemblages, indicating "invasion disharmony" in the global representation of beetle families. Similarities in composition among non‐native assemblages may reflect unobserved associations with invasion pathways and life‐history traits that shape invasion success of different insect groups. [ABSTRACT FROM AUTHOR]