Search

Copyright of Biological Invasions is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Laricobius nigrinus Fender (Coleoptera: Derodontidae), a predatory beetle native to western North America, has been released since 2003 for management of hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae), a non-native pest killing hemlocks in eastern North America. Over 420,000 L. nigrinus have been released in the eastern USA from field and lab-reared sources, 14,000 of which were deployed in the Commonwealth of Virginia, USA. In order to determine the establishment rates of L. nigrinus in Virginia, surveys were conducted in 2017 and 2018 at all release sites within this state. During the study, stand-level HWA densities were estimated, and hemlock tree health and predator–prey ratios were quantified. The identification of Laricobius spp. recoveries were made using microsatellite analysis. During the period of the study, L. nigrinus were found to have established at 82% of Virginia release sites and were the primary species recovered (80%). Both Laricobius rubidus (18%) and hybrids (2%) were also recovered. Stand-level HWA densities varied greatly over sites and years but showed a general decline in year two of the study. Establishment at such a high percentage of release sites suggests that the climate in Virginia is suitable for the predator and the insect is adaptable to the wide variety of site conditions where hemlocks typically grow. [ABSTRACT FROM AUTHOR]

Studies increasingly indicate host resistance likely influences hemlock woolly adelgid (HWA) populations. We describe coexisting HWA populations in four hemlock species, three from HWA's native range (Tsuga chinensis, T. dumosa, and T. sieboldii) and one from its introduced range: T. canadensis. HWA populations were greater in T. canadensis and lesser or absent in T. chinensis and T. dumosa. HWA stylet insertion was observed the least in T. chinensis and T. dumosa, suggesting a physical and/or chemical feeding deterrent. While T. chinensis and T. dumosa consistently and distinctly differed from T. canadensis, T. sieboldii grouped with T. canadensis or T. chinensis and T. dumosa in different experiments, suggesting mechanisms influencing HWA populations differ by host species. HWA were found more often on tops of T. chinensis and T. dumosa branches but equally on tops and bottoms of T. canadensis branches, corresponding with locations of trichomes (which T. sieboldii lacks). Evidence from the literature about dissimilarities in hemlock hosts (e.g., HWA interactions and vulnerability, feeding damage response, cuticle thickness, terpenoid chemistry, arthropod and microbial communities) and native and introduced HWA populations (e.g., losses of sexual reproduction and primary spruce host) suggests a limit to applying information from native systems to management in introduced systems. [ABSTRACT FROM AUTHOR]

The article discusses the article ‘‘Media representation of hemlock woolly adelgid management risks: a case study of sciencecommunication and invasive species control,'' by Leppanen et al. in the September 18, 2018 issue and mentions limitations to media reporting of science. It also mentions the comments made by Salom et al. on this article in terms of scientific communications, methods used in the study, and biological control of insects.

In eastern North America, the invasive hemlock woolly adelgid (Adelges tsugae Annand), has expanded northward at a pace that exceeds predictions from mechanistic models, suggesting successful long-distance dispersal despite the only viable dispersive phase being a flightless nymph, or "crawler." We hypothesize that migrating birds may contribute to long-distance dispersal of crawlers by passively transporting them in their plumage during northward migration. We collected hemlock woolly adelgid crawlers from the plumage of wild birds in Connecticut hemlock forests in spring and summer 2016–2017 and evaluated the factors that influence crawler loads on wild birds. Of 456 birds examined, 40 individuals of 22 species carried adelgid crawlers. Crawler loads varied strongly over time, showing a mid-spring peak that mirrored the phenological pattern in crawler abundance. However, crawler load was not affected by either local crawler abundance at capture sites or the degree of bird species association with hemlock forests. To test whether dispersed crawlers could start new invasions, we experimentally simulated avian-assisted dispersal of adelgids onto uninfested nursery hemlocks. Although rare, crawlers placed on birds did settle successfully on experimental branches during the adelgid's summer generation. Our study confirms that birds carry hemlock woolly adelgid crawlers most often during the period of peak spring songbird migration, and that crawlers can move off bird plumage to settle on hemlock foliage. Bird-mediated, long-distance dispersal of crawlers likely has played a key role in hemlock woolly adelgid spread, and with warming temperatures, this mechanism may continue to be important for future range expansion. [ABSTRACT FROM AUTHOR]

Public support can aid invasive species control and thus reduce negative impacts. Scientific communication can help or hinder efforts when associated risk and uncertainty are exaggerated or neglected, creating fear or distrust. Review of 104 media articles about managing a devastating forest insect, the hemlock woolly adelgid (Adelges tsugae), revealed that uncertainties and value judgments associated with claims of success were usually obscured or omitted, legitimate disagreement among experts about efficacy was omitted, and risks to non-targets were usually unaddressed. Discussion of chemical control in 83 articles included mention of non-target effects (e.g., to water quality, pollinators, and other native taxa) in only 11 articles and specificity was mentioned in only five instances. Biocontrol non-target impacts were mentioned in 11 of 83 cases and agent specificity was not mentioned in 71 of those cases. Ironically, while the value of the native ecosystem is used to justify management, possible non-target impacts of management on native ecosystems are largely ignored, notably hybridization between an introduced non-native biocontrol agent (Laricobius nigrinus) and a native beetle (L. rubidus) and ongoing releases of two non-native beetles, L. osaskensis colonies contaminated with a poorly understood, newly described species (L. naganoensis). To increase the public's ability to make informed decisions, benefits of management techniques should be discussed along with risks, scientific disagreement, and uncertainty. [ABSTRACT FROM AUTHOR]

Eastern hemlock ( Tsuga canadensis) is a critical species in eastern North American forests, providing a multitude of ecological and societal benefits while also acting as a foundation species in many habitats. In recent decades, however, hemlock has become threatened by hemlock woolly adelgid (HWA; Adelges tsugae), an invasive sap-feeding insect from Asia. In addition to causing the more commonly assessed metrics of foliar damage, crown decline, and hemlock mortality, HWA also decreases hemlock growth and productivity. Dendrochronological methods provide a more nuanced assessment of HWA impacts on hemlock by quantifying variable rates of radial-growth decline that follow incipient infestation. This information is necessary to better understand the variable response of hemlock to HWA, and identify the characteristics of stands with the highest potential for tolerance and recovery. To quantify decline, we calculated changes in hemlock yearly radial growth using basal area increment (BAI) measurements to identify periods of growth decline from 41 hemlock stands across New England covering a range of infestation density, duration and hemlock vigor. The onset of growth decline periods were predominantly associated with either HWA infestation or drought. However, the magnitude of change in BAI values pre- and post-decline was significantly related to HWA infestation density and crown impacts, indicating that radial growth metrics can be used to identify locations where HWA infestations have incited significant reductions in hemlock health and productivity. Additional site characteristics (slope, hillshade, and January minimum temperatures), were also significantly associated with hemlock health and productivity decline rates. In order to develop a model to identify stands likely to tolerate HWA infestation, these metrics were used to build a logit model to differentiate high- and low-BAI-reduction stands with 78% accuracy. Independent validation of the model applied to 15 hemlock sites in Massachusetts classified high and low BAI reduction classes with 80% accuracy. The model was then applied to GIS layers for New England and eastern New York to produce a spatially-explicit model that predicts the likelihood of severe hemlock growth declines if/when HWA arrives. Currently 26% of the region's hemlock stands fall into this high risk category. Under projected climate change, this could increase to 43%. This model, along with knowledge of current HWA infestation borders, can be used to direct management efforts of potentially tolerant hemlock stands in eastern North America, with the intention of minimizing HWA-induced hemlock mortality. [ABSTRACT FROM AUTHOR]

The invasion of non-native species is considered among the most important causes of the loss of native biota. An example of a devastating exotic pest impacting eastern forests is the hemlock woolly adelgid (HWA) ( Adelges tsugae), a xylem feeding insect native to Asia that feeds on all ages and species of hemlock ( Tsuga spp.), and has the capacity to functionally eliminate eastern hemlock ( T. canadensis) from the landscape. Eastern hemlock is an important component of forested riparian communities in southern and central Appalachia where it maintains stable stream conditions important for aquatic biota. We investigated differences between eastern hemlock and deciduous dominated headwater streams in eastern Kentucky to determine the extent to which HWA invasion may affect benthic invertebrate shredders. Shredders form the basis of a resource chain within headwater streams, thus they are invaluable links in stream-riparian interactions. We found that eastern hemlock contributed energy in the form of leaf litter to the riparian zone at a consistent rate throughout the growing season in contrast to the autumnal pulse of deciduous material. We also detected significant vegetation by season interactions for shredders which suggest that some shredders are more abundant in eastern hemlock streams than in their deciduous counterparts during the summer. This could be linked to the consistent addition of food resources that eastern hemlock provides. Our results indicate that stream communities will likely change following adelgid associated mortality of eastern hemlock in headwater stream riparian zones. [ABSTRACT FROM AUTHOR]

Recent studies have identified a small number of individual eastern hemlock trees that demonstrate relative resistance to the introduced sap-feeding insect, the hemlock woolly adelgid. Using gas chromatography, we compared concentrations of twenty-two terpenoids in susceptible and relatively resistant trees, both in the forest and in propagated cuttings in a common-garden setting. Terpenoid concentrations were higher in twig tissue of resistant versus susceptible trees, across six sampling dates and at both sites. These changes may be particularly important because the hemlock woolly adelgid feeds on twig tissue. Because the common-garden cuttings were free of herbivores, the higher terpenoid concentrations are interpreted as a constitutive defense. Increased levels of monoterpenes and sesquiterpenes imply an overall increase in the input of carbon precursors to both terpenoid synthesis pathways. [ABSTRACT FROM AUTHOR]

The invasive hemlock woolly adelgid ( Adelges tsugae Annand, Hemiptera: Sternorrhyncha: Adelgidae) causes significant mortality to eastern and Carolina hemlock ( Tsuga canadensis Carrière and T. caroliniana Engelmann, respectively) throughout the eastern United States. Adelges tsugae produces vast quantities of a wax covering that surrounds most of the instars as well as the adult and eggs. Using direct probe EI mass spectrometry, this wax covering was characterized as a diketoester wax, 17-oxohexatriacontanyl 11-oxotriacontanoate, and accounted for ≈ 42 % of A. tsugae total biomass. The presence of the anthraquinone, chrysophanol, and its precursor anthrone, chrysarobin, in A. tsugae has only been briefly described. Further study confirmed these compounds in all A. tsugae life stages. Additionally, several predatory beetles in use or under consideration as biological control agents for this species appear to ingest and excrete these compounds when feeding on A. tsugae. The production of both a physical and a chemical defense may represent a significant energy investment by A. tsugae. [ABSTRACT FROM AUTHOR]

Spread dynamics of biological invasions are influenced by both the availability and spatial arrangement of suitable habitat. As such, invasive spread can be considered to occur across a network of nodes, representing patches of suitable habitat, with linkages representing the potential for movement between habitat patches. While static network models can provide valuable insight into the potential framework of nodes and linkages across which spread could occur, they offer little information on the actual spatiotemporal dynamics of range expansion processes. Here, we explore the development and application of dynamic network models (DNMs) to model the spread of invasive species. DNMs accommodate temporal dynamics in the utilization of nodes and the connections between them and can flexibly perform simulations at the spatial scales of observational data. As case studies, we develop DNMs to simulate the spread of a generalist forest pathogen and the hemlock woolly adelgid ( Adelges tsugae Annand). We highlight the utility of DNMs for identifying habitat patches that contribute most to spread across the landscape and for visualizing emergent spread dynamics. While currently underutilized in ecology as compared to static network models, DNMs are potentially applicable to numerous research and management questions relevant to biological invasions and the more general phenomena of range expansion. [ABSTRACT FROM AUTHOR]

Hemlocks are significant components of temperate forests of Asia and North America, and in eastern North America, they are threatened by an exotic herbivore, the hemlock woolly adelgid, Adelges tsugae. The adelgid is native to Asia and northwestern North America, but is highly invasive in eastern North America where natural enemies are unable to regulate populations and eastern hemlock, Tsuga canadensis, is highly susceptible. In order to gain a better understanding of the metabolic effects of A. tsugae on eastern hemlock, we evaluated its effects on photosynthesis and also evaluated photosynthesis on Tsuga species from various geographic origins. We measured light-saturated photosynthesis ( A) and dark respiration of T. canadensis that were infested with adelgid and found a significant decrease in A and a small but significant increase in dark respiration, suggesting that A. tsugae triggers a physiological response in eastern hemlock by decreasing metabolic activity. In a separate experiment, we also measured A of five different hemlock species, including eastern hemlock, the Pacific Northwestern T. heterophylla and T. mertensiana, and the Asian T. diversifolia and T. chinensis. Only weakly significant differences in A were found, with the highest rate in the eastern North American T. canadensis and the lowest in the Pacific Northwestern T. mertensiana. The relatively high photosynthetic rate of T. canadensis could possibly play a role in its susceptibility to A. tsugae. A better understanding of this metabolic response could help develop effective management strategies for combating the highly invasive A. tsugae. [ABSTRACT FROM AUTHOR]

Eastern hemlock ( Tsuga canadensis) is in rapid decline because of infestation by the invasive hemlock woolly adelgid ( Adelges tsugae; 'HWA') and, to a lesser extent, the invasive elongate hemlock scale ( Fiorinia externa; 'EHS'). For many conifers, induced oleoresin-based defenses play a central role in their response to herbivorous insects; however, it is unknown whether eastern hemlock mobilizes these inducible defenses. We conducted a study to determine if feeding by HWA or EHS induced changes in the volatile resin compounds of eastern hemlock. Young trees were experimentally infested for 3 years with HWA, EHS, or neither insect. Twig and needle resin volatiles were identified and quantified by gas chromatography/mass spectrometry. We observed a suite of changes in eastern hemlock's volatile profile markedly different from the largely terpenoid-based defense response of similar conifers. Overall, both insects produced a similar effect: most twig volatiles decreased slightly, while most needle volatiles increased slightly. Only HWA feeding led to elevated levels of methyl salicylate, a signal for systemic acquired resistance in many plants, and benzyl alcohol, a strong antimicrobial and aphid deterrent. Green leaf volatiles, often induced in wounded plants, were increased by both insects, but more strongly by EHS. The array of phytochemical changes we observed may reflect manipulation of the tree's biochemistry by HWA, or simply the absence of functional defenses against piercing-sucking insects due to the lack of evolutionary contact with these species. Our findings verify that HWA and EHS both induce changes in eastern hemlock's resin chemistry, and represent the first important step toward understanding the effects of inducible chemical defenses on hemlock susceptibility to these exotic pests. [ABSTRACT FROM AUTHOR]

Herbivores can trigger a wide array of morphological and chemical changes in their host plants. Feeding by some insects induces a defensive hypersensitive response, a defense mechanism consisting of elevated HO levels and tissue death at the site of herbivore feeding. The invasive hemlock woolly adelgid Adelges tsugae ('HWA') and elongate hemlock scale Fiorinia externa ('EHS') feed on eastern hemlocks; although both are sessile sap feeders, HWA causes more damage than EHS. The rapid rate of tree death following HWA infestation has led to the suggestion that feeding induces a hypersensitive response in hemlock trees. We assessed the potential for an herbivore-induced hypersensitive response in eastern hemlocks by measuring HO levels in foliage from HWA-infested, EHS-infested, and uninfested trees. Needles with settled HWA or EHS had higher HO levels than control needles, suggesting a localized hypersensitive plant response. Needles with no direct contact to settled HWA also had high HO levels, suggesting that HWA infestation may induce a systemic defense response in eastern hemlocks. There was no similar systemic defensive response in the EHS treatment. Our results showed that two herbivores in the same feeding guild had dramatically different outcomes on the health of their shared host. [ABSTRACT FROM AUTHOR]

As the highly invasive hemlock woolly adelgid, Adelges tsugae, continues to expand its distribution in eastern North America, affected forests will incur drastic changes in composition and structure. While these changes have been well-studied in dense hemlock forests in the Northeast, relatively little work is known about the effects of the adelgid at the western edge of the range of eastern hemlock, Tsuga canadensis. We evaluated the nature and extent of these changes using vegetation assessments coupled with growth simulations. The woody plant community was assessed in three strata (upper, mid- and lower) and was used to predict forest succession. Using the Forest Vegetation Simulator (FVS), we then projected the growth of hemlock forests 20 years into the future with and without the effects of the adelgid. In forest simulations lacking adelgid invasion, little change in composition or structure is forecast. In contrast, our projections predict a near complete loss of the hemlock forest type within 20 years of adelgid establishment, with widespread conversion to hardwood forest types, most notably white oak-red oak-hickory, chestnut oak-black oak-scarlet oak, and yellow poplar-white oak-red oak. Hemlock loss will result in denser deciduous forests with thinner canopies and multiple gaps, and significant alterations to terrestrial and aquatic wildlife habitat. [ABSTRACT FROM AUTHOR]

Global climate change has already affected the abundances, range limits, and interactions of many species. The hemlock woolly adelgid (Adelges tsugae), an invasive insect introduced to eastern North America from Japan, has decimated stands of eastern hemlock (Tsuga canadensis) and Carolina hemlock (T. caroliniana) from Georgia to Connecticut. However, its spread across central and northern New England has been slowed substantially by its inability to tolerate cold winter temperatures. Using data from previous lab and field studies collected over the past 17 years, including adelgid spread and overwintering mortality, we first characterize the temperature conditions that may limit adelgid spread. We then show how, in the future, rising winter temperatures due to climate change are likely to remove the conditions currently limiting adelgid spread, and facilitate the northward expansion as more suitable habitat becomes available. [ABSTRACT FROM AUTHOR]

Hemlock woolly adelgid, Adelges tsugae Annand (Homoptera: Adelgidae), is native to Japan where it is an innocuous inhabitant of Tsuga diversifolia Masters and T. sieboldii Carriere throughout their natural growing areas. Native adelgid populations are regulated by host resistance and natural enemies, in particular the oribatid mite, Diapterobates humeralis (Hermann) and the coccinellid beetle, Pseudoscymnus tsugae Sasaji and McClure. Invading populations of A. tsugae in western North America on T. heterophylla Sargent and T. mertensiana Carriere are mainly regulated by host resistance. However, invading populations in eastern North America attain damaging levels on T. canadensis (L.) Carriere and T. caroliniana Engelmann and are regulated mainly by weather and negative density-dependent feedback mechanisms related to host deterioration. Although A. tsugae is only passively dispersed by wind, birds, forest-dwelling mammals and humans, it is spreading at an alarming rate and is sufficiently cold hardy to threaten the existence of the two eastern hemlock species throughout their natural ranges. The current hope for suppressing invading populations of hemlock woolly adelgid in eastern North America lies with the exotic predator, P. tsugae. Extensive laboratory studies of the biology and predatory ability of P. tsugae revealed that it feeds on all life stages of its prey, that its multivoltine life cycle is well synchronized with that of the adelgid, and that it has great potential for biological control. We have reared and released nearly 130,000 adults of P. tsugae in forests in Connecticut, New Jersey and Virginia during the past four years. P. tsugae has reproduced, dispersed, overwintered and reduced densities of hemlock woolly adelgid by 47–88% in only five months on release branches at these sites. Current studies are investigating the long-term ability of P. tsugae to regulate invading populations of A. tsugae in eastern North America. [ABSTRACT FROM AUTHOR]