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The hemlock woolly adelgid (HWA), Adelges tsugae (Hemiptera: Adelgidae), is native to the Pacific Northwest and Asia and is an invasive insect in the eastern United States causing widespread decline in health and increased mortality of native eastern and Carolina hemlock. Laboratory experiments conducted at ambient field temperatures were done to determine the adult and larval feeding totals on HWA and fecundity of the introduced predators Laricobius nigrinus and L. osakensis, and the native L. rubidus (Coleoptera: Derodontidae). During the 22-week period when Laricobius spp. adults are active in Virginia, from early November until late March the total mean ($\bar{x}$ x ¯ ± SE) of HWA eggs, nymphs, and adults were projected to be consumed per L. nigrinus (33.8 ± 4.0), L. osakensis (33.2 ± 4.0), and L. rubidus (16.4 ± 2.5) adults. Laricobius osakensis (102.1 ± 13.7) and L. nigrinus (72.0 ± 10.5), oviposited a similar number of eggs while L. rubidus (24.5 ± 5.2) oviposited a lower number of eggs. Mean larval consumption of HWA progrediens eggs was: L. nigrinus (169.6 ± 7.1), L. osakensis (140.1 ± 8.7), and L. rubidus (135.8 ± 12.8). The mean egg production of HWA was 74.5 ± 2.2. Based on predation and fecundity totals, L. osakensis was predicted to have a greater impact in reducing the number of HWA progrediens eggs than L. nigrinus and L. rubidus. [ABSTRACT FROM AUTHOR]

The hemlock woolly adelgid (HWA), Adelges tsugae Annand, has invaded eastern North America and caused significant mortality to eastern hemlock, Tsuga canadensis (L.) Carrière. In eastern North America, HWA's range is theorized to be limited by minimum winter temperatures. As climate change reduces the severity of winter, the risk of northward expansion of HWA increases. This study used maximum entropy species distribution modeling in conjunction with HWA occurrence records and future climate projections to model habitat suitability for HWA throughout the range of eastern hemlock. Species distribution models were created for present and future climatic conditions using both historical climatic data and future climatic emissions scenarios for mid- and late-century. In addition, present climatic condition reference models for western North America and Asia were generated for comparison with HWA's current range and earlier predictions of the potential range in eastern North America. Under a low emissions scenario, HWA will be capable of invading almost the entire range of eastern hemlock by the end of the century. More extreme warming scenarios result in a more rapid northwards shift by mid-century. The consequences for eastern hemlock are significant, with infestations likely to become more widespread and severe due to climate change. [ABSTRACT FROM AUTHOR]

Tsuga canadensis (eastern hemlock) is an important tree species in North America, but it has been subject to threats from invasive insects such as Adelges tsugae (hemlock woolly adelgid). A. tsugae is native to Asia, and Tsuga species from Asia are typically resistant to this insect. In this study, we examined the phyllosphere microbiome of two hemlock species native to North America and susceptible to A. tsugae (T. canadensis and T. caroliniana) as well as two species native to Asia and resistant to A. tsugae (T. chinensis and T. diversifolia). Because pesticide application is often used to treat native Tsuga species impacted by A. tsugae, we also examined the response of the microbiome and overall plant physiology to the pesticide dinotefuran in T. canadensis. We found significant differences in the bacterial and fungal microbiome among the four species of Tsuga. Dinotefuran also significantly affected bacterial communities, but not fungal communities, of T. canadensis. The genus Methylobacterium, which uses methanol produced during plant cell elongation and growth, was a significant indicator of trees not subject to dinotefuran. This suggests that dinotefuran may have reduced cell growth in treated trees. Despite changes in the microbiome, dinotefuran application did not significantly affect plant physiology; however, the coefficient of variation in dinotefuran-treated trees was larger than that in non-treated trees. Our results suggest that the microbiome could play a role in mediating insect resistance in Tsuga species and that pesticide application could affect the phyllosphere microbiome, with implications for plant growth and resistance. [Figure: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Simple Summary: Understanding where insect pests inhabit and how they interact with their environment is important for creating sampling and management plans. This study focused on the hemlock woolly adelgid, a pest that affects hemlock trees, to find the best way to sample these pests and understand their distribution in hemlock stands in the USA. We randomly selected 24 branches from each of 46 infested hemlock trees and counted the egg sacs of hemlock woolly adelgid on each branch to determine the best sampling unit. We also divided three hemlock forest areas into grids and counted the egg sacs in each grid cell to study the spatial distribution pattern of hemlock woolly adelgid. This study found that hemlock woolly adelgids tended to aggregate at the tips of branches and that a 50 cm branch from the lower canopy was the best sampling unit. The hemlock woolly adelgid also showed spatial aggregation in the hemlock stands, and its abundance was correlated with tree height and tree diameter at breast height. These findings help in better sampling and managing hemlock woolly adelgid. Understanding the spatial patterns of insect pests and their associations with their environments is crucial for developing effective sampling and management plans. This study was conducted to identify optimal sampling units for the hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae) and to characterize its spatial distribution patterns in hemlock (Tsuga canadensis (L.) Carrière) stands in West Virginia, USA. To determine the optimal sampling unit, we randomly selected 24 branches from each of 46 A. tsugae-infested hemlock trees. The locations and number of A. tsugae ovisacs on each branch were recorded and the coefficient of variation was used to choose the optimal sampling units. To determine the spatial patterns of A. tsugae, each of the three 1-ha hemlock stands was divided into 100 grids, and ovisac counts were taken from the center of each grid. Semivariograms and spatial analysis by distance indices (SADIE) were used to analyze the spatial patterns of A. tsugae. In addition, various environmental and biological factors were measured to explore their spatial associations with A. tsugae. The results of this study revealed that the A. tsugae ovisacs exhibited spatial aggregation within branches, predominantly at the tips, and a 50 cm branch approximately 3 m above the ground was the optimal sampling unit. The spatial aggregation of A. tsugae in the hemlock stands was evident, and positive spatial associations were found between A. tsugae populations and factors including the aspect, tree diameter at breast height, and tree height. These findings offer valuable insights for the sampling and management of A. tsugae. [ABSTRACT FROM AUTHOR]

Increasing efficiency of data gathering at the landscape scale on the growing number of pests and pathogens threatening forests worldwide has potential to improve management outcomes. Citizen science is expanding, with growing support and utility in environmental and conservation fields. We present a case study showing how citizen science observations can be used to inform research and management of a devastating forest pest. Hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), was introduced to eastern North America, leading to decline and mortality of eastern [ Tsuga canadensis (L.) Carrière] (Pinales: Pinaceae) and Carolina hemlock (Tsuga caroliniana Engelmann) trees. Management activities, most notably biological control, rely on observations of A. tsugae phenology to inform the timing of releases and monitoring surveys of their highly synchronized specialist predators. In this article, we outline a citizen science program and report phenological observations on A. tsugae. Additionally, we report data comparing A. tsugae estivation break in Virginia (VA) and New York (NY) State, revealing that estivation break is synchronized between NY and VA. This observation is supported by 6 years of citizen scientist observations, showing similar patterns throughout NY, with egg laying shown to be much more variable than estivation break. [ABSTRACT FROM AUTHOR]

Forest insect outbreaks cause large changes in ecosystem structure, composition, and function. Humans often respond to insect outbreaks by conducting salvage logging, which can amplify the immediate effects, but it is unclear whether logging will result in lasting differences in forest structure and dynamics when compared with forests affected only by insect outbreaks. We used 15 years of data from an experimental removal of Tsuga canadensis (L.) Carr. (Eastern hemlock), a foundation tree species within eastern North American forests, and contrasted the rate, magnitude, and persistence of response trajectories between girdling (emulating mortality from insect outbreak) and timber harvest treatments. Girdling and logging were equally likely to lead to large changes in forest structure and dynamics, but logging resulted in faster rates of change. Understory light increases and community composition changes were larger and more rapid in the logged plots. Tree seedling and understory vegetation abundance increased more in the girdled plots; this likely occurred because seedlings grew rapidly into the sapling‐ and tree‐size classes after logging and quickly shaded out plants on the forest floor. Downed deadwood pools increased more after logging but standing deadwood pools increased dramatically after girdling. Understory light levels remained elevated for a longer time after girdling. Perhaps because the window of opportunity for understory species to establish was longer in the girdled plots, total species richness increased more in the girdled than logged plots. Despite the potential for greater diversity in the girdled plots, Betula lenta L. (black birch) was the most abundant tree species recruited into the sapling‐ and tree‐size classes in both the girdled and logged plots and is poised to dominate the new forest canopy. The largest difference between the girdling and logging treatments—deadwood structure and quantity—will persist and continue to bolster aboveground carbon storage and structural and habitat diversity in the girdled plots. Human responses to insect outbreaks hasten forest reorganization and remove structural resources that may further alter forest response to ongoing climate stress and future disturbances. [ABSTRACT FROM AUTHOR]

BACKGROUND: Dinotefuran, a systemic neonicotinoid insecticide, is approved for control of hemlock woolly adelgid (HWA) (Adelges tsugae Annand), an invasive sap‐feeding insect that can kill eastern hemlocks (Tsuga canadensis). Dinotefuran is highly water soluble, facilitating more rapid translocation and HWA control than other neonicotinoids, but its persistence is not well‐known. Samples of needles and twigs were collected in spring 2021 from 50 hemlocks treated with a dinotefuran basal trunk spray in 2018 or 2019 (131–145 weeks and 85–93 weeks before sampling, respectively). Processed samples were analyzed with ultra‐performance liquid chromatography‐tandem mass spectrometer (UPLC‐MS/MS) and enzyme‐linked immunosorbent assays (ELISA). RESULTS: Dinotefuran residues were 4.6–6.1 times higher in needles than in twigs collected from the same trees. Average (±SE) residues in foliage samples collected from trees treated in 2019 ranged from 0.663 ± 0.243 to 0.564 ± 0.119 mg kg−1, compared with 0.213 ± 0.033 and 0.225 ± 0.132 mg kg−1 in foliage from trees treated in 2018. Foliage residues from UPLC‐MS/MS were consistently lower but strongly related to those from ELISA. Matrix effects appeared to disrupt ELISA analysis of twigs. None of the 25 trees treated in 2019 had live HWA when samples were collected in 2021 while low densities of HWA were observed on 52% of trees treated in 2018. CONCLUSIONS: Dinotefuran was recovered from hemlock foliage, and to a lesser extent twigs, >2 years post‐treatment. This, along with its relatively rapid translocation, suggests dinotefuran is a viable option for protecting declining or heavily infested hemlocks from HWA. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

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Adelges tsugae Annand, the hemlock woolly adelgid, is an invasive insect pest of Tsuga canadensis (L.) Carriere, eastern hemlock, in the eastern United States. An A. tsugae infestation often results in the death of T. canadensis within years and has caused significant changes to hemlock forests. Cycles in T. canadensis health and A. tsugae densities seem to be an important feature in A. tsugae population dynamics in the eastern United States. To investigate mechanisms leading to such cycles, we construct a model composed of systems of ordinary differential equations with time‐dependent parameters to represent seasonality. The model captures the coupled cycles in T. canadensis health and A. tsugae density. We use field data from Virginia to develop the model and to perform parameter estimation. The mechanisms we represent in the model include an A. tsugae density‐dependent T. canadensis growth rate, a T. canadensis health‐dependent A. tsugae mortality rate, and a density‐dependent A. tsugae mortality rate, which produce cycles in T. canadensis health and A. tsugae density commonly seen with the A. tsugae system in the eastern United States. We test sets of initial conditions to determine the scenarios that will likely lead to T. canadensis mortality and explore longer term dynamics of the system. In general, low and high T. canadensis health initial condition values result in likely T. canadensis mortality while T. canadensis with medium health initial condition values are predicted to survive. [ABSTRACT FROM AUTHOR]

Widespread mortality of eastern hemlock (Tsuga canadensis [L.] Carr.) has been occurring due to the introduction of hemlock woolly adelgid (Adelges tsugae Annand) (HWA), threatening millions of hectares of hemlock-dominated forests in the eastern United States. HWA feeds at the base of needles and removes stored carbohydrates, which can impact leaf-level physiology, contributing to the decline of the tree. However, these physiological mechanisms in HWA-infested hemlocks are still not clearly understood. We investigated hemlock leaf physiology year-round at three forested sites with various degrees of infestation. At each site, half the trees were treated with imidacloprid (Merit® 2 F, Bayer, Kansas City, MO, USA) while the rest were left untreated. Imidacloprid is widely used to control HWA but can itself have phytotoxic effects. After one growing season, there was an increase in photosynthetic rates (7.5%, p = 0.0163) and stomatal conductance (7.1%, p = 0.0163) across sites in the trees treated with imidacloprid. After two years, the imidacloprid treatment also increased bud break from 22.5% to 88.7% at Fishburn (the most severely impacted site) and from 22.7% to 58.9% at Mountain Lake (the least impacted site), and slightly increased chlorophyll fluorescence for treated trees at Fishburn. Chemical treatment also slightly increased water use efficiency at Mountain Lake. These results suggest that HWA is causing tree mortality largely through a reduction in leaf area caused by decreasing bud break and also by a slight, but significant, reduction in leaf-level photosynthesis and stomatal conductance. [ABSTRACT FROM AUTHOR]

Abstract Environmental DNA (eDNA) analysis can be a powerful tool for the early detection of invasive organisms. However, research on terrestrial eDNA detection from foliage surfaces has been limited. In this study, we developed methods to capture and detect eDNA using qPCR from an invasive forest pest, hemlock woolly adelgid (Adelges tsugae), and three of its biological control predators Leucotaraxis piniperda, Leucotaraxis argenticollis, and Laricobius nigrinus. We designed four highly efficient qPCR assays with a low limit of detection (1–10 copies/reaction). The assay targeting A. tsugae was species‐specific. The assays targeting Le. piniperda, and Le. argenticollis were biotype‐specific in addition to being species‐specific demonstrating applications of eDNA analysis beyond species‐level detection. The La. nigrinus assay also detected DNA from closely related and hybridizing Laricobius rubidus. The eDNA methods were evaluated against traditional detection methods. We collected foliage samples from three strata (bottom, middle, and top) of eastern hemlock trees to detect the presence of A. tsugae. The detection of the biological control predators was evaluated using western hemlock foliage samples collected from the predators' native range in western Washington. The eDNA methods had significantly higher positive detection rates (2.8–4.5 times) than conventional methods of all target species. The strata of sampling were not significant in determining the presence of A. tsugae infestation. The eDNA concentration positively correlated with the observed density for all species. This study demonstrates the efficacy of eDNA analysis as a more sensitive tool for early detection of A. tsugae and to track the establishment of its biological control predators.

Abstract Adelges tsugae Annand, the hemlock woolly adelgid, is an invasive insect pest of Tsuga canadensis (L.) Carriere, eastern hemlock, in the eastern United States. An A. tsugae infestation often results in the death of T. canadensis within years and has caused significant changes to hemlock forests. Cycles in T. canadensis health and A. tsugae densities seem to be an important feature in A. tsugae population dynamics in the eastern United States. To investigate mechanisms leading to such cycles, we construct a model composed of systems of ordinary differential equations with time‐dependent parameters to represent seasonality. The model captures the coupled cycles in T. canadensis health and A. tsugae density. We use field data from Virginia to develop the model and to perform parameter estimation. The mechanisms we represent in the model include an A. tsugae density‐dependent T. canadensis growth rate, a T. canadensis health‐dependent A. tsugae mortality rate, and a density‐dependent A. tsugae mortality rate, which produce cycles in T. canadensis health and A. tsugae density commonly seen with the A. tsugae system in the eastern United States. We test sets of initial conditions to determine the scenarios that will likely lead to T. canadensis mortality and explore longer term dynamics of the system. In general, low and high T. canadensis health initial condition values result in likely T. canadensis mortality while T. canadensis with medium health initial condition values are predicted to survive.

The non-native hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae), has caused a significant decline of eastern hemlock, Tsuga canadensis L. (Pinales: Pinaceae), and Carolina hemlock, Tsuga caroliniana Engelmann (Pinales: Pinaceae), in eastern North America. Biological control of HWA has focused on the use of 2 Laricobius spp. (Coleoptera: Derodontidae), natural predators of HWA, which require arboreal and subterranean life phases to complete their development. In its subterranean phase, Laricobius spp. are subject to abiotic factors including soil compaction or soil-applied insecticides used to protect hemlock from HWA. This study used 3D X-ray microcomputed tomography (micro-CT) to identify the depth at which Laricobius spp. burrows during its subterranean lifecycle, characterize pupal chamber volume, and determine whether soil compaction had a significant effect on these variables. The mean burrowing depth in the soil of individuals was 27.0 mm ± 14.8 (SD) and 11.4 mm ± 11.8 (SD) at compaction levels of 0.36 and 0.54 g/cm3, respectively. The mean pupal chamber volume was 11.15 mm3 ± 2.8 (SD) and 7.65 mm3 ± 3.5 (SD) in soil compacted at 0.36 and 0.54 g/cm3, respectively. These data show that soil compaction influences burrowing depth and pupal chamber size for Laricobius spp. This information will help us better identify the effect of soil-applied insecticide residues on estivating Laricobius spp. and soil-applied insecticide residues in the field. Additionally, these results demonstrate the utility of 3D micro-CT in assessing subterranean insect activity in future studies. [ABSTRACT FROM AUTHOR]

Terrestrial and stream ecosystems are interconnected, with changes in one system cascading to affect the other. Tree mortality related to nonnative pest infestation has increased, yet we do not understand the effects that riparian tree species losses will have on the structural characteristics of stream ecosystems. We compared riparian canopy cover, algal standing crop, and diatom assemblage composition in 8 southern Appalachian headwater stream reaches within the Coweeta Hydrologic Laboratory in North Carolina, USA, before and after a massive die-off of riparian eastern hemlock (Tsuga canadensis [L.] Carr.) related to the introduction of hemlock woolly adelgid (Adelges tsugae Annand), an invasive insect. We analyzed historical preserved algal samples collected prior to hemlock die-off, in both summer (September 2005) and winter (January 2006), and used multivariate analyses to compare them to samples collected in the same 8 reaches and seasons 13 y following hemlock die-off (2018–2019). We predicted that increased canopy openness following hemlock death would change light availability and lead to higher standing crop and increases in the relative biovolume of high-profile diatoms. Contrary to our expectations, we found little difference in canopy cover and lower algal standing crop 13 y post-hemlock die-off, likely due to increased basal area of the understory shrub, Rhododendron maximum L., that replaced shade cover formerly provided by hemlock. Diatom assemblages were dominated by acidophilic taxa (e.g., Eunotia spp.) across all stream reaches before and after hemlock die-off. We observed some shifts in diatom assemblage composition, but the relative biovolume of a majority of the top 20 most abundant taxa, including Eunotia incisa W. Sm. ex W. Greg., Nupela lapidosa (Krasske) Lange-Bert., and Meridion alansmithii Brant (an endemic taxon), remained relatively unchanged 13 y after hemlock mortality. Diatom assemblages differed post-hemlock die-off in summer but not winter due to a decrease in the relative biovolume of Eunotia metamondon complex and an increase in the relative biovolume of Eunotia rhomboidea complex. Our study highlights the relative stability of diatom assemblage composition in southern Appalachian streams and the importance of long-term studies following a major riparian disturbance. [ABSTRACT FROM AUTHOR]

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]

Previous research demonstrated that elevated sunlight improves carbon balance and growth of eastern hemlock (Tsuga canadensis (L.) Carrière) seedlings infested with the invasive hemlock woolly adelgid (Adelges tsugae Annand).This study examined the hypothesis that elevated visible and ultraviolet sunlight directly affects the settling behaviour of A. tsugae crawlers.Hemlock seedlings were manually infested with equal densities of A. tsugae and placed into artificial shade treatments (0%, 40% and 80% shade). The density of settled nymphs of the ensuing generation on shaded seedlings was three times higher than the density on unshaded seedlings.Adelges tsugae ovisacs were also attached to hydrated hemlock branches placed beneath acrylic filter treatments that selectively allowed transmission of various sunlight wavelengths. The proportion of adelgid crawlers that settled on the branch (vs. dropping from it) was higher beneath filters that blocked the widest spectrum of solar radiation (opaque and amber filters) than beneath full sun. In the March‐April trial, exposure to full sun and the full visible spectrum only (clear‐UV filter) significantly increased the proportion of crawlers that settled on the bottom (vs. top) side of the branch.Our results suggest that A. tsugae crawlers are negatively phototactic and/or thermotactic, with behaviour influenced more by visible light than ultraviolet light. [ABSTRACT FROM AUTHOR]

1. Interactions between invertebrate herbivores with different feeding modes are common on long‐lived woody plants. In cases where one herbivore facilitates the success of another, the consequences for their shared host plant may be severe. Eastern hemlock (Tsuga canadensis), a canopy‐dominant conifer native to the eastern U.S., is currently threatened with extirpation by the invasive stylet‐feeding hemlock woolly adelgid (Adelges tsugae). The effect of adelgid on invasive hemlock‐feeding folivores remains unknown. 2. This study evaluated the impact of feeding by hemlock woolly adelgid on gypsy moth (Lymantria dispar) larval preference for, and performance on, eastern hemlock. To assess preference, 245 field‐grown hemlocks were surveyed for gypsy moth herbivory damage and laboratory paired‐choice bioassays were conducted. To assess performance, gypsy moth larvae were reared to pupation on adelgid‐infested or uninfested hemlock foliage, and pupal weight, proportional weight gain, and larval period were analysed. 3. Adelgid‐infested hemlocks experienced more gypsy moth herbivory than did uninfested control trees, and laboratory tests confirmed that gypsy moth larvae preferentially feed on adelgid‐infested hemlock foliage. Gypsy moth larvae reared to pupation on adelgid‐infested foliage gained more weight than larvae reared on uninfested control foliage. 4. These results suggest that the synergistic effect of adelgid and gypsy moth poses an additional threat to eastern hemlock that may increase extirpation risk and ecological impact throughout most of its range. [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]

Biological control entails introducing non‐native natural enemies to control weeds and pests. Instances of poorly regulated biocontrol have had harmful consequences leading to significant efforts to improve risk assessment of agents before release.Laricobius naganoensis (Coleoptera: Derodontidae) was inadvertently imported to eastern North America with Laricobius osakensis, introduced from Japan to control the hemlock woolly adelgid Adelges tsugae (Hemiptera: Adelgidae). The United States Department of Agriculture (U.S.D.A.) subsequently permitted introduction of L. naganoensis as a biocontrol agent and contaminant, requiring no study or monitoring owing to difficulty of the effort required to distinguish it from L. osakensis.The Plant Protection Act of 2000 (7 U.S.C. § § 7701–7786) assigns U.S.D.A. responsibility for vetting and reducing risk from biocontrol agents while ensuring the process is transparent, accessible, and based on scientific evidence. Typically, release of a new agent involves a 30‐day period when the public may review and comment on an assessment of risk associated with the introduction, an Environmental Assessment (EA). No public review and comment period was allowed before L. naganoensis' introduction, and the EA was not made public.Biocontrol practitioners and stakeholders agree that critical scientific evaluation of multiple lines of evidence is necessary to evaluate risk associated with new introductions. The importance of accurate agent identification and avoidance of contamination has long been recognised, and procedures to minimise risk are well known. While such processes might be difficult to implement, those challenges should not justify a release that circumvents regulatory safeguards. [ABSTRACT FROM AUTHOR]

Bacterial endosymbionts of sap‐sucking insects provide their host with a number of beneficial qualities, including the supply of nutrition, defense against parasitoids, and protection from heat stress. Damage to these bacterial associates can therefore have a negative impact on the fitness of their insect host. We evaluated observational and experimental factors regarding the nonnative hemlock woolly adelgid (Adelges tsugae Annand) (Hemiptera: Adelgidae) to help understand the roles of its three recently identified symbionts, including under heat stress conditions. The prevalence of A. tsugae's facultative symbiont (Serratia symbiotica) was examined at different spatial scales to determine how variable infection rates are for this symbiont. There was no significant difference found in infection rates between adelgids on a tree, within a plot, or within a state. However, significantly more adelgids in Georgia (95%) had S. symbiotica compared to those in New York (68%). Microsatellite genotyping of the adelgids found that this difference was most likely not the result of a second introduction of A. tsugae into eastern North America. Comparison of S. symbiotica proportions between first and fourth instars showed that symbiont absence did not affect the ability of A. tsugae to survive aestivation. Evaluations of symbiont densities within each adelgid found that when S. symbiotica was absent, the density of obligate symbionts was significantly higher. Exposure to heat stress (32.5 °C) was not consistently correlated with changes in symbiont densities over a 4‐d period. Overall, we have shown that symbiont prevalence and densities vary within the broad population of A. tsugae in eastern North America, with potentially significant effects upon the ecology of this important pest. [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]

Tsuga canadensis (L.) Carr. (eastern hemlock) is dying across much of eastern North America from the invasive hemlock woolly adelgid (HWA, Adelges tsugae Annand). Survey studies show that eastern hemlock populations with high foliar nutrient concentrations are associated with low infestation rates, and also suggest that deeply shaded trees may be more susceptible to infestation. Here we examined (1) how foliar nutrient concentration of eastern hemlock changes with varying shade levels; and (2) how nutrient concentration might further change with sustained shade and subsequent HWA infestation. Foliar samples from three years--pretreatment, post-shade, and post-shade and infestation--were collected and analyzed for [N], [P], and [K]. Pretreatment, all seedlings had similar foliar nutrient concentrations. After nine months in the shade tents, seedlings under higher levels of shade exhibited increased foliar [N]. For each 10% increase in shade, foliar [N] increased 35.09 µg/mg over baseline levels. The combined effects of prolonged shade with HWA infestation increased foliar [N], [P], and [K]. The mechanism for increasing foliar nutrients is unknown, but may be due to reduced growth causing a concentration effect, or nutrients mobilized by the plant in response to infestation. [ABSTRACT FROM AUTHOR]

The ability to predict key phenological stages of insect pests is of prime importance in sampling and management programs. Hemlock woolly adelgid, Adelges tsugae (Annand) (Hemiptera: Adelgidae), is a non-native invasive pest of eastern and Carolina hemlock that is currently expanding its range westward through the central Appalachian region. We conducted intensive sampling of A. tsugae across four sites in West Virginia and western Maryland from March 2013 to May 2014, and developed a degree-day model (minimum temperature threshold of 4°C) to predict the temporal distribution of progrediens eggs, progrediens egg hatch, newly hatched sistens, and settled first-instar sistens. We then linked degree-day predictions to recent weather data collected from our study region from 2012 to 2016 to provide a range of calendar days over which these key phenological events occur. The initial occurrence of progrediens eggs and progrediens egg hatch is predicted to occur at 209 (mean date of 19 April) and 346 (mean date of 8 May) degree days, respectively. The initial occurrence of newly hatched sistens and settled first-instar sistens is predicted to occur at 852 (mean date of 19 June) and 1010 (mean date of 30 June) degree days, respectively. Because our study region represents a region in which A. tsugae continues to spread, this information should be useful in optimizing sampling programs and the timing of control tactics in the central Appalachian region. [ABSTRACT FROM AUTHOR]

The hemlock woolly adelgid (HWA), Adelges tsugae, is an invasive pest of Tsuga spp. in eastern North America. Scymnus coniferarum is a predaceous beetle that was collected from HWA in the western United States. Limited knowledge of this insect in its native habitat led to studies to evaluate its potential for biological control of HWA. Seasonal abundance was sampled at six sites in Tacoma, WA, twice monthly, for one year on different host trees of potential adelgid prey. Tree species included Pseudotsuga menziesii, Pinus contorta, Pinus monticola, and Tsuga heterophylla. Scymnus coniferarum adults were found on all conifer species, except P. menziesii. Each conifer species supported a different adelgid species, suggesting S. coniferarum feeds on multiple adelgid species. More S. coniferarum were found on pine than hemlock. DNA barcoding of S. coniferarum found two distinct clusters that differed by 6% divergence. Beetles in each cluster were co-habiting the same conifer species, and they could not be distinguished morphologically. Further taxonomic studies are needed to understand the significance of DNA barcode sequence divergence. Because S. coniferarum was more frequently associated with pine adelgids than HWA, and because of remaining taxonomic uncertainty, S. coniferarum may not be suitable for HWA biological control. [ABSTRACT FROM AUTHOR]

Nutritional bacterial symbionts enhance the diets of sap-feeding insects with amino acids and vitamins missing from their diets. In many lineages, an ancestral senior symbiont is joined by a younger junior symbiont. To date, an emergent pattern is that senior symbionts supply a majority of amino acids, and junior symbionts supply a minority. Similar to other hemipterans, adelgids harbor obligate symbionts, but have higher diversity of bacterial associates, suggesting a history of symbiont turnover. The metabolic roles of dual symbionts in adelgids and their contributions to the consortium are largely unexplored. Here, we investigate the symbionts of Adelges tsugae, the hemlock woolly adelgid (HWA), an invasive species introduced from Japan to the eastern United States, where it kills hemlock trees. The response of hemlocks to HWA feeding has aspects of a defensive reaction against pathogens, and some have speculated that symbionts may be involved. We sequenced the genomes of "Ca. Annandia adelgestsuga" and "Ca. Pseudomonas adelgestsugas" symbionts to detail their metabolic capabilities, infer ages of relationship, and search for effectors of plant defenses. We also tested the relationship of "Ca. Annandia" to symbionts of other insects. We find that both symbionts provide nutrients, but in more balanced proportions than dual symbionts of other hemipterans. The lesser contributions of the senior "Ca. Annandia" support our hypothesis for symbiont replacements in adelgids. Phylogenomic results were ambiguous regarding the position of "Ca. Annandia". We found no obvious effectors of plant defenses related to insect virulence, but hypothetical proteins in symbionts are unknown players. [ABSTRACT FROM AUTHOR]

In the eastern United States, hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae) is considered an invasive pest of eastern hemlocks; an ecologically foundational tree species. Current management of HWA focuses on chemical and biological controls, with recent research suggesting that these two tactics could be integrated successfully. The approach is to protect a subset of hemlocks with systemic insecticides while releasing predatory insects onto adjacent, unprotected trees. The goal of this study was to assess the effects of chemical and biological control tactics, alone and in combination, on hemlock health and HWA densities at three southern Appalachian sites (KY, WV, and TN) from 2010 to 2016. Although insecticide applications were effective at protecting individual trees, none of the overall treatments (chemical, biological, or combined) had a significant effect on tree health or HWA population index values relative to untreated plots. Tree health generally declined at all sites over time. HWA populations were highly variable over time and were likely more strongly influenced by extremely low, winter temperatures than by the treatments. Cross-correlation analysis of tree health and HWA population indicated a time-lag effect. At two of the three sites, recovery of tree health lagged 0 – 3 years behind decline in HWA population, and decline in HWA populations lagged approximately 0 – 1 years behind decline in tree health. The predatory beetle, Laricobius nigrinus , was recovered two-years, post-release at the KY and WV sites in 2012 and 2013, but was not recovered from the TN site. The lack of sustained recovery of L. nigrinus may be attributable to the occurrence of extremely low, winter temperatures in 2014 and 2015, which produced subsequent crashes in the HWA populations. In TN, the L. nigrinus population may have been unrecoverable due to a decline in the HWA population shortly after initial release. [ABSTRACT FROM AUTHOR]

Foundation species are locally abundant and uniquely control associated biodiversity, whereas dominant species are locally abundant but are thought to be replaceable in ecological systems. It is important to distinguish foundation from dominant species to direct conservation efforts. Long-term studies that remove abundant species while measuring community dynamics have the potential to (1) aid in the identification of foundation vs. dominant species and, (2) once a foundation species is identified, determine how long its effects persist within a community after its loss. Long-term data on ant assemblages within two canopy-manipulation experiments--the Harvard Forest Hemlock Removal Experiment (HF-HeRE) and the Black Rock Future of Oak Forests Experiment (BRF-FOFE)--provide insights into how ant assemblages change and reassemble following the loss of Tsuga canadensis or Quercus spp. Previous research documented foundation species effects on ants in the HF-HeRE for up to four years after T. canadensis loss. Six additional years of data at HF-HeRE presented for the first time here show that removal of T. canadensis resulted in taxonomic and some measures of functional shifts in ant assemblages that persisted for ten years, further supporting the hypothesis that T. canadensis is a foundation species at Harvard Forest. In contrast, ant assemblages at BRF-FOFE varied little regardless of whether oaks or other tree species were removed from the canopy, suggesting that Quercus species do not act as foundation species at Black Rock Forest. Deer and moose exclosures within each experiment also allowed for comparisons between effects on ants of foundation or dominant tree species relative to effects of large herbivores. At HF-HeRE, effects of T. canadensis were stronger than effects of large herbivores on taxonomic and functional diversity of ant assemblages. At BRF-FOFE, in contrast, effects of Quercus species were weaker than effects of large herbivores on ant taxonomic diversity and some measures of ant functional diversity. These findings illustrate the importance of distinguishing between the roles of irreplaceable foundation species and replaceable dominant ones in forested ecosystems along with other drivers of biodiversity (e.g., herbivory). [ABSTRACT FROM AUTHOR]

• The invasive insect Adelges tsugae threatens ecologically important conifer species. • Classical biological control in North America has been pursued for three decades. • Efforts with coccinellid predators have not yielded a successful biocontrol agent. • Two Derodontid predators are established and spreading but do not prevent host decline. • Two Chamaemyiid predators show promise for complementing existing agents. The hemlock woolly adelgid (HWA, Adelges tsugae , Hemiptera: Adelgidae) is an invasive insect that threatens the ability to maintain eastern hemlock (Tsuga canadensis) and Carolina hemlock (Tsuga caroliniana) as ecologically functional components of eastern North American forests. Since the early 1990 s, a classical biological control program for HWA has been pursued using insect predators from regions of Asia and western North America where the adelgid is native. Early efforts to establish ladybird beetles (Coleoptera: Coccinellidae) resulted in the establishment of Sasajiscymnus tsugae from Japan, but consistently poor field recovery of this species suggests it has not been an effective biocontrol agent in the introduced range. Two additional ladybird beetles, Scymnus ningshanensis Yu & Yao , and S. camptodromus Yu & Liu, were released but did not establish. Subsequent introduction, widespread establishment and spread of Laricobius nigrinus and La. osakensis (Coleoptera: Derodontidae) has provided substantial predation on winter stages of HWA, but has not provided overall regulation of adelgid populations below levels that cause hemlock shoot growth loss and mortality. Recently, efforts have focused on prey-specific genetic lineages of Leucotaraxis argenticollis and Le. piniperda (Diptera: Chamaemyiidae), which co-occur with La. nigrinus in their native range of the Pacific Northwest and show promise for eventual establishment in eastern North America. This review provides a brief introduction on the ecology, evolution, and population dynamics of HWA and its hosts, detailed coverage of the predators that have been (and are being) evaluated as biological control agents, and a discussion of the overall biological program with considerations for its future implementation. [ABSTRACT FROM AUTHOR]

Eastern (Tsuga canadensis) and Carolina hemlocks (T. caroliniana) of eastern North America have been attacked by the non-native hemlock woolly adelgid (Adelges tsugae Annand) (HWA) since the first half of the 20th century. Unlike most insects, HWA develops through one generation from fall to late winter, exposing this insect to the lethal effects of winter temperatures. The mortality inflicted by winter temperatures on HWA determines the surviving population density as well as its ability to spread to uninfested areas. With the ongoing changes in climate, knowledge of this species' ability to survive and spread in the future can help land managers prepare for its management. This study began during the winter of 2014 and ended in the spring of 2017. During this period, winter mortality of HWA was recorded at 100 sites from Maine to Georgia (n = 209). Changes in population density from the sistens to the succeeding progrediens generation were recorded at 24 sites (n = 35). Models were developed to predict HWA mortality using the lowest minimum temperature prior to the mortality assessment date, the number of days with mean temperature < 1 °C, and the mean daily temperature of the three days preceding that minimum. Models were also developed to predict population density changes from the overwintering sistens generation to the following progrediens generation. Future projections under climate change showed increases in winter survival and population growth rates over time. Especially towards the northeastern edge of T. canadensis' distribution as minimum temperatures are predicted to increase at a greater rate. This will result in an increase in density throughout its current distribution and expansion northward causing an increase in its impact on eastern Tsuga spp. [ABSTRACT FROM AUTHOR]

The ability to survive winter temperatures is a key determinant of insect distributional ranges and population dynamics in temperate ecosystems. Although many insects overwinter in a state of diapause, the hemlock woolly adelgid [ Adelges tsugae (Annand)] is an exception and instead develops during winter. We studied a low density population of A. tsugae, which undergoes two generations per year, in a forested area in which its only available host plant, eastern hemlock ( Tsuga canadensis), was patchy and scarce. In January 2014, this area also experienced an exceptionally cold winter due to a southward shift in the North Polar Vortex. We used 3 years of systematic sampling prior to the 2014 cold wave, and 1 year following, to quantify the effect of the 2014 cold wave on A. tsugae population dynamics. We observed a strong negative correlation between the number of days below sub-zero temperature thresholds and A. tsugae, and estimated that the 2014 cold wave resulted in at least a 238% decrease in its population growth rate. However, we also observed that the detrimental effect of the 2014 cold wave to A. tsugae was short-lived, as populations measured in the late summer of 2014 rebounded to pre-2014 cold wave densities. This study highlights the effect that cold winter weather events can have on a winter active insect species, and the speed at which populations can recover from stochastic mortality events. [ABSTRACT FROM AUTHOR]

To better understand the potential impact of the invasive hemlock woolly adelgid (HWA, Adelges tsugae Annand) and presalvage activities on carbon (C) dynamics in northern stands of eastern hemlock ( Tsuga canadensis (L.) Carr.), we used the Forest Vegetation Simulator and Forest Inventory and Analysis data to model C storage and successional pathways under four scenarios: presalvage harvesting; HWA-induced mortality; presalvage harvesting plus HWA-induced mortality; and no disturbance (control). Our simulation showed that all treatments differed in total C storage in the short term, with HWA-induced mortality providing the highest total C storage due to regeneration and ingrowth of replacement species combined with retention of standing and downed deadwood. At the end of the 150-year simulation, all disturbance scenarios had significantly lower total C than the control. The cumulative net C gain was lower for the two presalvage scenarios than for the HWA scenario, indicating that allowing HWA to progress naturally through a stand may result in the least impact to long-term C sequestration and net C storage. While differences were not significant on low hemlock density stands, impacts to the estimated 267 000 ha of northeastern forests where hemlock is dominant could result in conversion to red maple ( Acer rubrum L.) and a net loss of over 4 million metric tons of potentially sequestered C over the next 150 years. [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]

Hemlock woolly adelgid (HWA), Adelges tsugae Annand, an invasive insect native to the Pacific Northwest and Asia, is responsible for widespread health decline and mortality of native hemlocks (Tsuga spp.) in the eastern United States. Shading and fertilizer has been found to affect the survival and health of both HWA and hemlocks. These abiotic factors have been studied separately but not in combination. In this three year study, eastern hemlock trees (1-2 m tall) were treated with pruning, fertilizer, and shade to determine their effects on hemlock tree health and HWA survival and density. Shade cloths were erected over individual trees, granulated fertilizer was applied, and trees were pruned annually. The total number of HWA were counted during the sistens and progrediens adult stages on the low, mid, and high branches on the north, east, south, and west sides of each tree for three years. Survival of aestivating sistens was recorded in artificially, naturally, and unshaded hemlocks. The mean of percent tips alive, branches alive, and foliage density was used to calculate a hemlock health index (scale of 0-100). Shade cloth reduced solar radiation to the trees to levels similar to a naturally-forested hemlock canopy, but did not alter temperature. Trees exposed to shade alone and shade plus fertilizer maintained the greatest HWA density. On unshaded trees, branches on the west side of the tree had lower HWA densities and branches high on the tree had the lowest HWA densities. Pruning plus fertilizer and shading plus fertilizer reduced tree health. Shaded trees had reduced branchlet new growth length. Survival of summer aestivating sistens was nearly twice the survival under artificially- and naturally-shaded trees compared to unshaded trees. There was an inverse density-dependent survival response for aestivating HWA under artificially-shaded and unshaded trees but not naturally-shaded trees. Unshaded hemlock trees had lower HWA densities due to increased mortality of summer aestivating sistens. Unshaded trees had better health and longer new growth branchlets due to increased exposure to solar radiation and lower HWA densities. Silvicultural thinning of hemlocks in forest stands could increase direct sunlight reaching the trees and help decrease HWA densities and improve hemlock health. [ABSTRACT FROM AUTHOR]

The hemlock woolly adelgid (HWA) (Hemiptera: Adelges tsugae Annand) is an invasive insect causing damage to Eastern ( Tsuga canadensis (L.) Carr.) and Carolina ( Tsuga caroliniana Engelm.) hemlock trees in the eastern United States. Maine and New Hampshire are currently the northernmost front of HWA's range. Developing methods to locate newly infested stands is paramount in the effort to monitor HWA range expansion; presently, the most reliable method of detection requires extensive on-the-ground manual surveying. Field surveys for invasive pests like HWA consume multiple resources, limiting the amount of area that can be surveyed, and the results often misrepresent the true extent or patchiness of an invasion. Satellite based remote sensing, using vegetation indices, enables us to detect insect driven changes in forest health at a landscape scale. Our objectives were to classify HWA infested hemlock stands along the infestation front and demonstrate how the classification product could be used to improve HWA survey planning. Our workflow consisted of 1) modeling hemlock habitat suitability using a Maximum Entropy algorithm; 2) developing decision tree rules to classify likely infested stands from a Landsat time series, using the habitat suitability model to mask out non-hemlock areas; and 3) field check the final classification product. The hemlock habitat suitability model attained an overall accuracy of 68.2%. Partitioning of leaf-on multi-year (1995–2013) Landsat 5 and 8 data resulted in seven probability of infestation classes with a training R 2 = 0.782. Agreement between the classification and previously reported HWA infestations was 75.0% in conifer forests, 33.3% in mixed forests and 50.0% in deciduous forests. Agreement between the classification and test-survey locations was 78.6%; verified new infestations were detected as far as 19 km away from previously reported infestations. The methods presented outline how Landsat could be used to detect low-level HWA infestations. Classification products such as this ultimately could be used by federal and state agencies to target specific areas for efficient survey, suppression, and eradication efforts. [ABSTRACT FROM AUTHOR]

Mycopathogens of economically important exotic invasive insects in forests of northeastern USA have been the subject of research at the Entomology Research Laboratory, University of Vermont, for the last 20 years. Elongate hemlock scale, European fruit lecanium, hemlock woolly adelgid and pear thrips were analyzed for the presence of mycopathogens, in order to consider the potential for managing these pests with biological control. Fungal cultures isolated from insects with signs of fungal infection were identified based on morphological characters and DNA profiling. Mycopathogens recovered from infected insects were subdivided into three groups, i.e., specialized entomopathogenic; facultative entomopathogens; ubiquitous opportunistic contaminants. Epizootics were caused by fungi in the specialized group with the exception of M. microspora, P. marquandii and I. farinosa. Inoculation of insects in laboratory and field conditions with B. bassiana, L. muscarium and Myriangium sp. caused insect mortality of 45 to 95%. Although pest populations in the field seemed severely compromised after treatment, the remnant populations re-established themselves after the winter. Although capable of inducing high mortality, a single localized aerial application of a soil-dwelling fungus does not maintain long-time suppression of pests. However, it can halt their range expansion and maintain populations below the economic threshold level without the use of expensive insecticides which have a negative impact on the environment.

Abstract Disturbances such as outbreaks of herbivorous insects and pathogens can devastate unique habitats and directly reduce biodiversity. The foundation tree species Tsuga canadensis (eastern hemlock) is declining due to infestation by the nonnative insect Adelges tsugae (hemlock woolly adelgid). The decline and expected elimination of hemlock from northeastern U.S. forests is changing forest structure, function, and assemblages of associated species. We assessed 10 years of changes in occupancy, detection probability, and relative abundance of two species of terrestrial salamanders, Plethodon cinereus (eastern red‐back salamander) and Notopthalmus viridescens viridescens (eastern red‐spotted newt), to the experimental removal in 2005 of T. canadensis at Harvard Forest. Salamanders were sampled under cover boards and using visual encounter surveys before (2004) and after (2005, 2013, 2014) canopy manipulations in replicate 0.81‐ha plots. In 2004, occupancy of P. cinereus was 35% lower in stands dominated by T. canadensis than that in associated mixed‐hardwood control stands, whereas detection probability and estimated abundance of P. cinereus were, respectively, 60% and 100% greater in T. canadensis stands. Estimated abundance of N. v. viridescens in 2004 was 50% higher in T. canadensis stands. Removal of the T. canadensis canopy increased occupancy of P. cinereus but significantly reduced its estimated detection probability and abundance. Estimated abundance of N. v. viridescens also declined dramatically after canopy manipulations. Our results suggest that ten years after T. canadensis loss due to either the adelgid or pre‐emptive salvage logging, and 50–70 years later when these forests have become mid‐successional mixed deciduous stands, the abundance of these salamanders likely will be

The rapid loss of eastern hemlock ( Tsuga canadensis ) due to infestation with hemlock woolly adelgid ( Adelges tsugae , HWA) has greatly altered structure and function of eastern forests. Numerous control strategies including local pesticide use and biocontrol with predator beetles have been implemented with considerable cost and varying success. Silviculture treatments that increase incident light on surviving hemlock trees to reduce infestation and ameliorate carbon starvation have been proposed as another possible conservation strategy, yet no controlled studies have evaluated the coupled plant-insect responses to increased light. We conducted a nursery experiment on artificially infested eastern hemlock seedlings under varying levels of ambient light, ranging from 0 to 90% shade. We measured HWA infestation (ovisac density), short- and long-term indicators of carbon balance (leaf chlorophyll fluorescence, net photosynthesis, total nonstructural carbohydrate content, and shoot growth), and nutrition (leaf N content). We hypothesized that higher light would result in reduced HWA densities, higher C assimilation rates, and improved tissue non-structural carbohydrate balance; and these effects would ameliorate the effects of infestation on C balance and lead to improved seedling growth. HWA density decreased with increasing light, and was highest in the 90% shade treatments. However, photosystem II efficiency and net assimilation were also lower under the higher light treatment. Despite tradeoffs between reduced infestation and reduced leaf function from higher light, and little variation in sugar content among treatments, both leaf and root starch content and seedling growth were higher under the higher light treatment. Increasing light levels improves long-term carbon balance for hemlock seedlings in the presence of HWA. Although hemlock typically occurs in deeply shaded forests, our results suggest that silvicultural treatments such as forest thinning that increase light exposure may reduce HWA abundance and lead to better tree C balance, and may be an effective component of large-scale conservation and restoration strategies. [ABSTRACT FROM AUTHOR]

The hemlock woolly adelgid, Adelges tsugae Annand is an invasive insect that frequently causes hemlock ( Tsuga spp.) mortality in the eastern United States. Studies have shown that once healthy hemlocks become infested by the adelgid, nutrients are depleted from the tree, leading to both tree decline and a reduction of the adelgid population. Since A. tsugae is dependent on hemlock for nutrients, feeding on trees in poor health may affect the ability of the insect to obtain necessary nutrients and may consequently affect their physiological and population health. Trees were categorized as lightly or moderately impacted by A. tsugae based on quantitative and qualitative tree health measurements. Population health of A. tsugae on each tree was determined by measuring insect density and peak mean fecundity; A. tsugae physiological health was determined by measuring insect biomass, total carbon, carbohydrate, total nitrogen, and amino nitrogen levels. Adelges tsugae from moderately impacted trees exhibited significantly greater fecundity than from lightly impacted trees. However, A. tsugae from lightly impacted hemlocks contained significantly greater levels of carbohydrates, total nitrogen, and amino nitrogen. While the results of the physiological analysis generally support our hypothesis that A. tsugae on lightly impacted trees are healthier than those on moderately impacted trees, this was not reflected in the population health measurements. Adelges tsugae egg health in response to tree health should be verified. This study provides the first examination of A. tsugae physiological health in relation to standard A. tsugae population health measures on hemlocks of different health levels. [ABSTRACT FROM AUTHOR]

The hemlock woolly adelgid, Adelges tsugae Annand, is an invasive pest of eastern (Tsuga canadensis (L.) Carrière) and Carolina hemlock (Tsuga caroliniana Engelmann) forests in the eastern United States. Scymnus (Pullus) coniferarum Crotch (Coleoptera: Coccinellidae) is a lady beetle that preys on A. tsugae in the western United States, where A. tsugae infestations on western hemlocks are not lethal. It is thought that S. coniferarum could be an important predator that helps keep A. tsugae populations from reaching damaging levels in this region. This study assesses the potential of this predator as a biological control agent for A. tsugae in the eastern United States. S. coniferarum predation, reproductive potential, and survival were evaluated in field-cages on adelgid-infested T. canadensis at two sites in southwestern Virginia. Sampling was conducted between December 2012 and June 2014 to evaluate the impact of S. coniferarum on both generations of A. tsuage (sistens and progrediens). Adult S. coniferarum fed on both generations and all life stages of A. tsugae during both field trials at rates comparable to other adelgid-specific predators. Evidence of S. coniferarum oviposition was minimal, and may be attributed to low temperatures and prey availability. S. coniferarum mortality was greatest when exposed to winter temperatures at the higher elevation site in 2013, and least throughout the 2014 spring sample period. S. coniferarum demonstrated a high predation rate on A. tsugae and survived for extended periods of time at sites in southwest Virginia, indicating that this species could be an effective predator of hemlock woolly adelgid in similar climates. [ABSTRACT FROM AUTHOR]

From 2010 through 2013, adult emergence and seasonality of Laricobius nigrinus Fender, an introduced predatory species native to western North America, as well as hybridization with the native species Laricobius rubidus (LeConte), were evaluated using emergence traps and beat-sheet sampling in areas of previous release against hemlock woolly adelgid, Adelges tsugae Annand. The shortest emergence period of adult L. nigrinus was 7 wk beginning 22 October 2010, and the longest emergence was 15 wk beginning 17 October 2012. Native L. rubidus also were collected from emergence traps placed on the ground surface and beat-sheet samples all 3 yr, with emergence of L. rubidus initiating later than L. nigrinus each season. Seasonality of both Laricobius species was similar across a 44-mo study period. Adult L. nigrinus were present from October through April, and larvae of Laricobius spp. were collected from February to May. The average number of L. nigrinus from emergence traps was significantly greater than the average number of beetles collected from beat-sheet samples in 2010, while the converse was observed during 2012. Hybridization between L. nigrinus and L. rubidus was documented from 10.75% of specimens collected during 2010 and 2011, indicating periodic interbreeding between the introduced and native species. These findings suggest emergence trapping may be a useful method to assess establishment, population densities, and seasonality of Laricobius species in areas of release to enhance their use in management of A. tsuage. [ABSTRACT FROM AUTHOR]

Disturbances such as outbreaks of herbivorous insects and pathogens can devastate unique habitats and directly reduce biodiversity. The foundation tree species Tsuga canadensis (eastern hemlock) is declining due to infestation by the nonnative insect Adelges tsugae (hemlock woolly adelgid). The decline and expected elimination of hemlock from northeastern U.S. forests is changing forest structure, function, and assemblages of associated species. We assessed 10 years of changes in occupancy, detection probability, and relative abundance of two species of terrestrial salamanders, Plethodon cinereus (eastern red-back salamander) and Notopthalmus viridescens viridescens (eastern red-spotted newt), to the experimental removal in 2005 of T. canadensis at Harvard Forest. Salamanders were sampled under cover boards and using visual encounter surveys before (2004) and after (2005, 2013, 2014) canopy manipulations in replicate 0.81-ha plots. In 2004, occupancy of P. cinereus was 35% lower in stands dominated by T. canadensis than that in associated mixed-hardwood control stands, whereas detection probability and estimated abundance of P. cinereus were, respectively, 60% and 100% greater in T. canadensis stands. Estimated abundance of N. v. viridescens in 2004 was 50% higher in T. canadensis stands. Removal of the T. canadensis canopy increased occupancy of P. cinereus but significantly reduced its estimated detection probability and abundance. Estimated abundance of N. v. viridescens also declined dramatically after canopy manipulations. Our results suggest that ten years after T. canadensis loss due to either the adelgid or pre-emptive salvage logging, and 50-70 years later when these forests have become mid-successional mixed deciduous stands, the abundance of these salamanders likely will be <50% of their abundance in current, intact T. canadensis stands. This study adds to our understanding of how forest disturbance, directly and indirectly caused by invasive species, can contribute to declines in the relative abundance of amphibians. [ABSTRACT FROM AUTHOR]