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Pre-emptive silvicultural treatments can enhance host-tree vigor as a component of an integrated management approach to mitigate invasive species' impacts. Hemlock woolly adelgid (HWA, Adelges tsugae Annand, 1928) threatens the health and existence of eastern hemlock-dominated forests. We propose that increasing canopy light exposure via silvicultural thinning can reduce hemlock's vulnerability to HWA. Three stands with high hemlock densities on the Allegheny National Forest were selected for thinning. There was no HWA infestation and half of each stand was thinned. Circular plots were established surrounding 96 hemlock "subject trees" targeted for crown release on 3–4 sides. Similar criteria were used to select 90 hemlocks in untreated plots. We visited subject trees pre-thinning and 5 and 10 years post thinning and measured the following: diameter, total height, live crown ratio, and crown area. Temporal changes in diameter were not significant between treatments, but trees in thinned plots averaged 5 cm larger after 10 years. Live crown ratio was maintained in thinned stands and decreased after year 5 in controls. Crown area increased in thinned plots and decreased in controls. Residual basal area significantly influenced growth but varied between treatments and among stands. [ABSTRACT FROM AUTHOR]

Winter‐season extreme minimum temperatures may play a major role in limiting population growth and spread of the hemlock woolly adelgid (HWA) (Adelges tsugae Annand) (Hemiptera: Adelgidae), an invasive sap‐feeding insect that has caused extensive mortality of hemlock trees (Tsuga spp.) in many eastern United States (US) forests. This atypical insect feeds throughout the winter but populations can sustain high mortality when winter‐season extreme minimum temperatures drop below −20 to −30°C. Detection of HWA in Michigan during 2015 motivated interest in HWA winter survival in the US Great Lakes region. Here, we used the parameter‐elevation regressions on independent slopes model (PRISM) gridded daily minimum temperature dataset to construct a 1981–2018 climatology of extreme minimum temperatures in the Great Lakes region, the first such effort for this region. Metrics examined include absolute and mean annual extreme minimum temperatures (defined as the lowest daily minimum temperature during the study period and the study‐period mean lowest daily minimum temperature during each calendar year, respectively), and the frequency of daily minimum temperatures below −20 and −30°C. Minimum temperature patterns we identified support the following two hypotheses: first, proximity to water, surface elevation and latitude are the principal controls for extreme minimum temperatures in the Great Lakes region; second, the modifying influence of the relatively warm Lake Michigan serves to protect locations within about 10–25 km of the lakeshore from severe and potentially lethal temperatures for HWA. Analysis of projected minimum temperatures at the end of the 21st century (2080–2099) reveals a range of HWA distribution expansion scenarios. Although the original motivation for this study arose from interest in potential HWA mortality, a climatological study of extreme minimum temperatures has potentially broad relevance to, for example, human health and safety and forest ecology. [ABSTRACT FROM AUTHOR]

Imidacloprid, a neonicotinoid pesticide, is used to prevent the spread of the hemlock woolly adelgid, currently affecting Eastern Hemlock trees across North America. When the pesticide is sprayed directly onto soil around infested trees (soil drenching), it can run off into aquatic systems, with potential negative effects on biota. Simultaneously, climate change may lead to faster pool drying, which acts as an additional stressor for sensitive species such as amphibians. We evaluated the sublethal effects of imidacloprid (10 ppb), and interaction with shorter hydroperiods on the larval behavior, growth, and survival of a model organism, the wood frog (Rana sylvatica). We performed 3 behavioral experiments evaluating swimming speed, time spent swimming, and distance the larvae swam. We found that larvae raised in 10 ppb imidacloprid or shorter hydroperiod did not differ in their swimming time, distance, and speed from nonexposed larvae. Naïve larvae exposed for 20 min to 10‐ to 500‐ppb concentrations also showed similar performance to nonexposed larvae. However, when we applied a stimulus halfway through each experiment, we found that larvae exposed to 10 ppb imidacloprid (short and long term) swam shorter distances and spent less time swimming, suggesting that imidacloprid exposure may slow reaction time, potentially increasing the risk of predation. To minimize impacts on pool‐breeding amphibians, imidacloprid application to combat the invasive hemlock woolly adelgid should use trunk injection and avoid soil drenching. Environ Toxicol Chem 2021;40:1840–1849. © 2021 SETAC [ABSTRACT FROM AUTHOR]

Eastern hemlock (Tsuga canadensis [L.] Carrière) is an important component of the riparian ecosystem. Due to the widespread establishment of hemlock woolly adelgid (Adelges tsugae Annand)(HWA) across the range of eastern hemlock, woodland trees may be infested for extended periods (years), resulting in their decline. Imidacloprid, a systemic neonicotinoid insecticide, may be used as a strategy in forested settings to manage HWA while more long-term solutions become established, such as biological controls. Symptoms of prolonged infestation include extensive dieback and thinned canopies. In this study, trees with a diameter at breast height (DBH) of 24.7 ± 2.7 SD cm in poor condition were treated with imidacloprid. Trees were treated once by trunk-injection (IMA-jet) or by soil drench in the Greenbrier area of the Great Smoky Mountains National Park, Gatlinburg, TN, USA. Changes in tree growth and HWA density were measured for 3 consecutive years. Imidaclopridtreated trees recovered, whereas the untreated trees declined. Imidacloprid treatments resulted in significantly higher 3-year mean percent growth (65.6% to 71.7% of tips) compared to the untreated controls (10.5% of tips). HWA density 3-year means in the imidacloprid-treated trees (0.10 to 1.09 per cm) likewise were statistically different to the untreated trees (2.72 per cm). The extended activity of imidacloprid-treated hemlock was attributed to storage in the symplast (xylem ray parenchyma) and to perennial needle retention. This study demonstrates that trunk-injection with IMA-jet is effective against HWA and comparable with soil drench to protect trees in the long term (≥ 4 years). [ABSTRACT FROM AUTHOR]

The hemlock woolly adelgid (Adelges tsugae Annand - HWA) is invasive in eastern North America where it causes extensive mortality to hemlock communities. The future of these communities under projected climate change is an issue of landscape ecological interest and speculation. We employed the MaxEnt algorithm with the random subset feature selection algorithm (RSFSA) in creating HWA niche models. Final models were ensembles of 12 statistically best models with six predictors each. Out of 119 climatic, topographic, and soil variables, 42 were used in at least one final model. Soil features, followed by climate and topographic features, were most common in selected models. The three most important variables among all models were November potential evapotranspiration, slope, and percent Ochrepts soil. The potential distributions of HWA within eastern North America were projected under historical and four future climate scenarios for 2050 and 2070 under low and high CO2 emissions. The mean of the minimum values for the minimum temperature of the coldest month from the 12 MaxEnt model projections in eastern North America was -15.8°C. This value was close to -15°C, the extreme minimum temperature found for both HWA occurrence points and previously reported HWA cold temperature limits. These results indicate that HWA may be close to equilibrium distribution in eastern North America under current climate. We also reverse-casted the eastern North American MaxEnt model back onto the HWA native ranges in eastern Asia and western North America. The projections match best with native ranges in Asian islands, such as Japan, and the Cascade Mountains in western North America. Statistically significant HWA range shifts of 221-468 km northwards and 110-164 km eastwards were projected by the 12 models for 2050-2070. The 2070 high CO2 emission scenario models projects HWA suitability throughout most of the northern range of eastern hemlock. [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]

The spread of invasive species can have far-reaching environmental and ecological consequences. Understanding invasion spread patterns and the underlying process driving invasions are key to predicting and managing invasions. We combine a set of statistical methods in a novelway to characterize local spread properties and demonstrate their application using simulated and historical data on invasive insects. Our method uses a Gaussian process fit to the surface of waiting times to invasion in order to characterize the vector field of spread. Using this method, we estimate with statistical uncertainties the speed and direction of spread at each location. Simulations from a stratified diffusion model verify the accuracy of our method. We show how we may link local rates of spread to environmental covariates for two case studies: the spread of the gypsy moth (Lymantria dispar), and hemlock woolly adelgid (Adelges tsugae) in North America. We provide an R-package that automates the calculations for any spatially referenced waiting time data. [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]

Exploring genetic diversity within species of biological control agents can expose previously overlooked beneficial genotypes. This may be the case for two species of silver flies, Leucopis argenticollis and L. piniperda , predators of the hemlock woolly adelgid ( Adelges tsugae ) in the Pacific Northwest of North America. The same Leucopis species occur in eastern North America, where they feed on other adelgid species, but not on hemlock woolly adelgid, which became a pest in the region after its introduction from Japan earlier this century. We collected DNA sequence data from one mitochondrial and two nuclear genes for 606 Leucopis individuals to examine variation correlated with geographic origin and prey association. Specimens of L. argenticollis and L. piniperda collected from adelgids on hemlock and spruce in the West are phylogenetically divergent from conspecifics collected from adelgids on pine and spruce in the East. These results suggest that within each species, there are distinct lineages that specialize on different adelgid prey on different hosts in western versus eastern North America. The western lineages appear to be strong candidates for enhancing biological control of Japanese hemlock woolly adelgid in the eastern United States, given their widespread occurrence on western hemlock woolly adelgid in the Pacific Northwest, and the absence of these genotypes in the East. We also developed a PCR-RFLP assay based on the mitochondrial COI gene as an inexpensive and reliable way to distinguish the four genetic groups to document establishment and impact following release. [ABSTRACT FROM AUTHOR]

Abstract: A species’ distribution and abundance are determined by abiotic conditions and biotic interactions with other species in the community. Most species distribution models correlate the occurrence of a single species with environmental variables only, and leave out biotic interactions. To test the importance of biotic interactions on occurrence and abundance, we compared a multivariate spatiotemporal model of the joint abundance of two invasive insects that share a host plant, hemlock woolly adelgid (HWA; Adelges tsugae) and elongate hemlock scale (EHS; Fiorina externa), to independent models that do not account for dependence among co‐occurring species. The joint model revealed that HWA responded more strongly to abiotic conditions than EHS. Additionally, HWA appeared to predispose stands to subsequent increase of EHS, but HWA abundance was not strongly dependent on EHS abundance. This study demonstrates how incorporating spatial and temporal dependence into a species distribution model can reveal the dependence of a species’ abundance on other species in the community. Accounting for dependence among co‐occurring species with a joint distribution model can also improve estimation of the abiotic niche for species affected by interspecific interactions. [ABSTRACT FROM AUTHOR]

Hemlock woolly adelgid (Adelges tsugae Annand) (HWA) is an invasive insect that feeds upon the foliage of eastern hemlock (Tsuga canadensis (L.) Carrière) trees, leading to a decline in health and often mortality. The exact mechanism leading to the demise of eastern hemlocks remains uncertain because little is known about how HWA infestation directly alters the host's physiology. To evaluate the physiological responses of eastern hemlock during early infestation of HWA, we measured needle loss, xylem hydraulic conductivity, vulnerability to cavitation, tracheid anatomy, leaf-level gas exchange, leaf water potential and foliar cation and nutrient levels on HWA-infested and noninfested even-aged trees in an experimental garden. HWA infestation resulted in higher xylem hydraulic conductivity correlated with an increase in average tracheid lumen area and no difference in vulnerability to cavitation, indicating that needle loss associated with HWA infestation could not be attributed to reduced xylem transport capacity. HWA-infested trees exhibited higher rates of net photosynthesis and significant changes in foliar nutrient partitioning, but showed no differences in branch increment growth rates compared with noninfested trees. This study suggests that HWA-induced decline in the health of eastern hemlock trees is not initially caused by compromised water relations or needle loss. [ABSTRACT FROM AUTHOR]

Forest pests drive tree mortality through disruption of functional traits linked to nutrient acquisition, growth and reproduction. The impacts of attack by individual or multiple above-ground herbivores on root functional traits critical to tree health have received little attention. This is especially true for exotic herbivores, organisms often found in disturbed forests., We excavated whole-root systems from eastern hemlock ( Tsuga canadensis) individuals experimentally infested with hemlock woolly adelgid ( HWA: Adelges tsugae) and elongate hemlock scale ( EHS: Fiorina externa) individually, or in combination, for periods of 2 and 4 years. Below-ground root biomass, functional traits and storage nutrients were measured to assess impacts of herbivory. We also quantified ectomycorrhizal fungal ( EMF) colonisation of fine roots and used culture-independent methods to examine EMF diversity., Trees infested with HWA had a greater root mass fraction (root to total biomass ratio), although feeding had no observable effects on root functional traits (e.g. specific root length) or on resource allocation to roots. HWA feeding did significantly reduce EMF colonisation of hemlock fine roots, though surprisingly, EMF diversity and that of other fungal associates were unaffected. In contrast to HWA, EHS (alone or in conjunction with HWA) feeding had no observable effect on below-ground traits or EMF colonisation alone; however, its presence mediated HWA effects when trees were co-infested. Simultaneous infestation within the same year yielded significant reductions in EMF colonisation, whereas prior EHS attack weakened HWA effects., Our results collectively suggest that prior EHS attack dampens the impact of HWA on below-ground functional traits. This highlights how the timing and sequence of herbivore arrival can alter plant-mediated interactions between herbivores and their effects on above-below-ground linkages and associated tree health., A is available for this article. [ABSTRACT FROM AUTHOR]

The isolated effects of a single insecticide can be difficult to assess in natural settings because of the presence of numerous pollutants in many watersheds. Imidacloprid use for suppressing hemlock woolly adelgid, Adelges tsugae (Annand) (Hemiptera: Adelgidae), in forests offers a rare opportunity to assess potential impacts on aquatic macroinvertebrates in relatively pristine landscapes. Aquatic macroinvertebrate communities were assessed in 9 streams in Great Smoky Mountains National Park (southern Appalachian Mountains, USA). The streams flow through hemlock conservation areas where imidacloprid soil drench treatments were applied for hemlock woolly adelgid suppression. Sites were located upstream and downstream of the imidacloprid treatments. Baseline species presence data (pre-imidacloprid treatment) were available from previous sample collections at downstream sites. Downstream and upstream sites did not vary in numerous community measures. Although comparisons of paired upstream and downstream sites showed differences in diversity in 7 streams, higher diversity was found more often in downstream sites. Macroinvertebrate functional feeding groups and life habits were similar between downstream and upstream sites. Downstream and baseline stream samples were similar. While some functional feeding group and life habit species richness categories varied, variations did not indicate poorer quality downstream communities. Imidacloprid treatments applied according to US Environmental Protection Agency federal restrictions did not result in negative effects to aquatic macroinvertebrate communities, which indicates that risks of imidacloprid use in forest settings are low. Environ Toxicol Chem 2017;36:3108-3119. © 2017 SETAC [ABSTRACT FROM AUTHOR]

Leucopis argenticollis (Zetterstedt) and Leucopis piniperda (Malloch) are known to feed on the lineage of Adelges tsugae Annand that is native to western North America, but it is not known if they will survive on the lineage that was introduced from Japan to the eastern USA. In 2014, western Leucopis spp. larvae were brought to the laboratory and placed on A. tsugae collected in either Washington (North American A. tsugae lineage) or Connecticut (Japanese lineage). There were no significant differences in survival or developmental times between flies reared on the two different adelgid lineages. In 2015 and 2016, western Leucopis spp. adults were released at two different densities onto enclosed branches of A. tsugae infested eastern hemlock (Tsuga canadensis (L.) Carr.) in Tennessee and New York. Cages were recovered and their contents examined 4 weeks after release at each location. Leucopis spp. larvae and puparia of the F1 generation were recovered at both release locations and adults of the F1 generation were collected at the Tennessee location. The number of Leucopis spp. offspring collected increased with increasing adelgid density, but did not differ by the number of adult flies released. Flies recovered from cages and flies collected from the source colony were identified as L.argenticollis and L. piniperda using DNA barcoding. These results demonstrate that Leucopis spp. from the Pacific Northwest are capable of feeding and developing to the adult stage on A. tsugae in the eastern USA and they are able to tolerate environmental conditions during late spring and early summer at the southern and northern extent of the area invaded by A. tsugae in the eastern USA. [ABSTRACT FROM PUBLISHER]

Parthenogenetic reproduction is generally associated with low genetic variance and therefore reduced ability for environmental adaptation, and this could limit the potential invasiveness of introduced species that reproduce asexually. However, the hemlock woolly adelgid is an asexual invasive insect that has spread across a large geographic temperature gradient in its introduced range. Consequently, this insect has shown significant variation in cold hardiness among populations. We hypothesized that the increased cold hardiness of northern populations represents an adaptation to the colder temperatures. To test this, we collected individual adelgid from populations spanning their invaded range and inoculated them into a common thermal environment. We then experimentally sampled the supercooling point of the progeny of these adelgids and compared these results with tests of the supercooling point of adelgid sampled directly from their source populations. The results showed that the same significant differences in supercooling that was found among geographically distinct populations existed even when the adelgid was reared in a common environment, indicating a genetic basis for the variation in cold hardiness. These findings support the hypothesis that the adelgid has adapted to the colder environment as it has expanded its distribution in its invaded range. [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]

First-instar hemlock woolly adelgid Adelges tsugae nymphs were observed on eastern hemlock Tsuga canadensis in Blount County, Tennessee, 3 months earlier than all previous worldwide accounts and during the warmest recorded December (2015) in North America., Subsequent quantification of maturing nymphs, adults and egg-laying adults, followed by the hatching and development of first-instar nymphs into egg-laying adults and implantation of their offspring, indicates newly documented, early A. tsugae reproduction in Blount and Knox Counties, Tennessee, shifted in time and with life stages overlapping within an earlier and shorter window., Warm winter temperatures may accelerate the A. tsugae life cycle, contributing offspring to A. tsugae populations outside of recognized cycles and possibly confounding management., Historic warm winter temperatures throughout the introduced range of A. tsugae in eastern North America may have contributed to its escalation from 'introduced' to 'invasive'. [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]

Hemlock Woolly Adelgid (HWA) is a devastating non-native pest of North American Tsuga canadensis (Eastern Hemlock) and Tsuga caroliniana (Carolina Hemlock). I analyzed 15 years of data collected during the period 2000–2015 to determine important winter variables influencing HWA mortality in the 3 Connecticut climatic divisions. Absolute minimum daily winter temperature, the number of subzero days (temperature drops below -17.8 °C [0 °F]), and a new interaction variable—negative degree days (NDD)—were identified as significant predictors of HWA winter mortality. The absolute minimum daily winter temperature was the most critical factor. Minimum daily winter temperatures of -24 °C, 5.5 subzero days, and -130 NDD in Division 1(Northwest); -22.4 °C, 6 subzero days, and -100 NDD in Division 2 (Central); and -21.2 °C, 2.6 subzero days, and -45 NDD in Division 3 (Coastal) resulted in 90% HWA mortality. Patterns of HWA winter mortality in coastal Division 3 were distinct from the interior and suggest cold adaptation in northern interior populations. Recent, consecutive, arctic cold air outbreaks associated with weak polar vortex events have greatly reduced HWA populations statewide, with implications for the survival, spread, and control of HWA in the northeastern US. [ABSTRACT FROM AUTHOR]

Stand thinning is being tested as a means to limit the impacts of the invasive hemlock woolly adelgid (HWA; Adelges tsugae Annand) on eastern hemlock ( Tsuga canadensis (L.) Carriere). The efficacy of this strategy may be reduced if thinning increases hemlock foliar nutrients because HWA densities are correlated with foliar concentrations of N, P, K, Ca, and Mn. We determined foliar N, P, K, Ca, and Mn concentrations in 1-year-old and all other (older) needles prior to and for 4 years after thinning in northwestern Pennsylvania stands of eastern hemlock without HWA. Average foliar concentrations in 1-year-old needles were 1.30-1.80 g N·100 g−1, 1300-1700 mg P·kg−1, 4200-6300 mg K·kg−1, 2500-5200 mg Ca·kg−1, and 2393 μg Mn·g−1. N, P, and K decreased, Ca increased, and Mn first increased and then stabilized. Thinning by itself did not affect the tested foliar nutrients. The interaction between treatment and year was significant and evident in temporal trajectories of foliar N and K. However, the differences between thinned and unthinned plots within years averaged only 0.03 g N·100 g−1 and 340 mg K·kg−1. We concluded that even though thinning changed the temporal trajectories of foliar N and K, the nutritional shifts were minimal, brief, and unlikely to affect the efficacy of thinning in limiting the impacts of HWA. [ABSTRACT FROM AUTHOR]

Systemic imidacloprid is the most widely used insecticide to control the hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), an exotic pest of eastern hemlock, Tsuga canadensis (L.) Carriére in the United States. This study was conducted to 1) determine the effect of treatment timing (spring vs. fall) and application method (trunk injection vs. soil injection) on the spatial and temporal distribution of imidacloprid within the crown of A. tsugae-free eastern hemlock using a competitive enzyme-linked immunosorbent assay (ELISA), 2) compare ELISA to gas chromatography-mass spectrometry (GC/MS) for the detection of imidacloprid in xylem fluid, and 3) determine the concentration of imidacloprid in leaf tissue using high performance liquid chromatography with tandem mass spectrometric (LC/MS/MS) detection methods. Xylem fluid concentrations of imidacloprid were found to be significantly higher for spring applications than for fall applications and for trunk injections than soil injections in the first year posttreatment. A total of 69% of samples analyzed by ELISA gave 1.8 times higher concentrations of imidacloprid than those found by GC/MS, leading to evidence of a matrix effect and overestimation of imidacloprid in xylem fluid by ELISA. A comparison of the presence of imidacloprid with xylem fluid and in leaf tissue on the same branch showed significant differences, suggesting that imidacloprid moved intermittently within the crown of eastern hemlock. [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]

We analyzed data from a woodland site for a 59-year period to determine whether changes in bird populations are related to changes in the diversity and relative abundance of woody plant species even when vegetation structure, degree of forest fragmentation in the surrounding landscape, and regional changes in bird populations are taken into account. Principal component analyses generated vegetation factors encompassing variables such as total basal area, shrub density, basal area of common tree species, and measures of tree and shrub species diversity. We also calculated a forest edge/forest area index based on GIS analysis of the landscape within 2 km of the study site. Poisson regression models revealed relationships between these covariates and population changes for 19 bird species and for seven groups of species characterized by similar migration strategies or habitat requirements. All groups of habitat specialists showed a positive relationship with the first vegetation factor, which indicates that they declined as total basal area and dominance of oaks and maples increased and as tree and shrub diversity decreased. This suggests that floristic diversity may be important for determining habitat quality. Bird species associated with the shrub layer and with hemlock stands showed positive relationships with the second vegetation factor, suggesting that the recent decline in eastern hemlocks ( Tsuga canadensis) because of hemlock woolly adelgid ( Adelges tsugae) had an adverse impact on these species. Forest migrants, shrub-layer specialists, long-distance migrants and permanent residents showed negative relationships with the forest edge/forest interior index, indicating that conservation efforts to protect bird communities should take the wider landscape into account. The strongest relationship for most species and species groups was with the first vegetation factor, which suggests that species composition and diversity of trees and shrubs may be especially important in determining abundance of many forest bird species. [ABSTRACT FROM AUTHOR]

Seven species of hemlock (Tsuga spp.)--four from North America and three from Asia--were evaluated in replicated plots in Katonah, New York, United States (USDA Plant Hardiness Zone 6b) as potential replacements for eastern hemlock (Tsuga canadensis), which is gradually being extirpated from landscapes in the eastern United States. by the invasive hemlock woolly adelgid (Adelges tsugae). Trends reported in an earlier study (Weston and Harper 2009) continued but were exaggerated after an additional three years of observation. For example, Chinese hemlock (T. chinensis) continued to show the greatest potential as a replacement for T. canadensis as mortality was very low, overall plant health was exceptional, and tolerance to A. tsugae was robust. Early indicators suggest that T. chinensis may also be readily propagated from hardwood cuttings under appropriate greenhouse conditions. These characteristics suggest that T. chinensis may indeed become a viable replacement for T. canadensis, and a valuable addition to landscapes in the eastern U.S. [ABSTRACT FROM AUTHOR]

An aerial spray deposition project was designed to evaluate aerial application to an eastern hemlock (Tsuga canadensis) canopy to combat hemlock woolly adelgid (Adelges tsugae). This adelgid, residing in the forest canopy at the nodes of branchlets, offers a difficult target. The study collected 1840 deposition samples on live and artificial collectors (not including auxiliary studies) positioned to evaluate canopy penetration of spray applied from above the canopy by helicopter. The results of the study show that canopy penetration is achieved with 3% to 8% of applied material (corrected for foliar area) deposited on the lowest samplers and 6% to 12% deposited on samplers positioned in hard-to-reach locations in the mid-canopy. The study also suggests that it might not be necessary to apply as fine a droplet distribution (release DV0.5 values of 87 and 108 m are used in most of the trials described here) as originally thought to achieve coverage in this deep canopy. A second article will compare these data to existing models. [ABSTRACT FROM AUTHOR]

Adelges tsugae infested western hemlock trees were sampled periodically for 1 year at two locations in Oregon and Washington to compare the phenology and abundance of three associated predators (Leucopis argenticollis, Leucopis piniperda, and Laricobius nigrinus) and their host. On each sample date, two 3–10 cm long terminal twigs were collected from each tree and brought to the laboratory to count all life stages of A. tsugae and the three predators. Peak larval abundance of Leucopis spp. and La. nigrinus coincided with the presence of A. tsugae adults and eggs. Leucopis spp. larvae were present for a much longer period of time than were La. nigrinus larvae. Furthermore, Leucopis spp. larvae were present during both the progrediens and sistens egg stages, while La. nigrinus larvae were only present during the progrediens egg stage. Overall, we collected 2.3–3.5 times more Leucopis spp. of all life stages than La. nigrinus. These results support the continued study of Leucopis spp. from the Pacific Northwest as biological control agents for A. tsugae in the Eastern USA. [ABSTRACT FROM AUTHOR]

Tsuga canadensis (Eastern Hemlock) and T. caroliniana (Carolina Hemlock) are important components of western North Carolina forests. The invasive Adelges tsugae (Hemlock Woolly Adelgid [HWA]) was first reported in NC in 1995, and by 2007 the entire range of hemlock in the state was infested. An examination of the Forest Inventory and Analysis (FIA) program data for FIA Unit 4 (21 mountainous counties in western North Carolina), looking at remeasured trees for the time period 1999-2013, demonstrated that diameter net growth of hemlock decreased and mortality increased with increasing duration of HWA infestation. Hemlock trees in this study had a ∼50% chance of survival after 12 years of confirmed HWA infestation in the county where they occur, and growth of surviving trees was reduced by ∼50% over the same time period. This study demonstrates the utility of FIA data for examining effects of an introduced, invasive pest on tree growth and mortality over a relatively small area. Some advantages and limitations to our approach are discussed. [ABSTRACT FROM AUTHOR]

Hemlock woolly adelgid, Adelges tsugae, is an invasive pest of hemlock trees ( Tsuga) in eastern North America. We used 14 microsatellites and mitochondrial COI sequences to assess its worldwide genetic structure and reconstruct its colonization history. The resulting information about its life cycle, biogeography and host specialization could help predict invasion by insect herbivores. We identified eight endemic lineages of hemlock adelgids in central China, western China, Ulleung Island (South Korea), western North America, and two each in Taiwan and Japan, with the Japanese lineages specializing on different Tsuga species. Adelgid life cycles varied at local and continental scales with different sexual, obligately asexual and facultatively asexual lineages. Adelgids in western North America exhibited very high microsatellite heterozygosity, which suggests ancient asexuality. The earliest lineages diverged in Asia during Pleistocene glacial periods, as estimated using approximate Bayesian computation. Colonization of western North America was estimated to have occurred prior to the last glacial period by adelgids directly ancestral to those in southern Japan, perhaps carried by birds. The modern invasion from southern Japan to eastern North America caused an extreme genetic bottleneck with just two closely related clones detected throughout the introduced range. Both colonization events to North America involved host shifts to unrelated hemlock species. These results suggest that genetic diversity, host specialization and host phylogeny are not predictive of adelgid invasion. Monitoring non-native sentinel host trees and focusing on invasion pathways might be more effective methods of preventing invasion than making predictions using species traits or evolutionary history. [ABSTRACT FROM AUTHOR]

During the last century, the eastern United States has functionally lost two major tree species (American chestnut and American elm), two more, eastern and Carolina hemlock, will likely be functionally extinct during much of their ranges by 2050. Carolina hemlock forests are geographically limited to high elevations in the southern Appalachian Mountains and are considered to be endangered. We collected forest stand, composition, and tree age data at the beginning of a hemlock woolly adelgid (HWA) infestation. Prior to the arrival of HWA, Carolina hemlocks were healthy and densely populated in the overstory and understory. While Carolina hemlock regenerated successfully and continuously from 1850 to 2010, the development of this Carolina hemlock forest will be altered by the HWA and may result in an increase in the density of northern red oak, white oak, mountain laurel, and Catawba rhododendron. Carolina hemlocks prefer cool, wet summers with older trees experiencing greater reductions in radial growth than younger trees during droughts. This study demonstrates that dendrochronological techniques can provide critical annual information on Carolina hemlock forest development and tree age-climate response. Our results provide a multicentury perspective for conservation efforts and management of Carolina hemlock forests in the southern Appalachian Mountains. [ABSTRACT FROM AUTHOR]

Hemlock woolly adelgid (Adelges tsugae Annand, HWA) is an introduced invasive forest pest in eastern North America. Herbivory by this insect results in mortality to eastern hemlock (Tsuga canadensis L. Carr.) and Carolina hemlock (Tsuga caroliniana Engelm.). These species occur in landscapes where extreme topographic variation is common. The vegetation communities within these landscapes feature high diversity of tree species, including several other conifer species. Traditional forest inventory procedures and insect pest detection methods within these limited-access landscapes are impractical. However, further information is needed to evaluate the impacts of HWA-induced hemlock mortality. Accordingly, our goal was to develop a semi-automatic method for mapping patches of coniferous tree species that include the living hemlock component and tree mortality by the HWA using aerial images and LiDAR (light detection and ranging) to increase our understanding of the severity and pattern of hemlock decline. The study was conducted in the Linville River Gorge in the Southern Appalachians of western North Carolina, USA. The mapping task included a two-phase approach: decision-tree and support vector machine classifications. We found that about 2% of the forest canopy surface was covered by dead trees and 43% by coniferous tree species. A large portion of the forest canopy surface (over 55%) was covered by deciduous tree species. The resulting maps provide a means for evaluating the impact of HWA herbivory, since this insect was the only significant coniferous mortality agent present within the study site. [ABSTRACT FROM AUTHOR]

The hemlock woolly adelgid (HWA) ( Adelges tsugae Annand) is an invasive insect in the eastern United States. Since its initial detection in Richmond, Virginia, in 1951, HWA has spread to half of the eastern hemlock ( Tsuga canadensis (L.) Carr.) natural range. Detection of early infestation symptoms via remote sensing requires the knowledge of the changes in reflectance resulting from physiological changes in the host as inflicted by the insect and the selection of equipment with the appropriate sensor characteristics. Laboratory-based reflectance measurements of infested and non-infested hemlock foliage collected from four sites in southern New Hampshire and Maine occurred biweekly over 6 months in 2012 and weekly over 5 weeks in 2013. Vegetation indices (red edge inflection point (REIP), normalized difference vegetation index (NDVI), moisture stress index (MSI), and near infrared (NIR) 3/1 ratio) were associated with concurrent chlorophyll and moisture content data. Infested first-year foliage contained greater concentrations of chlorophyll and moisture, resulting in reduced visible spectral reflectance, greater REIP and NDVI values, and lower MSI and NIR 3/1 values than non-infested foliage. Furthermore, fluorescence measurements indicated greater photosystem function during the early stages of infestation, suggesting a possible compensatory response by hemlock to infestation. Significant differences in reflectance between infested and non-infested foliage were observed in late June and July in the weeks immediately following HWA settlement on new growth. Implementing these observations during remote sensing mission planning may increase the likelihood of detecting early HWA infestation symptoms at landscape scales. [ABSTRACT FROM AUTHOR]

Tsuga chinensis Franch. is described and illustrated here and details of its distribution and habitat are also provided. Its history in cultivation and its resistance to the woolly adelgid, ( Adelges tsugae) which is so damaging to T. canadensis in North America, are discussed. [ABSTRACT FROM AUTHOR]

Large-scale delimiting surveys are critical for detecting pest invasions and often undertaken at different governance levels. In this study, we consider two-level hierarchical planning of surveys of harmful invasive pests including a government agency with a mandate to report the spatial extent of an invasion, and regional governments (counties) concerned about the possible threat of an outbreak. The central agency plans delimiting pest surveys across multiple administrative subdivisions. Counties could participate in these surveys if funds become available. Our goal is to find the optimal levels of cooperation between the central agency and regional governments in the form of the central agency sharing funds with regional governments in a way that benefits both it and the other entities. We propose a Stackelberg game model that finds optimal levels of collaboration between two levels of government in large-scale pest survey campaigns. We apply the model to surveillance of hemlock woolly adelgid, a harmful pest of hemlock trees in Ontario, Canada. Our solutions help anticipate the underperformance of surveys conducted by regional governments because their goals do not fully align with the central agency survey objective. The methodology can be adapted to explore governance hierarchies in other regions and political jurisdictions. • We find optimal levels of cooperation between two levels of governments in pest survey campaigns. • Our model finds optimal cost-sharing strategy between a biosecurity agency and regional governments. • We demonstrate the approach for delimiting surveys of hemlock woolly adelgid in Ontario, Canada. • The approach can be adapted to improve a governance of biosecurity projects in other regions. [ABSTRACT FROM AUTHOR]

In 2003,Laricobius nigrinusFender was introduced into the eastern United States as a biological control agent of the hemlock woolly adelgid (Adelges tsugaeAnnand). Following its release, it was discovered thatL. nigrinuswas hybridising and producing viable progeny withLaricobius rubidusLeConte, a species native to eastern North America. Recently,Laricobius osakensisMontgomery and Shiyake was imported from Japan into the USA as a potential biological control agent of hemlock woolly adelgid. Hybridisation betweenL. nigrinusandL. rubidusled to interest in the outcome of interactions betweenL. osakensisand the other twoLaricobiusspp. The purpose of this study was to determine ifL. osakensiscould mate withL. nigrinus, if they could produce hybrid progeny, and whether mating interferes with reproductive output.Laricobiusspp. were observed mating directly following emergence and found to be capable of producing sterile eggs in the absence of a mating event. Laboratory and confined field studies found no evidence thatL. osakensisandL. nigrinuscould produce hybrid progeny and the interaction between the two species did not result in a lower reproduction associated with interspecific mating attempts. Interbreeding should therefore not have an impact on biological control using these species. Fecundity experiments showed thatL. osakensisproduced eggs earlier in the season and at a higher rate thanL. nigrinus, suggesting thatL. osakensismay have the potential to be an even more successful biological control agent thanL. nigrinus. [ABSTRACT FROM AUTHOR]

The article presents an in-depth exploration of environmental conservation efforts to protect eastern hemlock trees from the invasive insect species Adelges tsugae, or the hemlock wolly adelgid. Topics addressed include a profile of the features and ecology of the eastern hemlock, description of how the pest damages and eventually kills the tree, and the efforts of several forestry scientists such as Jesse Webster and Will Blozan, to prevent further damage.

Quantifying economic damages caused by invasive species is crucial for cost-benefit analyses of biosecurity measures. Most studies focus on short-term damage estimates, but evaluating exclusion or prevention measures requires estimates of total anticipated damages from the time of establishment onward. The magnitude of such damages critically depends on the timing of damages relative to a species' arrival because costs are discounted back to the time of establishment. Using theoretical simulations, we illustrate how (ceteris paribus) total long-term damages, and hence the benefits of prevention efforts, are greater for species that a) have short lags between introduction and spread or between arrival at a location and initiation of damages, b) cause larger, short-lived damages (as opposed to smaller, persistent damages), and c) spread faster or earlier. We empirically estimate total long-term discounted impacts for three forest pests currently invading North America — gypsy moth ( Lymantria dispar ), hemlock woolly adelgid ( Adelges tsugae ), and emerald ash borer ( Agrilus planipennis ) — and discuss how damage persistence, lags between introduction and spread, and spread rates affect damages. Many temporal characteristics can be predicted for new invaders and should be considered in species risk analyses and economic evaluations of quarantine and eradication programs. [ABSTRACT FROM AUTHOR]

Two adelgid predators, Laricobius nigrinus Fender and Laricobius rubidus LeConte, were recently discovered to produce hybrid progeny in the eastern United States. L. rubidus is native to eastern North America where it feeds on pine bark adelgid ( Pineus strobi Hartig) and L. nigrinus is native to western North America and was introduced to the eastern United States in 2003 for biological control of hemlock woolly adelgid ( Adelges tsugae Annand). Currently, L. nigrinus and L. rubidus form a mosaic of hybrid zones throughout the eastern United States. It is not known whether these zones will be maintained over time and whether hybridization will impact the efficacy of biological control or result in displacement of L. rubidus . Sampling from 2007 to 2012 on eastern hemlock ( Tsuga canadensis Carrière) showed a clear increase in L. nigrinus , a decrease in L. rubidus , and a steady proportion of hybrids. Sampling from 2010 to 2012 on both eastern hemlock and white pine ( Pinus strobus L.) at ten sites showed that L. nigrinus was more dominant on hemlock and L. rubidus was more dominant on white pine, which may demonstrate habitat preference and promote segregation between the two species. Site factors were tested for a relationship with the proportion of hybrids. The number of years L. nigrinus had been present at the site was the only factor that showed a relationship. The results suggest that L. nigrinus may displace L. rubidus on hemlock, but not on white pine at sites where they are both present. [ABSTRACT FROM AUTHOR]

The systemic insecticide imidacloprid is commonly used to protect trees against attack by the Adelges tsugae (Hemlock Woolly Adelgid [HWA]), an invasive pest that threatens Tsuga canadensis (Eastern Hemlock) and T. caroliniana (Carolina Hemlock) in eastern North America. Although there have been some studies documenting the short-term (1-3 years) impact of imidacloprid on non-target arthropods in hemlock systems, almost nothing is known about the impact over longer time scales. Here, using a set of trees which were experimentally treated 3 and 9 years prior to this study, we found that while the impact of imidacloprid on HWA may be approaching the limits of detection and efficacy on trees treated 9 years ago, there is still an intermittently detectable impact on HWA density. Similarly, 9 years after application there is a subtle but detectable increase in arthropod richness and a shift in canopy-arthropod community composition. Results from the 3-year treated trees were, however, ambiguous, but may be the result of detectable cross-contamination of insecticide among trees. [ABSTRACT FROM AUTHOR]

Invasive insects may dramatically alter resource cycling and productivity in forest ecosystems. Yet, although responses of individual trees should both reflect and affect ecosystem-scale responses, relationships between physiological- and ecosystem-scale responses to invasive insects have not been extensively studied. To address this issue, we examined changes in soil nitrogen (N) cycling, N uptake and allocation, and needle biochemistry and physiology in eastern hemlock (Tsuga canadensis (L) Carr) saplings, associated with infestation by the hemlock woolly adelgid (HWA) (Adelges tsugae Annand), an invasive insect causing widespread decline of eastern hemlock in the eastern USA. Compared with uninfested saplings, infested saplings had soils that exhibited faster nitrification rates, and more needle 15N uptake, N and total protein concentrations. However, these variables did not clearly covary. Further, within infested saplings, needle N concentration did not vary with HWA density. Light-saturated net photosynthetic rates (Asat) declined by 42% as HWA density increased from 0 to 3 adelgids per needle, but did not vary with needle N concentration. Rather, Asat varied with stomatal conductance, which was highest at the lowest HWA density and accounted for 79% of the variation in Asat. Photosynthetic light response did not differ among HWA densities. Our results suggest that the effects of HWA infestation on soil N pools and fluxes, 15N uptake, needle N and protein concentrations, and needle physiology may not be tightly coupled under at least some conditions. This pattern may reflect direct effects of the HWA on N uptake by host trees, as well as effects of other scale-dependent factors, such as tree hydrology, affected by HWA activity. [ABSTRACT FROM AUTHOR]

Recent research describing host resistance of hemlocks to the lethal, invasive insect hemlock woolly adelgid has suggested that Chinese hemlock (Tsuga chinensis) may be a suitable pest-resistant urban landscape replacement for eastern hemlock (T. canadensis). Presented here are the research findings of an in situ field questionnaire survey and participant observations. The study's objective was to collect and evaluate arborists' and other horticulturists' perceptions and purchase preferences between eastern and Chinese hemlock to assess whether Chinese hemlock has potential to be accepted as an alternative landscape replacement for eastern hemlock. Fifty-five participants visually inspected both hemlock specimens and responded to questions about which one they would prefer to purchase, what their preferences would be in light of potential insect resistance, and the likelihood of fewer insecticide applications being required. Multiple cross-tabulations indicated that there was no statistical association (Fisher's Exact Test, P > 0.05) between participant background (i.e., arborists versus others) and questions related to general purchase preference, and purchase preference if a specimen exhibited natural pest resistance or required less pesticides. Over three-quarters of participants were more inclined to purchase the specimen that possessed resistance to a serious pest. These findings suggest that Chinese hemlock may potentially serve as a hemlock woolly adelgid-resistant alternative to eastern hemlock in the landscape. [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]

Populations of Tsuga canadensis (Eastern Hemlock) and Tsuga caroliniana (Carolina Hemlock) are declining due to infestation by Adelges tsugae (Hemlock Woolly Adelgid), an exotic insect pest. A better understanding of the environmental conditions required for seed germination is needed to more efficiently utilize the seeds collected for genetic-resource conservation and the establishment of seed orchards. This study examined the effect of cold-moist stratification treatments of varying duration (0, 1,15, 30, 60, 90, and 120 days) on total germination (%) and the number of days to first and peak germination (germination speed) on seeds of both species in experiments conducted at 22 °C and 16 h:8 h, light:dark photoperiod. Overall total germination for Eastern Hemlock was 33.3% and increased with increasing duration of the stratification treatments. Carolina Hemlock total germination was 17.1% and varied little among the treatments, although fewer seeds tended to germinate following longer durations of stratification. Stratification increased germination speed of Eastern Hemlock but not Carolina Hemlock. The results indicate that Eastern Hemlock seeds should be cold-moist stratified at 4 °C for at least 30-60 days prior to sowing to promote higher total germination. Carolina Hemlock seeds can be sown directly following a 24-h soak with no additional cold-moist stratification. [ABSTRACT FROM AUTHOR]

In light of the increasing need for long-term, sustainable management for Adelges tsugae (Hemlock Woolly Adelgid), researchers are investigating host-plant resistance as part of an integrated approach to combat the pest. This paper reviews the progress made towards developing a resistant hemlock in the southern Appalachians and highlights the importance of investing research and development resources in this field. Along with describing inter- and intraspecific resistance in hemlocks, this paper reviews investigations into resistance mechanisms and outlines the many options for actions that could be or are being taken to increase resistance and restore hemlock forests. [ABSTRACT FROM AUTHOR]

Adelges tsugae (Hemlock Woolly Adelgid; HWA) is a non-native forest insect that causes defoliation and mortality of hemlock in the eastern US. We quantified the extent to which people are potentially affected by the spread of HWA infestation where they live and where they recreate. We also considered how these impacts might change through time using data from 2007, 2009, and 2011. The study area included hemlock stands in a 7500-km² region of central Connecticut and central Massachusetts. We used sample-plot data on live basal area and vigor of hemlock stands to interpolate hemlock health characteristics for all hemlock stands in the study area. We estimated a loss of property values in the region of approximately $24.6 million USD. This estimate was conservative because there were insufficient data to fully quantify the economic losses associated with the death of hemlock trees and the degradation of recreational opportunities. The spatial extent of the HWA infestation suggests that both of the latter categories of economic losses are likely substantial. These data can be used to consider the economic efficacy of actions taken to ameliorate the effects of the HWA infestation. [ABSTRACT FROM AUTHOR]

Laricobius osakensis (Coleoptera: Derodontidae) was imported from Japan to the United States in 2006 for study in quarantine facilities as a potential biological control of Hemlock Woolly Adelgid. Laricobius osakensis was released from quarantine in 2010, but it was soon discovered that the colony also contained a cryptic species, Laricobius naganoensis. This led to the placement of L. osakensis back into quarantine and development of a method to purify the colony. To distinguish the two species, we designed a restriction fragment length polymorphism (RFLP) assay using mitochondrial DNA sequences and developed a non-lethal testing method. Twenty-one diagnostic nucleotide sites separated the two species, and they both exhibited extraordinary intra-specific haplotype diversity. Sequencing the ITS2 nuclear region did not produce evidence of hybridization between the species in the field or in the lab colony. Splitting the colony into small groups and testing their species composition was successful in isolating L. osakensis. Efforts should be made to maintain high genetic diversity in L. osakensis colonies. Continued genotyping of new colony stock will be necessary to fully characterize the diversity within both species. [ABSTRACT FROM AUTHOR]

Adelges tsugae (Hemlock Woolly Adelgid [HWA]) is rapidly spreading across Kentucky, yet the potential effects on bird communities of the region are not known. We surveyed birds in Tsuga canadensis (Eastern Hemlock) and other forest types across the Appalachian mountain region of Kentucky during the early stages of infestation when HWA was absent from most sites. Based on associations between birds and forest types, we identified 4 bird species likely to be negatively affected by Eastern Hemlock decline. For one of these species, Setophaga virens (Black-throated Green Warbler), we used landscape metrics of forest composition to make predictions about the density of Eastern Hemlock necessary for persistence. This type of information can help managers establish control strategies for HWA. [ABSTRACT FROM AUTHOR]

The invasive insect pest Adelges tsugae (Hemlock Woolly Adelgid) threatens the ecologically unique Tsuga canadensis (Eastern Hemlock)-dominated forest type throughout its range. Relatively little is known about how the loss of this forest type will affect the relative abundance of amphibians. This study assessed the relative abundance of the juvenile phase of Notophthalmus viridescens viridescens (Eastern Red-spotted Newt, Red Eft) in Eastern Hemlock-dominated stands (n = 5) and mixed deciduous stands (n = 5) at Harvard Forest in Petersham, MA, using both transect surveys of the forest floor surface (n = 368 Red Eft observations over four seasons), and intensive searches of quadrats (n = 27 Red Eft observations over two seasons). Using data from transect surveys, the average relative abundance of Red Efts was more than two times greater in Eastern Hemlock-dominated stands than in mixed deciduous stands, however the differences were not statistically significant (P = 0.146). Quadrat surveys yielded relative abundance estimates for Red Efts that were more than 5 times greater in Eastern Hemlock-dominated stands than in mixed deciduous stands, but again the differences were not statistically significant (P = 0.213). [ABSTRACT FROM AUTHOR]