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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]

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

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 FROM AUTHOR]

Abstract: Laricobius nigrinus (Coleoptera: Derodontidae) was first collected near the coastal city of Victoria, British Columbia, Canada for release as a biological control agent to suppress tree-killing densities of hemlock woolly adelgid, Adelges tsugae (Hemiptera: Adelgidae), in the eastern United States. Beetles established in warm areas of the invaded range of A. tsugae, but had a low probability of establishment in cold areas. With the goal of locating beetles with greater cold-tolerance, we collected hundreds of adults in the northern Rocky Mountains. To support planned releases of these inland L. nigrinus, the cold tolerance of field-collected coastal (Seattle, WA) and inland (Coeur d’Alene and Moscow, ID) adults and climate match index scores (CLIMEX v.2) of these collection areas and parts of the eastern United States were compared. We found that individuals of inland L. nigrinus were more cold tolerant than those of coastal L. nigrinus, based on higher survival in a winter field cage study in Massachusetts and a lower supercooling point in a laboratory assay. Inland L. nigrinus also had higher survival than coastal L. nigrinus after an 18h exposure to sub-zero temperatures in another laboratory assay. Areas of the eastern United States infested with A. tsugae and receiving L. nigrinus releases matched the climate of Seattle and Coeur d’Alene reasonably well, but Coeur d’Alene had higher index values over a considerably larger area than Seattle. Accordingly, inland L. nigrinus appears preferable for release in the colder portions of A. tsugae’s invaded range in the eastern United States. [Copyright &y& Elsevier]

We studied the adult ambulatory response of the predator, Laricobius nigrinus Fender (Coleoptera: Derodontidae), to odors from its prey, Adelges tsugae Annand, the hemlock woolly adelgid, and foliage of hemlock woolly adelgid, host hemlocks (Tsuga spp.), and other conifers. Both the predator and hemlock woolly adelgid are apparently native to western North America, but the predator is being released in the eastern United States, which has different hemlock species, for biological control of a lineage of hemlock woolly adelgid inadvertently introduced from Japan. L. nigrinus responded to odors from hemlock woolly adelgid host trees, but not to odors from hemlock woolly adelgid. L. nigrinus collected from hemlock woolly adelgid-infested western hemlock were more strongly attracted to odors from western hemlock [Tsuga heterophylla (Rafinesque) Sargent] than eastern hemlock [Tsuga canadensis (L.) Carrière] in most trials. Odors from western white pine (Pinus monticola Douglas ex D. Don) and white spruce [Picea glauca (Moench) Voss] were as attractive as western hemlock odors whereas odors from Douglas-fir [Pseudotsuga menziesii variety menziesii (Mirbel)] and ponderosa pine (Pinus ponderosa Douglas ex Lawson) were avoided. L. nigrinus reared on hemlock woolly adelgid-infested eastern hemlock in the laboratory were lethargic and were not attracted to either eastern or western hemlock odors. Predators collected in the field and tested monthly from December to March responded similarly each month, except February, when they flew rather than walked in the olfactometer, suggesting a period of dispersal or mate finding at that time of year. The implications of these results for programs to release L. nigrinus in the eastern United States for control of hemlock woolly adelgid are discussed. [ABSTRACT FROM AUTHOR]

Hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), is an invasive pest of eastern hemlock (Tsuga canadensis (L.) Carrière) and Carolina hemlock (T. caroliniana Englem.) in eastern United States. Host-range tests for Laricobius osakensis Montgomery and Shiyake (Coleoptera: Derodontidae), imported from Japan, were conducted under quarantine in Blacksburg, VA, to determine the suitability of this predator as a biological control agent of A. tsugae. Host-range testing for L. osakensis, involved no-choice and paired choice feeding, oviposition, and development tests with A. tsugae, three other adelgids, and three nonadelgid species. L. osakensis fed and laid more eggs on A. tsugae over all the other host species. The difference was greater in paired-choice tests. L. osakensis completed development only on A. tsugae. The overall results of the host range study indicate that L. osakensis is a specific predator of A. tsugae, supporting its potential as a biological control agent, and is not a threat to nontarget species populations. [ABSTRACT FROM AUTHOR]

Rigorous assessments of the economic impacts of introduced species at broad spatial scales are required to provide credible information to policy makers. We propose that economic models of aggregate damages induced by biological invasions need to link microeconomic analyses of site-specific economic damages with spatial-dynamic models of value change associated with invasion spread across the macro-scale landscape. Recognizing that economic impacts of biological invasions occur where biological processes intersect the economic landscape, we define the area of economic damage (AED) as the sum of all areas on the physical landscape that sustain economic damage from a biological invasion. By subsuming fine-scale spatial dynamics in the AED measure, temporal dynamics of the AED can be estimated from an empirical distribution of the AED effective range radius over time. This methodology is illustrated using the case of a non-native forest pest, the hemlock woolly adelgid (HWA; Adelges tsugae). Geographic Information Systems and spatially referenced data provide the basis for statistical estimation of a spatial-dynamic value transfer model which indicates that HWA is annually causing millions of dollars of economic losses for residential property owners in the eastern United States. [Copyright &y& Elsevier]

The hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), native to western North America and Asia, was accidentally introduced from Japan to the eastern United States. To potentially establish biological control of A. tsugae, we released a predator endemic to western North America, Lavicobius nigrinus Fender (Coleoptera: Derodontidae), from 2003 to 2005, in 22 localities from Georgia to Massachusetts. Release sites spanned the invasive range of the adelgid across five United States Department of Agriculture plant hardiness zones (5a to 7a). Release sizes were 75, 150, 300, 600, or 1,200 adult L. nigrinus per site in the fall, winter, early spring, or sequentially (i.e., fall or winter and early spring). We monitored establishment by annual sampling for L. nigrinus adults with beat sheets and for L. nigrinus larvae by branch clipping. At the end of 3 yr, L. nigrinus was established in 13 of the 22 sites. The following variables were evaluated for their correlation with the numbers of L. nigrinus larvae and adults recovered and for their effect on establishment (scored as F3 presence/absence): (1) Minimum winter temperature at the release site, (2) A. tsugae density at the time of release, (3) release size, and (4) release season. Only minimum winter temperature was correlated with larval recoveries and no variables were correlated with adult recoveries. Logistic regression modeling found that establishment was positively related to minimum winter temperature and release size. We recommend smaller release sizes in warm areas where establishment probability was high (i.e., zones 7a, 6b, and 6a) and larger release sizes in cold areas where establishment probability was low (i.e., zones 5b and 5a). Releases during fall-early spring and across the range of A. tsugae densities tested were successful. [ABSTRACT FROM AUTHOR]

The hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera Adelgidae), is a major introduced pest of eastern hemlock, Tsuga canadensis (L.) Carrière. Hemlock woolly adelgid in the United States is anholocyclic and an obligate parthenogen, because no suitable primary host (on which sexual reproduction occurs in Asia) is reported for this adelgid in the United States. Allozyme analyses were conducted to assess the relatedness between three hemlock woolly adelgid populations in the eastern United States (Connecticut, New Jersey, and Virginia) and to compare them with adelgids from the western United States (Washington) and China. Significant hemlock woolly adelgid allozyme variation was found between nonadjacent trees within a site in the eastern United States. There was a small difference between the two northern and the southern populations despite the relative genetic uniformity between the sites across the allozyme loci evaluated. There were low numbers of protein alleles in the eastern populations, whereas the western and Chinese populations had additional alleles not found in the eastern populations. Both heterozygote excesses and deficits were detected as would be expected in populations that are not randomly mating. There were only a few abundant genotypes and they tended to be more homozygous than the rarer genotypes. The hemlock woolly adelgid population from China that is cyclically parthenogenic was more genetically diverse than the other hemlock woolly adelgid populations that are presumed to be obligately parthenogenic. Allozymes provide some useful information about genetic variation in hemlock woolly adelgid but seem to be less suited to assess actual genetic diversity and structure of populations because of the small size of the hemlock woolly adelgid. [ABSTRACT FROM AUTHOR]

Abstract: Carolina hemlock (Tsuga caroliniana Engelm.) is a rare endemic found in the Appalachian Mountains and Upper Piedmont of the southeastern United States. It is being decimated by the hemlock woolly adelgid (Adelges tsugae Annand), an exotic pest introduced into the region from Japan several decades ago. We examine ecological, genetic and climatic factors in natural stands that characterize the species’ occurrence to better determine where ex situ conservation plantings should be established. To facilitate species/site matching, we use FloraMap™ software that quantifies climatic variables at provenance collection sites to predict other areas where Carolina hemlock could be planted in the U.S. and Latin America. Results indicate that based on analysis of 15 populations, Carolina hemlock is found on predominantly sandy-clay loam soils but occurs on a wider range of soil textural groups than previously thought. Its natural occurrence represents two different climatic groups, with the Cradle of Forestry, NC site most different than the rest. FloraMap™ predicts with high probability that Carolina hemlock populations can be successfully moved to central Chile, and with lower probability to the Ozark region of Arkansas and southern Brazil. Camcore, North Carolina State University, has now collected seeds from 12 provenances and 77 mother trees in natural populations of Carolina hemlock and distributed these to the three regions listed above. Our goal is to sample 150 trees from the 15 provenances which will sample most of the species’ genetic diversity for ex situ conservation. The ex situ approach offers an alternate means of protecting the species if efforts to control the adelgid fail in the southeastern US. [Copyright &y& Elsevier]

The article presents simple mathematical and graphical models derived from data quantifying the distribution of water flux within the stems and the seasonal variability of daily water use of eastern hemlock trees growing in New England and the southern Appalachians in the U.S. The models can be used to estimate tree water use based on tree size and climate conditions. They can also be used to ensure that insecticide is applied during periods of rapid water uptake and movement through the tree stem.

1 We assessed the importance of several factors potentially affecting the settlement rate of the invasive hemlock woolly adelgid Adelges tsugae (Hemiptera: Adelgidae) on uninfested foliage of the eastern hemlock, Tsuga canadensis. We conducted our experiments in Massachusetts (U.S.A.) with overwintering sistens adelgids, and applied standard densities of infested foliage to uninfested branches in a planned multiple-comparison design. 2 Settlement rates of progrediens crawlers produced by the overwintering sistens were highest when adelgid-infested foliage was loosely attached to uninfested foliage and both branches were then enclosed in a mesh sleeve. 3 Early-emerging crawlers settled at a higher rate than did late-emerging crawlers. 4 Increasing the density of infested branches did not affect settlement rates. 5 We also tested whether less severe winter conditions improved settlement, and found that overwintering infested foliage in a refrigerator decreased settlement rate relative to foliage overwintered outdoors. 6 Our results suggest a protocol for adelgid inoculations that could substantially increase the success rate of experimental manipulations and encourage additional research on the population dynamics of this pest. [ABSTRACT FROM AUTHOR]

Abstract: Eastern hemlock (Tsuga canadensis; hereafter hemlock) was once relatively common in the northeastern United States. However, recent disturbances – including exotic pests and white-tailed deer overpopulation – have exacerbated declines in hemlock forest in the 20th century. As a previously undisturbed stand, the Mianus River Gorge Preserve (MRGP) provided an ideal site to investigate the potential impact of these factors on the structure and composition of old-growth hemlock forests. The woody vegetation of this forest was first surveyed in 1965 and then again in 2004. The overstory tree community was similar between the two time periods with hemlock dominant in both samples. Conversely, seedlings, saplings, and transgressives exhibited sharp declines in most species, including hemlock, which resulted in dissimilar community composition and structure for these age classes between 1965 and 2004. Despite relative continuity in the dominance of mature hemlocks, low recruitment due to overbrowsing makes the long-term persistence of hemlock in the old-growth forest of MRGP tenuous. [Copyright &y& Elsevier]

The hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), is an exotic insect pest that is killing eastern hemlock, Tsuga canadensis (L.) Carrière, and Carolina hemlock, Tsuga caroliniana Engelmann, in the eastern United States. We used the sequential interval procedure to develop a binomial sequential sampling plan for A. tsugae sistens on individual eastern hemlock trees that uses nondestructive sampling of new shoots. The actual α (type I) and β (type II) error rates were essentially 5 and 10%, respectively. Tallies of new shoots infested by at least one A. tsugae sistens were compared with stop values for thresholds of 10 and 30% of new hemlock shoots infested. Twenty to 80 new shoots had to be examined per tree to render a low, high, or indeterminate classification, which took <2 min per tree regardless of the threshold used. This plan should be an efficient and cost-effective tool in the management of A. tsugae infestations on individual, high-value eastern hemlock trees. [ABSTRACT FROM AUTHOR]

Laricobius rubidus LeConte, native to eastern North America whose primary host is Pineus strobi Hartig, has been observed in association with Adelges tsugae, an exotic and lethal pest of hemlock trees in eastern North America. Pineus strobi and A. tsugae were used to evaluate host preference and suitability of this predatory beetle to determine in part its suitability as a potential biological control agent of A. tsugae. In a paired-choice oviposition test, L. rubidus preferred to oviposit in P. strobi ovisacs over those of A. tsugae. However, in the no-choice oviposition test, there was no significant difference in the mean number of eggs laid by L. rubidus females in P. strobi or A. tsugae ovisacs. There were no significant differences in larval developmental time or survivorship for L. rubidus reared on a diet of either P strobi or A. tsugae. Laricobius rubidus completed development to the adult stage on A. tsugae indicating that it is a suitable host and therefore has the potential to contribute to biological control of A. tsugae in the eastern United States. The introduction of a congener, Laricobius nigrinus to eastern North America may result in competition with L. rubidus on A. tsugae, but the inability of L. nigrinus to complete development on P strobi suggests that the two congeners will not compete on the primary host of L. rubidus. [ABSTRACT FROM AUTHOR]

Chinese hemlock (Tsuga chinensis) is native to mountainous regions in eastern, central, and southwestern China. Interest in the species has recently increased because of its potential resistance to hemlock woolly adelgid (HWA) (Adelges tsugae), an introduced insect that has been killing eastern hemlock (T. canadensis) in the eastern portions of its range since the 1980s. Despite the fact that Chinese hemlock was introduced into cultivation in 1901, its environmental tolerances are still largely unknown. This study reports on the performance of Chinese hemlock seedlings planted within a native stand of eastern hemlock (T. canadensis) at the Arnold Arboretum in Boston, Massachusetts, U.S., that was heavily infested with HWA. In comparison with a control group of eastern hemlock, Chinese hemlock seedlings were completely resistant to HWA damage after 4 years of exposure. The results of our investigation indicate that T. chinensis is fully hardy in USDA zone 6 and is a suitable replacement for T. canadensis in landscape situations because of its rapid growth rate, tolerance of shade, and resistance to HWA. [ABSTRACT FROM AUTHOR]

Abstract 1 The seasonal synchrony between the exotic predator, Pseudoscymnus tsugae and its prey, the hemlock woolly adelgid, Adelges tsugae, was investigated in field cages and in the forest in Connecticut, U.S.A. from 1997–1999. 2 In early spring, egg to adult development took 45 d at 18.7 °C, 39.7 d at 20.2 °C and 31.5 d at 22.7 °C. Earliest emerging F1 adults mated and oviposited in the same year. whereas F1 and F2 females emerging later in the summer mated and reserved most of their egg complement for the following year. 3 A second generation of P. tsugae is possible in Connecticut but may be delayed by cool mid-spring temperatures. Individuals of three generations of P. tsugae, including overwintering survivors, may coexist in July and August and adults can be found year-round with A. tsugae in infested hemlock forests. 4 A linear regression model for development from egg to adult under field temperatures gave good agreement with results from constant temperature findings. The model predicted a lower development threshold of 9.5 °C and a sum of effective temperatures of 405 day °C. Development time of P. tsugae is shorter relative to its prey A. tsugae and generation time ratios of predator to prey was 0.16–0.5, with an advantage conferred on the coccinellid. 5 Overwintering ability and behaviour were determined in 1998–1999 and adults remained on infested hemlock branches throughout a mild winter, becoming reproductively active in mid-April. Peak oviposition period extended from April to July, in synchrony with peak oviposition and developing stages of two generations of A. tsugae. [ABSTRACT FROM AUTHOR]

The hemlock woolly adelgid, Adelges tsugae Annand, is an invasive insect that threatens hemlock species in eastern North America. Several species from the genus Laricobius are predators of A. tsugae in its native areas of Asia and the western United States. Two Laricobius species have been released as biological control agents: Laricobius nigrinus Fender, and Laricobius osakensis Montgomery and Shiyake. Laricobius rubidus LeConte is an adelgid predator native to the Eastern United States, where it can feed and complete development on A. tsugae opportunistically. Laboratory assays were conducted to assess the cold hardiness of these three Laricobius species, including two distinct populations of L. osakensis, by measuring the supercooling points of each species from November 2016 through March 2017. This information may be useful for choosing the best-suited biological control agent for a particular region to control A. tsugae. There was a significant difference between the overall mean supercooling point of L. rubidus compared to the other Laricobius spp. There were also significant differences of supercooling points between L. rubidus and both strains of L. osakensis in January, and significant differences between L. rubidus and all other strains in February. L. rubidus appear better adapted to cold extremes in the eastern U.S. than imported Laricobius spp. [ABSTRACT FROM AUTHOR]