Woolly Adelgid Research Articles

Pattern and Rate of Decline of a Population of Carolina Hemlock (Tsuga caroliniana Engelm.) in North Carolina

We monitored a population of Carolina Hemlocks in northwestern North Carolina for four years to examine the rate and pattern of decline in response to infestation by Adelges tsugae (Hemlock Woolly Adelgid). Our yearly census of hemlock condition and severity of the adelgid infestation included trees of all sizes. We estimated declines in condition as the portions of the leaf canopy that were lost. Initially, infestation occurred throughout the population but was severe in only a small cluster of individuals. Within 1 year, the area of severe infestation increased in size to encompass 48% of the population. In another region of the population, there was a cluster of relatively healthy individuals comprised largely of seedlings. Of the 4 size-classes of trees, sapling-sized individuals experienced the highest rates of decline in condition. Most trees declined to poor health within 3 years of an observation of moderate to severe infestation.

Understanding and Developing Resistance in Hemlocks to the Hemlock Woolly Adelgid

Abstract 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.

Predicting Bird Community Changes to Invasion of Hemlock Woolly Adelgid in Kentucky

Abstract 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.

The Relative Abundance of the Juvenile Phase of the Eastern Red-Spotted Newt at Harvard Forest Prior to the Arrival of the Hemlock Woolly Adelgid

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).

Community Responses to Eastern Hemlock Loss Across a Latitudinal Gradient

Abstract Tsuga canadensis (Eastern Hemlock) forests are experiencing widespread mortality due to the invasive insect Adelges tsugae (Hemlock Woolly Adelgid). This study sought to document the community response to HWA across latitude. I selected two sensitive response groups—plants and ants— to use as biological indicators of ecosystem change to monitor differences along a natural gradient of Eastern Hemlock mortality among 3 forest types: relatively healthy Eastern Hemlocks, dead or dying Eastern Hemlocks, and hardwood stands. I sampled understory vegetation, ants, and soils at each site and compared sites using a linear mixed-model to discern the best predictors of species density. I also compared analyses of variances across forest types among response variables. There was an average two-fold increase in understory vegetation species density between Eastern Hemlock and hardwood forests; ant species density was not influenced by forest type. Analysis of variance comparisons for understory vegetation sho...

Impacts and Management of Hemlock Woolly Adelgid in National Parks of the Eastern United States

Abstract Introduced forest pests and pathogens are a major threat to national parks. This paper reviews existing impacts, projected impacts, and management options for Tsuga canadensis (Eastern Hemlock) forests in US national parks threatened by the introduced insect Adelges tsugae (Hemlock Woolly Adelgid [HWA]). Eighty-five national parks, or 21% of all parks in the US national park system, are encompassed within the range of Eastern Hemlock. These 85 parks include iconic areas such as national battlefields and the Appalachian National Scenic Trail. Four focal parks of this study—Delaware Water Gap National Recreation Area, Great Smoky Mountains National Park, Shenandoah National Park, and New River Gorge National River—are collectively visited by 16 million people annually and Eastern Hemlock is a forest component in 2–26% of their area. Results of research on HWA impacts to forest species composition, soil nutrient cycling, watersheds and fisheries, wildlife habitat, and visitor experiences and safety ...

Potential Social and Economic Impacts of the Hemlock Woolly Adelgid in Southern New England

Abstract 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 ...

A Molecular Clone and Culture Inventory of the Root Fungal Community Associated with Eastern Hemlock in Great Smoky Mountains National Park

Below- and above-ground microbial communities are expected to dramatically change following the loss of healthy Tsuga canadensis (Eastern Hemlock) ecosystems due to the effects of Adelges tsugae (Hemlock Woolly Adelgid [HWA]) infestation. In 2006, few healthy Eastern Hemlock stands remained in Great Smoky Mountains National Park (GRSM), and we sought to obtain baseline soil microbial data from these undisturbed areas to better understand them. This study surveyed root fungal communities (e.g., mycorrhizae) using molecular cloning and cultural methods at 2 remaining healthy Eastern Hemlock stands in GRSM. We sampled roots from 40 trees representing 2 age classes (<75 and >150 years old) and 2 elevations (486 m and 1158 m) to obtain molecular clones and isolated cultures. Molecular clones from the ITS region indicated the presence of 124 taxa in 23 genera. The dominant genera were Piloderma (8.2%), Russula (6.8%), Tomentella (4.0%), Meliniomyces (3.4%), and Clavulina (2.9%). Ninety-seven of the taxa identified occurred at <1.0% relative abundance. The most frequent fungal species were Meliniomyces variabilis (22.6%), Russula granulata (16.1%), Phialocephala fortinii (9.7%), and Cladophialophora chaetospira (16.1%). Species richness, diversity, and evenness for total fungi, ectomycorrhizal species, and saprobic species were similar at different elevations and stand ages. Using ITS sequence data, we identified 9 species from 1800 fungal isolates from Eastern Hemlock root tissue, the most common of which were Trichoderma harzianum (24.4%), Trichoderma viride (24.4%), Trichoderma asperellum (17.1%), and Ilyonectria radicicola (12.2%). Species richness, diversity, and evenness were not significantly different across locations for the molecular data. Baseline data for the fungal taxa identified in the study may be important for understanding ecological changes that can occur post-HWA damage and HWA-caused stand losses. These data could also be used to support Eastern Hemlock reforestation efforts within current or former habitats in GRSM and surrounding ecosystems.

Evaluation of Cold—Moist Stratification Treatments for Germinating Eastern and Carolina Hemlock Seeds for ex Situ Gene Conservation

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.

Canopy vegetation influences ant (Hymenoptera: Formicidae) communities in headwater stream riparian zones of central Appalachia.

In the eastern United States, eastern hemlock Tusga canadensis (L.) Carriere forests are threatened by the invasive hemlock woolly adelgid, Adelges tsugae, a pest that is causing widespread hemlock mortality. Eastern hemlock is an essential component of forested communities. Adelgid-induced hemlock mortality is causing a shift in forest composition and structure, altering ecosystem function and thereby influencing the arthropod community. Using pitfall traps at three sites, we monitored ground-dwelling arthropods at 30-d intervals in hemlock-dominated and deciduous-dominated forests in central Appalachia over 2 yr. Here, we focus on the ant community (Hymenoptera: Formicidae) collected in the summer months. Ants form a ubiquitous and integral component of the invertebrate community, functioning at various trophic levels as predators, herbivores, and omnivores, and fulfilling important roles in forest ecosystems. We found no difference in overall ant abundance between hemlock-dominated and deciduous-dominated forests but did detect significant differences in the genera Prenolepis between forest types ( P < 0.01) and Aphaenogaster across study locations ( P = 0.02). Three genera were unique to deciduous forests; one was unique to hemlock forests. Not surprisingly, total formicids and several genera demonstrated temporal differences in abundance, with greater numbers captured in July than in August. As hemlock woolly adelgid-induced mortality of eastern hemlock becomes more pervasive, changes in forest composition and structure are imminent, accompanied by shifts in hemlock associates.

Spatial Dynamics of Canopy Trees in an Old Growth Eastern Hemlock Forest in the Central Appalachian Highlands

ABSTRACT: Understanding the shifting spatial distribution of trees is central to our knowledge of forest dynamics. We studied the spatial distribution of Tsuga canadensis L. Carr (Eastern Hemlock) as a function of age and size of canopy trees (greater than 75 cm dbh) and proximity to a stream in a remnant old growth forest fragment that has no record of human clearing or logging (Cathedral State Park, West Virginia). There appeared to be relatively continuous regeneration; however, cohort peaks indicated some disturbance history. We found spatially distinct age structures, with trees up to 315 years old. Trees greater than 102 cm dbh, or greater than 241 years old, were, on average, significantly closer to the stream. We suspect that the oldest individuals are concentrated near the stream because they are sheltered from wind disturbance. This knowledge can help us prioritize sites that are most important to protect from the woolly adelgid (Adelges tsugae Annand) when treating individual trees.

Contamination Delays the Release of Laricobius osakensis for Biological Control of Hemlock Woolly Adelgid: Cryptic Diversity in Japanese Laricobius spp. and Colony-Purification Techniques

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.

Failure under stress: the effect of the exotic herbivore Adelges tsugae on biomechanics of Tsuga canadensis.

Exotic herbivores that lack a coevolutionary history with their host plants can benefit from poorly adapted host defences, potentially leading to rapid population growth of the herbivore and severe damage to its plant hosts. The hemlock woolly adelgid (Adelges tsugae) is an exotic hemipteran that feeds on the long-lived conifer eastern hemlock (Tsuga canadensis), causing rapid mortality of infested trees. While the mechanism of this mortality is unknown, evidence indicates that A. tsugae feeding causes a hypersensitive response and alters wood anatomy. This study investigated the effect of A. tsugae feeding on biomechanical properties at different spatial scales: needles, twigs and branches. Uninfested and A. tsugae-infested samples were collected from a common garden experiment as well as from naturally infested urban and rural field sites. Tension and flexure mechanical tests were used to quantify biomechanical properties of the different tissues. In tissues that showed a significant effect of herbivory, the potential contributions of lignin and tissue density on the results were quantified. Adelges tsugae infestation decreased the abscission strength, but not flexibility, of needles. A. tsugae feeding also decreased mechanical strength and flexibility in currently attacked twigs, but this effect disappeared in older, previously attacked branches. Lignin and twig tissue density contributed to differences in mechanical strength but were not affected by insect treatment. Decreased strength and flexibility in twigs, along with decreased needle strength, suggest that infested trees experience resource stress. Altered growth patterns and cell wall chemistry probably contribute to these mechanical effects. Consistent site effects emphasize the role of environmental variation in mechanical traits. The mechanical changes measured here may increase susceptibility to abiotic physical stressors in hemlocks colonized by A. tsugae. Thus, the interaction between herbivore and physical stresses is probably accelerating the decline of eastern hemlock, as HWA continues to expand its range.

Modeling the spread of invasive species using dynamic network models

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

Competitor avoidance drives within‐host feeding site selection in a passively dispersed herbivore

Evolutionary theory predicts that ovipositing females that can actively disperse should select hosts that increase offspring performance. However, for organisms that are exclusively passively dispersed, feeding site selection is possible only at the within‐host level. This is particularly important for their offspring, which have strong temporal and spatial dispersal constraints within a host. Such constraints are probably magnified by tissue quality heterogeneity caused by competing herbivores. We investigated within‐host feeding site selection of passively dispersed neonates of a sessile herbivore, the hemlock woolly adelgid (Adelges tsugae Annand), when it shares its eastern hemlock (Tsuga canadensis Carrière) host with another sessile herbivore, the elongate hemlock scale (Fiorinia externa Ferris). Within‐host feeding site selection was studied (a) at the shoot level (with or without F. externa) using choice tests, and (b) at the needle level by scoring insect presence in field surveys. Adelges tsugae avoided F. externa‐colonised foliage in both the choice tests and field surveys. As A. tsugae has no efficient predators or parasitoids in the study area, we conclude that our results are due to the presence of the competing herbivore. Although A. tsugae cannot actively disperse among hosts, we showed that within‐host feeding site selection is an important mechanism to minimise the co‐occurrence with a competing herbivore that has known negative impacts on A. tsugae population densities. Studying within‐host feeding site selection in a multiple‐species context could assist in understanding and predicting the impact of destructive pests such as A. tsugae and the interactions with their novel hosts.

Hemlock Woolly Adelgid and Elongate Hemlock Scale Induce Changes in Foliar and Twig Volatiles of Eastern Hemlock

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

Patterns and predictors of survival in Tsuga canadensis populations infested by the exotic pest Adelges tsugae: 20 years of monitoring

Infestations of the exotic pest, hemlock woolly adelgid (HWA; Adelges tsugae Annand), have resulted in the widespread decline and mortality of eastern hemlock (Tsuga canadensis (L.) Carrière) throughout much of the eastern United States. As HWA continues to spread across the range of eastern hemlock, forest managers need a better understanding of the projected rates of hemlock mortality and improved quantification of the site and environmental factors that influence this rate. Our main objectives in this study, encompassing 1993–2012, were: (1) to document the long-term patterns of hemlock tree mortality following HWA infestation and (2) to assess the importance of tree, site, and weather factors in influencing mortality patterns in hemlock trees infested with HWA. In addition, to provide forest managers with a means of assessing the risk of tree mortality in infested hemlock stands, we evaluated the use of crown condition rating data to predict hemlock mortality at various time scales.Our results suggest that HWA-induced mortality can be a slower process than has previously been reported. Ten-year survivorship at our study sites ranged from 70% to 94%. From 1993 to 2012, 65% of the studied hemlock trees survived, with survival by site ranging from 39% to 82%. When calculated across all sites, survivorship after ten years of HWA infestation was 73%. Our findings indicate that inaccurate dating of HWA arrival and interaction with weather patterns may contribute to reports of elevated mortality rates. Our analysis found no support for inclusion of tree and site factors in models of hemlock mortality. However, winter temperature and summer drought explained a significant proportion of the variation in reported time to mortality of HWA infested trees. In addition, our analysis suggests that the use of crown condition indices can provide a reliable means of estimating near-term risk of hemlock mortality in HWA infested stands. Models based on foliar transparency and crown dieback were able to predict hemlock mortality with excellent discrimination at one, three, and five years following measurement. These indices can be used to provide information about impending hemlock mortality on a time scale that is relevant to many management decisions.

Future species composition will affect forest water use after loss of eastern hemlock from southern Appalachian forests

Infestation of eastern hemlock (Tsuga canadensis (L.) Carr.) with hemlock woolly adelgid (HWA, Adelges tsugae) has caused widespread mortality of this key canopy species throughout much of the southern Appalachian Mountains in the past decade. Because eastern hemlock is heavily concentrated in riparian habitats, maintains a dense canopy, and has an evergreen leaf habit, its loss is expected to have a major impact on forest processes, including transpiration (E(t)). Our goal was to estimate changes in stand-level E(t) since HWA infestation, and predict future effects of forest regeneration on forest E(t) in declining eastern hemlock stands where hemlock represented 50-60% of forest basal area. We used a combination of community surveys, sap flux measurements, and empirical models relating sap flux-scaled leaf-level transpiration (E(L)) to climate to estimate the change in E(t) after hemlock mortality and forecast how forest E(t) will change in the future in response to eastern hemlock loss. From 2004 to 2011, eastern hemlock mortality reduced annual forest E(t) by 22% and reduced winter E(t) by 74%. As hemlock mortality increased, growth of deciduous tree species--especially sweet birch (Betula lenta L.), red maple (Acer rubrum L.), yellow poplar (Liriodendron tulipifera L.), and the evergreen understory shrub rosebay rhododendron (Rhododendron maximum L.)--also increased, and these species will probably dominate post-hemlock riparian forests. All of these species have higher daytime E(L) rates than hemlock, and replacement of hemlock with species that have less conservative transpiration rates will result in rapid recovery of annual stand E(t). Further, we predict that annual stand E(t) will eventually surpass E(t) levels observed before hemlock was infested with HWA. This long-term increase in forest E(t) may eventually reduce stream discharge, especially during the growing season. However, the dominance of deciduous species in the canopy will result in a permanent reduction in winter E(t) and possible increase in winter stream discharge. The effects of hemlock die-off and replacement with deciduous species will have a significant impact on the hydrologic flux of forest transpiration, especially in winter. These results highlight the impact that invasive species can have on landscape-level ecosystem fluxes.

Changes in the regional abundance of hemlock associated with the invasion of hemlock woolly adelgid (Adelges tsugae Annand)

Since its introduction, the non-native hemlock woolly adelgid (Adelges tsugae) has spread to infest hemlock (Tsuga spp.) in at least 18 states in the eastern USA. Previous studies have documented highly variable rates of hemlock mortality among infested stands making it difficult to estimate regional impacts. Here data from the US Forest Service Forest Inventory and Analysis program collected from 432 eastern U.S. counties reveals several surprising and conflicting regional patterns. First, median live and dead hemlock basal area has generally increased over the last two decades across the eastern U.S. This has generally been the case in both infested and uninfested counties. Second, the median percentage of hemlock which is alive has decreased over the past *20 years, again in both infested and uninfested counties. Third, the ages of infestations are negatively correlated with the percentage of live hemlock, as might be expected given the known impact adelgids can have on a stand through time; however this relationship depends on the exclusion of uninfested counties, as counties infested (12 years and uninfested counties have similar percentages of live hemlock. Combined, these data suggest increasing tree density associated with the past century of reforestation and succession in the eastern U.S. may currently be overwhelming the negative impacts of the adelgid at the regional scale, however, the long-term stability of this situation is not known, and data from long-infested counties suggest the landscape may be at a ''tipping point''.

A Sequential Sampling Plan for Counts of &lt;I&gt;Adelges tsugae&lt;/I&gt; on Individual Eastern Hemlock Trees

A sequential sampling plan was developed to estimate density of sistens of the invasive exotic hemlock woolly adelgid, Adelges tsugae (Annand), by counting adelgids on new shoots of four branch tips sampled from the lower half of the live crown of individual, asymptomatic eastern hemlock trees. The y-intercepts and slopes for the relationship between observed mean and variance of A. tsugae counts were similar for North Carolina and for 2 years of data collected from Virginia; thus, data were pooled to create one regression equation that was used to develop a count-based sequential sampling plan. Validation data sets were obtained in West Virginia and by randomly selecting half of the trees sampled in North Carolina and Virginia, trees not used previously to develop the sampling plan. Validation of the combined North Carolina–Virginia sampling plan showed that the model performed as specified. This plan should allow for estimation of adelgid population changes on a tree over time, provided the tree has not declined due to A. tsugae infestation. This plan can also be used to assess chemical or biological treatment effects on A. tsugae, provided such treatments do not fundamentally alter the mean–variance relationship.