Orientation behavior of the predator Laricobius nigrinus (Coleoptera: Derodontidae) to hemlock woolly adelgid and host tree odors in a multi-chambered olfactometer

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.     

Facilitation between invasive herbivores: hemlock woolly adelgid increases gypsy moth preference for and performance on eastern hemlock

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

Isolation and characterization of microsatellite markers for Carolina hemlock (Tsuga caroliniana)

We describe the isolation and characterization of 31 polymorphic di- and trinucleotide microsatellite marker loci for Carolina hemlock (Tsuga caroliniana Englem.). In addition, primer pairs for 16 loci amplified scoreable alleles in six other Tsuga species. In eastern North America, both Carolina hemlock and eastern hemlock (Tsuga canadensis [L.] Carr.) populations are declining due to infestation by hemlock woolly adelgid, Adelges tsugae. The markers described here should enhance population genetic studies of hemlocks, providing valuable information for conserving and restoring these important forest tree species.     

Arboreal spiders in eastern hemlock

Eastern hemlock [Tsuga canadensis (L.) Carrière] is a foundation species in forests of eastern North America that plays a key role in ecosystem function. It is highly susceptible to the exotic invasive hemlock woolly adelgid (Adelges tsugae Annand), which is causing widespread hemlock mortality. We surveyed the spider communities of eastern hemlock and deciduous canopies over 2 yr, collecting over 4,000 spiders from 21 families. We found that eastern hemlock canopies harbored a more abundant, rich, and diverse spider community than did deciduous canopies. Five spider families were present in our hemlock collections that were absent from the deciduous collections, including Mysmenidae, Theridiosomatidae, Mimetidae, Lycosidae, and Agelenidae. In hemlock canopies there were 4× the number of web builders, consisting primarily of the Tetragnathidae and Araneidae, than active hunters, consisting primarily of the Anyphaenidae and the Salticidae. Ours is the first in depth study of the spider community in eastern hemlock. Spider abundance in hemlock canopies suggest that they may play a role regulating herbivore populations, and could possibly affect the invasive hemlock woolly adelgid, either through direct consumption of the adelgids themselves or through interactions with classical biological control agents.     

Comparison of numerical response and predation effects of two coccinellid species on hemlock woolly adelgid (Homoptera: Adelgidae)

The hemlock woolly adelgid, Adelges tsugae Annand, is an introduced pest in North America that is native to Asia, and is causing extensive damage to eastern hemlock (Tsuga canadensis Carriere) and Carolina hemlock (Tsuga caroliniana Englemann) in the eastern United States. We compared two coccinellids imported for biological control of the adelgid: Scymnus ningshanensis Yu et Yao from China and Pseudoscymnus tsugae Sasaji and McClure from Japan. In a laboratory study, we measured the numerical response of each beetle species to a range of prey densities, and in field studies we examined the reproductive success and ability of the coccinellids to reduce populations of the hemlock woolly adelgid. In the laboratory, S. ningshanensis showed a positive numerical response as hemlock woolly adelgid density increased, and P. tsugae showed a density-independent response. In field cages, the presence of S. ningshanensis resulted in negative hemlock woolly adelgid population growth, in contrast to positive growth in both control cages and cages containing P. tsugae. Both our laboratory and field experiments suggest that S. ningshanensis has good potential as a biological control agent of hemlock woolly adelgid.     

Asymmetric priority effects influence the success of invasive forest insects

1. Settlement timing is often an important factor in interspecific herbivore interactions, as early‐arriving species may encounter higher resource availability and/or avoid induced defences. Despite the general importance of priority effects to the outcome of herbivore interactions, there has been little exploration of such interactions on woody host plants where their impact can only be measured over multiple years. 2. In the eastern U.S.A., two invasive species, the hemlock woolly adelgid Adelges tsugae and the elongate hemlock scale Fiorinia externa, share a native host, eastern hemlock Tsuga canadensis. Their interaction and its consequences were investigated for plant growth – hemlock saplings that had been inoculated with either A. tsugae or F. externa, starting in spring 2007, were cross‐infested with the other insect in spring 2009. A set of uninfested trees was simultaneously infested with A. tsugae, F. externa, both, or neither insect (= control), and insect density and plant growth was assessed in all treatments. 3. Adelges tsugae settlement rates did not differ if it settled alone or simultaneously with F. externa, but were ～45% lower on trees previously infested with F. externa. There was no difference in F. externa settlement rates, and plant growth did not differ substantively between any of the herbivore treatments. 4. At a temporal scale (i.e. multiple growing seasons) appropriate to interactions between woody plants and their herbivores, this work demonstrates that plant‐mediated priority effects can substantially affect herbivore settlement and thus the outcome of interspecific competition.     

Tree responses to an invasive sap-feeding insect

Although sap-feeding insects are known to negatively affect plant growth and physiology, less is known about sap-feeding insects on woody plants. Adelges tsugae (Annand Hemiptera: Adelgidae), the hemlock woolly adelgid, is an invasive sap-feeding insect in eastern North America that feeds on and kills Tsuga canadensis (L. Carrière), eastern hemlock. Newly hatched adelgid nymphs crawl to young unattacked tissue, settle and immediately enter diapause (aestivation) while attached to hemlock in summer. We assessed the effect of A. tsugae infestation on T. canadensis growth and physiology by analyzing hemlock growth on lateral and terminal branches, water potential, photosynthesis, stomatal conductance, and foliar nitrogen (%N). A. tsugae infestation greatly decreased terminal and lateral growth of eastern hemlock. In addition, A. tsugae presence reduced photosynthesis by 10 % in September and 36 % in October. Adelgid-infested hemlocks also exhibited signs of water stress that included notable reductions in water potential and stomatal conductance. These responses shed light on possible mechanisms of adelgid-induced mortality.     

Fitness and physiology of Adelges tsugae (Hemiptera: Adelgidae) in relation to the health of the eastern hemlock

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.     

Discriminating Tsuga canadensis Hemlock Forest Defoliation Using Remotely Sensed Change Detection

The eastern hemlock (Tsuga Canadensis) is declining in health and vigor in eastern North America due to infestation by an introduced insect, the hemlock woolly adelgid (Adelges isugue). Adelgid feeding activity results in the defoliation of hemlock forest canopy over several years. We investigated the application of Landsat satellite imagery and change-detection techniques to monitor the health of hemlock forest stands in northern New Jersey. We described methods used to correct effects due to atmospheric conditions and monitor the health status of hemlock stands over time. As hemlocks defoliate, changes occur in the spectral reflectance of the canopy in near infrared and red wavelengths—changes captured in the Normalized Difference Vegetation Index. By relating the differences in this index over time to hemlock defoliation on the ground, four classes of hemlock forest health were predicted across spatially heterogeneous landscapes with 82% accuracy. Using a time series of images, we are investigating temporal and spatial patterns in hemlock defoliation across the study area over the past decade. Based on the success of this methodology, we are no expanding out study to monitor hemlock health across the entire Mid-Atlantic region.     

Establishment and coexistence of two predators,Laricobius nigrinus and Sasajiscymnus tsugae,introduced against hemlock woolly adelgid on eastern hemlock

The coexistence of two introduced predatory species, Laricobius nigrinus Fender and Sasajiscymnus tsugae (Sasaji and McClure), and a native predator, L. rubidus LeConte, on eastern hemlock was documented for the first time. Details of their coexistence and implications to management of hemlock woolly adelgid, Adelges tsugae Annand, are discussed.     

Web orientation and prey resources for web-building spiders in eastern hemlock

We examined the arthropod community on eastern hemlock, Tsuga canadensis (L.) Carr, in the context of its role in providing potential prey items for hemlock-associated web-weaving spiders. Using sticky traps simulating spider webs, we evaluated what prey items are available to web-weaving spiders in eastern hemlock based on web orientation (horizontal versus vertical) and cardinal direction. We found that the overwhelming majority (>70%) of prey items available to spiders in hemlock canopies were Diptera. Psocoptera, Hymenoptera, and Hemiptera comprised most of the remaining potential prey. A significant direction × orientation interaction, and greater trap capture in some direction-orientation combinations, suggests that spiders might locate their webs in eastern hemlock canopies for thermoregulatory purposes, ultimately optimizing prey capture. We also evaluated these findings in the context of hemlock infestation by the invasive hemlock woolly adelgid, Adelges tsugae Annand. The adelgid is a sedentary insect with a mobile crawler stage that provides a readily available, easily obtained food source for predators in hemlock canopies. However, an abundance of alternative prey will affect within canopy spider distribution and the potential intensity with which spiders consume these prey. Understanding the response of spiders to potential prey availability is essential to understanding the trophic interactions involving these predators and their potential for influencing herbivore populations.     

Species shift drives decomposition rates following invasion by hemlock woolly adelgid

Insect and disease outbreak is an important cause of selective species removal and accompanying functional change in North American forests. Outbreak of hemlock woolly adelgid, Adelgies tsugae– HWA, is causing selective removal of eastern hemlock Tsuga canadensis at a regional scale. Impacts of outbreak‐caused canopy mortality and shifts in dominant species on litter decay were compared across sites that range in HWA‐caused canopy damage and subsequent canopy dominance by black birch Betula lenta. Senescent litter from eastern hemlock, black birch, and equal litter mixes were decomposed in the field for 36 months within nine sites in Connecticut and Massachusetts USA. Mass loss and % N accumulation of black birch was 65% and 52% greater compared to eastern hemlock. In contrast, outbreak related canopy damage increased litter mass loss by 11.5% in high mortality stands relative to uninfested stands but canopy damage had no impact on % N dynamics. Non‐additive effects of litter mixing influenced chemical dynamics of decaying litter; black birch accumulated less N and eastern hemlock accumulated more N compared to each species decaying alone. However, these changes offset and mixed litter bags overall showed no differences in N dynamics compared to values from each species decaying alone. In eastern hemlock stands invaded by hemlock woolly adelgid, canopy damage influences the rates and dynamics of decay but species differences between hemlock and black birch leaf litter are the dominant mechanisms of decomposition changes and a long‐lasting driver of increased N cycling rates. Species shifts may be the dominant driver of altered ecosystem processes for other insect outbreaks, particularly when replacement species have very different characteristics regulating decomposition and N cycling.     

云南丽江地区华山松上瓢虫种类记述(鞘翅目:瓢虫科)

本文记述的１８种瓢虫采自云南丽江的华山松上,其上有球蚜（Ｐｉｎｅｕｓｓｐ．） 寄生。包括１个新种——华山松小瓢虫Ｓｃｙｍ ｎｕｓ（Ｐｕｌｌｕｓ） ｈｕａｓｈａｎｓｏｎｇ, ｓｐ． ｎｏｖ． 和１个中国新记录种——团聚丽瓢虫Ａｄａｌｉａ ｃｏｎｇｌｏｍｅｒａｔａ （Ｌ．）, ３种鉴定到属或亚属。其中的１４种瓢虫同时采自铁杉,其上有铁杉球蚜（Ａｄｅｌｇｅｓ ｔｓｕｇａｅ）寄生。新种华山松小瓢虫Ｓｃｙｍ ｎｕｓ（Ｐｕｌｌｕｓ） ｈｕａｓｈａｎｓｏｎｇ （图１）体长２．６５ｍ ｍ ,体宽１．８０ｍ ｍ 。头黑色,口器及触角红褐色;前胸背板黑色;小盾片黑色;鞘翅红褐色。从头、前胸背板和小盾片黑色而鞘翅红褐色,该种易与它种区分;而从外生殖器而言,它与弯端小瓢虫Ｓ． （Ｐ．） ａｃｃａｍｐｔｕｓ Ｐａｎｇ ｅｔＰｕ 相似,但新种阳基较纤细,第１腹板上的后基线弯曲度大拱形明显而区分。新种模式标本１９９７年９月２４日虞国跃采于云南丽江文笔山,存北京市农林科学院植保环保研究所。     

Variation in the guild composition of herbivorous insect assemblages among co‐occurring plant species

Variation in plant traits among plant species may promote the development of a characteristic functional assemblage of insect herbivores associated with each plant species. However, only a small number of studies have detailed the representation of several herbivore guilds among co‐occurring plant species to determine whether the functional structure of herbivorous insect assemblages varies widely and consistently among plant species. The present study provides one of the few published data sets reporting on the density of several guilds of insect herbivores among numerous plant species. Variation in guild associations with plant phenology and season are also described. Insect herbivores were divided into 10 guilds, and the representation of these guilds was examined for 18 co‐occurring plant species. Guild densities and assemblage composition varied significantly among plant species, even when variation over time was taken into account. Variation in guild densities and assemblage composition were not strongly related to the taxonomic relationships of the plants. The highest densities of several guilds occurred in spring and summer, although other guilds were not strongly seasonal. Certain guilds were strongly associated with the presence of new leaves, whereas other guilds appeared to prefer mature leaves. This resulted in assemblage differences between samples containing new and mature leaves and samples containing mature leaves only. Even though the timing and duration of leaf and flower production varied among plant species, this did not explain all variation in guild densities among plant species. It is suggested that additional factors, including plant traits, are contributing to the wide and consistent variation in herbivore assemblage composition among plant species.     

Widespread inbreeding and unexpected geographic patterns of genetic variation in eastern hemlock (Tsuga canadensis), an imperiled North American conifer

Eastern hemlock (Tsuga canadensis [L.] Carr.) is an ecologically important tree species experiencing severe mortality across much of its eastern North American distribution, caused by infestation of the exotic hemlock woolly adelgid (Adelges tsugae Annand). To guide gene conservation strategies for this imperiled conifer, we conducted a range-wide genetic variation study for eastern hemlock, amplifying 13 highly polymorphic nuclear microsatellite loci in 1,180 trees across 60 populations. The results demonstrate that eastern hemlock exhibits moderate inbreeding, possibly a signature of a prehistoric decline associated with a widespread insect outbreak. Contrary to expectations, populations in formerly glaciated regions are not less genetically diverse than in the putative southern refugial region. As expected, peripheral disjunct populations are less genetically diverse than main-range populations, but some are highly genetically differentiated or contain unique alleles. Spatially explicit Bayesian clustering analyses suggest that three or four Pleistocene glacial refuges may have existed in the Southeastern United States, with a main post-glacial movement into the Northeast and the Great Lakes region. Efforts to conserve eastern hemlock genetic material should emphasize the capture of broad adaptability that occurs across the geographic range of the species, as well as genetic variability within regions with the highest allelic richness and heterozygosity, such as the Southern Appalachians and New England, and within disjunct populations that are genetically distinct. Much genetic variation exists in areas both infested and uninfested by the adelgid.     

Somatic embryogenesis and cryostorage of eastern hemlock and Carolina hemlock for conservation and restoration

Key message

Embryogenic cultures of eastern and Carolina hemlocks could be initiated, and somatic embryos and plantlets produced using standard conifer protocols and media. Embryogenic hemlock cultures were cryostored and recovered.

Abstract

Eastern hemlock (Tsuga canadenesis) and Carolina hemlock (Tsuga caroliniana) are threatened with extirpation from their native ranges in eastern North America by the introduction of the hemlock woolly adelgid (HWA; Adelges tsugae), an exotic insect pest that has already killed millions of hemlock trees. Efforts to conserve and restore these members of the Pinaceae could be greatly enhanced by the availability of an in vitro propagation system. We conducted experiments to initiate embryogenic cultures from eastern and Carolina hemlock zygotic embryos at different stages of development using three media supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D) and 6-Benzylaminopurine (BA). Cone collection date, medium and source tree had significant effects on induction of embryogenic tissue from zygotic embryo explants of both species, which ranged as high as 52 % for eastern hemlock and 17 % for Carolina hemlock. Embryogenic hemlock cultures could be cryostored using a protocol employing sorbitol and DMSO, and recovered following several months of frozen storage. Transfer of embryogenic tissue from proliferation media containing 2, 4-D and BA to a Litvay medium with abscisic acid promoted the development of somatic embryos, which were stimulated to mature by slow drying under semi-permeable plastic film. Embryos moved to an imbibition-germination medium without plant growth regulators and incubated in the light elongated and subsequently germinated. A small number of germinated embryos survived transfer to ex vitro conditions and grew into somatic seedlings. The embryogenesis and cryostorage systems developed in the study are already being integrated with hemlock breeding efforts to develop clones with resistance or tolerance to HWA.     

Exotic herbivores on a shared native host: tissue quality after individual, simultaneous, and sequential attack

Plants in nature are often attacked by multiple enemies whose effect on the plant cannot always be predicted based on the outcome of individual attacks. We investigated how two invasive herbivores, the hemlock woolly adelgid (Adelges tsugae) (HWA) and the elongate hemlock scale (Fiorinia externa) (EHS), alter host plant quality (measured as amino acid concentration and composition) when feeding individually or jointly on eastern hemlock (Tsuga canadensis), an important long-lived forest tree that is in severe decline. The joint herbivore treatments included both simultaneous and sequential infestations by the two herbivores. We expected resource depletion over time, particularly in response to feeding by HWA. In contrast, HWA dramatically increased the concentration and altered the composition of individual free amino acids. Compared to control trees, HWA increased total amino acid concentration by 330% after 1 year of infestation. Conversely, EHS had a negligible effect when feeding individually. Interestingly, there was a marginally significant HWA × EHS interaction that suggests the potential for EHS presence to reduce the impact of HWA on foliage quality when the two species co-occur. We suggest indirect effects of water stress as a possible physiological mechanism for our results. Understanding how species interactions change the physiology of a shared host is crucial to making more accurate predictions about host mortality and subsequent changes in affected communities and ecosystems, and to help design appropriate management plans.     

Effects of fertilization of four hemlock species on Adelges tsugae (Hemiptera: Adelgidae) growth and feeding preference of predators

Understanding how fertilization affects host resistance to hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), is important because fertilizers are often used to grow resistant selections to a suitable size for testing. We evaluated four hemlock species (Tsuga) under three different fertilizer regimes to assess whether fertility affected resistance to the adelgid and to determine whether it affected feeding preferences of the adelgid predators Laricobius nigrinus Fender and Sasajiscymnus tsugae (Sasaji & McClure). Treatments were long-term fertilization (from June 2008 to June 2009), short-term fertilization (from March to June 2009), and no fertilizer. Fertilizer was applied biweekly with 240 ppm N by using water-soluble fertilizer (N-P-K, 20:20:20). Plants (>1 yr old) were artificially infested with adelgids on 31 March 2009. Among unfertilized hemlocks (n=10 per species), foliar N was highest in Tsuga mertensiana (Bong.) CarriBre and lowest in T. chinensis (Franch.) E. Pritz. Significantly more progredien ovisacs or sisten eggs were present on T. mertensiana than on the other hemlock species with none on unfertilized T. chinensis. A. tsugae adults on T. heterophylla (Raf.) Sarg. were unaffected by fertility, but densities of developing A. tsugae nymphs were higher on unfertilized T. heterophylla plants than on fertilized T. heterophylla plants regardless of fertilizer treatment. Both L. nigrinus and S. tsugae consumed more adelgid eggs that developed on fertilized T. canadensis than from unfertilized plants. The predators did not exhibit this preference for adelgid eggs from females that developed on T. heterophylla or T. mertensiana.     

Interactive effects of disturbance and nitrogen availability on phosphorus dynamics of southern Appalachian forests

Understanding the main and interactive effects of chronically altered resource availability and disturbance on phosphorus (P) availability is increasingly important in light of the rapid pace at which human activities are altering these processes and potentially introducing P limitation. We measured P pools and fluxes in eighteen mixed forest stands at three elevations (low, mid, high) subjected to increasing atmospheric N deposition, where hemlock (Tsuga canadensis) was absent or declining due to infestation by the exotic hemlock woolly adelgid (Adelges tsugae). While total soil P was similar across the study area, phosphorus fractionation revealed distinct differences in the distribution of soil P fractions as elevation and N availability increased. Soils from high elevation plots where N availability was greatest had 139 % larger organic P pools and 55 % smaller residual and refractory P pools than soils from low elevation plots with less N availability, suggesting that increased N availability has driven the depletion of recalcitrant P pools by stimulating biotic demand and sequestration. These differences in P distribution among fractions influenced how tree mortality affected P dynamics. At high elevations, plots containing declining hemlocks had significantly greater foliar P concentrations and fluxes of P from the forest floor than reference plots at similar elevations, whereas at low and mid-elevations there were no consistent differences between plots. Across all elevation classes, hardwood foliar N:P ratios were lower in plots with declining hemlocks. Collectively, these results suggest that increased N availability enhances bioavailable P, which is sequestered in vegetation until disturbances liberate it.     

Indirect effects of an invasive exotic species on a long-distance migratory songbird

The loss of foundational tree species to non-native pests can have far reaching consequences for forest composition and function, yet little is known about the impacts on other ecosystem components such as wildlife. We had the opportunity to observe how the loss of eastern hemlock (Tsuga canadensis), due to the invasive hemlock woolly adelgid (Adelges tsugae), influenced the population ecology of the Black-throated Blue Warbler (Setophaga caerulescens) over a 7 year period. We followed the process of adelgid infestation and subsequent hemlock loss, which allowed us to investigate the patterns and mechanisms of population change. We document a precipitous decline in breeding pairs at one site where hemlock was most abundant in the understory, but not at our other two sites. We observed no changes in reproductive output or apparent survival, yet territory size increased dramatically at the most affected site, suggesting that the decline was due to a lack of colonization by new breeders. Our results demonstrate how an invasive insect pest can indirectly influence wildlife species not believed to be vulnerable and in ways not typically investigated.