Adelges tsugae Annand is a non-native invasive insect threatening the survival of eastern hemlock (Tsuga canadensis) and Carolina hemlock (T. caroliniana). A. tsugae is established in over half of the total range of eastern hemlock and the entire range of Carolina hemlock. Its continued spread, establishment and associated hemlock mortality make research into biological control of A. tsugae crucial. Field surveys of predators associated with A. tsugae in the Pacific Northwest identified a strong correlation between A. tsugae abundance with Laricobius nigrinus and two species of silver fly, Leucopis argenticollis and Leucopis piniperda. Flies in the genus Leucopis are known specialist predators of adelgids and recent studies have shown a strong synchronization between the lifecycles of Leucopis spp. and A. tsugae. The purpose of this study was to test the potential establishment of Leucopis spp. at the southern and northern extent of A. tsugae infested eastern hemlock in eastern United States. In 2015 and 2016, western Leucopis spp. adults were released at two different densities into enclosed branches of A. tsugae infested T. canadensis in Tennessee and New York. A. tsugae on the branches were counted before putting on the enclosure. Four weeks after set-up, all of the enclosures were collected. The number of Leucopis spp. offspring were counted and then stored in ethanol. The number of Leucopis spp. offspring collected were positively related to adelgid density, but did not differ by the number of adult flies per enclosure. Flies collected from enclosures and from the source colony were identified as L.argenticollis and L. piniperda using DNA barcoding. These results show that Leucopis spp. from the Pacific Northwest feed and develop to the adult stage on A. tsugae in the eastern USA. 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.

Environmental stressors such as nutrient deficiency and insect infestation can significantly impact tree health. Despite much research on the ecological effect on forests in the northeastern United States due to calcium depletion and hemlock woolly adelgid infestation, little is known regarding the physiological mechanisms altered by these stress factors. I tested the hypothesis that calcium depletion, associated with sugar maple decline, compromises water transport processes as a result of calcium-related reductions in cell growth and stabilization. A survey of forest-grown sugar maples from a long-term replicated calcium-manipulation study showed no significant impact of calcium deficiency on wood density, stem hydraulic conductivity (Ks), or vulnerability to cavitation (VC). In vitro removal of xylem-bound calcium showed no impact on VC or air seeding thresholds (Pt). Results suggest that sugar maple decline is not caused by compromises in xylem function due to calcium deficiency. I also tested the hypothesis that hemlock woolly adelgid (Adelges tsugae Annand) (HWA) infestations impact water transport processes and nutrient partitioning in eastern hemlock trees. HWA infestation resulted in higher Ks due to an increase in average tracheid lumen area associated with the proliferation of false rings. HWA-infested trees exhibited higher rates of net photosynthesis and significant changes in foliar nutrient partitioning. These results are the first to demonstrate increases in Ks and alterations in foliar cation levels in response to HWA infestation. In two additional studies, I investigated methods for evaluating the structure and function of xylem networks. Using sequential sectioning of aerial roots of epiphytic aroids, I directly quantified the topographic relation of vessels in a single organ with measurements of vessel length, diameter, vessel end overlap length, and vessel stelar orientation. In a separate study, I explored the relationship between vessel length and measurements of Pt. In establishing guidelines for estimating whole-stem cavitation with the use of single vessel air injection, I demonstrate that calculations of Pt are influenced by stem length measured and removal of native emboli prior to testing. Improvements in tools to quantify xylem structure and function will enhance our ability to understand the responses of forest trees to environmental stress.

Throughout the eastern United States, the spread of the hemlock woolly adelgid, Adelges tsugae Annand, has caused high mortality of eastern hemlocks Tsuga canadensis (L.). We recorded overwintering survival and fecundity of A. tsugae, and tree new growth at sites in the northeastern and southeastern United States and in a common garden experiment in Massachusetts. Overwintering mortality of A. tsugae was much higher in the north (87%) than the south (37%) in 2009, and showed significantly positive density-dependence in the north only. In 2010, overwintering mortality decreased in both regions but remained higher in the north (54%) than the south (34%), and, unlike 2009, density-dependent mortality was strongly negative in the north, and positive in the south. In both years, sistens fecundity was significantly higher in the south than the north, but we observed no density-dependent trends, and fecundity measurements were similar in the two years. The regional discrepancies in fecundity suggested the possibility of an evolutionary trade-off between overwintering mortality and sistens fecundity. However, when we reared samples in a common garden, we found that source region had no effect on either sistens fecundity or overwintering mortality, which suggests observed regional differences can be attributed to environmental factors rather than genetic differences. In our regional studies, branch samples from the north had significantly more new growth than those from the south in both 2009 and 2010, even though A. tsugae densities were comparable. This difference persisted in the common garden wherein branches inoculated with northern-derived A. tsugae had significantly higher new growth than those infested with southern-derived A. tsugae. These findings raise the possibility that A. tsugae may be evolving towards reduced virulence. If true, these findings may help explain why A. tsugae is killing hemlocks much more slowly now in New England than it did when it first invaded this region more than 20 years ago, or as it is doing now in more recently invaded regions in the southern United States.

Temperate mixed forests are complex ecosystems composed of multiple vegetation types with very different physiological characteristics which are distributed over the landscape. This dissertation investigates the influence of these mixed plant landscapes on eddy-covariance flux data, and in particular, uses an ecohydrological model to study the influence of climate variability and insect infestation on a mixed forest at the Harvard Forest Long Term Ecological Research site in Massachusetts. There are significant seasonal and interannual variabilities in the extent and the orientation of the footprints of a flux tower (EMS-tower) as the Harvard Forest. The Gross Primary Productivity (GPP) flux was found to be largely dependent on the vegetation density during the green-up and senescence periods, but not during the mature period. Half of the interannual anomalies in the mature period GPP flux can be explained by the variation in the proportion of coniferous evergreen needleleaf forest (ENF) in the footprint. Every 1% decrease of ENF resulted in the increase of the GPP flux by 20 gC m-2. The spatially-distributed process-based Regional Hydro-Ecological Simulation System (RHESSys) model was implemented in two headwater catchments at the Harvard Forest to simulate water and carbon cycles from 1992 to 2008. Results were evaluated using field measurements such as streamflow and the GPP and evapotranspiration (ET) fluxes at two flux towers. The simulated annual GPP flux of the deciduous forest showed strong and significant long-term increases, six times higher than the GPP flux of the coniferous forest, while the increase in ET flux of both forests was small yet significant. The Harvard Forest was infested by Hemlock Woolly Adelgid (HWA) between 2004 and 2008, and although there has not yet been a significant increase in the total annual mortality, the small stature stands have started to die off by 5.7%. The HWA infestation has already resulted in an increased streamflow in the catchment dominated by hemlock stands (44% in area). In 2014, the increased annual streamflow was estimated as 81 mm using the RHESSys model with an embedded representation of the HWA-induced loss of water conductivity (calibrated using the Hemlock tower ET flux).

No description available.

Competitive interactions among two specialist predators, <i>Laricobius nigrinus</i> Fender (Coleoptera: Derodontidae) and <i>Sasajiscymnus tsugae</i> Sasaji and McClure (Coleoptera: Coccinellidae), and a generalist predator, <i>Harmonia axyridis</i> Pallas (Coleoptera: Coccinellidae), of hemlock woolly adelgid were evaluated using laboratory, field and video studies. The two specialist predators are part of a biological control program for <i>A. tsugae</i>, and the potential for competition among these species and previously established generalist predators is unknown. In laboratory studies of predator groups in Petri dish assays, the only significant negative effects from competition occurred among conspecifics, resulting in reduced net egg production by <i>L. nigrinus</i> and <i>H. axyridis</i> and reduced feeding by <i>H. axyridis</i>. In contrast, heterospecific combinations showed non-interference. In longer duration field studies of predator groups, held in branch enclosures, predator survival and feeding were not significantly affected by additional predators. Net reproduction was again significantly reduced by conspecifics, while heterospecifics showed non-interference for all predator responses. All predators reduced the number of <i>A. tsugae</i> nymphs of the next generation relative to no-predator controls; however, <i>L. nigrinus</i> had much greater impact overall due to the large number of progeny produced. Video studies revealed that predator behavior varied qualitatively and quantitatively by species, and did not appear to be coordinated temporally or spatially. All species exhibited continuous activity patterns that were punctuated by longer periods of rest. The specialist predators were more selective of feeding and oviposition sites, and rested at more concealed locations than <i>H. axyridis</i>. Conspecifics significantly altered the time allocated to specific behaviors for <i>L. nigrinus</i> and <i>H. axyridis</i>, resulting in reduced predator effectiveness due to increased searching and decreased feeding and oviposition. All predator groups maintained a high degree of spatial separation relative to assay size, suggesting that chemical or tactile cues may be used to regulate their distributions. Overall, these studies suggest that the three predator species will be compatible in this system. Management implications include using multiple-predator species combinations over single-species for biological control of <i>A. tsugae</i> and implementing low-density releases to reduce the potential negative effects of intraspecific competition. / Ph. D.

The hemlock woolly adelgid (HWA) (Adelges tsugae [Annand]) (Hemiptera: Adelgidae) is a non-native lethal pest to eastern hemlock (Tsuga canadensis [L.] (Pinales: Pinaceae), and Carolina hemlock (Tsuga caroliniana [Engelmann]) (Pinales: Pinaceae). In the early 2000's, a robust biological control initiative using Laricobius spp. (Insecta: Coleoptera) was launched with the goal of decreasing HWA's impact to hemlock and the associated ecosystems on landscape level. Since then, two Laricobius agents, Laricobius nigrinus Fender (Coleoptera: Derodontidae) and Laricobius osakensis Montgomery and Shiyake (Coleoptera: Derodontidae) have been evaluated, approved, and released. The production and subsequent release of these agents has largely occurred through mass rearing efforts by Virginia Tech. A descriptive analysis of these rearing and release data over the past 16 years at Virginia Tech revealed that the mass production of these agents has been consistently limited by: 1) excessively high rates of subterranean mortality and 2) early subterranean emergence. Very little is known about the subterranean life cycle of these species in the field in terms of survivorship and timing of emergence. Additionally, the thermal limits and rates of development are unknown for L. osakensis and were thus further investigated. In 2019, surveys within the urban environment in two counties in southwest Virginia were conducted to determine if these agents have dispersed from their original release location. Laricobius nigrinus was documented to have established outside of release sites in 100 and 75% of the surveyed grids containing HWA infested hemlocks. The establishments of these species in easily accessible locations allowed for the use of field-caught larvae, in addition to laboratory-produced larvae, for experiments. Experiments were conducted in 2019-2020 to determine the overall subterranean survivorship in relation to site condition, differences in survivorship between field-caught vs. laboratory-reared, and the seasonal timing of emergence. We found that the average field subterranean survivorship (17.1 ± 0.4%) was significantly less than the historical production of these agents in the laboratory (37.5 ± 13.6%). We found that as soil pH and organic matter depth increased, survivorship decreased. While the majority of emergence occurred as expected in the fall, a surprising amount of emergence also occurred in spring and summer. The rate of development and the minimum threshold temperature for each life stage were determined through constant temperature experiments, and were used in the construction of a phenological forecast model. Laricobius osakensis minimum threshold temperature (3.6°) from egg to adult was similar to that of other Laricobius spp., but completed development at higher a constant temperature (22°C). Our results suggest L. osakensis can handle the same colder climates as L. nigrinus, but may be better adapted for warmer locations than L. nigrinus. Laboratory rearing, establishment, subterranean survivorship, and thermal requirements of Laricobius spp. (Coleoptera: Derodontidae), biological control agents released for Adelges tsugae (Hemiptera: Adelgidae) / Doctor of Philosophy / Eastern and Carolina hemlocks are long lived, shade tolerant evergreen tree species that support a unique ecological assemblage of plants and animals. However, following the accidental introduction of a highly invasive aphid-like insect pest first found in the 1950s, known as the hemlock woolly adelgid (HWA), significant mortality of hemlocks in the eastern U.S. was eventually observed. In order to mitigate this pest's impact and to prevent the further collapse of this unique ecological system, a robust management program was initiated. Today, the primary management strategy to reduce HWA's deleterious effects is through the use of chemical and biological treatments. Biological treatments in the form of insect biological control agents, have focused on the use of two closely related beetle species in the genus Laricobius spp. These species were imported from their respective native ranges, biologically evaluated, and approved for release by federal and state agencies. Since then, the beetles have been mass-produced by multiple governmental and academic agencies and released on infested landscape on mostly public land. Key aspects of these species' biology in terms of their population patterns, development, distribution capabilities, and potential supplementary diet remains unknown. Therefore, investigations into these aforementioned aspects were conducted from 2018-2021 in both laboratory and field experiments. In order to supply beetle larvae for field experiments and to better understand how well these predatory beetles were establishing across the landscape, we investigated heavily urbanized areas for their presence. We found that L. nigrinus was established outside of release locations, in 100 and 75% of the surveyed grids containing HWA in southwest Virginia. Laricobius spp. spend a significant amount of their lives in a presumed dormant state beneath the soil during the summer months. Observations over the past 17 yrs. of rearing Laricobius spp. revealed relatively high rates of subterranean mortality and subterranean early emergence, both of which are substantial mortality factors. Through field experiments, the survivorship of these beneficial beetles was found to be 17.1 ± 0.4% and their seasonal emergence was not limited to fall.Comparing the average survivorship from our field study (17.1 ± 0.4% ) to that of the past 17 yrs. of laboratory production (37.5 ± 13.6%), there was significantly less survivorship. The developmental and phenological biology of one of the two Laricobius spp., L. osakensis was determined and found to be similar to that of other beetles. However, L. osakensis was able to complete development at 22°C, the highest developmental temperature recorded for any Laricobius spp. The similar phenological biology of these two predators will allow for precise larval sampling as a metric for establishment. Results and conclusions from these data have provided further knowledge to scientists, land managers, and public stakeholders regarding the benefits of Laricobius spp.

The hemlock woolly adelgid (HWA), Adelges tsugae Annand, is an invasive pest of eastern hemlock, Tsuga canadensis (L.) Carriere and Carolina hemlock Tsuga caroliniana Englem. in the eastern United States. A newly reported beetle predator for HWA, Scymnus (Pullus) coniferarum Crotch (Coleoptera: Cocinellidae) preys on the pest in the western United States, and was approved for release in the eastern United States for the control of HWA. This research investigated the viability of S. coniferarum as a biological control agent of A. tsugae in the eastern United States, as well as the ecological dynamics between S. coniferarum and host prey species in its native range of western North America. In objective one, S. coniferarum predation, reproductive potential, and survival were evaluated in field-cages on adelgid infested T. canadensis in southwestern Virginia. Adult S. coniferarum fed on both generations and all life stages of A. tsugae at rates comparable to other adelgid-specific predators, and survived for extended periods of time in the field. In objective two, host-range tests for S. coniferarum were conducted in a series of no-choice and paired-choice feeding, oviposition, and development studies. Scymnus coniferarum adults fed on all adelgid species, and completed development on HWA and Adelges piceae Ratz. Scymmnus coniferarum oviposition was extremely low. In the final objective, Douglas-fir, Pseudotusga menziesii Mirb., Shore pine, Pinus contorta Dougl., western white pine, Pinus monticola Dougl., and western hemlock, Tsuga heterophylla (Raf.) Sarg. host tree species were sampled in Tacoma, Washington to investigate the life history of S. coniferarum and associated adelgid prey species in the western United States. Scymnus coniferarum adults were found on both pine species, Douglas fir, and western hemlock, and seemed to move between host tree species seasonally. Each host tree supports a different adelgid species, and a limited diet of strictly HWA in host-range tests could have contributed to low oviposition rates. This study suggested that S. coniferarum is a voracious predator of HWA in the field and laboratory. However, S. coniferarum laid very few eggs in laboratory studies, and zero eggs were recovered in field-cage analyses. This suggested that S. coniferarum may rely on multiple adelgid species to reproduce and establish in the eastern United States. / Ph. D. / Biological control is an economically and environmentally logical approach to pest management, through the introduction of a natural enemy or predator. This dissertation investigated the potential of Scymnus (Pullus) coniferarum as a biological control agent of the invasive pest species, hemlock woolly adelgid, otherwise known as HWA. The hemlock woolly adelgid is an invasive pest insect in the eastern United States, responsible for causing widespread death of eastern hemlock trees from southern Maine to Georgia. Scymnus coniferarum is a lady beetle that preys on HWA in the western United States, part of HWA’s native range. In objective one, S. coniferarum predation, reproductive potential, and survival were evaluated in field-cages on HWA-infested eastern hemlock trees in southwestern Virginia. Adult S. coniferarum beetles fed on HWA year-round, at a rate comparable to other successful biological control agents. In objective two, S. coniferarum beetles were confined to a selection of insect species similar to HWA and native to the eastern United States. Scymnus coniferarum predation, oviposition and development was observed in these tests in order to assess the potential impact of S. coniferarum on non-target species in the eastern United States. Scymnus coniferarum beetles fed on all adelgid species, and successfully laid eggs and developed to adults while feeding on the balsam woolly adelgid, another pest species in the eastern United States. Adult beetles laid very few eggs, and were very difficult to rear in a laboratory setting. In the final objective, Douglas-fir, Shore pine, western white pine, and western hemlock trees were sampled in Tacoma, WA to investigate the life history of S. coniferarum and other adelgid prey species in the western United States. Scymnus coniferarum adults were found on every species of sample tree except for Douglas-fir, and seemed to move among host trees seasonally. Host tree species support different adelgid species, and a limited diet of strictly HWA in host-range tests could have contributed to low oviposition rates. The lady beetle S. coniferarum was a voracious predator of HWA in field and laboratory studies. However, S. coniferarum laid very few eggs in laboratory studies, and zero eggs were recovered in field-cage analyses. This suggested that S. coniferarum may rely on multiple adelgid species to reproduce and establish in the eastern United States. This had either positive or negative implications regarding its viability to establish, flourish, and impact HWA in the eastern United States.

The hemlock woolly adelgid (HWA, Adelges tsugae Annand) is an invasive insect that threatens to eradicate native eastern hemlock (Tsuga canadensis (L.) Carr.) across the eastern United States. In southern New England and southern Appalachian forests, HWA-induced hemlock mortality has impacted carbon (C) flux by altering stand age, litter composition, species composition, and coarse woody debris levels. However, no one has examined how total C storage and sequestration may be impacted by these changes. Further, while projections are that HWA will ultimately infest hemlock across its entire geographic range, the majority of studies have been limited to southern New England and Appalachian forests where HWA infestation has been ongoing. To address these gaps, we examined how HWA might alter C dynamics in northern New England forests using the Forest Vegetation Simulator (FVS) and Forest Inventory Analysis (FIA) data to model C storage and successional pathways under three different scenarios: preemptive harvesting of hemlock, HWA-induced hemlock mortality, and a control mimicking natural stand development absent of disturbance. Our 150 year simulation showed that, while all treatments differed significantly in C storage in the short term, there was no significant difference in total C stocks between HWA infestation and presalvage treatments by the 75th year. Compared to the control, both simulated treatments resulted in a significant decrease in total C storage, with greater impacts on stands with higher hemlock densities. However, net C losses over the 150 year simulation were significantly higher for the presalvage scenario, indicating that allowing HWA infestation to progress naturally through a stand may result in the least impact to long-term C sequestration for the region's forests.

The high-elevation forests of the Southern Appalachian Mountains have been impacted and rearranged by a tiny introduced pest from Europe, known as the Balsam Woolly Adelgid (Adelges piceaea), creating a concern for conservation. Breeding bird censuses, along with botanical surveys, have been conducted periodically on an established 60-acre plot since 1967 on the virgin forested slopes of Mount Guyot, Great Smoky Mountains National Park, with the last census being completed in 2015. Breeding bird populations are shown to rise and fall in response to the forest’s changes over the last 48 years. Comparisons are made between all studies in order to assess how bird populations are being affected by the changed forest dynamics.