Thesis (M.S.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains vii, 55 p. : ill., maps. Includes abstract. Includes bibliographical references (p. 47-50).

An invasive insect, hemlock woolly adelgid (HWA), has initiated widespread hemlock decline and mortality in the Great Smoky Mountains National Park (GSMNP). Riparian hemlock mortality impacts on vegetative and aquatic systems of first-order, headwater streams were evaluated. Reference sites for this study were representative of the best available conditions within the GSMNP, with initial stages of HWA presence. Impacted sites were defined as areas with over 90 percent hemlock mortality. Impacted streams had decreased canopy coverage and increased light availability. Residual red maple, yellow birch, and sweet birch capitalized on the loss of hemlock, with increases in relative basal area and species importance values. Rosebay rhododendron responded with increased density and height at impacted sites, thereby preventing woody regeneration. Since long-term regeneration and post-mortality canopy recruitment are limited, alterations of vegetative composition and structure in the stream riparian zone are expected. A seasonal assessment (Sept. 2009 – March 2010) of aquatic impacts revealed increased diurnal variation in stream temperature and exhibited cooler temperatures during the colder months than reference streams. Impacted streams exhibited greater amounts and larger size classes of large woody debris (LWD). Higher concentrations for several nutrients, including silicon, sodium, potassium, magnesium, chlorine, and copper were detected in impacted streams than detected in reference streams. Impacted streams were characterized by higher pH and increased acid neutralization capacity, while reference streams exhibited nitrate concentrations three times higher than impacted stream concentrations. Reference streams were experiencing the initial stage of HWA-induced defoliations, increasing stream nitrate concentrations, while impacted sites had levels suggesting nitrate concentrations have returned to pre-infestation levels. A seasonal assessment of macroinvertebrates found species diversity, abundance, and taxa richness were not affected by hemlock mortality. Impacted streams had a lower density of Chironomidae and Ephemeroptera when compared to reference streams, while Pleuroceridae snails were virtually eliminated at impacted stream sites. Reference streams were dominated by the collector/filter functional feeding group (FFG), while impacted streams were dominated by the scraper FFG. Hemlock mortality induced by the presence of HWA has resulted in short-term impacts to vegetative and aquatic dynamics in stream riparian areas of the Great Smoky Mountain National Park.

The hemlock-silverbell (Tsuga canadensis-Halesia tetraptera) forest type is known to exist in only two places, the Great Smoky Mountains National Park (GRSM) and the Joyce Kilmer National Memorial Forest. The hemlock component of this forest type is currently threatened by the hemlock woolly adelgid (Adelgis tsugae), an invasive aphid-like insect native to Japan. This current status has given rise to the need to investigate the ecological resources of this rare forest type before the hemlock component dies out. The objectives of this study were to determine the nature of the plant/environment and plant/plant associations within this forest type. Within this forest type hemlock was negatively related to protection, aspect, and slope steepness and silverbell was positively related to aspect and slope steepness. This study also identified some interspecific associations such as the negative relationship in the understory between hemlock and striped maple, and provided evidence that understory stems are exhibiting a growth response to hemlock decline in these stands. The information obtained from this study characterizing the plant/environment interactions and even the structural and species components of this forest type will serve as a baseline of data from which to measure change and will provide insight into the mechanisms of species distribution and perhaps into short term scenarios of forest response to hemlock decline and mortality.

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.