Thesis (M.S.)--West Virginia University, 2010. / Title from document title page. Document formatted into pages; contains x, 78 p. : ill. (some col.), col. maps. Includes abstract. Includes bibliographical references.

Thesis (M.S.)--Villanova University, 2008. / Biology Dept. Includes bibliographical references.

Hemlock woolly adelgid (Adelges tsugae Annand) is causing defoliation and mortality of eastern hemlock (Tsuga canadensis (L.) Carrière) in the eastern United States. The objectives of this study were to quantify changes in tree-ring width and wood anatomy for trees that survived adelgid infestation, and to contrast dendroclimatic relationships across a latitudinal gradient. Six sites spanning the current range of hemlock woolly adelgid (HWA) infestation were selected. At each site, 23 infested eastern hemlocks were cored and two trees were felled at the Virginia site and thin-sectioned using a sliding microtome for analysis of wood anatomy. Tree cores were cross-dated and ring widths were measured. For each site, t-tests were used to determine if there was a difference in radial growth pre- and post-HWA arrival. To compare differences in pre- and post-HWA cell properties, t-tests were used. For dendroclimatic analysis, Pearson correlation coefficients were calculated between radial growth and monthly climate variables. Three sites showed significant suppression in radial growth after HWA arrival and latewood produced post- HWA arrival had significantly smaller cells with reduced cell-wall thickness than latewood produced before HWA arrival. This indicates that HWA can reduce a tree's photosynthate production. The relationship between hemlock growth and climate also varied with latitude and site, with trees growing further south or on shallower soils being more sensitive to moisture levels. This sensitivity to drought can also partially explain the variation in hemlock response to adelgid feeding, as trees affected by moisture stress tend to be more sensitive to insect attack. / Master of Science

Hemlock woolly adelgid, Adelges tsugae, native to Asia and the Pacific Northwest of North America (Pacific Northwest), has devastated eastern hemlock (Tsuga canadensis) in a major portion of its range in the eastern U.S. After many years and much effort directed towards rearing and releasing biological control agents to manage HWA, one of these agents, Laricobius nigrinus, native to the Pacific Northwest, is now well-established in sites from the southern to the mid-Atlantic states of the eastern U.S. However, there have yet to be studies of its efficacy in lowering A. tsugae densities, and there has been no noticeable drop in A. tsugae densities. Population models for A. tsugae have suggested that even upwards of 90% predation on eggs laid by the overwintering generation will have minimal effect in reducing the population densities of A. tsugae, if A. tsugae are at high density, due to compensatory density-dependent survival in the progrediens generation. Additionally, no studies showing insect predators are indeed what regulate A. tsugae in its native range exist. We established predator exclusion experiments, and recorded A. tsugae densities, mortality factors, and fecundity for multiple generations in both the native and invaded ranges. In the invaded range, we studied A. tsugae populations in sites with well-established populations of L. nigrinus to test its efficacy in reducing A. tsugae and tested model predictions of minimal difference in A. tsugae densities between treatments with and without predators. In the Pacific Northwest we tested the effect of insect predators and tree species, western (Tsuga heterophylla) and eastern hemlock, on populations of A. tsugae. In the invaded range we found that L. nigrinus predation was significantly higher in unbagged branches, however, model predictions were validated, and there was no effect of predation by treatment on the A. tsugae summer generation. In our plots in the Pacific Northwest we found that tree effects were not significant, but that summer-active predators were significantly lowering levels A. tsugae densities on unbagged branches. Our study demonstrates the importance of summer-active predators in reducing A. tsugae and suggest that summer- and winter-active predators are needed to suppress A. tsugae to innocuous densities.

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.

A new fossil species, Tsuga xianfengensis Xing et Zhou, n. sp., is reported based on two compressed seed cones. The fossil cones were discovered from the upper Miocene Xiaolongtan Formation at the Xianfeng Basin of Yunnan, southwestern China. The discovery of the Tsuga cones confirms the presence of Tsuga in the Miocene of central Yunnan and represents the earliest Tsuga macrofossils in the southwestern China. The new species reveals a close affinity with East Asian Tsuga species, T. chinensis and T. dumosa. It provides fossil evidence to support the molecular data that the Asian clade might be differentiated in the Miocene.

A new fossil species, Tsuga xianfengensis Xing et Zhou, n. sp., is reported based on two compressed seed cones. The fossil cones were discovered from the upper Miocene Xiaolongtan Formation at the Xianfeng Basin of Yunnan, southwestern China. The discovery of the Tsuga cones confirms the presence of Tsuga in the Miocene of central Yunnan and represents the earliest Tsuga macrofossils in the southwestern China. The new species reveals a close affinity with East Asian Tsuga species, T. chinensis and T. dumosa. It provides fossil evidence to support the molecular data that the Asian clade might be differentiated in the Miocene.

The hemlock woolly adelgid (HWA), Adelges tsugae Annand, (Hemiptera: Adelgidae) is an invasive species in the eastern United States and Canada. This scale-like insect feeds on the xylem ray parenchyma cells of eastern hemlock, Tsuga canadensis (L.) Carrière, (Pinales: Pinaceae) and Carolina hemlock, Tsuga caroliniana Englem., resulting in multiple physical and physiological symptoms, all of which commonly leads to tree mortality within 4 to 10 years. Currently, HWA has spread throughout most of the eastern hemlock range and all of the range of Carolina hemlock and threatens the forest ecosystems they serve. In its introduced range, there are no natural enemies specialized to feed on HWA and suppress HWA populations below damaging levels. In the urban environment and at some public locations, the use of chemicals, such as imidacloprid, have been used to temporarily protect hemlocks, however; this does not provide a permanent solution. In the 1990's a classical biological control program for HWA was created with the goal to suppress HWA populations below damaging levels to reduce tree mortality, and to reduce the negative effects associated with the loss of either hemlock species. Presently, four predators have become the main focus of this program: Laricobius nigrinus Fender, Laricobius osakensis Shiyake and Montgomery (Coleoptera: Derodontidae), Leucotaraxis argenticollis (Zetterstedt), and Leucotaraxis piniperda (Malloch) (Diptera: Chamaemyiidae). Throughout the eastern US, La. nigrinus has established populations and expanded its distribution beyond where it has been released. Although it has successfully established and continues to spread, its effect on eastern hemlock health has been unknown. A 1-year study, carried out in 2021, revealed that La. nigrinus predation on the sistens generation not only reduced the sistens generation, but also had a similar net photosynthetic rate to the negative control on 1-2 year old shoot growth. In addition, significantly more shoots were produced for treatment branches with the highest La. nigrinus density. This also led to a significantly reduced aestivating sistens density compared to the no predator treatment. However, predation was insufficient to reduce HWA populations below the suggested damaging threshold of eastern hemlock (< 4 HWA/cm), suggesting that additional predators would be needed. Recently, the western strain of Le. argenticollis had been released in the eastern US. However, its phenology in the eastern US was unknown. A 2-year study, from 2021-2023, revealed that Le. argenticollis eggs and larvae were present when both generations of HWA adults with eggs and HWA nymphs were present. In addition, Le. argenticollis was capable of completing development in NY and VA, showing promise that this species could establish populations in the eastern US. Timing the adult fly releases into cages at the time when sistens were producing eggs resulted in Le. argenticollis phenology to synchronize well with HWA phenology at both locations, thus providing additional support for its release in the eastern US. Another 2-year study conducted in 2021-2022, at five locations (MD, NC, PA, TN, and VA), sought to determine how the predation of La. nigrinus and Le. piniperda, alone and together, would impact the sistens and progrediens generations, as well as how their predation would affect the aestivating sistens density and new shoot growth production. From this study, La. osakensis was found as the dominant Laricobius species present at the TN site, and similarly to La. nigrinus, reduced intact ovisac density in. This provided a small preview in La. osakensis capabilities and how this predator may be impacting HWA populations at locations where it has established. In order to assess Le. piniperda's impact on the progrediens generation, mesh cages were applied to treatment branches at each site. The study found that Le. piniperda could reproduce at all field sites and that the percentage of disturbed progrediens was significantly higher for treatments with Le. piniperda present at all field sites, except at PA in 2022. However, the affect of both of these predators on the aestivating sistens density and eastern hemlock health was inconclusive. In addition, the percentage of new shoot growth was highly variable among treatments at all field sites, and there was no treatment effect on the mean length of new shoot growth produced at all field sites. The results of this study suggests that in order to fully understand the affects of these predators on HWA populations and on hemlock tree health, longer term studies should be conducted. However, this study does provide some insight on the capabilities of these predators in the short term and supports the continued release and redistribution of these predators. / Doctor of Philosophy / The hemlock woolly adelgid (HWA), is an invasive species in the eastern United States and in Canada. This small scale-like insect was introduced likely on nursery stock material from southern Japan and was first discovered in the eastern US in 1951 in Richmond, Virginia. Two generations of HWA occur each year known as the sistens and progrediens; both reproduce without males. This insect feeds on eastern hemlock and Carolina hemlock, and since its discovery has spread through most of their range. While this insect feeds, it weakens the tree, eventually causing tree death. In eastern North America, eastern hemlock is one of the major tree species in the forest and provides a unique habitat for various mammals, birds, fish, and invertebrate species. To protect this habitat, multiple management strategies have been developed. The two main management strategies that are in use are the use of pesticides and the release of predators of HWA. Pesticides have been useful in the urban environment and in parks and forests, but they only last for a short time and can lead to negative affects to the environment. Since the 1990's, the release of insect predators originally found in the native range of HWA, has occurred with the goal of predator establishment, to lower HWA populations, and to lower hemlock tree death in the eastern US. Four small insect predators have been the main focus of this program: Laricobius nigrinus, Laricobius osakensis, Leucotaraxis argenticollis, and Leucotaraxis piniperda. So far La. nigrinus and La. osakensis have populations at multiple locations throughout the eastern US, and a low number of sites have been recently found for Le. argenticollis and Le. piniperda. Past studies have indicated that La. nigrinus has a significant impact to the sistens generation of HWA, but its affect to eastern hemlock health has been unclear. A 1-yr study conducted in VA in 2021, released La. nigrinus adults into mesh cages, with two different population sizes of beetles, to determine if La. nigrinus predation on HWA populations lead to an indirect effect on eastern hemlock health at the branch level. Results confirmed that La. nigrinus had a significant impact to the sistens generation of HWA. Photosynthesis of branches with La. nigrinus, in June, was similar to the photosynthesis of the negative control branches, which started with a lower number of sistens present on the branch at the beginning of the study. Suggesting that branches with La. nigrinus may be healthier compared to branches without La. nigrinus. Laricobius nigrinus predation also significantly reduced the number of aestivating sistens on new shoot growth, but not below damaging levels (< 4 HWA/cm). This suggested that additional predators may be needed to target the progrediens generation of HWA so that HWA populations do not return to damaging levels after La. nigrinus predation. To learn more about the potential for Le. argenticollis to survive and reproduce in the eastern US, a 2-yr study was conducted in 2021 – 2023, to determine when different life stages of Le. argenticollis could occur in NY and VA. Results revealed that Le. argenticollis was able to reproduce in the mesh cages and complete its life cycle. In addition, Le. argenticollis eggs and larvae were present at the time when HWA adults were producing eggs and when HWA nymphs were present for both generations of HWA. These results provide insight on Le. argenticollis life cycle and shows that Le. argenticollis has a good chance in surviving throughout the eastern US. A 2-yr study at five locations in the eastern US (MD, NC, PA, TN, and VA), tried to combine two predators, La. nigrinus and Le. piniperda, to determine if their combined impact would be sufficient to reduce HWA populations and affect eastern hemlock tree health. Three assessments were conducted each year to determine the impacts of La. nigrinus and Le. piniperda on HWA populations and on eastern hemlock shoot growth production as a representation of tree health. Results confirmed that La. nigrinus significantly reduced the sistens generation at all locations, except at TN. At the TN site, La. osakensis was found to be the main predator of the sistens generation and had a similar affect on the sistens generation as La. nigrinus. Leucotaraxis piniperda was able to reproduce at all locations and also had a significant affect on progrediens ovisacs at four of the locations in 2021 (MD, NC, PA, and VA) and at three of the locations in 2022 (MD, NC, and VA). However, the results on the number of aestivating sistens on new shoot growth and eastern hemlock health were inconclusive. Therefore, it is unclear as to how the presence of both of these predators' affect eastern hemlock health. A long term study may be needed in order to understand the relationship between these predators and their indirect affect to eastern hemlock health.

Prey-mediated effects of imidacloprid were evaluated for Laricobius nigrinus Fender and Sasajiscymnus tsugae Sasaji and McClure after feeding on hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae). Two methods were evaluated for detecting imidacloprid in hemlock tissues: a commercially available enzyme linked immunoassay (ELISA) kit and a high performance thin-layer chromatography technique for detecting and quantifying imidacloprid residues in hemlock wood and needle tissues. ELISA is advantageous because of its cost, sensitivity, and ease of use. However, matrix effects in the form of false positives and overestimated imidacloprid concentrations were evident in hemlock wood and needle tissue extracts. Matrix effects could be reduced by dilution with water, effectively raising the lower detection range of the kit from 0.2 to 200 ppb. High performance thin-layer chromatography was accurate, quick, easy to use, and matrix effects were not evident. However, the technique is sensitive in the lower ppm range and tissue samples from field-treated hemlocks are often in the ppb range, making this technique less desirable than more sensitive analytical methods. Lethal and sublethal effects on both predators were evident after eastern hemlock branches infested with HWA were spiked with imidacloprid in the laboratory. HWA mortality increased with dosage and time, and its 30 d LC50 was determined to be 242 ppb. Both predator species exhibited reduced survivorship and fitness parameters after feeding on HWA from the treated branches. In a topical application bio-assay, 6 d imidacloprid LD50 values for L. nigrinus and S. tsugae were 2.43 and 1.82 µg/g, respectively. Imidacloprid and its major metabolites in hemlock tissues were analyzed by liquid chromatography-tandem mass spectrometry. Imidacloprid recovery from beetle cadavers was correlated with beetle mortality from feeding on treated hemlock branches. Olefin was the primary imidacloprid metabolite recovered from hemlock wood tissues. When predators fed on HWA from field-treated trees, impacts on survivorship and fitness were variable. In 2005, significantly higher proportions of both species of beetles were affected by feeding on control branches compared with treated branches. In 2006, beetles feeding on HWA from some of the trees treated in the field exhibited longer fliptimes compared with beetles feeding on controls, although beetle mortality was not significant among treatements. In the field, imidacloprid controlled HWA populations 1-3 years post-treatment. Hemlock health improved in the highest dosage group, with significantly greater lengths of new shoots compared with shoots from control trees. Eastern hemlock trees primarily metabolized imidacloprid into the olefin metabolite, which can have increased insecticidal toxicity compared with imidacloprid. Imidacloprid was detected in beetle cadavers after feeding on HWA from treated branches, suggesting that prey-mediated impacts of systemic imidacloprid are possible on nontarget predators. However, because of HWA's sensitivity to imidacloprid, in field situations predators are more likely to be affected by reduced adelgid density and quality. / Ph. D.

The hemlock woolly adelgid, an invasive non-native insect, is threatening eastern hemlock in Kentucky. This study examined three techniques to map the distribution of eastern hemlock using decision trees, remote sensing, and species distribution modeling. Accuracy assessments showed that eastern hemlock was best modeled using a decision tree without incorporating satellite radiance. Using the distribution from the optimal model, risk maps for susceptibility to hemlock woolly adelgid infestation were created using two species distribution models. Environmental variables related to dispersal were used to build the models and their contributions to the models assessed. The models showed similar spatial distributions of eastern hemlock at high risk of infestation.