Hemlock woolly adelgid is an invasive herbivore causing extensive mortality of eastern hemlock, an important foundation species that provides stable conditions influencing biological communities. Hemlock is often found in riparian areas and following its decline, broadleaved species, including birch, beech, and rhododendron, will replace it. These plants differ from hemlock in patterns of canopy cover and leaf properties, which influence conditions and resources within streams. My goal was to evaluate potential impacts of adelgid-induced alterations to riparian canopies and litter on benthic communities and litter breakdown in streams. I characterized benthic invertebrate communities, litter colonization and litter breakdown in streams with hemlock- or deciduous-dominated riparian canopies. Riparian canopy influenced abundance of some invertebrates, but litter species influences a range of benthic colonizers. Rhododendron and beech litter generally support more invertebrates and decomposes more slowly than birch or hemlock. When invertebrates are excluded, broadleaved litter breakdown is more hindered than hemlock breakdown. My findings suggest that invertebrates may be more affected by future increases in broadleaved litter inputs to streams than by hemlock litter loss. This is significant because benthic invertebrates are important for in-stream litter processing and are linked to aquatic and terrestrial food webs.

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.

Eastern hemlock hosts the hemlock woolly adelgid, an introduced sap-feeding insect that causes rapid deterioration of the host. Like most conifers, eastern hemlock produces a variety of constitutive and induced defenses, primarily terpenoids. To explore the relationship of terpenoid defenses with adelgid infestations, we artificially infested hemlocks at a forest site and a plantation site, and compared their terpenoid concentrations to those in control trees. Infested trees showed lower terpenoid concentrations than control trees, suggesting that eastern hemlock not only fails to induce production of terpenoids in response to adelgid infestation, but becomes less able to produce carbon-based defenses due to loss of carbon resources to the adelgid. Greater light intensity may account for consistently higher terpenoid concentrations at the plantation site, supporting the explanation that carbon limitation restricts terpenoid production. Recent studies have identified a small number of individual eastern hemlock trees that demonstrate relative resistance to the hemlock woolly adelgid. We compared concentrations of terpenoids in susceptible and relatively resistant trees, both in the forest and in propagated cuttings in a common-garden setting. Terpenoid concentrations were higher in twig tissue of resistant versus susceptible trees, across six sampling dates and at both sites. Because the common-garden cuttings were free of herbivores, the higher terpenoid concentrations are interpreted as a constitutive defense. Increased levels of monoterpenes and sesquiterpenes imply an overall increase in the input of carbon precursors to both terpenoid synthesis pathways. This result suggests either an altered growth-defense balance favoring allocation of carbon resources towards production of defenses, or overall greater carbon availability in growing twig tissue of adelgid-resistant eastern hemlock individuals. We contribute detailed terpenoid data to the study of the eastern hemlock – hemlock woolly adelgid system. Our solvent extraction method permits us to examine needle and twig tissues separately, capture minor components at low concentrations, and focus on stored rather than volatilized terpenoids. By relating terpenoid concentrations to insect densities, we explore the relationships of tentatively defensive chemistry to insect population dynamics. The question remains which terpenoids, if any, directly affect hemlock woolly adelgid and what role phenols may play in the system.

The hemlock woolly adelgid (HWA), Adelges tsugae Annand (Homoptera: Adelgidae), is forest pest introduced to eastern North America in the early 1950's. Although this pest occurs on both landscape and nursery stock as well as in natural stands of hemlock forest, pesticides are only practical and effective in urban settings. Ecological and economical considerations prevent utilization of chemical treatment in the forest setting, thus biological control is viewed as the most promising option for slowing the spread of HWA. It is essential for researchers to be able to accurately assess the population levels of biocontrol agents after release into the environment. No method currently exists for sampling HWA predators. This project was designed to determine whether two species of predators are able to utilize olfactory cues from eastern hemlock and/or HWA in host-finding. If predators use olfactory cues, we may develop an attractive sythnetic blend of compounds to draw them to a trap, thereby simplifying the sampling and improving its accuracy. To address this question we executed three experiments. The first involved examination of the antennae of the predators for the presence and abundance of olfactory sensilla. The second experiment was designed to detect a behavioral response by the predators following exposure to host volatile compounds. The final experiment involved identifying compounds emitted from eastern hemlock, and the affect of HWA-feeding on volatile emissions. Laricobius nigrinus Fender (Coleoptera: Derodontidae) antennae are densely populated with sensilla, several of which are potentially olfactory in function. In addition, we observed a behavioral response to olfactory cues which included altered flight behavior. However, the behavior was not clearly attraction. Pseudoscymnus tsugae Sasaji and McClure (Coleoptera: Coccinellidae) has few sensilla on a very short antennae and only one type of sensilla possesses wall pores suggestive of an olfactory function. In addition, we did not observe a significant behavioral response to host-volatiles. It seems unlikely that this species uses olfaction in long-range host location. We identified 10 monoterpenes that were consistently expressed in the hemlock volatile profile and were unable to isolate volatile emissions from HWA. There is an increased monoterpene release rate from HWA-infested hemlock foliage as compared to uninfested foliage apparently driven indirectly by HWA through a reduction in new growth at branch tips. In addition there was a slight but statistically significant change in the percent composition of the individual compounds. We see potential in developing a more efficient sampling procedure for L. nigrinus through utilization of olfactory cues. More biological assays must be conducted to determine whether an attractive blend exists and electrophysiological assays are required to isolate physiologically active compounds. However, our data suggest that P. tsugae is not likely to be reliant on olfaction in long-range host location. / Master of Science

The biology and host-specificity of <i>Laricobius kangdingensis</i> sp. n. (Coleoptera: Derodontidae), a new predator of hemlock woolly adelgid (HWA), <i>Adelges tsugae</i> Annand (Homoptera: Adelgidae) were investigated and compared with that of a related predator of HWA, <i>L. nigrinus</i> Fender. Adults became active in June 2003; the males emerged first and in greater numbers than the females. The sex ratio of female to male was 1: 1.1. <i>Laricobius kangdingensis</i> sp. n. has four larval instars. The total number of eggs laid between 7 July 2003 and 7 August 2004 was 1327. Mean lifetime fecundity per female was 196.4 ± 53.4 eggs and 97.9 eggs for the P1 (parental gen.) and F1 generations, respectively. In comparison, lifetime fecundity for F1 <i>L. nigrinus</i> was 100.8 ± 89.6 eggs. Developmental rates were studied in fall 2003 and spring 2004. Combined with data gathered previously at 12 and 15ºC in early 2003, the 6, 9, and 18ºC data were used to determine lower temperature development thresholds for the egg (2.8ºC), larval (1.6ºC), and pre-pupal (5.8ºC) stages. The egg and larval thresholds are lower than those observed for <i>L. nigrinus</i>. <i>Laricobius kangdingensis</i> sp. n. individuals completed development only at 12 and 15ºC; however, these adults did not emerge from aestivation after pupation. <i>Laricobius kangdingensis</i> sp. n. appears to be host-specific. In paired-choice feeding tests, adults consumed significantly more HWA than two other adelgid species [eastern spruce gall adelgid, <i>Adelges abietis</i> (L.), and pine bark adelgid, <i>Pineus strobi</i> (Hartig)], the pine needle scale, <i>Chionaspis pinifoliae</i> (Fitch), and the woolly alder aphid, <i>Paraprociphilus tessellatus</i> (Fitch). In paired-choice oviposition tests, females laid more eggs on HWA-infested eastern hemlock than on any other test prey. In no-choice host suitability experiments larvae fed on HWA; eastern spruce gall adelgid; the larch adelgid, <i>A. laricis</i> Vallot; the balsam woolly adelgid, <i>A. piceae</i> (Ratzeburg); pine bark adelgid; and pine needle scale, but not on woolly alder aphid or elongate hemlock scale, <i>Fiorinia externa</i> Ferris. Although no larvae completed development in any of the bioassays, 6 out of 15 larvae (40%) in the HWA treatment reached the pre-pupal stage. One larva out of 6 reached the pre-pupal stage on pine bark adelgid. / Master of Science

The genus Tsuga is comprised of eight extant species found in North America and East Asia and four species represented by fossils from Europe and Japan. This study presents the first phylogenetic analysis based on structural, biochemical, and molecular sequence data. Characters obtained from published and unpublished literature were combined with new morphological characters from seeds, seedlings, and leaf cuticle material. Results from parsimony analyses of these characters differed from the published molecular based phylogeny. The non-molecular based phylogeny resolves two separate clades, a North American and an Asian, but did not group the western North American species, as in the molecular based analysis. Character states were traced on the trees to interpret character evolution. The combined analysis resulted in a phylogeny that differed from the previously published molecular tree by resolving a clade between T. caroliniana and T. diversifolia and placing T. dumosa outside of the Asian clade.

Eastern hemlock (Tsuga canadensis) is in decline because of infestation by the invasive hemlock woolly adelgid (Adelges tsugae; ‘HWA’) and, to a lesser extent, the elongate hemlock scale (Fiorinia externa; ‘EHS’). Many conifers respond to insect herbivory by inducing oleoresin-based defenses, however it is unknown whether eastern hemlock is capable of this inducible response. We conducted a plantation setting study of artificially infested saplings to determine if feeding by HWA or EHS induces changes in the tree’s volatile chemistry. The induced changes in volatiles we found were unlike the terpenoid-based defenses of related conifers. Only HWA feeding elevated methyl salicylate, a plant signal for systemic acquired resistance, and benzyl alcohol, a known antimicrobial and aphid deterrent. The influence of environmental conditions and tree life-stage on hemlock volatile chemistry, potentially important factors for wild hemlock populations, is unknown. We investigated whether mature and immature forest trees respond to HWA infestation with the same patterns of volatile production as plantation saplings in full sun and amended soils. HWA induced volatile changes comparable to those of plantation saplings, with many-fold benzenoid increases and no terpenoid-based resinosis. Nearly all volatiles were substantially more abundant in forest than plantation trees, suggesting the effect of site conditions should be addressed in investigations of mechanisms operative in HWA-resistant biotypes of eastern hemlock. Our findings represent the first important step toward understanding the influence of inducible phytochemical responses on hemlock susceptibility to exotic pests, and highlight the possibility of salicylic acid-dependent biosynthetic activity in this gymnosperm system.

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