Native To: Asia (Anagnostakis 1997) Date of U.S. Introduction: First discovered in 1904 (Anagnostakis 1997) Means of Introduction: Introduced on nursery stock imported from Asia (Anagnostakis 1997) Impact: Fungal disease of chestnut trees (Castanea spp.) that virtually eliminated mature American chestnuts (Castanea dentata) from the U.S. (Griffin 2000) Current U.S. Distribution: Widespread throughout the U.S.

Brief History (from Using Science to Save the American Chestnut Tree (TACF)) During the past 100 years, chestnut blight (Cryphonectria parasitica) and ink rot disease (Phytophthora cinnamomi) decimated an estimated four billion American chestnut (Castanea dentata) trees and brought the iconic species to the edge of extinction. Human interference triggered the American chestnut’s demise–and now scientific innovation offers us the best chance to save it. The American chestnut tree was a vital component of the eastern U.S. ecosystem, economy, and landscape. Before the blight, it was an important food source for a wide variety of wildlife and a valuable cash crop for rural communities from Maine to Alabama. As reliable and productive as the American chestnut tree was, it cannot recover fast enough to sustain itself in the wild. That is why The American Chestnut Foundation (TACF) is leading an unprecedented rescue mission. Our species-saving strategy is a powerful combination of traditional breeding, biotechnology, and biocontrol. Since our founding in 1983, the field of genomics and biotechnology has burgeoned in scope and affordability. Based on new insights into the complex inheritance of blight resistance, TACF has charted a new course for our restoration program. We continue to improve the disease tolerance in our traditional breeding program, while embracing innovations which can integrate the mechanisms of disease tolerance at the molecular level. Our approach follows multiple pathways to create a disease tolerant and genetically diverse population of American chestnut that will be adaptable to broad and changing climate.

Breeding. Our traditional breeding program is carried out at our research farm in Meadowview, VA, and at more than 500 orchards planted, largely by volunteers and partners, across sixteen TACF chapters throughout the American chestnut’s native range. During the past 36 years, offspring from blight resistant hybrids have been bred with American chestnuts from across the species’ range. Four generations later, our traditional breeding program has produced a genetically diverse population of American chestnut hybrids with improved blight tolerance from Chinese chestnuts (Castanea mollissima). Moving forward, our breeding efforts are focused on further improving blight tolerance and incorporating resistance to Phytophthora cinnamomi, which causes a fatal root rot in chestnuts. We are using genomics to increase the speed and accuracy of selecting trees with the greatest tolerance to chestnut blight and root rot. Biotechnology. The core of our biotechnology program is transgenics. Scientists at the State University of New York, College of Environmental Science and Forestry (SUNY-ESF) discovered that a gene from wheat produces an enzyme, oxalate oxidase (OxO), which enhances blight tolerance significantly. TACF’s breeding program allows us to stack multiple blight resistance genes and increase the proportion of American chestnut genes in the resulting progeny. Biocontrol. The primary biological control method being explored by TACF and its partners is called hypovirulence. Here, the chestnut blight fungus is infected by a virus, thereby sickening the fungus and reducing the ability of chestnut blight fungus to cause lethal infections. Using this method, the natural defenses of the chestnut tree may enable the tree to halt canker growth and ultimately survive an infection. Other organisms are being investigated to further reducing the effect of the chestnut blight fungus.1

Photo: Blight Canker- Via Kendra Collins

1 The American Chestnut Foundation. “Using Science to Save the American Chestnut Tree.” Last modified 2020. https://www.acf.org/science-strategies/3bur/

Native To: Unknown, possibly Asia (Furnier et al. 1999) Date of U.S. Introduction: First detected in 1967, but may have been present before then (Farlee et al. 2010) Means of Introduction: Unknown (Ostry et al. 2004) Impact: Lethal disease of butternut trees (Juglans cinerea) (Farlee et al. 2010) Current U.S. Distribution: Northeastern and Midwestern U.S.

Brief History (from An Intraspecific Tree Breeding Program) “During the mid 1960's, over 500 square miles of butternut veneer, and millions of board feet of butternut lumber were cut annually. Today, over 90% of the remaining butternut is infected with a non-native disease called 'butternut canker', and virtually all cutting of butternut has stopped. Butternut canker disease was most likely introduced from Asia, through the St. Lawrence Seaway, into the ports around the Great Lakes and first noticed in the late 1960's. The disease has now spread east and south to the farthest extent of the butternut's native range. Like Chestnut Blight and Dutch Elm Disease, Butternut Canker has effectively eliminated butternut as a thriving tree species within the northeast forest ecosystem. Most butternut dies within 15 years of infection and virtually all known populations of butternut are now infected…The New Hampshire Division of Forests and Lands has created a project to harvest shoots and buds, called 'scion wood', from the few apparently disease resistant trees still alive in New Hampshire. By collecting scions from the few resistant trees, we can graft them to black walnut root stock to create a seed orchard of resistant butternut trees. When we cross pollinate between different resistant trees, within the orchard, it's hoped we will produce resistant seed which can then be out-planted in the native forest environment that butternut once dominated. The process is called 'intraspecific tree breeding'. The project was started in 1996. Since then, we have surveyed more than 3000 possibly resistant trees at over 300 different sites statewide…”2 -Kyle Lombard, New Hampshire Division of Forests and Lands, Forest Health Section

2 Lombard, Kyle “Butternut restoration Project: An Intraspecific Tree Breeding Program.” Last modified 2019. https://www.nh.gov/nhdfl/community/forest-health/butternut-restoration-project.htm Native To: Eastern Russia, Northern China, Japan, and Korea (McCullough and Usborne 2015) Date of U.S. Introduction: 2002 (McCullough and Usborne 2015) Means of Introduction: Arrived accidentally in cargo imported from Asia (McCullough and Usborne 2015) Impact: Ash trees lose most of their canopy within 2 years of infestation and die within 3-4 years (McCullough and Usborne 2015; Poland and McCullough 2006)

Brief History (from Biological Control of the Emerald Ash Borer, USFS NRS) In 2002, the emerald ash borer (EAB), Agrilus planipennis (Coleoptera: Buprestidae), an Asian beetle that feeds on ash trees (Fraxinus spp.), was discovered as the cause of widespread ash tree mortality in southeast Michigan and nearby Ontario. The results of subsequent studies showed that EAB was inadvertently introduced near Detroit, Michigan during the 1990s from northeast China, probably in EAB-infested solid-wood packing materials used in international trade. Despite federal and state quarantines that restricts the movement of ash out of infested areas, EAB continues spreading in the U.S. and eastern Canada. Although this beetle spreads naturally by flying short distances, long-distance spread is caused by people moving EAB-infested ash firewood, nursery stock, and timber. The rapid expansion of the EAB infestation across a wide range of climate zones suggests that this invasive beetle will continue spreading throughout the continent… Biocontrol of EAB began in the U.S. in 2007 when APHIS issued permits for the environmental release of three hymenopteran parasitoid species of EAB from China to EAB- infested ash stands in southern Michigan. These EAB biocontrol agents are: an egg parasitoid, Oobius agrili (Encyrtidae) (Fig.1) and two larval parasitoids, Tetrastichus planipennisi (Eulophidae) (Fig. 2) and Spathius agrili (Braconidae) (Fig. 3). In 2015, another EAB larval parasitoid, Spathius galinae (Braconidae) (Fig. 4) from the Russian Far East, was approved for release because S. agrili did not establish in northern regions.3

3 USDA Forest Service Northern Research Station. “Biological Control of the Emerald Ash Borer.” Last modified July 31, 2019. https://www.nrs.fs.fed.us/disturbance/invasive_species/eab/control_management/biological_control/ Native To: Japan (Orwig et al. 2003) Date of U.S. Introduction: Discovered on the West Coast in the 1920s, but it is disputed whether this was an introduced or native population; an introduced population was discovered on the East Coast in the 1950s (Havill et al. 2006; Orwig et al. 2003) Means of Introduction: Accidental (Wallace and Hain 2006) Impact: Destroys Eastern hemlock trees (Tsuga canadensis) (Orwig et al. 2003)

Brief History (from Hemlock Woolly Adelgid: A Non-Native Pest of Hemlocks in Eastern North America) It is the single most important pest of hemlocks in eastern North America and has a severe impact on the two susceptible species: eastern hemlock, Tsuga canadensis (L.) Carriere (Pinales: Pinaceae) and Carolina hemlock, Tsuga caroliniana Engelmann (Pinales: Pinaceae). Since the first report of hemlock woolly adelgid in Virginia in 1951, it has been slowly but steadily increasing its range. Recent establishments outside the contiguous range in Michigan and Nova Scotia have also occurred. At the stand level, hemlock trees are being replaced by hardwood trees in eastern North America, impacting some critical ecosystem processes. Several institutions are actively researching ways to protect the existing hemlock stands from further damage and to restore the ecosystems impacted by their loss. Although several control options for hemlock woolly adelgid have been developed, none are completely effective on their own, so a combination of all available control strategies is being used in an effort to save the existing hemlock stands. High-value hemlocks are being protected using chemicals, while a suite of predators is being released in forested areas. However, biological control has not provided immediate protection for heavily infested trees, so options for restoring hemlocks (hybrids with Asian species and punitively resistant stock) and finding viable replacements are being evaluated.4

4 S Limbu, M A Keena, M C Whitmore. “Hemlock Woolly Adelgid (Hemiptera: Adelgidae): A Non-Native Pest of Hemlocks in Eastern North America.” Journal of Integrated Pest Management, Volume 9, Issue 1, 2018, 27, https://doi.org/10.1093/jipm/pmy018

Native To: Unknown, possibly Asia (Brasier et al. 2001) Date of U.S. Introduction: First discovered in the U.S. during the 1930s (Olson et al.) Means of Introduction: Introduced accidentally on diseased logs imported from Europe (Flores 2006) Impact: Lethal fungal disease of elm trees (particularly American elms (Ulmus americana), which are more susceptible to the disease than other elm species) (Olson et al.) Current U.S. Distribution: Has been found throughout the entire U.S. except for the desert Southwest

Brief History (from communication with Cornelia Pinchot, Research Ecologist, US Forest Service, Delaware, OH) The accidental introduction of the Dutch elm disease (DED) fungal pathogen (Ophiostoma ulmi (Buisman.) C. Nannf.) into North America in the early 1900’s, followed by the more aggressive variant (O. novo-ulmi Brasier) in the 1940’s, marked the beginning of the decline for the American elm across the North American landscape. The DED fungal pathogens are vectored by elm bark beetles, specifically the European elm bark beetle (Scolytus multistriatus (Marsham)), the native elm bark beetle (Hylurgopinus rufipes Eichhoff), and the banded elm bark beetle (S. schevyrewi Semenov), which can carry the pathogens both externally on the exoskeleton and internally in the gut. Bark beetle feeding on twigs and branches introduces the fungus into the vascular system, subsequent mycelial growth penetrates the xylem producing conidia which are distributed throughout the tree via xylem sap. As the infection continues, the area of damage progresses to the trunk and can result in tree mortality in one year. While American elm is not faced with extinction because the species can reproduce before becoming infected with DED, the species has largely been relegated to existence as small stature and understory trees within its home range. Since the arrival of DED fungal pathogens, researchers and elm enthusiasts across Europe and North America have sought to find natural resistance in native elm populations. Efforts for American elm have focused on the screening of wild or natural and selection for resistance. Several selections with sufficient levels of field tolerance have been identified. Yet, restoration of the iconic American elm across the landscape requires genetically diverse populations of locally adapted American elm. The Northern Research Station (USDA Forest Service) partners with multiple collaborators, including The Nature Conservancy, to identify and test the DED tolerance of large surviving American elm trees found in New England and the Midwest. - Cornelia Pinchot

Native To: Unknown; the fungal pathogens may possibly be native, but the insect vector, Cryptococcus fagisuga, was introduced from Europe (Kasson and Livingston 2009; Gwiazdowski et al. 2006) Date of U.S. Introduction: First appeared in Canada during the 1890s, and in the U.S. during the 1930s (Gwiazdowski et al. 2006; Houston 1994) Means of Introduction: The insect vector (C. fagisuga) was introduced accidentally on imported European beech saplings (Gwiazdowski et al. 2006) Impact: Fungal disease that kills American beech trees after being attacked by the beech scale insect (C. fagisuga) (McCullough et al. 2005) Current U.S. Distribution: Northeastern U.S. and Great Lakes Region

Brief History (from Beech bark disease: patterns of spread and development of the initiating agent Cryptococcusfagisuga) Beech bark disease occurs when beech trees, predisposed by infestation of the beech scale Cryptococcusfagisuga (Lindinger) (C. fagi (Baer.)), are infected by species of the fungal genus Nectria. Infestation patterns of C. fagisuga on individual trees and in forest stands were studied. Fagussylvatica L. was infested artificially with C. fagisuga. After 3 years, secondary colonization on individual trees was generally restricted to within 1m from points of introduction. Cryptococcusfagisuga was associated positively with the bark lichen Lecanoraconizaeoides Nye ex Cromb. and negatively with the bark fungus Ascodichaenarugosa Butin. In a young plantation, patterns of scale infestation were related to distance from a large old relic tree and to wind- direction records for the insect's dispersal period. In another plantation the infestation patterns were associated with site topography. In North America, the pattern of continuous spread of C. fagisuga (and of associated disease development) since its introduction in 1890 strongly supports the sequential nature of the causal agent complex proposed by Ehrlich and suggests that susceptibility of F. grandifolia Ehrh. to infestation is so high, at least in the first encounter, that environmental factors which might influence this susceptibility are unimportant in the disease complex.5

5 D. Houston, E. Parker, D. Lonsdale. “Beech bark disease: Patterns of spread and development of the initiating agent Cryptococcus fagisuga.” Canadian Journal of Forest Research, Volume 9 2011. DOI: 10.1139/x79-057