Maine is the most forested state in the nation (with almost 90 percent of forest land) so we might be forgiven for taking trees for granted. But many of the tree species in Maine are or have been under threat. Fungal diseases have attacked chestnut and elm trees and invasive insects are threatening hemlocks, oaks, and ash trees. The Emerald Ash Borer is one such insect. An infestation of these beetles is decimating ash tree populations, killing tens of millions of Brown, White, Green, and Blue Ash trees across North America. Some foresters estimate that up to eight billion ash trees are at risk.
Background
The Emerald Ash Borer (EAB) is a little beetle, just a third of an inch long, with a speckled, metallic green body and red abdomen. Native to northeastern Asia , Emerald Ash Borers were once quite uncommon in Asia, known only to target trees that were already weak or dying. However, their numbers were bolstered by the arrival of nonnative species: American and European ash trees planted widely in Asia in the early 20th century. These new trees had no defense against beetle larva that were laid in bark crevices and emerged to feed on the inner bark and phloem. The species exploded in numbers, wreaking havoc on exotic trees and increasing the likelihood of accidental introduction elsewhere.
The first confirmed record in the U.S. was found near Detroit, Michigan, in 2002, and since then the species has been recorded in 36 states and the District of Columbia. It can spread naturally but also by humans and is spread in part by camp firewood, logs, or nursery stock being brought into Maine.
The beetles were first recorded in Maine in 2018, and now threaten ash trees across the state. Our native Brown Ash, Fraxinus nigra, is the species central to Wabanaki origin stories and is used by indigenous artisans to make baskets, while White Ash and Green Ash, F. americana and F. pennsylvanica, remain abundant in cities and towns as important landscape and street trees, many of which are already becoming infected and potentially unsafe.
Putting our property to work
Together, the Fraxinus genus hosts more than 125 species of butterflies and moths as a critical source of food for their caterpillars. Given the ecological, economic, and cultural significance of these trees, Maine Audubon is working across communities and nations to utilize our education, property, and network resources to help raise awareness, host research, and support solutions. Our Urban Forestry Education Specialist, Jeff Tarling, has been busy meeting with state and federal officials; city arborists in Portland, Lewiston, and Bangor; and working with partners at University of Maine’s Ash Protection Collaboration Across Wabanakik (APCAW) and the Maine Forest Service, to better understand the challenge and chart our response.
Maine Audubon’s Gilsland Farm Audubon Center in Falmouth has a substantial population of Ash trees and as such, provides an excellent place to study the spread of EAB, test various methods to protect Ash trees, and provide a source of seeds to help preserve genetic diversity. We are currently involved in three different projects: biocontrol, insecticide injection, and seed collection.
Biocontrol
Ash trees on our Gilsland Farm woodland are part of a collaborative study with the Maine Forest Service using applied research and integrated approaches to manage ash in a post Emerald Ash Borer forest. Our Gilsland Farm project began in July 2024 with the release of three species of ‘bio-control’ parasitoid wasps that will hopefully slow the spread of EAB.
The goal is to preserve local reservoirs—like Gilsland Farm—of ash genetic diversity for subsequent repopulation of ash through insect control and forest management strategies. The Maine Forest Service cooperates with USDA Animal and Plant Health Inspection Service (APHIS) in biological control efforts to manage emerald ash borer; experience gained by APHIS in fighting this outbreak in the Midwest gives us some hope that ash trees will continue to be part of Maine’s landscape for future generations.
The USDA labs provided Maine Audubon with three types of parasitoid wasps that will attack either EAB larvae or eggs. These insects are native to the same parts of Asia as EAB and have been fully vetted to ensure that they will not affect other species and are not a threat to humans. They specialize in attacking EAB and help reduce its numbers; all three have successfully been established in other trial areas and are spreading and helping to conserve species of ash. They are not expected to negatively impact native species.
Three larval parasitoids—Tetrastichus planipennisi and Spathius galinae along with the egg parasitoid Oobius agrili—were released on various ash trees at Gilsland Farm. The T. planipennisi is an endoparasitoid; it senses the EAB larvae, bores through the bark, and lays its eggs inside the larvae’s body to kill it from within. The egg parasitoid O. agrili attacks the eggs of the EAB and lays its own eggs, which hatch inside the ash borer eggs and consume the contents.
Some parasitoids are more important in the protection of older, larger ash trees, while others are more important in the protection of younger, smaller ash trees and saplings, due to differences in parasitoid ovipositor length in relation to bark thickness.
Injections
Gilsland Farm is also a participating Ash treatment demonstration site with the Maine Forest Service for an initiative that wrapped up in September. While there are limited treatment options available for EAB, injectable systemic insecticides have been shown to be effective at preventing mortality in individual trees. These types of treatments are focused on specific sites for the preservation of small pockets of ash, focusing on seed-bearing trees and larger heritage Ash. Twelve trees at Gilsland Farm were injected and tagged.
Ash seed collection
Ash trees at Gilsland Farm may also be able to contribute to the preservation of ash genetic diversity through seed collection. According to Ella McDonald, with University of Maine’s Ash Protection Collaboration Across Wabanakik (APCAW), “Seeds collected now can be used for future research in partnership with Tribal Nations, university researchers, and the state and federal Forest Service. Currently, wild ash seeds from the region of Wabanakik are understocked in long-term storage facilities, especially brown ash seed, and ash genetics in this region could be crucial to finding genetic resistance to EAB.”
APCAW hosted seed collection training and collected White Ash seed from three trees at Gilsland Farm in late September, with the help of Portland Parks, Recreation, and Facilities crew and bucket truck. Seeds collected here will go into deep storage at a facility in Ames, Iowa. McDonald says that individuals who have Ash trees on their property can help contribute to research efforts by collecting seeds. For more on seed collection, visit the APCAW website: umaine.edu/apcaw/
Hope for the future
Sites like Maine Audubon’s Gilsland Farm may thus help maintain ash genetic diversity and act as future sources of ash seed, acting as refugia for subsequent repopulation of ash forests following initial destruction caused by Emerald Ash Borer.
