Emerald ash borers (EAB) are small beetles, each less than an inch long. Adults have shiny green outer shells; larvae are white. They are diurnal creatures, preferring warm, sunny days. And when there’s signs of them in your area, you can rest assured that they will eat through every ash tree they come across.
The EAB is one of thousands of invasive species existing across the United States. As defined by the National Wildlife Federation, an invasive species is “any kind of living organism that is not native to an ecosystem and causes harm.” EABs have spread across Europe and North America despite being native to Asia. Everywhere they travel, they decimate the ash tree population, and Maine was recently added to their hit list.
In 2022, the state of Maine received its first report of definitive signs of EAB on the edge of the College’s campus. Since then, the relentless insects have overtaken the entire ash population within the Perkins Arboretum. According to Colby Senior Laboratory Instructor Abby Pearson, the person responsible for making the report, “everywhere that [she’s seen] ash on campus, [there has been] some indication of EAB, and anywhere that there’s EAB, the general understanding is that just about all the ash trees will be dead within ten years.”
This is a grim prophecy. Ash trees are a crucial part of the Arboretum’s ecosystem (and many other ecosystems across Europe and North America). They play an essential role in the life cycles of a wide variety of species. In some patches of the arboretum, ash are among the most common trees. And with these patches of ash trees dying out so suddenly, invasive plant species biding time underneath the canopy will take these openings as an opportunity to flourish.
Not only are ash trees important to Maine ecosystems, they are also very culturally significant for members of the Wabanaki Confederacy, a confederation made up of the four most prominent indigenous tribes in Maine. Basketmaking is a longstanding cultural tradition, a method of economic empowerment, and an outlet for artistic expression for Wabanaki peoples, and the brown ash is the main material used in this practice. For the Wabanaki, losing ash trees means losing part of their cultural identity.
Although the EAB is a worthy opponent, all hope is not lost. Shared interest in preserving ash trees has brought Wabanaki basketmakers, environmental conservationists, and the government together to form the Brown Ash Task Force. This group works to monitor ash population counts throughout Maine and harvest seeds from remaining ash trees to replenish the population and make sure they are not wiped out completely.
In the past, a major strategy employed to combat invasive species issues harming trees, such as chestnut blight and dutch elm disease, was to get ahead of the invasive species and cut down vulnerable trees, preventing the issue from spreading further.
The strategy the Brown Ash Task Force employs is the opposite. The hope, as explained by Pearson, is that “even though most will die, there will likely be a few that don’t, and those will be the resistant ones. Those are the genes that you want to propagate.” Collecting seeds from the trees that seem to be surviving the EAB influx will allow for the propagation of new trees that might be resistant.
Additionally, various research groups are utilizing the College’s arboretum to test other methods of protecting ash trees. A study currently being conducted by the Maine Forest Service and the Ash Protection Collaboration Across Waponahkik is centered around insecticide. Researchers have treated 200 ash trees on campus by drilling small holes in the bark and injecting the insecticide into the wood, where it is then carried up through the trunk by the tree’s vascular tissue and consumed by any EABs that attempt to feed on the tree. The results of the ten-year study will provide valuable insight into how the war against the EAB can be waged.
Another project, also led by the Maine Forest Service, focuses on introducing the EAB’s natural predator into the environment. Pearson has a hands-on role in this project, receiving shipments of tiny parasitoid wasps which feed on EAB larvae and releasing them into the arboretum weekly. These wasps pose no threat to humans and, though Pearson says there are “always questions about introducing new species,” she adds that “it should be that these parasitoid wasps are incredibly host-specific… and that’s what they’ve been shown to be so far.”
EABs are not the only invasive species to disturb the arboretum. Most recently, a nematode has brought a beech leaf disease to campus beech trees, which were already struggling due to a bark disease caused by a different invasive species. Various other species, such as the spruce budworm, whose population here waxes and wanes over time, and the spongy moth, a caterpillar that particularly likes apple trees and oaks, have come to call the College home. An especially unfortunate addition to the list is the browntailed moth which, in addition to doing a number on oak and fruit trees, causes an itchy rash on human skin.
Pearson predicts that the hemlock trees are next. The hemlock wooly adelgid, an insect native to Japan that feeds on hemlock sap, has made its way up the east coast from Virginia to Maine. It is only a matter of time before it reaches the College.
While efforts are being made to check the EAB population and protect our ash trees, there is no question that they have already made their mark. The scale of the damage will be measured this spring, in the Forest Ecosystems class, led by Professor Justin Bechnell, the Associate Professor of Environmental Studies. Each year, the class does an ash monitoring project, which includes revisiting permanent plots in the arboretum and collecting information on ash population and signs of EABs. The class wasn’t offered this past year, but it was for several years in a row before, and for those classes the ash project was primarily theoretical, predicting how the ecosystem would be changed when EABs eventually overtook it. Now that the ruthless little beetles have made a noticeable impact, the project will undoubtedly look very different.
Walking the trails, it is easy to spot dead ash trees with the EAB’s signature markings: serpentine tunnels underneath the bark where the larvae feast and small, D-shaped holes from which adult beetles emerge. For most of the year, while most of the trees are leafy and green, the barren, dead ash create a jarring contrast. Pearson left me with a haunting description of her view as she walked through the arboretum this past spring:
“It’s really obvious to me that…there’s a lot of dead trees, and their branches are just so stark and obvious. They have these big, thick branches because they have to hold up these big, compound leaves—their leaves are a foot long, and heavy. So they have these big, thick twigs, and they just look so stark against the sky.”
~ Anna Izquierdo `29
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