The Emerald Ash Borer (Agrilus planipennis), also referred to by the acronym EAB, is an invasive beetle species originating from north-eastern Asia. In North America, EABs primarily target stressed or dying ash tree species, although healthy ash trees are also susceptible. First sighted in Michigan twenty years ago, EAB are considered the most destructive and costliest forest species in the United States, killing more than one hundred million ash trees across the Midwest and East Coast. In June 2022, EAB reached Oregon. The arrival of this invasive species poses a grave risk to Pacific Northwest’s urban forests, as EAB are known to wipe out 99 percent of ash trees in some locations. Here is how you can identify and prevent the spread of the Emerald Ash Borer to protect our forests.
How to Identify
Emerald Ash Borers can be identified by their dark green, metallic wing covers, hence the species’ name. Beneath their wing covers, adult EABs have a purplish red, metallic body. In terms of size, EABs have a narrow, pointed frame and grow to be about 1/4 to 1/2 inches long. The insect has a slight indent on its head and differentiates itself from other beetle species due to its lack of antennas, spots, stripes, and grooved lines.
Emerald Ash Borers were predicted to have entered the United States through infested-solid wood material shipped from overseas. Since their arrival to the Great Lakes region in 2002, EABs have spread to 35 states and 5 Canadian provinces, causing nearly $2 billion in damages across the Eastern U.S. EABs can decimate entire ecosystems of ash trees within 10 years of detection, furthering the need for mitigation efforts to protect urban forests.
EABs lay their eggs in the crevasses of tree bark from May to July. Once hatched, EAB begin consuming the tree’s inner phloem, cambium and outer xylem which inhibit the flow of sugars and water from reaching the tree’s roots. Trees infested with EABs become nutrient deficient, effectively dying 2 to 5 years after infestation. There are several indicators of an EAB tree infestation including bark splitting, epicormic shoots, woodpecker activity, S-shaped tunnels behind outer bark, dead branches on the top third of trees and, most notably, quarter-sized D-shaped exit holes on bark surface.
Ash trees play a crucial ecological role in the health of wetlands and streams, providing shade for native fish, stabilizing streambanks to protect against erosion, and providing food to several species of animals, birds, and insects. The spread of Emerald Ash Borers to urban forests across the U.S. continues to cause irreversible damage to regional ecosystems by depriving species of the resources they need to survive. In addition, EABs can have devastating economic impacts, costing municipalities, property owners, nursery operators, and the forestry industry hundreds of millions of dollars in damages.
The Oregon Invasive Species Council have anticipated the arrival of EABs for several years, finalizing the Emerald Ash Borer Readiness and Response Plan in 2021. Additionally, the Oregon Department of Forestry (ODF) continues to collect and preserve ash tree seeds for future planting, while also testing them for EAB resistance. ODF has also established traps across Oregon to monitor the spread of EABs. To further mitigate the spread, the City of Portland Urban Forestry has removed ash trees from Approved Street Tree Planting Lists and continues to conduct inventories of street and park trees to better understand the location of ash trees and potential impacts.
For more information on how you can prevent the spread of EABs and to report sightings, visit the Oregon Invasive Species Online Hotline.