The Emerald Ash Borer (EAB), Agrilus planipennis, is an invasive insect pest native to Asia. Since its confirmed discovery near Detroit, Michigan, and Windsor, Ontario, in 2002, this metallic green beetle has caused the widespread death of millions of ash trees (Fraxinus species) across North America. Understanding the EAB’s habitat preference, particularly its relationship with “dead wood,” is important to managing its continued spread.
Why EAB Targets Living Ash Trees
The emerald ash borer is biologically dependent on the living tissues just beneath the bark of an ash tree. Adult females lay their eggs in the bark crevices of healthy or stressed ash trees, initiating the destructive life cycle. Once hatched, the larvae bore into the tree to feed on the phloem and the cambium layer.
This phloem and cambium layer is rich in nutrients and is responsible for transporting sugars and water throughout the tree. Larval feeding carves out distinct, winding patterns called serpentine galleries, which effectively girdle the tree. The larvae require this moist, nutrient-rich inner bark to complete their development, which is why a completely dead and dried-out tree is not a suitable host for an initial infestation.
Larvae can typically complete their life cycle within one to two years inside a newly infested tree. The resulting damage is so severe that most North American ash species will die within two to five years of initial attack.
How Long EAB Survive in Cut Wood
Whether EAB can live in cut wood depends entirely on the wood’s condition and moisture content. EAB larvae can and do complete their development in wood that has been cut, as long as the wood was already infested and still retains sufficient moisture and the bark remains attached.
Adult beetles can successfully emerge from infested ash firewood, logs, or branches for up to one or two years after the tree was cut. This emergence window is the primary mechanism for the artificial, long-distance spread of EAB, as people unknowingly move infested wood across quarantine lines. Once the wood is completely air-dried and the phloem layer desiccates, the larvae are unable to survive or pupate.
To prevent the emergence and spread of adult beetles from cut ash wood, management practices focus on rapidly destroying the larvae.
- Chipping the wood into pieces smaller than one inch in size is highly effective, as this process physically crushes the larvae.
- Immediate burning of the wood will ensure complete mortality.
- Heat treatment to an internal temperature of at least 56 degrees Celsius for a minimum of 30 minutes will also ensure complete mortality.
Identifying an Active EAB Infestation
The most conclusive evidence of an infestation is the presence of D-shaped exit holes left behind by the emerging adult beetles. These holes are small, measuring approximately one-eighth of an inch across, and have a flattened side.
Beneath the bark, the feeding of the larvae creates the characteristic serpentine galleries that are packed with frass, a fine mixture of sawdust and insect excrement. These S-shaped tunnels are often revealed when woodpeckers strip away the outer bark in search of the larvae, a phenomenon known as flecking. Woodpecker activity, especially high on the trunk and main branches, can be one of the earliest noticeable symptoms.
Visual symptoms that the tree is struggling include canopy dieback, which begins with the thinning of leaves in the upper third of the tree crown. As the tree attempts to survive the girdling, it may produce new shoots, known as epicormic sprouts, low on the trunk or at the base of the tree. Vertical bark splitting is another sign, as the tree’s growth attempts to callus over the damaged feeding galleries beneath the surface.