Ash Trees and a Small Green Beetle

Dorsal view of emerald ash borer adult with elytra and wings spread. (USDA-APHIS)

The Emerald Ash Borer (EAB) has become one of the most destructive invasive species affecting ash trees across North America. In the Hudson Valley, the damage caused by this tiny beetle has reached alarming levels.

Just as I do not have a favorite child, I don't really have a favorite wood species (perhaps, the one that I'm working with at the moment?). They all pose different challenges and have their own strengths. Ash wood is similar to oak, but lighter colored. It possesses a very striking, attractive and open grain pattern, but its light color can sometimes appear mottled. For this reason, I like to use milk paint to embellish the exterior of some of these bowls. (See the Decorative Bowls section here for some examples.) The grain lines remain visible beneath the painted exterior, and the eye is drawn to the unpainted interior of the bowl.

I am mindful, as I work with this beautiful wood, that its days are somewhat numbered.

Attractive grain pattern on a small, unfinished ash bowl.

What is the EAB and Where Did It Come From?

The Emerald Ash Borer is a small, metallic green beetle native to northeastern Asia. It was first discovered in North America near Detroit, Michigan, in 2002. It is believed to have arrived accidentally through wood packing materials used in international shipping. Since then, the EAB has spread rapidly, infesting most of the ash trees in the Northeast and Central US.

The Hudson Valley has seen the arrival of the Emerald Ash Borer within the last decade. The beetle’s ability to fly and the movement of infested firewood have helped it spread quickly through local forests and urban areas.

How the EAB Damages Ash Trees

The EAB targets all species of ash trees by laying eggs on the bark. When the larvae hatch, they burrow beneath the bark, creating winding tunnels called galleries. These tunnels disrupt the tree’s ability to transport water and nutrients, effectively starving the tree from the inside.

Galleries from Emerald ash borer on a large piece of ash.

Signs of infestation begin with thinning and yellowing of leaves in the canopy, then vertical splits in the bark caused by larval feeding, increased woodpecker activity as birds feed on larvae (often evidenced by light patches of bark where the birds have removed the outer, darker layer of bark in search of a meal), and finally D-shaped exit holes on the bark where adult beetles emerge.

Once infested, ash trees typically die within 2 to 4 years. It is estimated that in areas where there is a severe infestation, over 99% of Ash trees may succumb to EAB. All of North America's 8 billion ash trees are at risk from EAB.

Effects on Local Ecosystems and Communities

Ash trees play an important role in our ecosystem. The decline of these trees has several consequences, from impact on wildlife that rely on ash trees for shelter and food, to increased erosion, economic costs (as utility companies and homeowners remove and replace dead trees) and safety hazards as the dead trees fall on homes, power lines and roads.

Solutions and Management Strategies Being Implemented

While there are several ongoing efforts to manage and mitigate the impact of EAB, including the introduction of natural predators that target EAB, systemic insecticides, and replacing lost ash trees with diverse species and/or ash varieties with greater resistance to EAB, it appears unlikely that these efforts will do much in the short term. It is somewhat ironic that many of the ash trees currently affected were planted in response to the Dutch elm disease which wiped out native elms beginning in the 1930's. Other species will probably take their place, but we may soon be talking about the Ash tree in the past tense.

Sources: Department of Environmental Conservation, Wikipedia, Cary Institute for Ecosystem Studies