Are Emerald Ash Borers Expanding Their Diet?

Are Emerald Ash Borers Expanding Their Diet?

The recent announcement that the Emerald Ash Borer has arrived in Peekskill NY brings new urgency our local fight against this invasive insect. We strongly urge anyone who is the custodian of a healthy ash tree to consult with your arborist about the options for preserving the tree BEFORE the insect arrives in your area.

Ash Tree
The stately ash tree is one of our dominant forest trees, as well as a popular specimen tree used extensively in urban planting.

Since arriving in Michigan in 2002, the Emerald Ash Borer (Agrilus planipennis)
has cut a devastating swath through the Central and Eastern United States, killing tens of millions of ash trees — destroying over 99% of the ash population in many areas. There are currently over 8 billion ash trees in the U.S. The loss of these trees represents an environmental disaster and an economic one as well: the impact is estimated to reach $10 billion in the next 5 years.

Until recently, Emerald Ash Borer (EAB) damage had been confined to the ash species (Fraxinus). Now, researchers from Wright State University in Ohio have found evidence of EAB infestation in white fringetrees (Chionanthus virginicus), a species closely related to ash trees.

The white fringetree is a native understory tree found throughout the Eastern U.S. Although fringetrees are not important to the lumber industry, the trees fill an environmental niche in forests and are also popular as ornamental trees. In addition to the specter of another species-wide devastation, the appearance of EAB in white fringetrees causes concern because it may presage the migration of EAB to other tree species. Ash trees and white fringetrees are both members of the broader olive genus which includes common shrubs such as lilacs and forsythia.

White Fringetree
The white fringetree is named for the delicate flowers that cover it in spring.

How EAB Destroy Trees

EAB can fly about ½ mile in search of an ash tree to host their eggs. Unlike most species of boring insects that prefer to lay their eggs in already damaged trees, EAB will choose healthy as well as stressed specimens. They lay their eggs on the trunk and leave them to dine on the ash. As the larvae develop, they bore into the ash tree, carving serpentine galleries as they gnaw into the tender cambium just beneath the bark. Once infested, ash trees typically die within 2 to 3 years, as the damaged cambium becomes incapable of supplying water and nutrients to the branches.

Although EAB will relentlessly expand their territory every year, they have often had help in increasing their range. People unwittingly moving firewood have transported EAB to new locations, causing the epidemic to move even faster.

Emerald Ash Borer Larva
The serpentine galleries carved in the cambium nourish the larvae but kill the tree.

What Can We Do?

At this point, EAB has no natural predator in this country – unlike in Asia where it originated. Scientists are studying several species of wasp that prey on EAB in its native range for possible control, but no solution seems imminent.

Meanwhile, we have the ability to save individual ash trees. Keeping ash trees healthy will boost their immune systems and help them resist any opportunistic pests. Systemic injections will stop EAB larvae from damaging a valued ash tree. Depending upon the treatment chosen and the timing, a single treatment can provide control and protection for 2 to 3 years.

Investing in preserving specimen ash trees has multiple benefits. In addition to maintaining and enjoying an individual iconic American tree, every ash tree that survives the onslaught of EAB will act as a genetic reservoir for repopulating this beautiful species after the EAB is – hopefully – controlled or eradicated.