Green Menace: Emerald Ash Borer Lurks Under Cloak of Winter

Here in Madison, Wis., home of the Forest Products Laboratory, all has been covered in snow and ice. But within many of the finest shade trees in our parks and homes lurks big trouble, as the dreaded Green Menace is here. The emerald ash borer or EAB (Agrilus planipennis) is a beetle in the family Buprestidae, which are known as the metallic wood-boring beetles because of their metallic colors. Members of this family are found worldwide.


Adult emerald ash borer. Photo courtesy of Rachel Arango of the Durability and Wood Protection Research Unit.


The EAB is an invasive beetle that was introduced from China, most likely as a hitchhiker on wooden shipping pallets. It was first discovered in 2002 in Michigan and is now thought to have spread to more than a dozen states, including Wisconsin.


EAB larva. Photo courtesy of Rachel Arango.

Unfortunately, one of the traits about EAB that makes it so deadly is that it is nearly invisible in its early stages of infestation. The flying insects are only about an eighth of an inch wide and they lay their eggs very high in crevices of the trees’ upper branches. Once the eggs hatch, the larvae  bore into the tree and begin feeding on the soft wood beneath (the phloem), where they burrow long galleries. These tunnels affect the tree’s ability to transport water and nutrients and eventually girdle the tree. The larvae develop into pupae, which transform into adult beetles in the spring where the cycle continues. Characteristic D-shaped exit holes that adult beetles produce when they emerge from the tree are often used as indicators of EAB activity. Egg to adult is approximately 1–2 years.

EAB galleries in wood. Photos courtesy of Rachel Arango.

EAB galleries in wood. Photos courtesy of Rachel Arango.

Symptoms of EAB

A number of clues might indicate presence of EAB including, crown die-back, epicormic branching (epicormic branches are shoots arising spontaneously from dormant buds on stems or branches of woody plants), and the D-shaped exit hole.

Our colleagues at the Forest Service Northern Research Station have done major research on the EAB, whereas FPL has been more involved in researching the ways in which damage from EAB may be mitigated and options for utilizing wood from urban trees infested by invasive species.

Researchers are determined to find ways to slow, if not stop, the spread of this pest. Until then, we will continue to find ways to make the most of the damage they leave in their wake.