Cornell Cooperative Extension

June 17, 2013

Invasive insect pests can alter forests

When you think of a pest, who comes to mind? 

My dog, Oliver, brings his favorite toy to me as soon as I sit down to dinner, thinking that since I am not busy, I can throw it for him. Over and over again! He can be annoying sometimes, but the pest I am writing about today is more than annoying. It has the potential to cause an incredible amount of damage to our forests and landscape trees.

The emerald ash borer is arguably the most destructive forest pest ever seen in North America. The small, bright, metallic emerald-green beetle’s natural range is northern China, Japan, Korea and eastern Russia. It was first discovered in Michigan in 2002, although it’s likely that it was present there and in other areas for a number of years before discovery. It is thought to have arrived in North America via crates or packing materials on cargo ships. It has now been found in Michigan, Connecticut, Illinois, Indiana, Iowa, Kansas, Kentucky, Maryland, Massachusetts, Minnesota, Missouri, New York, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia, Wisconsin, and the provinces of Ontario and Quebec. 

The female adult emerald ash borer lays eggs in crevices in the bark of ash trees. When the eggs hatch, the larvae, which are cream colored and have distinct bell-shaped segments, chew through the bark and into the cambium of the tree. The cambium is where nutrients and water flow to nourish the tree. As the larvae feed on these nutrients, they form S-shaped tunnels, or galleries, under the bark. The tree becomes unable to transport the nutrients and water it needs and begins to die from the top down. This is called canopy thinning.

In late spring, when the adults emerge, they leave small D-shaped exit holes. Other signs of emerald ash borer infestation are increased woodpecker activity and shoots sprouting from the lower trunk of the tree, called epicormic branching. 

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Cornell Cooperative Extension