Emerald ash borer adults are very small, metallic green beetles. Only 3/8 - 1/2 inch long and 1/16 inch wide (about the size of a cooked grain of rice), they can easily fit on a penny with room to spare! Adult emerald ash borers emerge from beneath the bark of ash trees late May through mid-July, creating a D-shaped exit hole as they chew their way out of the tree. Adult beetles are most active during the day and prefer warm, sunny weather. They never wander far from where they exit a tree (less than one mile) in search of a mate. Once they find a mate, the female will lay 60 - 90 eggs, one at a time, in the crevices of ash tree bark. The adult beetles will feed lightly on ash tree leaves, but do not cause much harm by doing so. The adult beetles live a total of three to six weeks.
Larvae (immature stage of EAB)
Emerald ash borer larvae are white and slightly flattened, with a pair of brown pincher-like appendages (urogomphi) on the last abdominal segment. Their size varies as they feed under the bark on the ash tree's tissues and grow. Full grown larvae average 1.5 inches in length. They wind back and forth as they feed, creating characteristic S-shaped patterns called galleries under the bark (starting in the phloem and extending into the xylem layers). An example of this is shown in the picture above. Larvae will feed under the bark for one or two years (longest in healthier trees), and can survive in green wood, such as firewood, even if the tree is no longer standing. This Larvae stage is what actually causes the most damage and eventually kills the ash tree.
In autumn, after one or two years of feeding under the bark, larvae will create a chamber for themselves in the tree's sapwood. They stay in this chamber over winter and pupate in the spring, turning into adult beetles. The adults emerge from the pupa case and then emerge from the tree, completing the life cycle. The pupae, like the larvae, cannot be seen unless bark is pulled away from the tree.
Why is EAB important?
Emerald Ash Borer (Agrilus planipennis) is an invasive wood boring beetle that feeds on the tissues under the bark of ash trees (Fraxinus spp) and kills them. The metallic green beetle is native to East Asia and was accidentally imported to the United States within the wood of shipping crates from China. EAB was first discovered in North America near Detroit, Michigan in 2002. Since then the beetle has spread to several eastern and midwestern states, including Wisconsin. EAB has also been found in Canada.
EAB is not a threat to human health but it does threaten our forest and urban tree populations.
EAB is 100 percent fatal to our native ash trees of any size, any age, healthy or unhealthy, (according to research by Michigan State University and the US Forest Service).
The larva (the immature stage of EAB) spends its life inside ash trees, feeding on the inner bark where we cannot see it. This feeding disrupts the trees' ability to transport water and nutrients, causing the tree to starve and eventually die.
On its own, the beetle will only fly a few miles. However, it is easily and quickly transported to new areas when people inadvertantly move emerald ash borer larvae inside of infested firewood, ash nursery stock, and other ash items.
A tree that has been attacked by EAB can die within 2-4 years. It is estimated that more than 50 million ash trees are dead or dying in the Midwest because of this insect.