The emerald ash borer beetle (EAB) migrated to North America in 2002. Since then this exotic, metallic-green beetle has been decimating ash trees throughout the United States and Canada. This beetle species is native to Asia and eastern Russia as well as parts of Japan, where the trees are immune to its life cycles. The borer was first discovered in North America in the forests of southeastern Michigan. It has since spread to nine other states and two Canadian provinces. It is thought that the emerald ash beetles arrived in the western hemisphere via the wood packing material carried in cargo ships and airplanes.
The emerald ash beetle affects the ash tree by feeding on the vascular system of the trees. The vascular system, comparable to the human circulatory system, is the tree's life network, a series of vessels responsible for transporting water, nutrients, and carbohydrates to all parts of the tree. In early summer, when the female beetles are ready to lay their eggs, they seek out inner vascular tissue known as the cambium. The cambium lies between the bark and the wood, producing phloem and xylem cells, which create the heartwood. The eggs are laid here because of the region's high nutrient content. Once the larvae emerge form their eggs they began burrowing through the bark, using the wood's nutrient's for food. For up to two years they eat their way through the bark, creating winding holes and tunnels which obstruct the vascular system. When it breaks down, nourishment can't reach the outer branches of the tree, causing them to yellow and wilt. As the entire life system of the tree is cut off the ash tree begins to slowly die. The whole process can take several years. The irony is that the emerald ash beetle, once if finishes with the ash tree, only lives for a short time. Once the adult beetles emerge from the tree, their life-spans only last for three more weeks, in which they find another ash to lay their eggs in, perpetuating the epidemic destruction of the ash forests.
In Michigan alone tens of millions of trees have already died. The EAB generally infests stressed or already dying trees, but they have also been known to lay their eggs in healthy trees. Many tree owners aren't aware of the extent that the borer beetle has infested their tree. Aside from the canopy die-back, there are other signs of an infested ash tree. The mark of the borer beetle is a D-shaped hole in the trunk of the tree, which they make upon entering. Also, the larvae will create 2-4 inch slits in the bark. Occasionally as well, an increased interest by woodpeckers is a sign that the small beetle larvae are present.
The Michigan Department of Agriculture has had to quarantine all infested areas, or potentially infested trees. Some counties have gone so far as to cut down ash trees that could be targeted by the EAB to prevent an area epidemic. There are pesticides that can be used over a period of years, but they are so challenging to inject into the tree, as well as expensive, that at this point they are only used on individual ash trees. Researchers are trying to better understand ways to detect the emerald ash borer infestations, and are trying to find more effective pesticides. Many states have replacement programs, to help individuals replant healthy ash trees, and restore the lost populations. With citizen education and research, North America can hopefully find a way to save the ash tree.