In June 2002, scientists detected a new exotic wood-boring beetle feeding on ash trees in southeastern Michigan and adjacent Windsor, Ontario. The beetle has since been reported in northwest Ohio. Native to Asia, this new arrival is called the emerald ash borer (Agrilus planipennis), and it poses a potential threat to all species of native ash (Fraxinus). Larvae of the beetle feed on the phloem and outer sap of ash trees, creating borer galleries (holes) that can kill branches and, eventually, entire plants. The Michigan Department of Agriculture has set up a quarantine zone around the Detroit area in an attempt to limit the spread of the infestation.

Adult beetles grow between 7 and 13 millimeters long and have a metallic golden-green color. They begin to emerge in mid-May, and the females soon start to deposit eggs in the bark crevices of ash trees. Eggs hatch in seven to ten days. The developing larvae are cream colored and grow up to 22 millimeters long. They bore their way through the bark into the cambial region and feed on phloem cells and outer sapwood for several weeks. Full-grown larvae overwinter in galleries in the sapwood and begin to pupate around the end of April. Adult beetles emerge from small, 3- to 4-millimeter-wide D-shaped exit holes and continue the life cycle.

Ash trees are often killed after two to three years of infestation by the ash emerald borer. Control and management strategies for the beetle are still being developed. Systemic pesticide treatments (using products with chemicals such as imidacloprid and bidrin) are being administered in Michigan to trees that are no more than 50 percent dead. It's too early yet to say how effective these treatments are. Physical control methods, such as removal and chipping of infested trees prior to beetle emergence in May, are also being used.

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