The adult Emerald Ash Borer (EAB), (agrilus planipennis Fairmaire) is a metallic green beetle only 1/2 inch long and 1/8 inch wide. This native to Asia was discovered in Michigan in 2002 and in 2006 it moved into Illinois and spread aggressively throughout the state killing over 200 million trees since then.
EABs generally have a one year life cycle although that can be extended to two years in a vigorous host. These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees. They pupate in early spring and emerge as adults to seek out other ash trees, leaving characteristic D-shaped exit holes in the bark. Depending on where you live in Illinois, expect adults to emerge any time from late May to August.
After feeding on leaves, adults mate and the females lay eggs on the bark or in small cracks in the tree. Eggs hatch in 7 to 10 days. The whitish larvae, called flatheaded borers, tunnel under the bark, creating a series of winding, S-shaped galleries in the phloem and outer sapwood. These tunnels girdle the trunk and branches, inhibiting the vital flow of water and nutrients from the roots to the branch tips. The larvae feed until fall then overwinter as prepupal larvae. This internal feeding causes permanent damage which eventually leads to the death of the tree.