What EAB looks like
The EAB has four distinct life stages:
Typically, there is one generation each year, although development can take two years in newly infested trees that are still healthy.
The adult beetle is dark metallic green, bullet-shaped and approximately 1/2 inch long and 1/8 inch wide (about the size of a cooked grain of rice!). The body is narrow and elongated, and the head is flat with black eyes. Adult EAB emerge from beneath the bark of ash trees late May through early August, creating a distinctly 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. Adults feed on foliage for one to two weeks prior to mating. 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 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.
Emerald ash borer eggs are very small (1 mm), difficult to find and are rarely seen. Female adult beetles deposit them in the bark crevices and as larvae hatch from the egg, they immediately chew their way into the tree.
The EAB larva is white and flat, has distinctive bell shaped segments and can grow up to 1.2 inches long. As larvae hatch, they tunnel into the tree, where they feed through the summer and early fall on the phloem and outer sapwood, excavating S-shaped, serpentine galleries just under the bark. This feeding disrupts the flow of carbohydrates and water between the canopy and roots of the tree, which results in canopy thinning, branch dieback and finally tree death, typically within two to four years of initial infestation.
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 mid- to late spring, turning into adult beetles. Adults emerge soon thereafter to complete the typical one-year cycle. The pupae, like the larvae, cannot be seen unless bark is pulled away from the tree.