Emerald Ash Borer

Emerald Ash Borer

The emerald ash borer (EAB), Agrilus planipennis Fairmaire is a devastating exotic wood-boring pest threatening ash trees in North America. To date, EAB is responsible of killing more than 40 million ash trees in Michigan, Ohio, Illinois, Indiana and other surrounding states. Unfortunately, EAB can be easily spread either naturally as adult beetles can fly and travel to new areas, or by human assistance through the movement of infested firewood or ash logs from affected areas to neighboring places, including Minnesota. On May 13, 2009, EAB was confirmed in Minnesota (St. Paul). Because these beetles can wipe out all infested ash trees, it is our responsibility to work together to stop the aggressive movement of this invasive pest towards our parks, nurseries, forests, streets and backyards.

Adult EAB are about 3/8 to 5/8 inch long, flattened back with metallic green wing covers, and coppery red or purple abdominal segments beneath wing covers.   Adult beetles leave distinctive D-shaped exit holes in the outer bark of branches and the trunk.  Larvae are creamy white, legless with flattened, bell-shaped body segments. The terminal segment bears a pair of small appendages. Larvae bore through the bark and into the cambial region making S-shaped feeding gallery becoming progressively wider as the larva grows. Galleries weave back and forth across the wood grain.  Due to larvae feeding, canopy dieback begins in top one-third of canopy and progresses until tree is bare.

Other signs of possible EAB infestation include:

The sprouting of epicormic shoots around the base of the tree or at the junction of live and dead parts of the trunk or branches.

Leaves of infested trees often look larger than normal.

Vertical cracks or spilt on bark due to callous tissue formation. Usually under this spilt, galleries are exposed.

From mid May to mid August, adults are active and feed on ash foliage leaving small, irregularly shaped patches along the leaf margins. However, adult feeding causes little damage to the tree.  Generally, adults live a total of three to six weeks. During this period, males and females feed for a few days prior to mating. The feeding is continued for an additional 1 to 2 weeks before females actually begin laying eggs.  Females can mate multiple times during its lifespan and lay from 30-60 eggs. Eggs are deposited individually on the surface of the bark, in bark crevices or under outer bark or branches.  After depositing, eggs soon darken to a reddish brown and hatch in 7 to 10 days.   After hatching, the first instar larvae tunnel into the tree and feed on phloem for several weeks, creating S-shaped galleries packed with fine sawdust-like frass (larvae debris). As a larva grows, its gallery becomes increasingly wider.  Larvae feeding are usually completed in autumn and pre-pupae overwinter in cells found about a half-inch into the sapwood or outer bark.  Pupation usually takes place when it begins to warm up in the spring in April or May.  It takes two to three weeks for EAB pupae to become adults, but adults often remain in the pupal chamber or bark for one to two weeks before emergence. From May to early July adults chew a distinctive D-shaped exit holes in the bark and emerge from the ash trees.   In northern states, a two-year lifecycle can occur in newly infested ash trees that are relatively healthy; whereas in stressed trees, the lifecycle takes only a single year to complete.

EAB adults do not tunnel inside a tree after emergence from a tree trunk; they typically fly within a ½ mile from their emergence tree to feed on ash trees leaves and lay eggs. However, they can fly up to 10 miles, especially when ash trees are not available within their normal flying zone.  EAB larvae are the damaging stage. They live inside a tree and eat through the active phloem and xylem of the ash tree. This causes general yellowing and thinning of the foliage followed by canopy dieback and the eventual death of the tree in one to three years.