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Emerald ash borer (Agrilus planipennis)


Overview

Overview

Emerald ash borer (Agrilus planipennis) is an invasive, wood-boring beetle that kills ash trees (Fraxinus spp.) by eating the tissues under the bark. Native to northeastern Asia, emerald ash borer (EAB) was first detected in the United States in 2002 and is thought to have been introduced from China via the wood from shipping crates.

See where EAB has been found in Wisconsin and in the United States. Use the interactive map on the EAB portal to see if EAB has been found in your township and learn how to report new detections.

Life cycle

Adults: Late May to September

Adult beetles emerge from infested ash trees by creating a D-shaped exit hole that is about 1/8" wide. Most beetles will disperse less than 1/2 mile from their original location unless transported by humans in firewood or other unprocessed wood products.

Egg: June through September

Female beetles lay 40-200 eggs in the bark crevices of ash trees. EAB eggs are very small and difficult to see. They hatch in about two weeks.

Larva: June through October

Larvae tunnel and feed in the nutritious tissue beneath the bark. They wind back and forth as they feed, creating S-shaped patterns called galleries under the bark. The larval stage is the most destructive because their feeding behavior disrupts the flow of nutrients through the tree. They feed under the bark for 1–2 years and can survive in green wood, such as firewood, if the bark is still attached.

Larval overwintering: October through May

After one or two years of feeding under the bark, larvae will create a chamber for themselves in the wood beneath the bark. Mature "pre-pupal" larvae are usually J-shaped.

Pupa: Spring

The overwintering, mature larvae pupate inside the tree and gradually transform into adults. 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 the spring before turning into adults. The beetles emerge from the tree, completing the life cycle.

Identification

What does it look like?

Each of the four life stages (adult→egg→larva→pupa) of EAB look remarkably different.

Adult (beetle)

Adult beetle
Adult. Bill McNee, Wisconsin DNR.

Eggs
Eggs. David Cappaert, Bugwood.org.

Larva
Larva. Bill McNee, Wisconsin DNR.

Pupa
Pupa. Bill McNee, Wisconsin DNR.

EAB adults are very small, metallic green beetles. They are about the size of a cooked grain of rice: between 3/8- and 1/2-inch long and 1/16-inch wide. Due to their size, they can often go undetected, but they can be seen on ash bark and leaves during their brief lifespan (3–6 weeks).

Egg

EAB eggs are very small (1 mm), difficult to find and are rarely seen. Female beetles deposit them in bark crevices and as larvae hatch from the egg, they immediately chew their way into the tree.

Larva (immature emerald ash borer)

EAB larvae are cream-colored and slightly flattened, with a pair of brown pincher-like appendages on the last segment. Their size varies as they feed and grow under the ash tree's bark. Fully grown, they average about 1.5 inches in length.

Pupa

During the pupal stage, EAB larvae transform into adult beetles. During this process, features of the adult beetles become more apparent. The pupae, like the larvae, cannot be seen unless bark is pulled away from the tree.

Emerald ash borer look-alikes

There are many metallic green insects that are common in Wisconsin and often mistaken for EAB. For more information on these look-alikes, visit the University of Wisconsin–Madison's emerald ash borer webpage or see a side-by-side comparison of look-alikes. (Please note that the six-spotted tiger beetle may have any number of spots or none at all.)


Signs/symptoms

Do my trees have EAB?

It is important to look for at least two signs or symptoms when trying to figure out if EAB is in your ash tree because some symptoms can look like those caused by other pests and diseases.

Signs and symptoms

Symptoms are the characteristics expressed by an infested tree, such as crown dieback and epicormic sprouting. Signs are the physical evidence of the pest or disease, including larval galleries, exit holes and all life stages of the insect.

D-shaped exit holes
D-shaped exit holes

As adults emerge from under the bark they create a D-shaped exit hole that is about 1/8-inch in diameter. Photo by Linda Williams, Wisconsin DNR.

S-shaped larval galleries
S-shaped galleries

As larvae feed under the bark they wind back and forth, creating serpentine galleries packed with frass, or the digested woody materials created by wood-boring insects. Photo by Linda Williams, Wisconsin DNR.

Emerald ash borer larva
Larvae

Larvae are cream-colored, slightly flattened (dorso-ventrally) and have pincher-like appendages at the end of their abdomen. Fully grown, they reach about 1/2-inch in length. Photo by Linda Williams, Wisconsin DNR.


Adult emerald ash borer beetle
Adult beetles

Adult beetles are metallic green and about the size of one grain of cooked rice (3/8- to 1/2-inch long and 1/16-inch wide). The best time to see an adult EAB is a warm, sunny afternoon when they are likely to be either mating or laying eggs on the trunks of ash trees. Photo by Linda Williams, Wisconsin DNR.

Ash tree with crown dieback
Crown dieback

Dieback is a result of larval feeding, which disrupts the flow of nutrients and water to the upper canopy. Trees typically show thinning of leaves at the top of the tree within 1–3 years of infestation, followed by individual branch and tree death. Photo by Bill McNee, Wisconsin DNR.

Tree with branches growing from the base of the tree
Epicormic sprouting

When trees are stressed or sick, they will try to grow new branches and leaves wherever they still can. Trees may have new growth at the base of the tree and on the trunk, often just below where the larvae are feeding. Photo by Bill McNee, Wisconsin DNR.


Bark splitting
Bark splits

Vertical splits in the bark are caused due to callus tissue that develops around larval galleries. Larval galleries can often be seen beneath bark splits. Photo by Joseph O'Brien, Bugwood.org.

Tree with bark missing
Woodpecker flecking

Woodpeckers pick away at the outer bark of infested trees in search of nutritious larvae beneath the bark. This "flecking" usually begins higher in the tree where EAB tends to attack first. Once a tree becomes heavily infested, flecking may be seen all the way down its trunk and branches. Photo by Bill McNee, Wisconsin DNR.



Ash trees

Ash in Wisconsin's forestlands

An estimated 898 million ash trees are in Wisconsin's forestlands as part of northern hardwood, oak-hickory and bottomland hardwood forests. Ash species represent 3.9% of all trees in Wisconsin’s forests (counting all live trees 1-inch in diameter or larger). Black ash is the most common ash species and represents 4.0% of total tree density. White and green ash represent 2.0 and 1.8% of total tree density, respectively. Read more about Wisconsin’s ash resource.

EAB attacks all native species of ash in Wisconsin, including white, green, black and blue ash. While other woody plants, such as mountain ash and prickly ash, have “ash” in their names, they are not true ash species and therefore are not susceptible to attack by EAB.

True ash trees provide many ecological benefits: their seeds provide food for birds and small mammals; black ash twigs and leaves provide food for deer and moose; and trunk cavities provide nesting areas for birds such as the wood duck. Ash is also valuable to Native Americans for its excellent basket-making quality and cultural importance.

Ash in Wisconsin's urban forests

There are an estimated 104,000 ash trees in Wisconsin’s urban and community forests. This accounts for 14.7% of all trees reported in community tree inventories provided to the DNR. Green and white ash are the most common ash species in these settings, making up 11.2 and 2.6% of total street trees, respectively. Other ash species include black, blue and European ash, which together account for a combined 0.8% of all street trees.

Woodpecker feeding
Black ash

Black ash (Fraxinus nigra) can be found throughout the state, with the highest densities occurring in northern Wisconsin. This species prefers wet sites, such as riparian areas and swamps, and forest cover types, such as bottomland hardwoods, swamp hardwoods and swamp conifers. Currently, black ash is not very commercially important. However, it is valued by Native Americans due to its ability to split along growth rings, resulting in thin strips for making baskets, chair seats and barrels.


Woodpecker feeding
Green ash

Green ash (Fraxinus pennsylvanica var. lanceolata) is found throughout the state but is most common in southern Wisconsin. It grows in stands with green ash or in combination with black ash, red maple, silver maple, swamp white oak and elm. It is a component of upland hardwood stands but grows most commonly in and around stream banks, floodplains and swamps. Green ash wood is not as straight-grained as white ash and thus not as commercially desirable.


Woodpecker feeding
White ash

White ash (Fraxinus americana) grows on a variety of sites but is most frequently found on fertile, well-drained upland sites in both the northern and central hardwood forest types. White ash typically grows as part of other forest cover types and is rarely the dominant species. With its white, strong, straight-grained wood, it is the most commercially important ash species in Wisconsin. It is also valued for its high elasticity, shock resistance and low shrinkage.


Blue ash

Blue ash (Fraxinus quadrangulata) is the least common ash species in Wisconsin with a range limited to southern Wisconsin, particularly Waukesha County. It is listed as a threatened species in Wisconsin and is on the edge of its North American range here. It has inner bark that was used as a blue dye by Native Americans giving the species its common name. The species likes rich limestone hills but grows well on fertile bottomlands. Because of its small size and scattered distribution, blue ash is not commercially important.

Potential impact

Impact in Wisconsin

True ash species are highly vulnerable to EAB regardless of ash or total tree density, ash or total stand basal area, tree size and tree health. Researchers in Michigan and Ohio observed that ash survival decreased 30-50% over three years in infested stands in southeastern Michigan. Models developed from field observations predict that a healthy forest will lose 98% of its ash trees in 6 years.

While the insect spreads slowly on its own, EAB impacts are greatly accelerated when people unintentionally move it in firewood and nursery stock. See the spread of EAB detections in Wisconsin by county since it was first detected in 2008.

EAB commonly kills ash in urban areas and along roadsides in infested areas, costing municipal governments millions of dollars for tree removal and replacement. The financial impact of EAB in Wisconsin forests is unknown but is believed to be substantial.

Rays of hope for ash trees

Some progress has been made in managing EAB populations. A tiny, native wasp was discovered killing EAB larvae at two sites in Michigan. Between 24% and 56% of EAB larvae at these two sites in 2008 were parasitized by this native wasp. We may yet discover more native insects that attack EAB and help reduce their populations.

Parasitic insects from EAB’s native range in China show promise for biological control efforts. DNR forest health specialists in Wisconsin have released a total of four species of parasitic wasps in efforts to control EAB populations, although only three species have proven cold-tolerant enough to survive Wisconsin winters. To date, one wasp species (Tetrastichus planipennisi) has been successfully recovered in seven southeastern Wisconsin counties, which indicates that wasp populations are sufficiently stable in these locations to reproduce and parasitize new generations of EAB larvae.

What you can do

While EAB is present in many Wisconsin counties, more of Wisconsin is still free of EAB than not. Many counties where it has been found have only small areas of infestation. That is why it is still critically important to limit the movement of ash wood and raw ash products. By taking these precautions, we all help slow the spread of EAB.

For woodlot owners and managers

The Wisconsin Department of Natural Resources has partnered with other scientists and land managers to create EAB silviculture guidelines to help forest landowners manage their ash resources. It is important that landowners evaluate the potential impacts of EAB and take action.

For more information on EAB management in woodlots and forests, contact your local forester or DNR forest health specialist.

For homeowners and communities

For ash trees in urban and residential settings, protecting them from EAB requires insecticidal treatment. Federally approved insecticides can be effective in preventing individual trees from becoming infested. This option typically requires repeated applications for the life of the tree. Alternatively, homeowners and communities may opt to remove ash trees and replace them with non-susceptible species to maintain the many benefits that urban trees provide. It is important to note that removing ash trees should be done before EAB has killed the tree. EAB-killed trees are prone to breakage and are much more dangerous to remove.

To slow the spread of EAB into new, unaffected counties and townships, follow the suggestions on this page. These recommendations also apply to other harmful pests and diseases, such as gypsy moth and oak wilt.

  • Although Wisconsin is now under a statewide quarantine, we still recommend that you buy firewood within 10 miles of where you will burn it.
  • Wisconsin’s statewide firewood rule prohibits bringing firewood onto any state property from more than 10 miles away or from areas within the gypsy moth quarantine. Visit the firewood page for more information.
  • Buy certified firewood at state properties, retail locations or directly from firewood dealers.
  • Burn all firewood during your camping trip. Do not take it with you when you leave or leave any unused wood behind.
  • Look for firewood that is dry with either no bark or loose bark. EAB larvae live beneath the bark and can survive for up to two years on dead wood.
  • Consider using gas or charcoal instead of firewood. Explore new nighttime activities like star-gazing or viewing wildlife by flashlight.

For more information on EAB management in urban and residential settings, visit the emerald ash borer community toolbox and the University of Wisconsin-Extension's EAB website. You can also contact your regional DNR urban forestry coordinator or find a certified arborist.

Last revised: Monday March 18 2019