Connecticut Department of Energy & Environmental Protection

Emerald Ash Borer in Connecticut

Adult emerald ash borer with green wing covers

The emerald ash borer (Agrilus planipennis, EAB) was first detected in North America in 2002 in southeast Michigan. In 2012, Connecticut became the 16th state to have EAB within its borders. Since that first find in Prospect, EAB has spread throughout Connecticut.

The movement of ash through firewood, nursery stock, logs, and wood packaging materials has been cited as the most likely means by which EAB has spread.

EAB's numbers increase rapidly after infestation, often leading to the death of infected trees within 2 to 3 years. Stands of trees often succumb within 8 years of the insect entering the stand.

Trees at risk

EAB feeds on ash trees almost exclusively. In Connecticut, there are three species of ash trees - white ash (Fraxinus americana), green or red ash (F. pennsylvanica), and black ash (F. nigra). Despite its common name, mountain ash (Sorbus spp.) is not a true ash and does not attract the EAB. To date, the only non-ash genus EAB is known to feed on is Chionanthus (fringe-tree).

Native North American ash species did not evolve in the presence of EAB and have not developed the mechanisms to recognize or cope with EAB. Even healthy native ash trees cannot effectively resist the onslaught of this invasive, non-native beetle.

The elm/ash/red maple forest type is the third-most-common forest type in Connecticut. White ash is the most common ash species in the state. Ash is also part of Connecticut’s urban forest. It can be found along Connecticut's streets and in residential backyards.

Prior to EAB, ash in Connecticut had been in decline for several decades. This was due, in part, to a disease called ash yellows. Now that EAB is in Connecticut, the number of healthy ash trees in the state has been dramatically reduced.

The loss of ash trees from Connecticut’s forests affects wildlife and the economy. Butterflies and moths from nearly 30 different families use ash trees for food and shelter. Seeds of ash are eaten by wood ducks, purple finches, pine grosbeaks, and others.

The wood of the white ash is prized due to its combination of strength and flexibility. Due to its workability, it is used for shovel handles, baseball bats, and electric guitar bodies. Ash has a high-value role to play in Connecticut's timber markets.

Identification

The emerald ash borer is a small, green beetle belonging to the family Buprestidae, or metallic wood-boring beetles. It has green, iridescent wing covers. Adult EABs are between 0.3 and 0.5 inches in length.

Adult emerald ash borer with green wings extended.

Infested ash trees are likely to show thinning and dieback in the upper canopy, as EAB infests the top of the tree first. When ash trees are seriously infested, the entire upper crown of the tree can die. However, there are many causes for thinning and dieback in the crown of an ash tree; that symptom alone cannot be considered diagnostic. If you see crown dieback in an ash tree, look for additional evidence of EAB infestation:

  • Infested trees may grow numerous shoots from the lower trunk or the root flare.
  • The presence of a D-shaped exit hole in the bark of an ash tree is a definitive sign of EAB. This hole is left by the emerging adult as it chews its way out of the tree. There are several other borers that attack ash. None of them produces that same D-shaped hole.
  • S-shaped tunnels will be visible underneath the bark of infested trees. These tunnels are created by the burrowing EAB larvae.
  • If larvae are active in the tree, woodpeckers will likely strip the outer bark in patches and peck holes to feed on EAB grubs. Woodpecker activity on an ash tree is often the giveaway that the tree is heavily infested.

Emerald ash borer D-shaped exit hole on bark.

S-shaped tunnels under tree bark form the emerald ash borer

Life cycle and behavior

EAB lays eggs in the bark of ash trees, and their larvae burrow into the tree to feed. EAB larvae feed on the phloem and cambium layers, which are critical parts of the tree, responsible for the transport of nutrients and for growth.

Phloem tissue is located in the inner bark of the tree. It carries the sugars produced by the leaves throughout the tree. As the EAB feeds on the phloem, the tree loses its ability to use its food source, which causes its death. The cambial tissue, located between the bark and wood, generates new wood. EAB feeding on cambial tissue prevents the tree from forming new cells, thereby depriving it of its ability to respond to injury.

EAB undergoes a complete metamorphosis. It starts as an egg, becomes a larva, then a pupa, and an adult. The EAB life cycle takes 1 to 2 years to complete. Adults emerge from the pupa in June. Emergence continues for about 5 weeks.

The female lays her eggs on the bark of an ash tree about two weeks after she emerges. After 7 to 10 days, the eggs hatch and the larvae move into the bark to begin feeding on the phloem and cambium of the tree. The larval stage may last up to 2 years. Before becoming an adult, the insect overwinters as a larva. It then pupates in the spring and emerges as an adult during the summer.

Diagram illustrating the emerald ash borer life cycle.

Response

EAB is significantly established in North America, so eradication is no longer a goal. Instead, the focus is on slowing or preventing the spread of EAB into new areas while managing and reducing its numbers.

DEEP, the CT Agricultural Experiment Station (CAES), USDA APHIS PPQ, and the U.S.D.A. Forest Service are taking steps to minimize the impact of EAB, including:

  • A quarantine that restricted infested ash materials from leaving Connecticut, including ash logs, hardwood firewood, yard waste, and nursery stock, was in place starting in 2014. The quarantine was lifted in 2021, but regulations on the movement of firewood are still in place.
  • Regulations on the movement of firewood into and within the state.
  • Investigations into forestry techniques, biological control, and chemical control are ongoing. At the same time, there is potential for a genetic protective response in ash trees, or for the emergence of already occurring diseases or predators that can reduce EAB levels.

How to help

Property owners concerned about specific ash trees have options to protect their trees. Information on caring for ash trees can be found at the Emerald Ash Borer Network and on the CT Agricultural Experiment Station (CAES) website.

For people in the State of Connecticut, some ways in which an individual can help are:

  • Know how to identify an ash tree and keep a close eye on ash trees in your community.
  • Report declining ash trees that may pose a danger to people or structures. Public trees, such as those along streets and in parks, are usually under the care and control of the municipal tree warden. If you have concerns about these trees, contact your local tree warden. Trees along state highways are under the control of the State Department of Transportation. Private trees are the responsibility of the property owner.
  • Follow regulations when moving live trees or wood. The use of locally sourced firewood is very important in the effort to prevent further spread of the EAB and other invasive insects. EAB "hitchhikes" readily on firewood, which can then sit in a backyard for a year or more, giving ample time for the insect to emerge.

Because of the widespread nature of EAB, CAES is no longer asking for reports of EAB sightings. You can still share sightings and ask questions by contacting the CAES State Entomologist: CAES.StateEntomologist@ct.gov.

For forest trees, the best defense against EAB is resilient forest management that supports diverse species, age classes, and forest composition. Forestland owners can give careful thought to the management of their woodlands in the face of EAB. The most important recommendation is not to act hastily. Before removing ash or other trees, a range of options should be considered. For more information about the overall health of your forested land, contact your Service Forester.

Resources

Content last updated April 2026.