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Emerald Ash Borer

Agrilus planipennis[12]

The emerald ash borer is an invasive wood-boring beetle from Asia that has killed tens of millions of North American ash trees. Its larvae feed just under the bark, cutting off the flow of water and nutrients until the tree dies.[1][2][3]

Group
Insect
Order
Coleoptera
Family
Buprestidae
US records
34 states
Sources
12 cited
Updated
2026-11-11
Adult emerald ash borer, a slender metallic green beetle with a bronze sheen, standing on a green leaf
Adult emerald ash borer, a slender metallic green beetle with a bronze sheen, standing on a green leaf. Photo: Christine Stone, public domain (CC0), via iNaturalist
On this page
  1. Identification
  2. Look-alikes
  3. Where it lives
  4. Biology
  5. Damage and signs
  6. Health risk
  7. Control
  8. Quarantines and regulations
  9. Related profiles
  10. Common questions
  11. Sources

How to identify it

  • Adults are slender, metallic green beetles about 3/8 to 1/2 inch long and 1/8 inch wide, small enough to fit on a penny.[1][2][4]
  • The abdomen is coppery red, a contrast to the green body; Minnesota describes the back under the wings as bright metallic red.[1][4]
  • Emerging adults leave D-shaped exit holes about 1/8 inch across in the bark; the D is not always obvious and can look like an irregular circle.[2][3][1]
  • Larvae are flat, creamy white and legless, with a brown head, 10 bell-shaped body segments and a pair of small spine-like points (urogomphi) at the tail end.[2][4]
  • Peeling back the bark reveals winding, S-shaped tunnels just under the bark that widen as the larvae grow. Minnesota calls these galleries a definitive sign when found in ash.[1][2][4]

Look-alikes

Look-alikeHow to tell them apart
Other ash borersOther borers that attack ash leave round or oval exit holes, not the D-shaped holes of the emerald ash borer.[2]
Bronze birch borerMinnesota's list of insects confused with emerald ash borer includes this and other metallic wood-boring beetles. Identification is difficult if the insect is not found on an ash tree, so check the host and look for S-shaped galleries under ash bark.[5][4]
Six-spotted tiger beetleAlso on Minnesota's list of insects confused with emerald ash borer. Minnesota notes that look-alikes are hard to rule out when the insect is not found on an ash tree.[5][4]
Mountain ashDespite the name, mountain ash is not a true ash; it is related to roses and is not attacked by emerald ash borer.[2]

Where it lives

Native to East Asia, it was first found in North America in southeast Michigan in 2002, though it may have arrived as early as 1990 in solid wood packing material. It has since spread rapidly across the eastern United States, reaching Minnesota in 2009 and North Carolina in 2013, and abroad it has spread to European Russia and Ukraine. GBIF holds about 3,700 U.S. records since 1990, the most from New York, Minnesota and Pennsylvania.[4][1][3][6][7]

US map: public records from 34 states since 1990 (GBIF).

Biology and life cycle

It attacks true ash trees in the genus Fraxinus; green and white ash are readily killed, while blue ash is more resistant. Kentucky notes it has also been found in white fringetree, and researchers say its possible host range is broader than once thought.[2][8]

Development time varies with climate: Kentucky says it usually completes one generation a year there, while Minnesota says one generation takes one to two years.[2][4]

Sources describe the timing a little differently. Kentucky says larvae overwinter, pupate in spring and appear as adults by early summer; APHIS says they pupate in winter and emerge in spring, with adults active until the end of summer. Minnesota treats May 1 to September 30 as the flight season.[2][1][4]

Adults live about three weeks, are most active on warm, sunny days, and nibble ash leaves while mating, which does little harm. Females lay eggs one at a time in bark cracks and crevices from mid-June through August in Minnesota, and the eggs usually hatch within two weeks.[1][2][4]

Adults fly well on their own, but people move the beetle much farther in infested firewood, logs and nursery stock.[1][4][3]

Damage and signs

  • Early signs are dieback in the upper third of the canopy and sprouts growing from the lower trunk.[2][3]
  • Woodpeckers flake off bark to reach the larvae, so extra woodpecker activity on an ash is a warning sign; vertical bark splits appear as the tree declines.[1][2][3]
  • White and green ash usually die within 7 to 10 years of infestation, or within 1 to 2 years when beetle numbers are high or the tree is already stressed.[2]
  • Ash trees killed by the borer turn brittle and break apart quickly, creating dangerous hazard trees.[2]
  • The larvae stay just under the bark and don't damage the wood itself, but stressed and dying ash are quickly hit by bark and ambrosia beetles that cut timber value, so Kentucky advises harvesting before or soon after the trees die.[2]

Health risk

The emerald ash borer harms ash trees, not people; the main safety concern is dead ash limbs and trunks falling.[2]

Control

Prevention

Don't move firewood; buy local firewood or certified heat-treated firewood so you don't carry the beetle to new areas.[1][4]

Traps and physical control

Remove and replace ash that has lost more than half its canopy, has structural defects or isn't valuable, and plant a mix of tree species instead of a single kind.[2]

Biological control

USDA rears and releases tiny stingless parasitic wasps against the emerald ash borer. In New York forests the larval parasitoid Tetrastichus planipennisi established both where it was released early in the invasion and after the big ash had died, and together with woodpeckers it kept the borer's reproduction low. Insecticide injections did not keep the parasitoids from establishing.[1][10][9]

Pesticides

Healthy or newly infested ash trees can be protected with systemic insecticides, and treatment must be repeated regularly as long as the beetle is in the area.[2][3]

Start treatment before trees are infested, ideally once the beetle is known within 10 to 15 miles; if more than half the canopy is thinned or dead, it is too late.[3][2]

Options include soil drenches or injections of imidacloprid or dinotefuran, bark sprays of dinotefuran, and trunk injections of products such as emamectin benzoate or azadirachtin.[3]

In a USDA-led study, ash given emamectin benzoate trunk injections and retreated after three years kept healthy crowns in 90 percent of cases after five years, against 16 percent of untreated trees, but treated trees did not protect their untreated neighbors.[9]

When to call a professional

Trunk injections take some know-how, and the emamectin benzoate product in the guide is restricted use, so those treatments are usually left to licensed applicators.[3]

Quarantines and regulations

There is no longer a federal domestic quarantine. APHIS removed its domestic emerald ash borer quarantine regulations in 2020, with the final rule taking effect January 14, 2021, and its program now focuses on biological control, detection surveys and public outreach.[1]

States can still set their own rules. Minnesota, for example, quarantines counties where the borer is confirmed, regulates ash logs, ash tree waste, ash chips and mulch and all non-coniferous firewood, and bars moving them out of a quarantined area without a state certificate or bringing them into the state without approval. Check with your state department of agriculture before moving ash wood or firewood.[11][4]

Common questions

How do I know if my ash tree has emerald ash borer?
Look for thinning in the upper canopy, sprouts on the lower trunk, heavy woodpecker work, bark splits and small D-shaped exit holes on the trunk; under the bark, S-shaped galleries in ash are a definitive sign.[2][1][3][4]
Is it worth treating my ash tree?
Treatment makes sense for healthy, valuable ash with most of its canopy intact; trees with less than half their canopy left are better removed and replaced.[2][3]
How do I report emerald ash borer?
USDA APHIS takes reports of suspected infestations through an online form or its toll-free line at 1-866-322-4512.[1]
Is there still an emerald ash borer quarantine?
Not at the federal level: APHIS ended its domestic quarantine effective January 14, 2021. Some states still regulate ash wood and firewood; Minnesota, for one, quarantines infested counties.[1][11]
How often do treated ash trees need retreatment?
It depends on the product; follow the label. The N.C. Forest Service guide says imidacloprid soil drenches should be repeated every year for best control, and Kentucky says any treatment has to be repeated regularly for as long as the beetle is around.[3][2]

Sources

  1. USDA Animal and Plant Health Inspection Service, “Emerald Ash Borer.” www.aphis.usda.gov/plant-pests-diseases/eab (accessed 2026-11-11)
  2. University of Kentucky Entomology, “ENTFACT-453: Emerald Ash Borer (EAB) FAQs for Kentuckians.” entomology.mgcafe.uky.edu/ef453 (accessed 2026-11-11)
  3. N.C. Forest Service, Forest Health Branch (NCDA&CS), “Emerald Ash Borer Insecticide Guide.” ncagr.gov/divisions/nc-forest-service/EAB_InsecticideGuide/download (accessed 2026-11-11)
  4. Minnesota Department of Agriculture, “Emerald Ash Borer.” www.mda.state.mn.us/plants-insects/emerald-ash-borer (accessed 2026-11-11)
  5. Minnesota Department of Agriculture and Minnesota Department of Natural Resources, “Insects in Minnesota Confused with Emerald Ash Borer (reference sheet, 2025).” www.mda.state.mn.us/sites/default/files/docs/2025-07/Insect_Minnesota_Confused_with_Emerald_AshBorer_WEB.pdf (accessed 2026-11-11)
  6. Annual Review of Entomology, via PubMed, “Emerald Ash Borer Management and Research: Decades of Damage and Still Expanding (Sun et al. 2024).” pubmed.ncbi.nlm.nih.gov/37708417/ (accessed 2026-11-11)
  7. Global Biodiversity Information Facility (GBIF), “Agrilus planipennis: U.S. occurrence records since 1990 by state (GBIF occurrence search).” api.gbif.org/v1/occurrence/search?taxonKey=5878492&country=US&hasGeospatialIssue=false&occurrenceStatus=PRESENT&year=1990%2C2026&facet=stateProvince&facetLimit=400&limit=0 (accessed 2026-11-11). Exact count at access: 3,673 U.S. records since 1990 (New York 473; Minnesota 435; Pennsylvania 371; Wisconsin 261; Michigan 227).
  8. Oecologia, via PubMed, “The potential for host switching via ecological fitting in the emerald ash borer-host plant system (Cipollini and Peterson 2018).” pubmed.ncbi.nlm.nih.gov/29484497/ (accessed 2026-11-11)
  9. Journal of Economic Entomology, via PubMed, “Effects of emamectin benzoate trunk injections on protection of neighboring ash trees against emerald ash borer and on established biological control agents (Duan et al. 2023, USDA ARS).” pubmed.ncbi.nlm.nih.gov/37084325/ (accessed 2026-11-11)
  10. Journal of Economic Entomology, via PubMed, “Establishment and impacts of emerald ash borer parasitoids released at early- and post-invasion sites (Morris et al. 2023).” pubmed.ncbi.nlm.nih.gov/37335889/ (accessed 2026-11-11)
  11. Minnesota Department of Agriculture, “Emerald Ash Borer Quarantine.” www.mda.state.mn.us/plants-insects/emerald-ash-borer-quarantine (accessed 2026-11-11)
  12. iNaturalist, “Agrilus planipennis taxon page (order and family).” www.inaturalist.org/taxa/70057 (accessed 2026-10-06)

Updated 2026-11-11. Built from sourced records. Spot an error? Tell us.