EXOTIC PEST THREATS
UMD Entomology Bulletin, 2008
Emerald Ash Borer
Agrilus planipennis Fairmaire (Coleoptera: Buprestidae)
INTRODUCTION:
The Emerald Ash Borer (EAB) is an aggressive exotic wood boring beetle
native to Asia that attacks stressed and healthy ash trees, frequently causing
death within 3 years of infestation. First detected in the U.S. in Michigan in
2002, it has spread rapidly to neighboring states, threatening this important
resource of timber, landscapes, wildlife habitat and urban street trees. It is
estimated there are over 8 billion ash trees in the U.S. and to date EAB has
destroyed over 25 million trees, more than 15 million of those in Michigan
alone. It has cost property owners, nursery operators, municipalities and
forest products industries tens of millions of dollars. The USDA estimates
that losses could reach $20-60 billion nationwide if EAB is not controlled.
DISTRIBUTION/SPREAD:
EAB is native to northeastern China, Korea, Mongolia, Japan, Taiwan and
the Russian Far East. It is thought that EAB came to North America in UGA1241011
infested wood packaging materials from shipments originating in its native EAB adult with penny for size comparison. Howard Russell,
range. EAB was first confirmed in Michigan and Ontario, Canada, in 2002, Michigan State University, Bugwood.org
but it is believed to have been established there for about a decade prior to detection. It has since been found in Ohio (2003),
Maryland (2003), Indiana (2004), Virginia (2003, 2008), Illinois (2006), Pennsylvania (2007), West Virginia (2007),
Missouri (2008), and Wisconsin (2008). EAB is a competent flier, readily traveling about ½ mile (0.8 km), with several
reports of a mile or more (≥ 1.6 km). EAB is spread long distances primarily by people moving infested ash wood products
(firewood, branches, logs and nursery stock) into uninfested areas. This has resulted in regulatory agencies establishing
quarantines and fines to control the human activities responsible for spreading EAB.
HOST PLANTS:
In China, the only reported host for EAB is ash (Fraxinus), including, F. chinensis var. chinensis, F. chinensis var.
rhynchophylla, and F. mandshurica. In East Asia, host plants in addition to ash include elm (Ulmus), walnuts and hickories
(Juglandaceae), and wingnut species (Pterocarya). In North America, only ash trees have been attacked. Of the 16 native ash
species, those reported killed to date include green ash (F. pennsylvanica), white ash (F. americana), black ash (F. nigra), and
several horticultural varieties. EAB has killed stressed and apparently vigorous trees in woodlots as well as urban settings.
BIOLOGY and DAMAGE:
EAB typically completes one generation each year, although when healthy trees are attacked, it may take up to two years. In
a one-year cycle, mature larvae overwinter in pupal chambers excavated at a shallow angle into the outer sapwood, or into
the inner bark of thick-barked trees, and pupate in the spring. In the two-year cycle, larvae overwinter as early instars the first
winter, resume feeding throughout the next spring and summer, overwinter again as 4th instar larvae or prepupae, and finally
emerge as adults the second spring. Newly pupated adults bore through the bark to the outside, emerging head-first through a
D-shaped exit hole about ⅛” (3-4 mm) in diameter. EAB adults begin emerging in early to mid-May, peak in June, and may
continue emerging through July. Adult males live an average of 13 days and females approximately 22 days.
After emerging, adults walk to the crown of their host tree and begin feeding on the foliage, causing minimal damage but
creating small, irregularly shaped notches along leaf margins. Initial flight usually begins within 3 to 4 hours after the first
feeding. Adult EAB are most active during daylight hours when the weather is calm and sunny. At night, during overcast
weather, and at temperatures above 90ºF (32ºC), adult beetles rest in cracks in the bark or on foliage. Mating occurs during
the first 7-10 days after emergence and females mate multiple times. Egg laying begins a few days after mating, and occurs
from late-May through July/August. Each female lays an average of 77 eggs, usually deposited individually in crevices in the
bark along the upper trunk and major branches.
Emerald Ash Borer, Agrilus planipennis Fairmaire
Eggs hatch in 7 to 9 days and the larvae tunnel through the bark to the cambial layer and feed on the inner bark (phloem)
and outer sapwood for several weeks. The S-shaped feeding galleries become progressively wider as the larvae grow and are
packed with fine, sawdust-like frass. Galleries often meander over areas ranging from 4 to 20” (10-50 cm) in length. Larvae
feed until cooler fall temperatures arrive, when they prepare for overwintering. The larvae are the destructive stage, tunneling
through and feeding on cambial tissues under the bark and eventually girdling the tree or branch. This prevents the movement
of nutrients and water within the cambium and can lead to decline and death of a tree within 1 to 3 years of infestation.
IDENTIFICATION:
• Adults are slender, elongate beetles, about
½” long (13 mm), and 1/16” wide (1.6 mm),
lacking a defined waist, flattened laterally (top to
bottom).
• Adults are dark metallic green in color with
a coppery green head; the top of the abdomen
under the wings is purplish red.
• Larvae are creamy white flat-headed borers
with a small brown head retracted inside an
enlarged, distinct, flattened prothorax.
• Larvae have bell-shaped abdominal segments Adult EAB: slender, flattened laterally. David Cappaert, Michigan State
without legs, flattened laterally, with a pair of University, Bugwood.org
brown pincers (urogomphi) on the last segment.
• Mature larvae can reach 1-1¼” in length (25-
32 mm).
• Larvae are found under the bark in shallow
S-shaped galleries, feeding in the cambium.
WHAT TO LOOK FOR:
EAB have infested and killed ash trees in nursery,
landscape, and forest settings. They have been
found in branches and trees ranging from 1 to
55” in diameter (2.5-140 cm), although they seem
to prefer trees with a diameter greater than 10”
(25.4 cm). EAB appear to attack the upper trunk
and lower portions of main branches initially, Adult EAB: top of abdomen is purplish. David Cappaert, Michigan State
and then concentrate along the lower trunk in University, Bugwood.org
succeeding years. It is difficult to detect EAB in
newly infested trees because oviposition usually
begins along the upper trunk, eggs are laid deep
in bark cracks, and larval feeding occurs under
the bark. Most symptoms are not manifested until
a year after the summer of initial attack.
Symptoms of EAB infestation include:
• Woodpecker feeding injury (small bark
patches stripped away, jagged holes, usually
several holes are present).
• Foliage wilts and yellows; tree canopy thins
and die-back (flagging) of the crown occurs
(typically 30% to 50% of the canopy after 2 years
of infestation). Late instar larva: bell-shaped abdominal segments without legs, flattened
laterally. David Cappaert, Michigan State University, Bugwood.org
• Vertical splits in the bark 2-4” long (5-10 cm)
above larval galleries from the previous year.
2
Emerald Ash Borer, Agrilus planipennis Fairmaire
• D-shaped exit holes about ⅛” wide (3-4 mm) left by adults emerging the summer following initial infestation.
• Epicormic shoots (“sprouts”) growing from the lower trunk and on some major branches.
• Larval galleries beneath the bark in the cambium: typically S-shaped, meandering, frass-packed (no frass is pushed out of
boring holes), increasing in width as larvae grow.
• Larval galleries are sometimes surrounded by
an elliptical area of discolored sapwood caused
from secondary infection by fungal pathogens.
MONITORING:
State Departments of Agriculture or USDA
APHIS have implemented surveying in EAB
susceptible regions. In 2004, APHIS adopted a
girdled ash trap tree, with or without sticky
band, as the standard survey method for EAB
infestation. Trap trees are used to monitor
population locations and levels, but because EAB
initially attack in the crowns of trees, detection
from the ground can be difficult. Trap trees are
girdled in the spring; then cut down, debarked
and inspected for EAB larvae in the fall of the
same year.
Attractant sticky traps are gaining popularity
because they can be applied systematically, are D-shaped exit hole (left) and woodpecker damage (right). David Cappaert,
Michigan State University, Bugwood.org
less costly than trap trees, and are comparable in
terms of trap efficiency. The current APHIS
recommendation is to use purple Coroplast
panels, placed 6-12 ft. high (1.8-3.7 m), in sunny
spots on stressed ash trees in the woods, using
Manuka oil (a product extracted from tea trees)
as a lure. The panel traps are manufactured by
Coroplast, Inc., in Dallas, TX:
www.coroplast.com.
The public can help by being alert for signs of
active insects and damage to ash trees (see “What
to Look For”).
MANAGEMENT:
Management strategies for EAB should include
surveys for the presence of the beetles, trace
backs of infested ash nursery stock or wood
products, appropriate handling of infested trees
and materials, the use of trap trees to monitor
continued infestations, public education and,
where indicated, quarantine and regulation. If
possible, the number and location of ash trees
within a susceptible community or region should
be determined by visual survey before an EAB
infestation is even known to exist, in order to
provide baseline information to determine the
allocation of resources (manpower, equipment,
materials and funds) needed in the event of an
infestation. Larval galleries beneath the bark. Art Wagner, USDA APHIS PPQ, Bugwood.
3
Emerald Ash Borer, Agrilus planipennis Fairmaire
Regulatory
EAB is a pest of regulatory significance in the U.S., and detections of EAB
infestation bring immediate attention from the USDA APHIS and state
regulatory agencies. Surveying, eradication programs, and the establishment
of state and federal quarantines are currently the course of action in most EAB
infested areas. Surveys establish the boundaries of an infestation. Eradication
efforts include the removal and destruction of all host trees within a designated
radius of an infested tree (Maryland: 2 mile radius). Quarantines restrict the
movement of ash tree materials and hardwood firewood in an effort to contain
the further spread and impact of EAB. Public education programs are also
conducted to enlist the public’s help in preventing the spread of this pest.
Cultural Control
Since EAB attacks healthy trees, cultural practices to enhance vigor may have
little impact, although younger, healthier trees do appear to better withstand
EAB attacks than mature, less vigorous trees. Ash produces both male and
female trees, so plant breeders hope there may be some variability in seedlings
that could lead to the discovery of genes for EAB resistance. MacFarlane and
Meyer and others determined in 2005 that some ash cultivars may be resistant
to EAB, and research continues in this field. Michigan State University has
utilized “sink” trees in test sites, where a cluster of trees are girdled to attract
Vertical splits in bark, 2nd year. Pennsylvania Dept. of
EAB, then are removed in the fall, effectively killing overwintering larvae. Conservation and Natural Resources, Bugwood.org
Mechanical/Physical Control
Current USDA recommendations for EAB control and prevention include removing the bark and ½” (1.27 cm) of hardwood
from ash wood products, chipping wood and bark to less than ½” in any dimension, kiln drying or fumigating lumber per
International Standards for Phytosanitary Measures (ISBM), and heat treatment of logs and firewood. Scott Myers, the
Brighton Institute, investigated the use of heat treatments to kill EAB larvae in firewood and found that heating firewood to
149°F (65°C) for 30 minutes resulted in 100% mortality in his studies.
In January 2004, the U.S. completed an ash free zone (AFZ) from Lake Erie to Lake St. Clair at the leading edge of the EAB
infestation into Canada. Over 100,000 trees were removed in an area measuring nearly 19x6 miles (30x10 km). However,
EAB were found past the AFZ due to people moving infested host material, firewood and logs. Canada also tried creating a
firebreak to stop the spread of EAB, but it too failed. Canada stopped cutting down infested trees when it was found that the
practice was not cost effective.
Biological Control
There are no significant naturally occurring biological controls of EAB in North America. Although woodpeckers and a few
beetles are known to feed on EAB larvae in the U.S., and a few parasitoids and entomopathogenic fungi have been
identified as well, their efficacy has not yet been evaluated. EAB is typically not a significant pest in its native range because
of ash tree resistance and natural enemies that keep EAB populations low, so in 2002 researchers began searching for
predators and parasitoids that might be successfully introduced into the U.S. Three parasitoids of interest were found in China
and are being investigated. In 2007, there were small scale releases of parasitoids in Michigan and more are planned. APHIS
plans to construct a production facility for rearing EAB parasitoids. The parasitoid species under consideration include:
Spathius agrilli (Hymenoptera: Braconidae) – Larval parasitoid. This wasp is currently being successfully reared in the
laboratory and host range testing is being done in quarantine in the U.S. Adult wasps paralyze EAB larvae, then lay 1-20 eggs
on its skin. The eggs hatch and the wasp larvae use the paralyzed EAB larvae as a food source. In China, Spathius sp.
parasitism rates were up to 90% at some sites. This wasp has 4 generations per year. (Gould et al. 2005)
Tetrastichus planipennis (Hymenoptera: Eulophidae) – Larval parasitoid. Rearing methods are currently being developed
in quarantine in the U.S. This wasp has 4 generations per year and parasitism rates in China were up to 50% at one site.
(Gould et al. 2005)
Oobius agrilli (Hymenoptera: Encyrtidae) - Egg parasitoid. Currently being reared in quarantine in the U.S. for future host
range testing. The adults are parthenogenic, meaning they reproduce without male fertilization. (Gould et al. 2005)
A braconid wasp parasitoid, Atanycolus spp., possibly nonindigenous, has established at multiple sites at a state park near
Fenton, MI. From 2-83% of EAB larvae were parasitized in some trees at 9 out of 10 sites tested in the park. The wasp was
found again in another park 15 miles (24 km) away. Efforts are underway to determine if this surprise volunteer can join the
forces of biological control of EAB in North America.
4
Emerald Ash Borer, Agrilus planipennis Fairmaire
Chemical Control
Foliar and trunk sprays and chemical injections hold some promise for
control, but these methods are more practical in landscape settings than in
natural areas. Studies indicate that foliar spraying during maturation feeding
(on foliage) by newly emerged adults (May-June in MD) is more effective
than pesticide injection. Natural and chemical pesticides and methods of
application are currently being evaluated. Contact your local Cooperative
Extension Service office for current pesticide recommendations.
LOOK-ALIKE INSECTS and DAMAGE:
The adult EAB differs from the many native species of Agrilus in the U.S.
in that EAB is slightly larger, is a brighter green color, and the top of the
abdomen beneath the wings is purplish.
Two native and somewhat common Agrilus borers sometimes mistaken for
EAB are:
• Bronze birch borer (Agrilus anxius): adults bronze or dark brown in color,
about ½” long (1.27 cm), similar in shape to EAB, D-shaped exit holes, attack
only birch trees.
• Two-lined chestnut borer (Agrilus bilineatus): adults dark in color with two
lighter colored lines down the back, ½” long (1.27 cm), similar in shape to
EAB, attack oaks. Epicormic sprouts on trunk. Edward Czerwinski,
Ontario Ministry of Natural Resources, Bugwood.org
There are also a number of very common but unrelated native borers destructive to ash which may be mistaken for EAB.
Virtually every stressed or dead ash tree will at some point be colonized by native borers. Although many signs and
symptoms of native borer infestations resemble those of EAB, the important distinguishing characteristics are the nature of
the galleries (serpentine and shallow for EAB), the flattened shape of EAB larvae, and the distinctly different D-shape exit
holes of EAB. Native ash borers of significance include clearwing borers, roundheaded borers and Eastern ash bark beetles.
• Native clearwing borers: Banded ash clearwing borers (Podosesia aureocincta) and ash/lilac borers (P. syringae)
o Adults are moths that are wasp-like in appearance.
o Larvae are round, with legs, a distinct brown head, and no pincers at tail end.
o Galleries go deep into the sapwood.
o Frass is expressed from tree; sawdust may accumulate on the trunk and at the base of the tree.
o Round exit holes, usually greater than or equal to ¼” (6 mm) diameter.
o Pupal cases may protrude out of exit hole.
o Attack stressed ash trees.
• Native roundheaded borers: Redheaded ash borer (Neoclytus acuminatus), Banded ash borer (Neoclytus caprea), Ash and
privet borer (Tylonotus bimaculatus)
o Adults are longhorned beetles (having very long antennae), marked with stripes or bands on the elytra.
o Larvae are round, legless, with enlarged pronotum. (“Michelin Tire Man” shape)
o Galleries less S-shaped than EAB; initiate under bark then extend into sapwood.
o Oval/round exit holes, greater than or equal to ¼” (6 mm) diameter.
o Attack stressed, dying and dead ash trees.
• Eastern ash bark beetles (Hylesinus aculeatus)
o Adults are small, cylindrical beetles that tunnel beneath the bark.
o Infested tree trunks are peppered with tiny 1/16” (0.06 mm), round exit holes.
o Attack stressed, dying and dead ash trees.
Miscellaneous other beetles that have been confused with EAB include:
• Six-spotted tiger beetle (Cicindela sexguttata): adult iridescent green or blue with white spots around edge of abdomen, ½”
long (1.27 cm), abdomen wider than head and thorax. Ground dweller, preys on insects.
• Caterpillar hunter (Calosoma scrutator): adult green with darker head, thorax and legs, 1” long (2.5 cm), abdomen wider
than head and thorax. Preys on caterpillars, usually active at night.
• Japanese beetle (Popillia japonica): adult metallic greenish/purplish, ¼”
(6.35 mm).
• S-shaped, frass-packed galleries just beneath the bark, restricted to the phloem. (Instead of straight, slightly winding, or
radiating from a straight central gallery.)
Non-specific EAB symptoms such as wilt, discolored leaves, thinning canopy, top dieback and water sprouts can also be
confused with certain other pathogens or abiotic stress factors:
• Diseases such as ash yellows.
• Other phloem feeders such as the two-lined chestnut borer.
• Abiotic stress factors such as compacted soil, poor site selection, drought and other cultural or environmental factors.
How to Report a Possible Sighting/Infestation
In Maryland:
University of Maryland Cooperative Extension Exotic Pest Threats Website:
http://www.PestThreats.umd.edu/content/pestreport_form.cfm Adult EAB
Actual Size:
Maryland Department of Agriculture: call 410-841-5920 to report suspect pests;
visit http://www.mda.state.md.us/plants-pests/invasive_species.php for information.
Nationally: USDA-Animal and Plant Health Inspection Service (APHIS):
http://www.aphis.usda.gov/services/report_pest_disease/report_pest_disease.shtml
Where to Get More Information:
UMD Cooperative Extension Exotic Pest Threats Website: http://www.PestThreats.umd.edu/index.cfm
Emerald Ash Borer Field Guide: http://www.forestpests.org/acrobat/eabfg.pdf
Emerald Ash Borer Home Page, USDA Forest Service: http://na.fs.fed.us/fhp/eab/
Emerald Ash Borer Website: http://www.emeraldashborer.info/
Look-alikes:
Michigan State University Extension Bulletin E-2944, 2005: http://www.emeraldashborer.info/files/E2944.pdf
Ohio State University EAB Outreach Team, rev. 2007: http://ashalert.osu.edu/native_borers.pdf
Project Participants: Chris Sargent, Research Assistant; Michael Raupp, Entomologist; Sandra Sardanelli, IPM Coordinator;
Paula Shrewsbury, Entomologist; David Clement, Pathologist; Mary Kay Malinoski, Entomologist.
Selected References:
Martin, Tunyalee. 2006. Emerald Ash Borer Update. The Nature Conservancy:
http://tncweeds.ucdavis.edu/moredocs/agrpla01.pdf
Raupp, Michael J. and Paula M. Shrewsbury. 2005. CSI for EAB. University of Maryland:
http://www.dnr.state.md.us/forests/forester/eab.asp
USDA APHIS Emerald Ash Borer Webpage, rev. 2008:
http://www.aphis.usda.gov/plant_health/plant_pest_info/emerald_ash_b/background.shtml
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, University
of Maryland, College Park, and local governments. Cheng-i Wei, Director of Maryland Cooperative Extension, University of Maryland.
The University of Maryland is equal opportunity. University policies, programs, and activities are in conformance with pertinent Federal and State laws
and regulations on nondiscrimination regarding race, color, religion, age, national origin, gender, sexual orientation, marital or parental status, or disability.
Inquiries regarding compliance with Title VI of the Civil Rights Act of 1964, as amended; Title IX of the Educational Amendments; Section 504 of the
Rehabilitation Act of 1973; and the Americans With Disabilities Act of 1990; or related legal requirements should be directed to the Director of Human
Resources Management, Office of the Dean, College of Agriculture and Natural Resources, College Park, MD 20742.
6