Emerald Ash Borer
(Agrilus planipennis)
Introduction
The emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), commonly referred to as “EAB”,
is an invasive wood-boring beetle. Its native range is eastern Russia, northern China, Mongolia, Korea, Japan and
Taiwan. The beetle’s first North American populations were confirmed in the summer of 2002 in southeast
Michigan and in Windsor, Ontario. Judging by the size of the infestations and the stage of damage to the infested
trees, the beetle was likely introduced to the area several years prior to its discovery. It is |
 |
| believed that the beetle was introduced into North America in ash wood used for shipping pallets
and wooden packing materials in cargo ships or shipping containers. |
Multi-state distribution December 2, 2009 |
Since its introduction into North America, EAB has spread into 13 states (Illinois, Indiana,
Kentucky, Maryland, Michigan, Minnesota, Missouri, New York, Ohio, Pennsylvania, Virginia, West Virginia and Wisconsin)
and two Canadian provinces (Ontario and Quebec). EAB was first confirmed in New York in June 2009 near Randolph, in
western Cattaraugus County. [Click to read NYS DEC / NYS DAM press release]
Emerald ash borers are not
particularly strong fliers, with adults typically flying less than ½ mile from their emergence tree. The natural dispersal of EAB in
North America is assumed to be 5 miles (8 kilometers) or less per year. The rapid spread of the |
NYS EAB distribution and threat levels |
| beetle since its North American introduction is most likely due to the unintentional transport of infested ash
nursery stock, firewood, unprocessed ash logs, and other ash products. In an effort to slow the continued spread of EAB, both
the Federal and State governments have instituted various quarantines of infested area to regulate the continued transport
of ash products. [Click to read about the NYS quarantine] |
USDA APHIS (the United States Department of Agriculture Animal and Plant Health Inspection Service), in cooperation with state natural resources
agencies and others, has instituted an EAB survey to identify the leading edge of known infestations and to locate new or outlying populations.
Traps are generally placed in a 1 1/2 miles by 1 1/2 mile grid where ash is found within a 100-mile band of known EAB infestations. The survey detection
tool is a 24 inch (60 cm) corrugated purple plastic prism-shaped trap that is coated with non-toxic glue on all three sides and is baited with an oil lure
to attract the adult beetles. [Click here to
find out more about the 2009 EAB Survey]
Biology and Identification
Emerald ash borers are members of a group of insects called metallic wood-boring beetles (Buprestidae). Adult |
EAB trap |
| EAB have bronze, golden, or reddish-green bodies, with dark metallic
emerald green wing covers. The dorsal side of the abdomen, which can
be seen when the wings |
are spread, is a metallic purplish red. Adult beetles average 3/8 inch to 3/4 inch (10 mm to 20 mm) long and 1/6 inch (4 mm) wide (males
are slightly smaller than females). EAB generally have a 1-year life cycle, emerging from beneath the bark of ash trees from
late-May through early-June with peak activity between mid-June and early-July, tapering off by the middle of August. Adult
beetles are most active during the day and favor sunny, warm weather, sheltering in bark crevices or under foliage when it
is rainy, windy or cooler. The life span of adult EAB is about 3 weeks.
EAB adults feed along the margins of leaves, leaving small, irregular shaped edges. Newly emerged
adults must feed for at least several days before mating; mated females feed for an additional 1 to 2 weeks before laying eggs
(females can mate multiple times; males do not). An “average” female may lay between 60 and 90 eggs during her lifespan, placing
the reddish-brown eggs singly in bark crevices or under bark flaps on the trunk or branches (some long-lived females may lay more than 200 eggs).
EAB larvae |
Eggs hatch in 7 to 10 days. The slightly flattened, white to cream-colored larvae have 10 abdominal segments
with a pair of brown, pincher-like appendages on the last segment. EAB larvae go through five life stages (instars) with mature larvae reaching an
average length of 1 1/2 inches (38 mm). After hatching, the first instar larvae chew through the bark and the phloem (the inner bark, the pipeline
through which food is passed to the rest of the tree) and into the cambium (the growing part of the trunk, located between the bark and the sapwood). |
As they feed (for several weeks), the larvae wind back and forth. This creates the serpentine (S-shaped)
“galleries”, characteristic of this wood-boring beetle. The galleries are filled with “frass”, a fine sawdust-like material. The final galleries,
which are generally from 4 inches to 20 inches (10 to 50 cm) in length, extend from the phloem to the outer layer of the sapwood.
Larval feeding ends by autumn, at which time the fifth instar larvae overwinter in (1 cm) deep pre-pupal
chambers in the outer portion of the
sapwood. Pupation generally |
EAB gallery |
takes place the following spring (late-April to May), with adults staying in the
pupal chambers for 1 to 2 weeks, at which time they emerge headfirst through a distinctive 1/8 inch to 1/6 inch (3 mm to 4 mm)
D-shaped exit hole, beginning the cycle of life over again. The presence of the exit holes typically goes undetected until
trees show other, more visible symptoms of being infested.
It should be noted that when EAB is developing in healthy, newly infested ash trees whose defenses are still strong and capable of
retarding larval survival and growth, larvae may need an additional 1 to 2 years before pupating and emerging as adults. As larval
densities increase, the 1-year life cycle becomes the norm. |
D-shaped emergence hole |
Hosts
In the U.S. and Canada, emerald ash borers only attack ash trees (the one exception being privet, (Ligustrum Spp.)). The ash species of
concern in NY are black ash (Fraxinus nigra), green ash (F. pennsylvanica),
and white ash (F. americana).
Black
ash (F. nigra) |
Green ash (F. pennsylvanica) |
White ash (F. americana) |
Signs of Infestation
Early detection of EAB in newly infested trees can prove very difficult, particularly for the lay property or woodland
owner as the trees tend to exhibit few, if any, visible external symptoms of infestation. One of the first noticeable
signs of infestation is often the presence of unusually abundant uneven holes drilled by woodpeckers as they feed on prepupal
larvae [note: this symptom is not exclusive to EAB infestation].
| A very clear indication of EAB infestation is the presence of the D-shaped emergence holes
chewed through the bark on branches or the trunk by adults when they emerge in the spring. These holes are 1/8 inch
(3 mm) in diameter. If the holes are not D-shaped, then they were not caused by EAB (native wood borer emergence holes
are round or oval and are much larger, 1/4 inch (6 mm) or larger). |
D-shaped emergence holes |
Split bark (gallery visible beneath) |
Thin, 2 to 5 inch (5 to 12 cm) long vertical splits through the bark of living trees [again, this sign is not exclusive to EAB
infestation]. In the event of EAB infestation, the splits may form over the feeding galleries. If the bark is removed and frass-filled
serpentine, S-shaped galleries are found tunneled just beneath the bark or etched into the underside of the bark, this is a sign
of EAB infestation [common native borers that infest ash trees bore into the sapwood]. |
The presence of white to cream-colored, legless, flattened, 10-segmented, 1 to 1 1/2 inch (25 to 38 mm) long larvae found in the
galleries beneath the bark of living ash trees is another sign of the presence of emerald ash borers.
Canopy thinning due to EAB |
As the density of EAB infestation in an ash tree increases, the tree’s foliage will wilt, branches start to die back, and the tree canopy
will thin out. Several years of infestation will cause many trees to lose 30 to 50 percent of their summer canopy. Trees may die after 3
to 4 years of heavy infestation [note: canopy thinning and top dieback followed by tree mortality is not necessarily a sign exclusive to EAB]. |
Epicormic shoots |
Another sign of possible EAB infestation (but not limited to EAB) is 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. Epicormic shoots or sprouts are stems and suckers that often
appear in trees due to stress or injury (such as defoliation or die-back) as a way for the tree to compensate for the loss of productive
leaf surface. Certain species, such as oak and basswood are more prone to producing epicormic shoots than are ash, so the formation of
such shoots, combined with crown thinning or die-back are a strong indication of EAB infestation. |
Impacts of EAB Infestation
Stressed ash trees are more attractive to emerald ash borers than are healthy trees in the early stages of an invasion. However, once EAB is
established in an area, all ash trees greater than 1 1/2 inch (3 cm) in diameter are susceptible to attack. EAB infestation is always fatal to ash
trees, even healthy ash trees, in approximately 2 to 4 years.
EAB kills ash trees when the larvae galleries damage the phloem, which is responsible for transporting nutrients made during photosynthesis,
and the xylem (sapwood), which is responsible for transporting water and dissolved nutrients throughout the tree. This “girdling” of the tree starves
all parts of the tree beyond the galleries of nutrients and water, killing the tree from the top down.
More than 40 million ash trees have died or are dying from emerald ash borer attack in the United States since the beetle’s introduction
sometime shortly before its discovery in 2002. More than 7.5 billion ash trees remain at risk.
In NY, ash was widely planted to replace native elm trees that were killed by Dutch elm disease. In some areas of the state, ash is a prevalent urban and
suburban street tree. The loss of large numbers of mature ash trees can have a devastating impact on the urban and suburban canopy, leading to temperature
changes, increased air pollution, the economic impact of removing and replacing thousands of dead trees in yards and along streets, and a potential public safety
hazard and potential liability issues of dead ash trees along streets and in parks and yards.
In natural forest settings, native ash trees are very common (white, green and black ash make up almost 8% of all trees in NYS forests), providing
canopy habitat, and a good food source (seeds) for both birds and mammals.
| Ash trees are valuable commercially, used for the manufacture of flooring, furniture, and shipping pallets, as well as that
all-American device, the baseball bat. The almost 114 million board feet of ash lumber grown annually in the eastern U.S. is worth about $25 billion.
Black ash is important to the culture of Native Americans, including NY’s Akwesasne, as it is used for traditional basket making. |
Ash billet in baseball bat factory |
Management and Control
The emerald ash borer is unusually difficult to kill. Please see the “Emerald ash borer general information and educational resources”
page of this website for information on managing and controlling EAB infestations.
Photo and Graphic Credits
Close-up of adult EAB - David Cappaert, Michigan State University, Bugwood.org
Multi-state distribution map - Cooperative Emerald Ash Borer Project; APHIS-PPQ, USFS
EAB trap - NYS DEC
Mixed larval stages - David Cappaert, Michigan State University, Bugwood.org
Gallery - Joseph O'Brien, USDA Forest Service, Bugwood.org
D-shaped emergence hole - David R. McKay, USDA APHIS PPQ, Bugwood.org
Black ash - USDA-NRCS PLANTS Database / Herman, D.E., et al. 1996. North Dakota tree handbook
Green ash - Tom DeGomez, University of Arizona, Bugwood.org
White ash - Richard Webb, Self-employed horticulurist, Bugwood.org
Emergence holes - Joseph O'Brien, USDA Forest Service, Bugwood.org
Split bark - Pennsylvania Department of Conservation and Natural Resources - Forestry Archive, Bugwood.org
Crown thinning - Jana Albers, Minnesota Department of Natural Resources Archive, Bugwood.org
Epicormic shoots - Pennsylvania Department of Conservation and Natural Resources, Forestry Archive, Bugwood.org
Ash billet in baseball bat factory - Pennsylvania Department of Conservation and Natural Resources, Forestry Archive, Bugwood.org