Emerald Ash Borer: Biology and Life Cycle
Emerald Ash Borer
||Adult: metallic green in color with purple/red metallic abdominal
segments beneath their wing covers.
Larvae: Creamy white
||Adult: ¼ to ½ inches long
Larvae: 3cm long
||Adult: Feeds along the margins of leaves
Larvae: Chews through the outer bark and feed in the phloem
||They in any forested area with a population of ash trees
||Females can mate multiple times. An “average” female may lay from 60 to 100 eggs
during her lifespan, placing the eggs singly in bark crevices or under bark flaps on
the trunk or branches
||Eggs hatch in 7 to 10 days
||A variety of woodpecker species.
||They are not social. They are capable of flying at a speed of 3 mph.
The Emerald Ash Borer, Agrilus planipennis Fairmaire, commonly referred to as 'EAB',
is an invasive wood-boring beetle native to Asia. The beetle’s first North American populations
were confirmed in the summer of 2002 in southeast Michigan and in Windsor, Ontario.
EAB was likely introduced to the area in the mid-1990’s in ash wood used for shipping pallets
and packing materials in cargo ships or shipping containers.
The Emerald Ash Borer is a member of a family of insects called metallic wood-boring beetles.
Emerald ash borers feed on and eventually kill all native ash trees. Slowing their spread is
Adult Emerald Ash Borers are elongate, cylindrical, slender beetles that can grow to be
approximately ¼ to ½ inches long and 0.1 inches wide. They can be recognized by
a metallic green sheen with a coppery-red abdomen that is hidden under the wings. Males
are densely covered with setae, a stiff structure resembling a hair or a bristle,
on their thorax.
Adult females lay eggs that are 1 mm in diameter on the bark of ash trees. Eggs are white when
laid, and turn amber as they develop.
Larvae are cream-colored, with bell-shaped body segments. Their size varies as they feed and
grow under the ash tree’s bark, but reach a length of 1½ inches long.
Adult females lay eggs that are 1 mm in diameter on the bark of ash trees. The eggs hatch within
15 days into their flattened, segmented larval state. Larvae chew their way through the bark and
tunnel into the tree's inner cambial layer. By tunneling through the phloem, they disrupt the tree's
transportation of nutrients. The larval stage is the longest within the life cycle, lasting about 300
days. This generally occurs between June to April of the next year.
Emerald ash borers have four larval stages. In late summer and early fall, larvae in their final stage
enter the layers of bark and prepare a chamber where they remain during the winter months as
pre-pupae. Larvae can reach 23 to 26 mm in length. The larvae have a pincer-like appendage called
a urogomphi, paired "horns" at the posterior tip of the abdomen of larvae, attached
to the last abdominal segment.
The overwintering physiology of the emerald ash borer prepupae allows them to accumulate
glycerol in high concentrations along with other antifreeze agents. This behavior
contributes to the emerald ash borer's ability to tolerate cold temperatures. The larvae complete
development within their pupation chambers in the summer.
Emerald Ash Borers are folivores, an insect that feeds on leaves, in the adult phase,
and lignivores, an insect that feeds on wood, in the larval phase. As adults, Emerald
Ash Borers feed upon the leaves of ash trees, leaving behind noticeable ridges along the leaf edge.
Upon hatching on the bark, larvae chew their way inward and feed upon the phloem and cambial
region of the tree. This action prevents nutrients from photosynthesis from being transported and
eventually leads to the tree's death.
After maturing into adults within their chambers, fully developed adults chew their way out from their
chamber within the bark. This process generally occurs on days with high temperatures and begins
in mid-May, with adult activity peaking in June and July.
Integrated pest management involves pest monitoring and the use of multiple control strategies
(cultural control, plant resistance, biological control and pesticides) to mitigate losses from insect
Several methods are being used in survey efforts for EAB. Large purple prism traps are used in
government-sponsored survey programs for EAB and are very visible to the public in parks and
Prism traps are pre-coated with an insect-trapping adhesive. Lures are attached to the trap and
are effective in the field for 20 days as an attractant. The chemical component of the lure has gotten
better in recent years but still has room for improvement. Prism traps are hung over sturdy
branches in the mid to lower canopy of ash trees of at least 8 inches in diameter before EAB
emergence is expected.
In addition to the prism traps, girdled “trap trees” also have been used for locating EAB, but this
method is time-consuming and, therefore, expensive. Other traps that have been developed included
green funnel and prism traps, but these are not widely used in the U.S.
One of the main cultural methods for preventing the spread of EAB is NOT MOVING INFESTED
FIREWOOD, LOGS OR NURSERY STOCK to uninfested areas. Much of the rapid spread of EAB
outside of its original detection sites near Detroit, Michigan, was due to direct, human-assisted
movement of these products. Larvae of EAB are hidden underneath the bark of living trees or
boards cut from infested logs where they can be transported easily into non-EAB-infested areas.
Another cultural control method is TIMELY REMOVAL OF EAB-INFESTED TREES and then chipping
the trees to a small size - less than 1 inch - on each of two sides or burning the trees that were removed.
This will kill EAB and help prevent further spread. Many cities are proactively removing and replacing
diseased or unhealthy ash trees. This has been done to increase diversity of tree species with new
plantings to prepare for the arrival of EAB.
In North America, all native species of Fraxinus are susceptible to EAB, although some species are
preferred more than others. For example, blue ash (F. quadrangulata) is a less-preferred species.
However, researchers have observed that ash trees native to Asia have reduced larval tunneling and
only stressed trees (for example, from drought) are colonized.
Ash trees in the native range of EAB may be more resistant because their natural defenses have
co-evolved throughout time. Researchers are studying Asian ash species as a possible source
of resistance genes against EAB. Identification of resistant ash genotypes is important for reforestation
and maintaining a market demand for ash in the nursery industry.
Biological control involves the use of natural enemies (predators or parasitoids) to control insect
pests naturally. Biological control primarily is being targeted at EAB in forests. The EAB has no
known predators other than woodpeckers that occasionally feed on larvae and kill about 30-50%
of large EAB larvae.
Research has demonstrated that insecticides can protect individual ash trees from EAB effectively.
Insecticides are recommended only if the EAB infestation is within 15 miles, or the ash trees are in
an EAB-infested (or quarantined) area.
Systemic insecticides are applied to the soil as a drench or through an injection technique, absorbed
by the roots and then translocated throughout the tree.
The best timing for soil injection and drenches is likely early to mid-May. A fall application also can be
made as an alternative timing, but generally is not as effective.
Insecticide uptake and translocation may take up to 4-6 weeks in trees with trunks smaller than 12 inches
in diameter. Larger trees with trunks greater than 12 inches in diameter require more time for uptake,
so treatment should be initiated earlier.
Insecticides can be sprayed on the trunks, branches and foliage to kill EAB adults as they feed on foliage
and newly hatched EAB larvae before they bore into the tree. This technique does not kill larvae already
feeding internally in the tree. They are available to homeowners and professional applicators, depending
on the label restrictions.
For good control, non-systemic insecticide sprays need to have complete coverage and be properly
timed for adult EAB emergence. Treatments would need to be repeated at least 2 times per year and as
many as 4 times per year.
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