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The Life Stages of the Emerald Ash Borer

Emerald ash borer has now been found in Connecticut - specifically, in sections of New Haven County.  These pages have been assembled to assist arborists and others in the identification of the emerald ash borer, and in being prepared for dealing with this insect.

The emerald ash borer is a highly mobile insect that has a history of establishing rapidly into new areas after being introduced.  The most common means of introduction are the movement of infested logs, firewood and nursery stock.  For those reasons, it is important to be aware of the potential to move the insect, and to comply with all regulatory efforts to limit that spread.  In particular, the quarantine to be placed on movement of material out of New Haven County should be followed.

Also Note: If you do find Emerald Ash Borer, you must report your find to the Connecticut Agricultural Experiment Station.  EAB is an insect of federal regulatory concern.  You may report your find by sending a digital photo via email or by calling the Station.  The email address is CAES.StateEntomologist@ct.gov.  The phone number is 203-974-8474.  Include any information that would be helpful to finding the site (GPS coordinates, street address, etc.)  DO NOT MOVE EITHER THE INSECT OR THE WOOD FROM THE SITE!

The three additional pages associated with this page are:

How to Find the Emerald Ash Borer
Dealing with the Emerald Ash Borer
Regulatory Matters

Please visit these pages as well.

Another Great Resource is www.emeraldashborer.info

The Life Stage Sections on this page are
Life Cyle Chart
Additional Images


adult emerald ash borer

Appearance:  The emerald ash borer adult is a small, bright green beetle of the buprestid family - a family of insects sometimes knowns as the metallic, wood-boring beetles.  The typical size for an adult EAB is between 0.3 and 0.5 inches - large for a buprestid beetle, but small by human standards.  Males and females are very similar in appearance.

Found:  Research in Michigan shows that the emergence of EAB adults begins about 450-500 growing degree days and peaks at around 1,000 GDD (base 50).  In Connecticut, that corresponds to around the end of May / beginning of June for initial emergence, and late-June into mid-July for  peak emergence, depending upon location and the current year's weather.

Feeds:  On ash leaves.  The adults feed for about two weeks before they mate and the females begin laying eggs.  Adult feeding does little damage to the tree.

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Emerald Ash Borer Eggs Appearance:  The eggs of the emerald ash borer are very small (approximately 1 mm or 0.04 inches) and are reddish-brown.  They may be laid in groups or individually.

Found:  When newly infesting a tree, EAB tends to lay eggs up in the crown of ash trees, in places where the bark is beginning to furrow. The eggs may be laid on the surface of the bark, in bark cracks and crevices or just under the outer bark of ash trees.  In one study, on relatively small ash trees (4-8" dbh), 40% of the infestation was found between 6 and 12 feet up the tree.  EAB favors all North American ash trees, including white, green and black ashes.  In Connecticut, the vast majority of native ash trees are white ashes.

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emerald ash borer larva Appearance:  The buprestid beetles are sometimes known as flat-headed borers for the form of the larva - flat, white grubs.  The emerald ash borer larva is a clearly segmented, flat-headed borer that goes through four growth stages, or instars.  The life-cycle of the EAB may be one year or two years in length, depending upon the extent of the infestation (outlier populations tend towards a two year life cycle).  Larval development is faster on stressed trees.

Found:  After the egg hatches, the larva burrow into the inner bark and cambial layer.  The larva is noted for its serpentine (S-shaped) feeding galleries under the bark.  (See the How to Find page for an illustration).

Feeds:  On the phloem (inner bark) tissues and the cambium. Older larvae may score the outer sapwood.

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pre-pupal emerald ash borer Appearance:  The winter before it pupates, the last instar EAB larva will excavate a tiny chamber and curve back on itself into a posture that is indicative of the pre-pupal form.  This form is transitional between the larval and pupal stages.

Found:  The larva will excavate its pre-pupal chamber either approximately 0.5 inches into the outer sapwood or into the outer bark.  The thickness of the bark will influence which happens.  On thicker-barked trees, the pre-pupae may be found in the bark; on thinner-barked trees, they may be found in the outer sapwood.

Feeds:  In this form, the beetle does not feed.

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emerald ash borer pupa Appearance:  During the pupal stage, the larval EAB turns into the adult beetle.  At each succeeding point during this stage, the features of the adult beetle become more apparent.  Coloration tends to be among the last features to appear.

Found:  Either in the outer sapwood or in the bark, depending on the thickness of the bark.  On thicker-barked trees, pupae may be found in the bark; on thinner-barked trees, they may be found in the outer sapwood.

Feeds:  In this form, the beetle does not feed.

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Life Cycle Chart

EAB Life Cycle
From: USDA Emerald Ash Borer Program Manual
Note:  This chart does not include the pre-pupal form, which is transitional between the larval and pupal stages.
Also, this chart is based on a one year life cycle.

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Additional Images Relating to Life Stages

Relative Larval Instars
EAB pre-pupa Single EAB larva
EAB Larva Adult with wings spread

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The best advice is to keep firewood local.