Meet the Maple Nemesis

This post is by Bill Cook, MSU Extension Forester/Biologist.  Mr. Cook can be contacted at cookwi@msu.edu.

The Asian long-horned beetle has the potential to inflict forest damage in epic proportions, the likes of which we have not seen since chestnut blight forever changed the character of forests in eastern North America.  Early observations of this beetle have led to successful eradication.  However, people must be able to identify this pest in order for successful early intervention to occur.

The Asian long-horned beetle could create a nightmare that would make the emerald ash borer and beech bark disease seem like mere daydreams.  And, the emerald ash borerhas already cost an estimated 15 billion dollars, nationwide.

Well-established Asian long-horned beetle (ALHB) populations would inflict severe damage to our maple resource.  Not only would the ALHB significantly diminish our northern forests, but it would also disrupt the social and economic ties.

The ALHB has a long and growing list of host tree species, although they prefer maples.  Unlike some exotic pests, the ALHB doesn’t necessarily kill a tree, outright.  Rather, it mechanically weakens the tree creating increased risk of breakage and renders trees unsuitable for forest products.

Maples represent about 25% of our forest volume (35% in the Upper Peninsula) and are also common residential trees.  Many cities have already suffered the loss of elms and ashes.  Sugar maple is, arguably, the most financially valuable tree species in Michigan for forest products, including maple syrup.

The ALHB has a striking appearance.  The beetle is one to one and a half inches long, black, with white blotches.  The antennae are at least as long as the body and consist of alternating segments of black and white.  It’s in the family of long-horned beetles, Cerambycidae, which has many native representatives.

Trained observers often look for oviposition sites on tree bark.  These sites are shallow excavations where the eggs are laid, circular or oval, about a half-inch across.  Fresh oviposition sites have a different color than the bark.  The City of Toronto has had some success in ALHB location in this way.

Exit holes in the bark, from emerging adults, are large, about a half-inch across.  They’re about the size of maple syrup tapping holes.  The tree grows over the holes in a year or two, with the scars resembling a belly-button.

Current outbreaks have been identified in Massachusetts, New Jersey, Ohio, and Toronto.  Outbreaks have been successfully eradicated (hopefully) in Chicago, New York, and (possibly) Toronto.  Detection of the ALHB is difficult.  Therefore, “eradication” is declared with caution.

The ALHB has not yet been found in Michigan or Wisconsin.  However, vigilance will be required to prevent the beetle from establishing in new territory.  Most exotic infestations are brought to the attention of experts by citizens.  When more citizens know what to look for, the likelihood of early detection increases.

Unfortunately, the ALHB will not (and is not) the only forest threat from exotic pests.  Other important threats include the hemlock woolly adelgid, balsam woolly adelgid, thousand cankers disease, and oak wilt.  Michigan has much of the last, largest reserves of eastern hemlock in North America.  These pests are among the growing list of reasons to not move firewood.

It is not easy to know about all these threats, or how to separate them from native pest symptoms and cycles.  And, most of us face higher priorities in our daily lives.  Nevertheless, for those that highly value forest health and urban trees, learning about these pests is important, and will require an ongoing effort.

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