Asian Longhorned Beetle damage and host trees

Which trees does the Asian Longhorned Beetle prefer?

The Asian Longhorned Beetle attacks hardwood trees across roughly a dozen genera in North America, and its clear favorite is maple. Maples of every kind — sugar, red, silver, Norway, and boxelder — are the trees most at risk, which is what makes the beetle such a threat to the northeastern forests and urban canopies where maple dominates. Beyond maple, the confirmed host genera include:

A handful of other trees — including alder, rose-of-Sharon, mulberry, and some fruit trees — are occasionally reported as hosts, but they are not primary targets. Two boundaries are worth remembering: the beetle strongly prefers maple, and it does not attack conifers such as pines and spruces at all.

How the Asian Longhorned Beetle kills a tree

The Asian Longhorned Beetle kills a tree by tunneling through the living wood that carries its water and nutrients. After a female lays eggs in pits she chews in the bark, each larva bores inward — first through the nutrient-conducting tissue just under the bark, then deep into the sapwood and heartwood. As larvae grow, their galleries widen and multiply, progressively severing the tree's internal transport and structurally weakening trunk and limbs. A tree cannot wall off or outgrow this damage; over one to several years of repeated attack, branches die back and the tree ultimately dies. Unlike some pests, there is no reliable way to cure an already-infested tree.

The damage tends to build from the top down and over several seasons. Females often begin high in the crown and on larger limbs, so the first dieback usually shows in the upper canopy while the lower tree still looks healthy. As successive generations reuse the same tree — a female can lay her eggs on the very tree she emerged from — the number of galleries compounds, limbs weaken and snap, and what began as a few dead branches becomes a hollowing trunk. A heavily infested tree is not only dying but structurally unsound, liable to drop limbs in a storm.

Signs of an Asian Longhorned Beetle infestation

Because the larvae work unseen, an infestation is usually found by its outward signs rather than the beetle itself. On a host tree — a maple especially — look for:

• Round exit holes about ⅜ inch across (roughly pencil-width), where adults chewed out of the wood.
• Oval egg-laying pits, shallow chewed niches in the bark about ½ to ¾ inch across.
• Frass — coarse, sawdust-like wood shavings collecting in branch crotches and at the base of the tree.
• Oozing sap and dark streaking on the bark near larval tunnels.
• Canopy dieback — dead limbs, thinning crowns, and leaves that yellow or wilt out of season.

No single sign is proof on its own — woodpeckers, other borers, and ordinary storm damage can each mimic one of them. What sets ALB apart is the combination and the scale: large, perfectly round exit holes on a hardwood, coarse frass, and shallow oval egg pits together, often high in the tree. When you see that pattern on a maple, it is worth reporting even if you never spot the beetle itself. For the visual field marks of the beetle and its holes, and how to rule out look-alikes, see the identification guide.

What happens to infested trees

Once a tree is confirmed to be infested with the Asian Longhorned Beetle, it is removed — cut down and chipped or burned — because an infested tree cannot be saved and, left standing, it becomes a source of new beetles and a falling-limb hazard. In an eradication program, crews also survey and sometimes treat nearby healthy host trees with an insecticide (imidacloprid) to kill beetles before they can bore in. This is why an ALB find can mean the loss of many trees in a neighborhood, and why catching an infestation early — before it spreads tree to tree — matters so much.

The removals are hard on the communities that go through them, which is another reason early detection matters: the fewer trees a program has to take, the less of a neighborhood's canopy is lost. Programs typically replant afterward with non-host species, but a mature shade tree cannot be replaced in a season, and a street can look very different after an eradication cut. Every report that catches an infestation while it is small is a report that keeps that number down.

The economic and ecological stakes

The stakes are enormous because the Asian Longhorned Beetle targets trees that are central to both the economy and the landscape. Maple alone underpins the syrup industry, the fall-foliage tourism of the Northeast, and a huge share of the hardwood used for furniture and flooring — and maples, along with the other hosts, make up much of the shade canopy in American towns. US eradication programs have already had to remove tens of thousands of trees (more than 30,000 by one extension estimate) at very large public cost. An unchecked spread into the wider maple forests would be a loss with no practical remedy, which is what makes early detection and reporting the whole game.

Not sure a beetle is behind your tree's decline? Work through the symptoms first with What's killing my tree?