Pests to Watch For: Asian Longhorned Beetle

In a world of global commerce and travel, it's inevitable that species will find themselves living in new places both by accident and by design. Some of our most beloved garden plants are from other continents, and they get along quite well with our native plants. However, some non-native species can invade an ecosystem and cause all kinds of damage to the unsuspecting native flora and fauna. Today we'll introduce a particularly insidious new invader with the potential to change both our wild and managed landscapes: the Asian Longhorned Beetle.
 

What is the Asian Longhorned Beetle, and why is it important?

As you may guess, the Asian Longhorned Beetle (ALB) is from Asia - specifically China and the Korean Peninsula - and it probably got here on wood packing materials like crates (this is also the way the invasive Emerald Ash Borer made it's way here). The insect attacks a wide range of trees including all maples, ashes, elms, sycamores, birches, and many more. An un-treated infestation will inevitably result in tree death. With such a wide range of vulnerable trees, it is estimated that communities could lose 30% or more of their trees if ALB becomes established. The good news is that so far this beetle has only been found in the wild in Ohio, New York, New Jersey, Illinois, and Massachusetts, and all of those outbreaks have been successfully contained. The bad news is that the beetles have been found in packing materials in warehouses in an additional 11 states (including Indiana), so we have to be vigilant to prevent a catastrophe in our state's cities and forests.
 

How does ALB affect a tree?

The distinctive adult beetles are easy to spot, but it's the larvae that do damage to a tree. Adult females lay eggs on the bark of a tree, and once the larva hatches it burrows into the wood of the tree in the trunk or a large limb. When it first emerges it feeds on the outer layers of wood, and these are the layers that are critical for transporting water and nutrients and growing new wood. As the larva grow they burrow deeper into the heartwood where they can significantly weaken branches. The larvae can grow up to 2.5" inches long and nearly half an inch in diameter. After spending time as a pupa deep within the tree, it emerges as an adult and chews its way out of the tree to mate and feed on leaves and bark. The tree is gradually weakened as its ability to transport food and water is reduced by the larvae feeding on the critical outer layers of wood. The tree starts to visibly struggle 3-4 years after the initial infestation, and the tree will usually die 10-15 years after being attacked. In the meantime, large limbs may fall and damage property as they are weakened by the burrowing of the larvae.
 

ALB signs clockwise from top right: exit holes, egg sites, sawdust-like frass, tunneling in trunk and branches. Images courtesy of the USDA APHIS

ALB signs clockwise from top right: exit holes, egg sites, sawdust-like frass, tunneling in trunk and branches.
Images courtesy of the USDA APHIS

How can I tell if my tree has ALB?

There are several indicators to watch out for. For one thing, the adult beetles are hard to miss. At 1-1.5" long they're fairly big, and with their long curving antennae, black bodies with white spots, and blue feet, they don't look like many other beetles you'll see. They can emerge at just about any time of year, but their activity peaks in late summer and early fall. Two other easy-to-spot indicators are the adult exit holes and frass. Adult exit holes are round circles about 3/8" of an inch across (see photo to the left), large enough to fit a pencil inside. Frass is the excrement from the larvae as they feed on the wood. It looks a lot like sawdust and can be found on the ground under the tree or on branches. ALB is not the only tree pest that has exit holes or produces sawdust-like frass, but most other borer beetles we see around here don't make holes nearly as big as ALB. If you look closer you may also notice little oval-shaped depressions in the bark where the female lays her eggs. Branches that fall off of an infested tree will have large holes bored through them from the larvae feeding. Infested trees will have yellowing or dying branches after a few years, but many other insect, disease, and environmental factors can also cause yellowing leaves or canopy dieback.
 

Trees infested by ALB are cut down, and can be used as traps to lure in other adult beetles in the area. Image courtesy of USDA

Trees infested by ALB are cut down, and can be used as traps to lure in other adult beetles in the area.
Image courtesy of USDA

What can be done for an ALB-infested tree?

Unfortunately, not much. It is very difficult for insecticides to reach the larvae once they make it into the heartwood of the tree. The best response is to cut down the tree and destroy it to ensure that no eggs, larvae, pupae, or adults survive to attack another tree. Since treatment isn't an option, the best course of action is to make sure your trees are healthy (stressed trees are always more vulnerable to insect and disease invaders than healthy trees) and to spread the word to make sure everyone is on the lookout for this dangerous beetle.
 

What is being done to keep ALB out?

The Animal and Plant Health Inspection Service (APHIS) of the USDA is on red alert to prevent the beetle from making it here in the first place whenever possible. Wood packing materials coming from Asia are now subject to new regulations to ensure that no living things are present before they are shipped to the U.S. Travelers coming from regions where ALB lives have their luggage inspected if they are carrying any plant material (already standard practice to catch a whole range of potentially dangerous species). Any piece of cargo that is suspected of carrying ALB is immediately quarantined, and the area is searched in case any escaped. APHIS is doing what they can to prevent another outbreak, however it's impossible to be 100% effective. That's why it's so important that average citizens like you and me are informed an on the lookout. If you think you see ALB, it is important that you report it immediately. Here in Indiana you can call the Indiana Department of Natural Resources on their toll-free line: 1-866-663-9684 (1-886-NO-EXOTIC)

Want to learn more?
Asian Longhorned Beetle (APHIS)
Exposed: The Asian Longhored Beetle (The Nature Conservancy)
This lethal beetle could be on its way to Indiana (Indy Star)


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