Your Maples—Next on the Menu?
Annemarie Nagle
If you thought that emerald ash borer was bad news for your woods, just wait until you hear about its’ bigger, hungrier cousin—Asian longhorned beetle.
ALB adults are large, shiny blue-black beetles with irregular white spots, and very long black and white striped antennae.
Unfortunately you only have to go to Bethel, Ohio, a small rural community near Cincinnati and 40 miles from the Indiana state line, to find a forest that has been infested with this pest. The Asian longhorned beetle (ALB), an invasive wood-boring insect native to China and Korea, was discovered inflicting fatal damage on Bethel’s trees in June of 2011. ALB is a federally regulated pest, and eradication is the goal whenever ALB is found.
Both the beetle’s feeding damage and efforts to eradicate it have profound impacts on infested communities. To date, nearly 9,000 of Bethel’s deciduous trees have met the saw and chipper. Sixty-one square miles remain under strict quarantine, limiting movement of potentially infested tree materials, while survey crews still struggle to gain a handle on how far the infestation has spread. Ohio is the fifth state to attempt eradication of this devastating tree killer, which has also been found in New York (Brooklyn, 1996), Illinois (Chicago, 1998), New Jersey (Jersey City, 2002), and Massachusetts (Worcester, 2007). Success is possible; ALB has been eradicated from Chicago, parts of New York and New Jersey, and several European countries. 
A fully grown ALB larva. These voracious larva create 1/2" wide tunnels through wood.
Although the road to eradication can be long and expensive, the alternative—allowing ALB to spread beyond control—is far more costly. Unlike other exotic tree-killers like emerald ash borer, Dutch elm disease, and chestnut blight, which devastate a single host genus, ALB can kill 13 different tree genera. Here in the Midwest, that means about 60% of our forest canopy is at risk. If ALB were to spread out of control, it would threaten 19% of basal area nationally. In comparison, emerald ash borer threatens 3%.
ALB is also a major pest in its native China, where it has destroyed millions of elms, poplars, and willows in windbreaks and plantations. Many of these plantations produce poor-quality lumber used to construct crates and pallets, which in turn are used to ship goods (and resident ALB larvae and adults) around the world. Though international trade is typically responsible for initial ALB introductions, movement of infested branches and logs from killed trees can begin new, satellite infestations. If you bring firewood onto your property, buy local, USDA or Indiana certified wood. Certification ensures that the wood has been properly treated or seasoned to minimize presence of pests. Similarly, think twice about moving firewood from your own property, especially if source trees have died from an unknown cause.
Fortunately, ALB has yet to be found in Indiana. Because early detection of ALB infestations is key to the success of any eradication effort, you can help protect Indiana’s forests by keeping your eyes peeled for the ALB and its’ damage on trees in your town and on your property.
ALB Diagnostics
Look for ALB damage on LIVING trunks and branches of its preferred host trees: Acer (all maples), Aesculus (buckeyes and horsechestnuts), Ulmus (elms), Salix (willows), Betula (birches), Platanus (sycamores), Populus (poplars), Albizia (mimosa), Cerciphyllum (katsura), Fraxinus (ashes), Koelreuteria (goldenraintree), Sorbus (mountain ash), and Celtis (hackberry).
Holes or Round Pits in Tree Branches or Trunk
ALB creates very characteristic damage on the trunks and limbs of infested trees. During egg-laying, adult females chew oblong bowl-shaped pits into the tree’s bark. Egg-laying pits are typically about ½” diameter and weeping sap is sometimes present. Emergence holes are created when newly formed adults chew their way out from their larval home. These large, 3/8” to ½” holes (about the diameter of a #2 pencil) penetrate deep into the tree. Heavily infested trees are often riddled with egg-laying pits and emergence holes, and coarse sawdust may collect around the tree base or in branch crotches. Woodpeckers also create holes in infested trees to consume ALB larvae. Holes created by woodpecker feeding tend to be much wider than egg-laying pits, and extend deep into the wood of the tree.
Broken Branches with Large Larvae
The juvenile, or larval stage of ALB packs the tree-killing punch. Larvae are legless off-white grubs that may be visible in freshly cut wood. After hatching just beneath the bark, larvae feed only briefly on the tree’s nutrient-conducting tissue. Most feeding is in the structural wood of infested trees, creating ½” wide tunnels until the heartwood resembles Swiss cheese. The relatively minor damage to the tree’s vascular system allows it to stay green and appear healthy, making canopy dieback an unreliable diagnostic. Undetected infestations are extremely dangerous because they can fill the canopy with healthy-looking but structurally unsound limbs, which often snap off during storms and wind events.
Egg-laying pits and adult emergence holes on a heavily infested maple tree near Bethel, OH. Despite the damage, the tree had a healthy canopy.
Large Black and White Adult Beetles
All U.S. infestations have been identified by alert citizens reporting these unique and conspicuous beetles. ALB adults are large (1-1 ½” long) shiny black beetles with irregular white spots on their backs, sometimes with blue tinged feet. They are named for their long, black and white striped antennae, which exceed the length of their bodies. Beetles begin emerging from infested trees in late May, and continue through October. Adults are capable of flight, but typically do not move far from their parent tree, tending to re-infest it until the tree is dead.
Think You’ve Found ALB? Report It!
Never assume invasive pests are “somewhere else.” If you see any beetle that looks like ALB or any signs that resemble ALB damage, take a photo and send to Indiana DNR Division of Entomology and Plant Pathology at DEPP@dnr.in.gov. Capture and hold onto the insect for identification if you can. You can also call DNR’s Invasive Species Hotline at 1-866-NO EXOTIC (1-866-663-9684). To learn more about signs and symptoms visit www.beetlebusters.info.
Annemarie Nagle is the Forest Pest Outreach Coordinator in the Dept. of Entomology at Purdue University. Ph: (765) 494-0822, naglea@purdue.edu.
References:
Hobson, D.A.; Tyrrell, M.L.; Camp, A.E., eds. “New Threats to North American Forests.” Yale Forest Forum Review. 2003. Vol. 6 (1). http://environment.yale.edu/gisf/files/pdfs/yff_reviews/02.03.pdf (accessed Jan. 15, 2013).
Boggs, J. and Stone, A. “Asian Longhorned Beetle: The Threat in Black and White.” Tree Care Industry Magazine. April 2012. http://www.tcia.org/digital_magazine/tci-magazine/2012/04/index.html (accessed Jan. 15, 2013).