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Invasive Asian longhorned beetle threatens forests

black beetle on cut surface of wood with holes in it

The Asian longhorned beetle is a non-native pest that threatens a number of hardwood trees in North America. The larva damage living trees as they tunnel through.

History of Asian Longhorned Beetle

The Asian longhorned beetle was first identified in New York City in 1996. It is believed that this insect arrived in North America in wooden packing material from China. Two years later it was detected in a Chicago neighborhood and in 2002 in New Jersey. 

When entomologists and resource managers from numerous organizations first learned of the destructive potential of the insect they quickly made plans to try and eradicate it. The first steps were to survey for damage and then to establish quarantine zones. Surveys were done using aerial lifts and tree climbers to thoroughly inspect all tree parts. Infested trees were removed and destroyed. Non-infested trees within the quarantine zones were treated with a systemic insecticide as a precautionary approach. After a long battle with this invasive insect, Illinois declared eradication in 2008.

Figure 3. Accumulation of frass caused by emerging ALB. Photo courtesy of E. Richard Hoebeke, Cornell University,  

Damage, symptoms and host trees

The greatest damage to trees is caused by the larva as they tunnel through the living tissues of the phloem and xylem (Figure 1: Tunneling caused by Asian longhorned beetle larvae. Photo courtesy of E. Richard Hoebeke, Cornell University, Ultimately the tree loses its ability to transport water and nutrients to its canopy and roots and dies. Because the ALB can be quite large it can also weaken the structural integrity of a tree.   

Visual symptoms of an infested tree can include the accumulation of frass on tree branch collars below holes cause by exiting beetles (Figure 3). Exit holes can be quite large and distinct from other long-horned beetles; up to 3/8 inch in diameter and almost perfectly circular (Figure 4). Adult beetles can also be found chewing on the veins of leaves leaving the other leaf tissues intact. Egg sites can also be an important visual clue to their presence.   

Asian Longhorned Beetles have a wide range of preferred host trees. Most studies show that they prefer maple trees of any species. Its other top choices include birch, horse chestnut, poplar, willow, elm, ash, hackberry, sycamore, mountain ash, and London plane tree as well as many others. 

Life stages

Figure 2. Lifestages of the Asian longhorned beetle. Photo courtesy of USDA Animal and Plant Health Inspection Service.  

This woodboring beetle goes through four life stages: egg, larva, pupa, and adult (Figure 2). The eggs are laid by adult beetles on the bark of living trees. A single female can lay up to 90 eggs each year with a single egg being placed in its own site. Eggs are encased in a brownish protective secretion about ¼ inch in diameter. 

The larva emerges from this egg site in about 10 to 15 days and begins burrowing into the tree's bark. They begin by feeding on the sapwood around the tree but later feed on the heartwood and overwinter in there. In the springtime, they continue feeding until they begin their pupa stage. This may last over a week as it begins transformation into its adult form.   

Adults are generally present from June through October. They can range in size from 1 to 1 ½ inches long. They are black with white specks on its elytra (wing covers) and have long white and black banded antennae. Females tend to be a bit larger than males. 

Suspect a case?

Four months after the beetle was declared eradicated from the Chicago-land area it was found in Deerfield in August 2008. However, extensive survey efforts have not found any infestation or other signs of this invasive pest. The reintroduction of ALB is still a threat.

If you suspect the Asian longhorned beetle anywhere in Illinois please contact The Illinois Department of Agriculture at 1-800-641-3934. 

Learn more about Illinois invasive species

ABOUT THE AUTHOR: Kelly Estes coordinates surveys for harmful or economically significant plant pests and weeds that have eluded first-line inspections at ports of entry for the Illinois Cooperative Agriculture Pest Survey.