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TREES & Plants

Asian longhorn beetle

Asian longhorned beetle
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The Asian longhorn beetle is an insect that can do very serious damage and even kill trees while in its larval stage. It is believed that the beetle, while in the larval or pupal stage, was transported here in the wood of shipping crates from Asia.  It was first discovered in the Ravenswood area of Chicago in 1998.  Through a combination of tree removal and chemical treatments, the Illinois Department of Agriculture was able to eradicate this insect in Illinois.  The eradication was announced in 2008.  This insect does occur in other states and could return to Illinois in the future.

HOSTS

In the Chicago area, the major host tree was maple (Acer spp.), specifically Norway, sugar, and boxelder. However, horse chestnut, black locust, elm, rose of Sharon, and green ash were also attacked. The insect is native to China, Korea, and Japan, where it attacks maple (primarily silver maple and boxelder), poplar, willow, mulberry, plum, pear, black locust, and elm. In New York, in addition to maples and horse chestnuts, poplars and willows have been attacked.

LIFE CYCLE

Adult beetles emerge from the trees from May to October by chewing their way out of the trunks. Peak emergence time is thought to be July. The exit holes are between 3/8" and 1 and 1/4" inches in diameter, round and very deep. Most of the exit holes found in Chicago were in the larger branches of the trees. Sometimes heavy sap is seen oozing out of the emergence hole or egg niches, and occasionally an accumulation of coarse sawdust and frass is seen at the base of an infested tree.

The adult Asian longhorn beetle is about 1 and 1/4" in length, and glossy jet black with small white spots on its wing coverings. It has long antennae that are distinctly banded black and white. The antennae of the males are 2 and 1/2 times their body length, while the female antennae are 1 and 3/4 times their body length. Because they are heavy-bodied insects, they cannot fly great distances.

After mating, female beetles chew depressions in trees to lay eggs. These depressions can be oval to round in shape. In Chicago, oviposition scars (where eggs are deposited) were frequently found lower in the trunk, as low as a few inches above the soil line. When the eggs hatch, the larvae begin feeding under the bark. The first three instars (larval stages) feed in the tree’s phloem (food-conducting vessels), then late third and early fourth instars feed on xylem (water-conducting vessels). Mature larvae burrow winding galleries in the heartwood.

MANAGEMENT

Presently management includes destroying infested trees and limited use of insecticides targeted at the adult beetles.  Because most of the Asian longhorn beetle’s life cycle is spent deep inside the tree, they are difficult to control. The beetles do have a few natural enemies in their native Asia, including nematodes, woodpeckers, and parasites, but their natural enemies are unable to keep them from being a serious problem even there.

Early detection of infestations and quick response treatment is important to limit the spread of this insect because it may become a significant tree pest in this country. If you believe you have seen the Asian longhorn beetle, please collect an adult beetle in a jar, place the jar in the freezer, and notify the U.S. Department of Agriculture in your state. In Illinois, contact the Illinois Department of Agriculture.

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