Pest Alerts

Banded Elm Bark Beetle

A new menace is threatening elm trees in the United States. In April 2003, banded elm bark beetles were found in Colorado and Utah, and since then the pest has spread throughout 21 states, mainly in the west. The U.S. Department of Agriculture reported that as of March 2006 the beetle has been collected in Maryland and New Jersey. Vigilance and early detection will go a long way toward battling the bug.

Photo: Pest and Diseases Image Library, Bugwood.org

The banded elm bark beetle (Scolytus schevyrewi) is sometimes called the "chevy beetle" due to the pronunciation of its species name. It is native to China, Russia, and many countries of Central Asia. Although detected in the US in 2003, the beetle may not actually be a recent immigrant; museum specimens were collected in Colorado and western states as early as 1994. Like many of its destructive relatives, the banded elm bark beetle (BEBB) is believed to have arrived in the U.S. in packing crates made from infected wood.

Thought to be more aggressive than its dangerous cousin the European elm bark beetle (Scolytus multistriatus), the BEBB attacks weakened or diseased trees and devours their phloem and cambium, eventually killing the trees. Even more troublingly, the BEBB may be capable of spreading Dutch elm disease, which previously only the European elm bark beetle was thought to carry.

Identification

Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

About the size of a grain of rice (3–4 millimeters long), the banded elm bark beetle is brown and often has a dark band across its wings. The females cut entrance holes in tree bark, mate with the male beetle there, and then dig an egg gallery in the tree, laying between 20 and 120 eggs. The larvae are white and legless grubs that bore into the tree, carving out mines as they eat through layers of phloem. When the larvae are ready to pupate, they dig outward to the bark.

The adult BEBB cannot fly very far and often relies on the wind to carry it from tree to tree. Therefore, its range is not expansive. However, it is capable of producing two to three generations a year and is hardy: The pupae overwinter in trees.

Trees infested with BEBB can show these telltale signs: bore holes in the bark, with sap flowing if the wounds are fresh; stripped bark revealing phloem completely devoured by larvae; or pupae breaking through the outer bark, visible still in their grub form.

Susceptible Species

So far, the banded elm bark beetle has only attacked four species of elm in the U.S.:

American elm (Ulmus americana);
English elm (Ulmus thomasii);
Siberian elm (Ulmus pumila); and
Rock elm (Ulmus procera).

In its native countries, the BEBB has a wider host range that includes elms; willows; fruit trees of the rose family, such as apricot, cherry, peach, and plum; Russian olive trees; and others. It is not known if the beetle will begin to attack such trees in the U.S. as well.

Treatment

Although there is as of yet no known treatment for BEBB infestation, it is clear the beetle attacks weakened trees: Illness and drought make elms particularly susceptible. Proper watering of elms helps to ward off BEBB attacks, as does prompt removal of dead and dying trees, broken branches, and cut logs.

If You Think You've Seen the Banded Elm Bark Beetle

Do not hesitate to contact your local state department of agriculture or state extension office if you believe you have spotted the banded elm bark beetle.

In New York City, call these numbers: