Extension Communications Extension 4-H Youth Building Ames, Iowa 50011-3630 (515) 294-9915

12/1/03

Contacts:
Mark Shour, Entomology, (515) 294-5963, mshour@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033, jmcguire@iastate.edu

Yard and Garden Column for the Week Beginning Dec. 5, 2003

Emerald Ash Borer is Beautiful but Destructive

Insects have been the subject of artistic expression throughout human history because of their beauty and intrigue. A quick review provides numerous entomological examples from postage stamps, jewelry, paintings, poems, children's books, movies, photographs and songs. A recently introduced insect to the United States has a name and coloration that would initially evoke a positive response from the uninformed: the emerald ash borer. However, further examination reveals that a person should keep a careful watch for this pest since it is potentially far more devastating than Dutch Elm disease.

From Asia
Emerald ash borer, Agrilus planipennis, was accidentally introduced into Detroit, Mich. from Asia. The natural range of this insect is eastern Russia, northern China, Japan, Taiwan and Korea. How the insect was introduced is still being investigated, but the most likely source was solid wood packaging. Although the emerald ash borer was first identified July 2002, it entered the United States at least 5 years previously based on symptoms displayed by affected trees. From Michigan, this new pest moved north into Windsor, Ontario, Canada, east to Maryland, and south to Ohio. To date, Iowa is apparently free of this pest.

Atypical Attack
It is generally considered that insect borers are only successful in colonizing stressed or declining plants. Two common relatives of the emerald ash borer are the twolined chestnut borer and the bronze birch borer, which attack declining oaks and birches, respectively. Unlike other borers, the emerald ash borer has successfully attacked apparently healthy ash trees of a variety of ages in landscape and forest settings.

Ash Resource at Risk
To date, the known host plants in the United States are white, green and black ash trees. All of the 16 North American ash (Fraxinus) species should be considered susceptible to this pest. More than 8,000 ash trees (largely saplings) were destroyed in Ohio during eradication procedures. An estimated 6 million ash trees have been killed by the emerald ash borer in Detroit, Michigan. During an ash tree survey of 2,000 square miles in southeast Michigan, about half of the 650,000 landscape and 11 million forest ash trees displayed borer symptoms, were already dying, or were dead. The United States Forest Service estimates there are more than one billion ash trees in the country.

Beautiful Beetles
You can recognize emerald ash borer adults by their dark, metallic, emerald green body. The beetles are small and slender, measuring one-half inch long and one-sixteenth of an inch wide. Adult beetles feed on host foliage, producing a marginal notching on the leaflets. Mating occurs on the host plant. Female beetles in lab tests laid from 2 to 258 eggs/female, with an average of 60-90 eggs. Eggs are laid in bark crevices. Upon hatching larvae chew through the bark.

Life Cycle
The life history of the emerald ash borer still is being examined by researchers in Michigan, but a few basics have been established. This pest is considered to produce one generation a year, although it may take more than one year for this insect to develop. The emerald ash borer larvae feed just under the bark in the nutrient-rich cambial and phloem tissues. The creamy white larvae produce winding tunnels that girdle branches and the trunk. Mature larvae (approximately 1.5 inches long) overwinter in the host plant. The transition from larva to adult (pupal stage) occurs in early spring. Adult beetles chew their way out of the pupal chambers, producing D-shaped emergence holes about one-eighth of an inch wide. In 2003, beetles were first observed in Michigan on June 4 and the last adult was observed on August 15.

Signs and Symptoms
Infestations of the emerald ash borer can be difficult to detect. Symptomatic trees display thinning and dieback of the upper one-third of the crown. Root and stem suckers (epicormic shoots) are produced by affected ash trees directly below borer activity. Tissue produced by the host tree in response to larval tunneling may cause vertical splits on the trunk. Removal of the bark in these areas reveals the tunnels. A definitive sign of this exotic pest is the D-shaped adult emergence holes; native borers attacking ash trees have round emergence holes. Unfortunately, signs of early infestations on a tree are limited to the upper part of the tree. Tree deaths can occur within 3 years of initial attack.

Natural and Assisted Movement
Early research has observed natural movement of the emerald ash borer by adult flights. It is known the beetle can fly one-half mile from an infested host tree and researchers speculate the natural spread may be farther. People have inadvertently spread this new exotic pest through interstate commerce. A satellite infestation in Maryland resulted from two shipments of 121 ash trees for landscaping purposes. The infestations in three areas of Ohio are considered the result of ash firewood, branches, and log movement. Michigan and Ohio have imposed state quarantines on movement of ash trees and ash wood products to limit the spread of this pest. The USDA Animal and Health Inspection Service and the Canadian Food Inspection Agency have imposed federal plant quarantines.

Management Efforts
Eradication of this pest in the focal areas has consisted of removing infested trees and all susceptible host trees within a specified buffer zone. Researchers in Michigan conducted experiments during 2003 aimed at remedial control measures. Systemic insecticides (targeting the larval stage) and contact insecticides (targeting the adults) were examined. Their results are forthcoming.

The primary preventive strategy in Iowa involves nursery stock inspections by the State Entomologist office of the Iowa Department of Agriculture and Land Stewardship (IDALS). Suspected sightings of emerald ash borer adults or symptomatic trees should be reported to the State Entomologist's office, any local Iowa State University Extension office, or any district forester with the Iowa Department of Natural Resources. Remember, there are native insect borers that colonize declining or dying ash trees and are not of special concern.

For more information about the emerald ash borer, visit the U.S. Forest Service Web site for this new exotic insect: http://www.na.fs.fed.us/spfo/eab/.

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ml: isugarden

Editors: Two color photos, suitable for publication, are available at right. Click on each thumbnail photo to go to the fullsized photo. The top picture's fullsize photo is 228K and the bottom picture's fullsize photo is 448K. Caption: Emerald ash borer adult. Photo by David Cappaert, Michigan State University, www.insectimages.org.
Caption: Epicormic shoots from ash tree are common symptoms of emerald ash borer infestation. Photo by Ed Czerwinski, Ontario Ministry of Natural Resources, www.insectimages.org.

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