Emerald Ash Borer
A Emerald Ash Borer an exotic beetle from Asia was discovered in July 2002 feeding on ash trees in southeastern Michigan. More than 3000 square miles in southeast Michigan are infested and more than 5 million ash trees are dead or dying from this pest.
Larvae feed in the cambium between the bark and wood, producing galleries that eventually girdle and kill branches and entire trees. Evidence suggests that the Emerald Ash Borer beetle has been established in Michigan for at least six to ten years. More than 300 square miles in southeast Michigan are infested and more that 5 million ash trees are dead or dying from this pest. This exotic beetle is also established in Windsor, Ontario, Canada. In 2003 newly established populations were detected in other areas of southern Michigan and several locations in Ohio. Infested ash nursery trees were also found in Maryland and Virginia.
Adult beetles are generally larger and a brighter green than the native North
Larvae reach a length of 26 to 32 mm, are white to cream-colored and dorso-ventrally flattened. The brown head is mostly retracted into the prothorax and only the mouth-parts are visible externally. The 10-segmented abdomen has a pair of brown, pincer-like appendages on the last segment.
The emerald ash borer generally has a one-year life cycle in southern Michigan but could require two years to complete a generation in colder regions. Adult emergence begin in early June, peak in late June and early July, and continued into late July. Beetles usually live for about 3 weeks and are present into mid-August. Adult beetles are active during the day, particularly when conditions are warm and sunny. Most beetles remain in protected locations in bark crevices, or on foliage during rain, heavy cloud cover, high winds, or temperatures about 32°C (90°F). Emerald Ash borer beetles feed on ash foliage, usually in small, irregularly-shaped patches along the margins of leaves.
Females can mate multiple times and egg laying begins a few days after the initial mating. Females can lay at least 60 to 90 eggs during their lifetime. Eggs are deposited individually in bark crevices on the trunk or branches. Eggs hatch in 7 to 10 days.
After hatching, first instar larvae chew through the bark and into the cambial region. Larvae feed on phloem and the outer sapwood for several weeks. The S-shaped feeding gallery winds back and forth, becoming progressively wider as the larva grows.
Feeding is completed in autumn and pre-pupal larvae overwinter in shallow chambers excavated in the outer sapwood or in the bark on thick-barked trees. Pupation begins in late April or May. Newly enclosed adults often remain in the pupal chamber for 1 to 2 weeks before emerging head-first through a D-shaped exit hole that is 3-4 mm in diameter.
Distribution and Hosts
The emerald ash borer is native to Asia and is known to occur in China, Korea, Japan, Mongolia, the Russian Far East and Taiwan. In North American, this borer has only attacked ash trees. Green ash, white ash and back ash, as well as several horticultural varieties of ash have been killed.
It is difficult to detect emerald ash borer in newly infested trees. Jagged holes excavated by woodpeckers feeding on pre-pupal larvae may be the first sign that a tree has become infested. When a tree has been infested for at least one year, the D-shaped exit holes left by emerging adults will be present on the branches and the trunk. Bark may split vertically above larval feeding galleries. When the bark is removed from infested trees, the distinct, frass-filled larval tunnels that etch the outer sapwood and phloem are readily visible on the trunk and branches. An elliptical area of discolored sapwood, usually a result of secondary infection by fungal pathogens, sometimes surrounds larval feeding galleries.
Serpentine tunnels excavated by feeding larvae interrupt the transport of nutrients and water within the tree during the summer. Foliage wilts and the tree canopy becomes increasingly thin and sparse as braches die. Many trees appear to lose about 30% to 50% of the canopy after 2 years of infestation and trees often die after 3-4 years of infestation.
Emerald ash borer has killed trees of various size and condition in Michigan. Larvae have developed in trees and branches ranging from 2.5 cm (1 inch) to 140 cm (55 inches) in diameter. Stress likely contributes to the vulnerability and rapid decline of infested ash trees. However, emerald ash borer has killed apparently vigorous trees in woodlots and urban trees under regular irrigation and fertilization regimes.
Yu, Chengming 1992. Agrilus marcopoli Oberberger. In Xiao, G., ed. Forest insects of China 2d ed. Beijing, China: China Forestry Publishing House; 400-401.
Jendek, E. 2002. Agrilus planipennis fact sheet. PDF file provided by Eduardo Jendek, Institute of Zoology, Slovak Academy of Sciences, Bratislava, Slovak Republic.
Authors: Deborah g. McCullough, Michigan State University
Photo Credits: David L. Cappaert and Howard Russell, Michigan State University and Steven A Katovish, USDA Forest Service.