Emerald Ash Borer
Emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), a beetle from Asia, was identified in July 2002 as the cause of widespread ash tree (Fraxinus sp.) decline and mortality in southeastern Michigan and Windsor, Ontario, Canada. Larval feeding in the tissue between the bark and sapwood disrupts transport of nutrients and water in a tree, eventually causing branches and the entire tree to die. Tens of millions of ash trees in forested, rural, and urban areas have already been killed or are heavily infested by this pest.
Since 2002, emerald ash borer has been found in many states and parts of Canada. Closer to home, emerald ash borer was found in Wayne County in southeastern Missouri in 2008 and has since spread to four additional counties in that region. Then in the summer of 2014 emerald ash borer was found in six counties in southwest Arkansas. The insect is likely to be found in additional areas as detection surveys continue through the next few years. Evidence from other states suggests that emerald ash borer is generally established in an area for several years before it is detected. Emerald ash borer is now known in Arkansas, Colorado, Connecticut, Georgia, Indiana, Illinois, Iowa, Kansas, Kentucky, Maryland, Massachusetts, Michigan, Minnesota, Missouri, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia and Wisconsin. Infestations have also been found in areas of Ontario and Quebec.
The broad distribution of this pest in the United States and Canada is primarily due to people inadvertently transporting infested ash nursery stock, unprocessed logs, firewood, and other ash commodities. Federal and state quarantines in infested states now regulate transport of these products.
You can find more information about the emerald ash borer at the following web site:
Adult beetles are generally larger and brighter green (Fig. 1) than the native North American Agrilus species.
Adults are slender, elongate, and 1/3 to 1/2 inch (8 to 13 mm) long. Males are smaller than females and have fine hairs, which the females lack, on the ventral side of the thorax. Adults are usually bronze, golden, or reddish green overall, with darker, metallic emerald green wing covers.
The dorsal side of the abdomen is metallic purplish red and can be seen when the wings are spread (Fig. 2). The prothorax, the segment behind the head and to which the first pair of legs is attached, is slightly wider than the head and the same width as the base of the wing covers. Larvae reach a length of 1 to 1.25 inch (25 to 32 mm), are white to cream-colored, and dorso-ventrally flattened (Fig. 3).
The brown head is mostly retracted into the prothorax, and only the mouthparts are visible. The abdomen has 10 segments, and the last segment has a pair of brown, pincer-like appendages.
Emerald ash borer generally has a 1-year life cycle. In the upper Midwest, adult beetles begin emerging in May or early June. Beetle activity peaks between mid June and early July, and continues into August. Beetles probably live for about 3 weeks, although some have survived for more than 6 weeks in the laboratory. Beetles generally are most active during the day, particularly when it is warm and sunny. Most beetles appear to remain in protected locations in bark crevices or on foliage during rain or high winds.
Throughout their lives beetles feed on ash foliage, usually leaving small, irregularly shaped notches along the leaf margins. At least a few days of feeding are needed before beetles mate, and an additional 1 to 2 weeks of feeding may be needed before females begin laying eggs. Females can mate multiple times. Each female probably lays 30-60 eggs during an average lifespan, but a long-lived female may lay more than 200 eggs. Eggs are deposited individually in bark crevices or under bark scales on the trunk or branches, and soon darken to a reddish brown. Eggs hatch in 7 to 10 days. After hatching, first instar larvae chew through the bark and into the phloem and cambial region. Larvae feed on phloem for several weeks, creating serpentine (S-shaped) galleries packed with fine sawdust-like frass.
Beetle galleries etch the outer sapwood. As a larva grows, its gallery becomes progressively wider (Fig. 4) and reaches a length of 4 to 20 inches (10 to 50 cm). Feeding is usually completed in autumn.
Prepupal larvae overwinter in shallow chambers, roughly 0.5 inch (12 mm) deep, excavated in the outer sapwood or in the bark on thick-barked trees. Pupation begins in late April or May. Newly emerged adults often remain in the pupal chamber or bark for 1 to 2 weeks before exiting head-first through a D-shaped hole they bore toward the exterior of the tree.
Studies in Michigan indicate 2 years may be required for emerald ash borer to develop in newly infested ash trees that are relatively healthy. In these trees, many emerald ash borers overwinter as early instars, feed a second summer, overwinter as prepupae, and emerge the following summer.
In trees stressed by physical injury, high emerald ash borer densities, or other problems; all or nearly all larvae develop in a single year. Whether a 2-year life cycle will occur in warmer southern states is not yet known.
Distribution and Hosts
Emerald ash borer is native to Asia and is found in China and Korea. It is also reported in Japan, Mongolia, the Russian Far East, and Taiwan. In China, high populations of emerald ash borer occur primarily in Chinese ash (Fraxinus chinensis Roxb.), usually when those trees are stressed by drought or injury. Other Asian hosts (F. mandshurica var. japonica, Ulmus davidiana var. japonica, Juglans mandshurica var. sieboldiana, and Pterocarya rhoifolia) may be colonized by this or a related species.
In North America emerald ash borer was found only in ash trees until recently. In early 2015 a report was published of emerald ash borer identified in our native white fringetree. Host preference of emerald ash borer or resistance among North American ash species may vary. Green ash (F. pennsylvanica) and black ash (F. nigra), for example, appear to be highly preferred, while white ash (F. americana) and blue ash (F. quadrangulata) are less preferred. At this time all species and varieties of native ash in North America appear to be at risk from this pest.
Signs and Symptoms
It is difficult to detect emerald ash borer in newly infested trees because they exhibit few, if any, external symptoms. Jagged holes excavated by woodpeckers feeding on late instar or prepupal larvae may be the first sign that a tree is infested (Fig. 5). Distinctive D-shaped exit holes about 0.1 inch (3 to 4 mm) diameter (Fig. 6) left by emerging adult beetles may be seen on branches or the trunk, especially on trees with smooth bark.
Bark may split vertically over larval feeding galleries. When the bark is removed from infested trees, the distinct, frass-filled larval galleries that etch the outer sapwood and phloem are readily visible. An elliptical area of discolored sapwood, usually a result of secondary infection by fungal pathogens, sometimes surrounds galleries.
As emerald ash borer densities build, foliage wilts, branches die, and the tree canopy becomes increasingly thin. Many trees appear to lose about 30 to 50 percent of the canopy after only a few years of infestation (Fig. 7).
Trees may die after 3 to 4 years of heavy infestation. Epicormic shoots (Fig. 8) may arise on the trunk or branches of the tree, often at the margin of live and dead tissue. Dense root sprouting sometimes occurs after trees die.
Emerald ash borer larvae have developed in branches and trunks ranging from 1 inch to 55 inches (2.5 to 140 cm) in diameter. Although stressed trees are initially more attractive to emerald ash borer than healthy trees are, in many areas all or nearly all ash trees greater than 1 inch in diameter have been attacked.
Stop the Spread
There are several things foresters and landowners can do to slow or stop the spread of emerald ash borer. First, educate yourself about emerald ash borer. Learn to recognize the symptoms displayed by infested trees and learn how the pest is moved by people. Second, read this quarantine notice. Third, don’t move firewood. The initial infestation identified in Missouri was found in a U.S. Army Corps of Engineers recreation area. The source could easily have been firewood taken there by a camper. Buy firewood where you plan to use it. Never haul firewood out of an emerald ash borer quarantine area. Fourth, if you buy ash nursery stock, make sure the nursery stock does not come from an emerald ash borer quarantine area. Fifth, if you buy or sell ash logs, follow quarantine regulations for handling and processing ash logs.
Let’s work together to keep emerald ash borer out of Arkansas. If you find an ash tree showing symptoms of emerald ash borer infestation, contact the Arkansas State Plant Board at EAB@aspb.ar.gov.