Emerald ash borer - Agrilus planipennis (Fairmaire)
Introduction
The emerald ash borer, Agrilus planipennis Fairmaire, is an invasive insect species that was first found in North America in June 2002. Shortly after the Detroit, Michigan discovery, forest health monitoring staff from the Ontario Ministry of Natural Resources (OMNR) and Canadian Forest Service (CFS) determined the beetle was also present in Windsor, Ontario. The Canadian Food Inspection Agency (CFIA) was immediately notified. Surveys conducted in Canada and the U.S. found the beetle was well-established in the Detroit and Windsor areas.
Little information was known about the beetle at the time. Arriving in North America through improperly treated wooden packaging material from Asia, the insect didn’t even have a common English name. Despite substantial research and control efforts, the beetle has continued to spread to new areas. Some of this spread has been natural dispersal, but the long distance spread has been helped by people, especially through the movement of nursery stock or infested firewood from infested areas.
Emerald ash borer is now found throughout much of Essex County and part of Chatham-Kent in Ontario. In Michigan, the beetle is concentrated in the southeastern portion of the state, but has also spread to multiple locations in the Lower Peninsula and as far north as the Mackinac Bridge. Spot infestations have also been found in Ohio and Maryland. Researchers, regulators, and urban foresters are in a race to halt the spread of the insect long enough to develop effective control measures to save native ash trees, an important hardwood species in North America.
The Threat
- The emerald ash borer is able to attack and kill healthy trees.
- All native ash species are at risk.
- Ash trees of all sizes are susceptible to attack, from 5 cm DBH (diameter at breast height) to 90 cm DBH or greater. Larvae have been found in branches as small as 1.1 cm in diameter.
- Ash trees are widespread in Canada and the United States, both in natural and urban settings, and green ash is one of the most commonly planted species in the urban forest.
- Emerald ash borer is very difficult to detect early. When infested trees are found, it’s often 1 year or more after the attack occurred. In addition, there are several other factors affecting ash health which may disguise its presence.
- Estimates show the emerald ash borer has killed several hundred thousand ash trees in Essex County, Ontario, and 8 to 10 million ash trees in southeastern Michigan. Tree loss includes ornamental, rural and woodlot trees.
- If not effectively controlled, the emerald ash borer is expected to spread across the entire range of ash, causing widespread tree mortality.
Adult Recognition
Adult beetles are metallic blue-green, narrow, hairless, elongate, 8.5 to 14.0 mm long and 3.1 to 3.4 mm wide. The head is flat and the vertex is shield-shaped. The eyes are bronze or black and kidney shaped. The prothorax is slightly wider than the head and is transversely rectangular, but is the same width as the anterior margin of the elytra. The posterior margins of the elytra are round and obtuse with small tooth-like projections on the edge.
Mature larvae are 26 to 32 mm long and creamy white. The body is flat and broad shaped. The posterior ends of some segments are bell-shaped. The abdomen is 10-segmented. The 1st 8 segments each have one pair of spiracles and the last segment has one pair of brownish, pincer-like appendages.
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Egg Recognition
Eggs are light yellow or cream-colored, turning yellow-brown prior to hatching. They are approximately 1mm long and 0.6 mm in diameter, and are very difficult to spot on the tree.
Larva Recognition
Larvae are slender, cream-coloured, flattened, with a brown head. Mature larvae are 26-32 mm long and have a pair of brown pinchers at the tip.
Pupa Recognition
Pupae are10-14 mm long, cream-coloured, with terminal abdominal segments that curve upwards. Antennae extend to the base of the wings.
Symptoms and Damage
Ash trees in Ontario and much of the north central region of the U.S. have been exhibiting a range of poor tree health conditions, including generalized crown dieback, leaf diseases and drought. Thorough investigation is critical in identifying whether symptoms of ash decline are caused by the emerald ash borer or some other factor.
What to look for:
Tunnels
Tunnels are oriented vertically, shallow, meander under the bark with abrupt turns and are packed with sawdust-like waste. Total length of the tunnels may be 50cm. Galleries are exposed 1-2 years after tree death as bark sloughs off.
Bark cracks
Vertical splits in the bark over larval galleries are often present and are usually 7-10 cm long. The cracks are more noticeable on young or pole-sized trees than on older trees with thick bark where close inspection is required to distinguish the bark splits from normal expansion caused by vigorous growth. Removing the bark will expose the galleries and larvae, if present.
Exit holes
Once fully mature, the adult beetle will emerge through an exit hole it has chewed through the bark. These exit holes are distinctly D-shaped and measure 3.5-4.1 mm across. Exit holes may be found anywhere on the tree trunk, root flare, exposed roots or in the crown. Sawdust may be visible in the exit hole or on the bark just outside it, especially in June and July.
Non-emerged adults
Dead adults are sometimes found in exit holes where the beetle was unable to fully emerge. Frequently, the head of these beetles is absent, leaving behind a hollow exoskeleton, suggesting the beetle was killed by another insect.
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Trees
Severely attacked trees may exhibit crown dieback from the top down in the first year of infestation. Often, one-third to one-half of the branches die in one year and the entire tree dies the following year. Foliage may wilt or turn yellow during the growing season. New, or epicormic, branches are common on the trunk of dying trees and dense root sprouts are often present at the base of dead trees or around stumps of cut trees.
Woodpeckers
Woodpeckers are very good at finding larvae under the bark. Look for increased woodpecker feeding activity in the trees or for signs of their probing of the bark.
What it does:
- The adult beetles will colonize a tree by laying eggs on the bark and in bark crevices on the trunk and branches. The larvae then tunnel beneath the bark and feed on the cambium, a layer of live cells between the bark and the sapwood.
- The larval galleries meander in an S-shaped or serpentine pattern. Eventually, high numbers of larval tunnels girdle the trunk, cutting off the transport of nutrients and water. The tree then starts to die from the top down – foliage on the tree wilts and the canopy may appear sparse.
- Feeding by adult beetles also occurs on the leaves of ash trees, but this feeding damage is minor compared to the larval tunneling.
Life Cycle
- The beetle appears to have a one-year life cycle, but there is evidence that some may take two years to mature.
- Single eggs are laid in bark crevices from late May through July, and hatch in about 20 days. The larvae go through four development stages (instars) as they feed on the phloem and outer sapwood, scoring deeper into the sapwood as they increase in size.
- Larvae feed aggressively until cooler fall temperatures arrive in October or November, and then overwinter in the tree.
- Pupation occurs late April to June. Newly-formed adults remain in their pupal chambers for 8-15 days, then bore through the bark to the outside.
- Adults begin to emerge in mid- to late May, with peak emergence in mid-June. Adults live about one month.
- Adults prefer the sunnier, warmer sides of the trees and are often found resting or flying in the sunlit portions of the crown and are more active on clear days with little wind.
- Mating occurs 7-10 days after emergence, with females mating multiple times. Females average about 70 eggs, but laboratory studies show some may lay as many as 250 eggs.
- The beetles will feign death and drop to the ground when disturbed.
- The adults are capable fliers. Although it’s unknown how far they will fly in the wild, laboratory experiments show they are capable of flying 10 km or more.
Host Species
All ash trees native to North America appear to be susceptible to attack. Anecdotal evidence suggests green ash and red ash appear to be preferred over white ash, followed by blue ash, black ash, or European black ash. There is no clear evidence that these latter species are resistant to attack. Even if green and red ash trees are attacked first, the insect appears to be able to attack and kill the remaining ash species.
Ash is an important species because it grows readily in disturbed habitats where it can be a major component of woodlots, fence rows or shelterbelts. They often grow along stream banks where they provide wildlife habitat, shelter, soil protection, and bank stabilization. Ash species are also important to wildlife because of their seed production which serves as an important food source. Commercially, ash wood is used for flooring, furniture, sports equipment, native baskets and items, tool handles and numerous products requiring strong, hard wood with less rigidity than maple.
How you can Help
- Report signs and symptoms of infested trees to the CFIA by phone 1 800 442-2342 (toll free) or online at www.inspection.gc.ca, or contact the OMNR at 1 800 667-1940 (toll free), or your local municipal parks or forestry department.
- Manage for healthy trees and healthy forests. Follow best management practices for woodlots, and encourage a diversity of tree species.
- Don’t move infested wood material to new areas.
- Firewood should be obtained locally, burned on-site, and not left behind.
- The CFIA program is focused on the leading edge of the infestation to slow its spread. Property owners within the rest of the infested area should watch for signs of infestation and keep trees well-watered and fertilized. Trees dead or dying from emerald ash borer should be cut and burned, chipped. If the appropriate permit is obtained from a CFIA inspector, trees from within an infested area may be properly processed for lumber.
For more information, please consult the website of the Canadian Food Inspection Agency
News Release from the Canadian Food Inspection Agency, dated May 7, 2013 - Emerald Ash Borer Regulated Areas Expanded.