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Home * Meet the Species * Insects * Emerald Ash Borer

Emerald Ash Borer

French common name: Agrile du frêne
Scientific name: Agrilus planipennis Fairmaire
Order: Coleoptera

The emerald ash borer (EAB) is an invasive wood-boring beetle, native to parts of Asia. It was detected in the Detroit, Michigan and Windsor, Ontario area in 2002, but likely existed undetected in North America since the 1990's. Experts believe the EAB was introduced to Detroit hidden inside wooden packaging materials or shipping crates. Since its arrival, the EAB has been rapidly spreading across North America, having devastating effects on the ash tree population, killing up to 99% of ash trees in its path. The EAB continues to spread in all directions across North America where ash trees are present.

Photo: David Cappaert, Michigan State University, Bugwood.org 

Learn about the Emerald Ash Borer

The Insect

Physical Description

Adults: bright metallic green wood-boring beetles, 8 -14 mm (about ½ inch) long and 3-3.5 mm (1/8 inch) wide, body elongated, head flat. The dorsal surface of the abdomen (underneath wings) is usually a bright red colour. 

Pupae: 10 -15 mm long, creamy white in colour when it first forms and takes on adult colouration as it develops. 

Larvae: 25 - 32 mm long at maturity, creamy white in colour, brown head, flat, broad shaped body; 10-segmented abdomen (bell-shaped segments) and a fork-like appendage on the tip of the abdomen. 

Photo provided by Taylor Scarr, OMNRF
Photo provided by Taylor Scarr, OMNRF

Emerald ash borer adult and larvae (left), and adult with extended wings (right)

Life Cycle

Adult beetles actively feed on host plant foliage throughout their lives. Adults lay eggs in crevices on host tree bark, under bark scales; peak oviposition period typically occurs between late June and early July in temperate regions (Bauer et al., 2004) but may vary depending on factors such as latitude and local climate. To hatch, larvae chew through the side of the egg that is stuck to the bark, and bore into the sapwood, phloem, or cambium part of the bark, where they form pupal chambers and overwinter. When EAB populations become large enough, larval feeding under the bark girdles the tree, eventually leading to tree death. Pupation occurs in the early spring. When development is complete, the adult EAB will chew out of the bark of the tree, leaving a distinctive D-shaped exit hole in the bark (Bauer et al., 2004). Adult EAB begin to emerge from trees in late spring, depending on temperature, and are able to fly immediately after emergence.


Host Trees

EAB attacks and kills all species of North American ash (Fraxinus spp.) that it has encountered. A total of 20 species of ash are found in North America, six of which are native to Canada; green ash (F. pennsylvanica), white ash (F. americana), black ash (F. nigra), and much less common blue ash (F. quadrangulata), and pumpkin ash (F. profunda), and Oregon ash (F. latifolia) in B.C. Blue ash may succumb to EAB, however, research indicated that it is mostly resistant. Recent evidence from the U.S. suggests that EAB may also attack the white fringetree (Chionanthus virginicus). Fraxinus and Chionanthus both belong to the olive family (Oleaceae), so likely have similar chemical composition and lack of appropriate defenses.

The green ash (Fraxinus pennsylvanica), pictured below, is a preferred host tree of the emerald ash borer.

 Photo: Karan A. Rawlins, University of Georgia, bugwood.org 

Signs & Symptoms

Signs and symptoms include crown dieback, bark deformities, woodpecker feeding holes, D-shaped exit holes in the tree, epicormic branches (shoots growing out of the lower trunk(commonly), but can be found on all parts of the trunk or branches), yellowing of foliage, and vertical cracks in the trunk (FIAS, NRCan, 2013).

Photo: Taylor Scarr, OMNRF (edited) 

Galleries formed under the bark from EAB larval
feeding. D-shaped exit holes are circled in red. 
         Photo: Daniel Herms, The Ohio State University, bugwood.org

     Typical signs of EAB infestation include             crown dieback and epicormic branches. 


City of London (2013) 
(CFS, 2006)


Distribution in North America

Initial surveys in 2002 revealed the presence of EAB in seven counties in Southeastern Michigan. Currently, EAB has been detected in 25 states in the U.S. and two provinces in Canada, and continues to spread (see map) (emeraldashborer.info, 2015). In an attempt to control the spread of EAB in Canada, the Canadian Food Inspection Agency (CFIA) has developed regulations that restrict the transport of ash materials (such as firewood) out of affected areas, under the Plant Protection Act (CFIA, 2011).


Economic Impacts

Ash trees provide many benefits within urban environments, such as increased property values, windbreaks, temperature regulation, pollution abatement, runoff prevention, and provision of wildlife habitat. With extensive ash tree mortality caused by EAB, the cost of replacing such services can be immense for municipalities. Further, the costs of treating infested trees, removing damaged and dead trees, and replanting where trees have been lost has already been very large (NRCan, 2014). You can calculate the cost estimate of treating vs. removing your ash tree by visiting the Canadian Forest Service Ash Projection Model (CFS-APM).

The City of Toronto, for example, estimates that it will cost the city $37 million over five years to cut and replace the city-owned ash trees that are killed by the insect. Further, as of 2012, the Canadian Food Inspection Agency had already spent over $30 million to manage the invasion of EAB and had cut over 30,000 trees to slow the spread of the beetle (Ontario Ministry of Natural Resources, 2012). Over the next decade, some estimates suggest that 17 million trees will need to be removed and replaced within communities in the U.S. alone. This would cost approximately $10.7 billion, but could double if both urban and rural land is taken into account (Kovacs et al, 2010).

Ash is also commonly used for commercial lumber, pulp, tool handles, furniture and crating (Cappaert, 2005). Loss of ash could have a significant impact on these industries. As described in Poland and McCullough (2006), ash comprises approximately 7.5% of total hardwood saw-timber volume in the U.S., with a stumpage value of at least $25.1 billion (Federal Register, 2003).

Photo: Taylor Scarr, OMNRF

Ash trees removed from an urban area in response to an emerald ash borer infestation. Urban tree removal comes at a high economic and ecological cost for municipalities across infested areas. The City of Toronto alone anticipates costs of $37 million to cut and replace ash trees throughout the city, resulting in loss of aesthetic value to neighbourhoods, and a loss of ecological services that the trees provide.  

Ecological Impacts

Emerald Ash Borer has already done extensive damage to ash tree populations in North America, killing millions of ash trees in Ontario, Quebec, and many U.S. states.

Although the direct effects of EAB on ash trees are fairly conspicuous, the indirect or downstream ecological impacts of EAB are much more difficult to quantify. Some potential ecological impacts are as follows: changes to forest structure, altered canopy gaps, reduced coarse woody debris, altered biogeochemical and nutrient cycling, and altered ecological interactions among organisms (both aquatic and terrestrial). Specifically, populations of native species that have specialized interactions with the threatened host, such as terrestrial arthropod species with a high level of association with ash, might be at increased risk (Gandhi and Herms 2010). Poland and McCullough (2006) suggest that the loss of green and black ash, which dominate riparian corridors and poorly drained sites, respectively, could produce the most significant ecological impacts.

Photo: David Nisbet, Invasive Species Centre 
Canopy openings caused by EAB damage can increase light penetration to the forest floor, and make the area more susceptible to understory plant invasions. 

Social Impacts


The aesthetic and recreation values that people place on forests and parks could be negatively impacted by EAB, since many ash trees within these natural areas have already died, or are susceptible to EAB infestation. Ash is a commonly planted street and park tree, and the loss of mature trees will negatively impact the aesthetic value of residential neighbourhoods and urban greenspace.

Photo: Taylor Scarr, OMNRF

 A mature ash tree is removed from a residential neighbourhood after being attacked by the emerald ash borer. Urban areas are at high risk to EAB infestations, as ash trees line many streets, and are commonly found in parks, and urban greenspace.