Emerald Ash Borer

Karen Schiltz - Tuesday, March 19, 2013


You may have started hearing about the Emerald Ash Borer (EAB), and its dramatic effects on the population of ash trees in the East – especially Ontario and Michigan. EAB as of yet has not been observed west of Sault Ste. Marie, however pest strategies are being developed to deal with this especially lethal pest.

**2011** Update

The following 2008 article states that the pest has moved ‘as far east as Toronto,’ but as of now EAB has been identified in the Ottawa/Gatineau region, Sault. St. Marie, and as far east as Carignan in southwestern Quebec.

Forest Health and Biodiversity Newsletter Volume 12, No. 1, Spring 2008

By Dr. Barry Lyons

Emerald Ash Borer

Adult Emerald Ash Borer In an earlier issue of this newsletter (Volume 8, No. 1, Spring 2004), Hopkin et al. discussed the introduction, basic biology, signs and symptoms of attack, and research needs for control of the emerald ash borer (EAB), Agrilus planipennis. At that time, the known North American distribution of EAB was restricted to Essex County in Ontario, southeastern Michigan and northwestern Ohio. The spread of an invasive alien species can occur slowly by natural dispersal or more rapidly by human-assisted movement. For wood-boring beetles, like EAB, the latter may occur through the movement of unprocessed wood material, infested firewood, or nursery stock. Tree-dating techniques suggest that EAB was present in the Detroit area for about 10 years prior to its discovery in 2002. Consequently, the insect had a long period in which to spread unchecked and unregulated before it was discovered. In the intervening years, the beetle has been found widely distributed in Michigan, Ohio, Indiana, and in localized populations in Illinois, Maryland, Pennsylvania, and West Virginia. The recent discovery of EAB in Toronto is the most easterly population detected to date in Canada. Many of these populations were well-established when found and some may have pre-dated the imposition of quarantine regulations. 


Dead ash trees in a woodlot in southwestern Ontario

EAB, as its name suggests, attacks all species of true ash trees (Fraxinus spp). Since its arrival in North America, the beetle has killed millions of ash trees. In northeastern North America, there are five species of native ash trees: green ash (F. pennsylvanica, a.k.a. red ash), white ash (F. americana), black ash (F. nigra), blue ash (F. quadrangulata); and pumpkin ash (F. profunda). The first two are important hardwood species used in the manufacture of cabinetry and sporting goods. Black ash is favoured by First Nations people for the fabrication of baskets and other crafts. Pumpkin ash and blue ash are uncommon species in Canada that grow in extreme southwestern Ontario. Blue ash was designated a ‘Threatened’ species in Canada in April 1983 by the Committee on the Status of Endangered Wildlife in Canada. Its status was re-examined in November 2000 and the species was downgraded to ‘Special Concern’. Blue ash appears to have some resistance to the beetle, but pumpkin ash, a species that was unknown in Ontario until 1992, is very susceptible. All native ashes are thus candidates for genetic conservation. Eleven other species of ash grow elsewhere in North America and, along with exotic ashes, are also at risk. Asian species appear less susceptible. 


If the invasion rate of alien insects like EAB can be slowed, costs associated with managing the insect’s impacts can be prorated over time. A slow-the-spread strategy also buys time for the development of other control options. Quarantines and regulations, under the authority of the Plant Protection Act, prohibiting or restricting the movement of potentially infested materials, are designed to slow the spread of invasives. Regulated materials for EAB include nursery stock, trees, logs, wood, rough lumber including pallets and other wood packaging materials, bark, wood chips or bark chips from ash (Fraxinus spp.), and firewood of all species. Currently in Ontario, the combined regions of Essex Co. and Municipality of Chatham-Kent (formerly Kent County), Lambton Co., Elgin Co. and Middlesex Co. are each quarantined under an Infested Places (Ministerial) Order prohibiting or restricting the export of ash materials and firewood beyond their borders. Within Lambton, Elgin and Middlesex Counties, properties within 5 km of infested trees are also quarantined via Notices of Quarantine issued to individual property owners. These quarantine measures restrict the movement of regulated materials from these properties. The net effect is a nested-quarantine (quarantine within a quarantine) structure.Distribution and regulated areas for emerald ash borer in Canada (prepared by Canadian Food Inspection Agency). For counties like these that are not believed to be completely infested, the nested structure reduces the risk of EAB being spread through human activities from known infested (and regulated) areas to other areas of the county that may not be infested, while still regulating high risk materials from leaving the county. This has the dual benefit of slowing both intra- and inter-county spread of EAB. For localized infestations, such as those recently discovered in Norfolk County and Toronto, only individual infested properties have been quarantined to this point through the issuance of Notices of Prohibition of Movement. This is an interim solution until other quarantines can be applied.


The greatest challenge to managing this insect has been our inability to locate new low-density populations. Although significant research efforts have been made in the identification of an attractant, an efficient lure for detection traps remains elusive. Thus, we must rely on the presence of signs and symptoms of the insect’s activity to detect infested trees. Signs and symptoms include thinning and Dieback of the tree Crown, deformities of the bark, development of shoots from the bark, D-shaped adult emergence holes, and holes created by woodpeckers searching for the larvae. The Canadian Forest Service (CFS) has produced two publications describing methods for detecting and surveying EAB populations. These are available at the following website: However, by the time these signs and symptoms are evident, the beetles are well established and have spread further.Biological control (the use of natural enemies to regulate pest populations) is one control strategy that might benefit from the slow-the-spread methodology. The classical biological control tactic involves exploration for natural enemies of the invasive alien species in their native habitats and re-associating the host insects with their natural enemies in their new habitats. The Animal and Plant Health Inspection Service (APHIS) and the Forest Service (FS) of the United States Department of Agriculture (USDA) have been actively involved in classical biological control of EAB since its discovery in Detroit.


Steps in a classical biological control program include: assessment of native natural enemies; foreign exploration and collection; propagation, mass rearing, biological investigations and host-specificity testing; field release; impact assessment; and long-term monitoring. Having satisfied the first three of these steps, the USDA released three parasitoids of EAB from China into Michigan in the summer of 2007. These included two parasitoids of larvae [Spathius agrili (Hymenoptera: Braconidae) and Tetrastichus planipennisi (Hymenoptera: Eulophidae)] and one parasitoid of eggs [Oobius agrili (Hymenoptera: Encyrtidae)].

The USDA plans to develop a mass-rearing facility for these parasitoids with the goal of making future releases. A second biological control tactic known as augmentation involves moving established or natural biocontrol agents from areas where they occur to areas where they don’t occur (inoculation) or supplementing low numbers by propagation (inundation).

For step 1 of the classical tactic described above, USDA-FS scientists evaluated the impact of native parasitoids on EAB populations. Observations from Michigan populations indicated that native parasitism rates were 1%. However, through our regular rearing of EAB from log bolts in our quarantine facility in Sault Ste. Marie, we located an Ontario population of EAB that had high numbers of two larval parasitoids. The most abundant parasitoid was Phasgonophora sulcata (Hymenoptera: Chalcididae) and the less abundant parasitoid was Balcha indica (Hymenoptera: Eupelmidae). The former species is the most common parasitoid encountered in native Agrilus populations. The second species is itself an alien species that probably arrived in North America from Asia on some host other than EAB because it was first encountered in 1994 in Virginia. Subsequent trapping at this Ontario location using sticky bands suggested a parasitism rate of ~40% by P. sulcata. Both species were encountered during the Michigan study. Investigations will continue to evaluate the impact these parasitoids are having on EAB populations and their potential value as augmentative biological control agents.


Adult Emerald Ash Borer

Ash trees are often important components of our urban forests because ashes are resistant to the harsh conditions we impose on our landscape trees. The Canadian Forest Service (CFS), in cooperation with the Canadian Food Inspection Agency, the Ontario Ministry of Natural Resources and the City of London, is developing a science-based management plan for EAB in urban/suburban areas. During the summer of 2007, a project was undertaken in London to demonstrate the usefulness of some of the tools currently available to manage this pest. Among the tools used was the systemic injection of ashes in the vicinity of infested trees with a formulation of the biological insecticide neem, which was developed by the CFS in Sault Ste. Marie. The efficacy of this tool will be assessed in 2008.

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