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Emerald Ash Borer in Ontario

Emerald Ash Borer (EAB) (Agrilus planipennis) is an invasive insect species that originates from Asia and was first detected in Ontario in 2002 (Haack et al. 2002). The adult is between 7.5 to 15.0 mm in length and can be identified by its metallic green colour. The Emerald Ash Borer feeds on and damages all ash tree species (Fraxinus spp.). The insect has spread rapidly in Ontario through the movement of infested ash materials such as firewood and nursery stock. Infestations can be found from Windsor to the Greater Toronto Area with many isolated infestations occurring as far north as Sault Ste. Marie and the District of Algoma, and as far east as Ottawa and the United Counties of Prescott and Russell (OMNR 2014; Natural Resources Canada 2015).

In North America, the Emerald Ash Borer has few effective natural enemies, and native ashes have limited resistance to attack. The Emerald Ash Borer attacks both healthy and stressed ash trees when its larvae tunnel through the tree’s vascular system (Natural Resources Canada 2015). Infestations often result in more than 99% mortality of ash tree species causing a major impact on the biodiversity of both forested and urban areas in Ontario. Some of the effects include altered nutrient cycles and understory environment by changing successional patterns and encouraging growth of invasive species through newly created canopy openings. Also, the Emerald Ash Borer impacts populations of insect species that rely on ash trees for food (Herms and McCullough 2014). In urban areas, ash is one of the most commonly planted trees and therefore the removal and management of infested trees has an economic cost to municipalities.

Figure 1.  Emerald Ash Borer (Photo credit: Ontario Ministry of Natural Resources and Forestry).

Figure 1. Emerald Ash Borer (Photo credit: Ontario Ministry of Natural Resources and Forestry).

Emerald Ash Borer will spread a few kilometres per year on its own; however it can be dispersed long distances by people moving infested firewood, logs, lumber, and woodchips (Natural Resources Canada 2015). The Canadian Food Inspection Agency prohibits the movement of potentially infested materials by issuing ministerial orders in the designated regulated area. In Ontario, the regulated area starts from the southernmost tip of the province to the midway point of Algoma district, Sudbury district and includes all of Nipissing district.

Currently, trees can be protected to some degree from attack by Emerald Ash Borer by injecting them with a registered insecticide and removing any trees in a stand that have already been infested (OMNRF 2015). In response to this threat, many municipalities have developed management plans to address the invasion of Emerald Ash Borer. Actions by municipalities include monitoring of all ash trees in municipalities, removal of infested or high risk trees, the use of insecticide to protect trees that have not yet been infested, and replanting trees that have been removed.

There has also been considerable research conducted in the US and Canada on biological controls for Emerald Ash Borer. Three exotic species of parasitoids that specifically prey on Emerald Ash Borer have been released in the US by the United States Department of Agriculture. One of these parasitoids, Tetrastichus planipennisi, was approved for release in Canada. The Canadian Forest Service conducted releases in 2013 and 2014 with plans to continue this work into 2015. Native species of parasitoids have also been observed to attack EAB in increasing numbers which is an encouraging development (Herms and McCullough 2014). As the technology and experience develops in the realm of mitigating the impacts and stemming the spread of Emerald Ash Borer, municipalities will see more successes in addressing this threat to their economy and ecosystems.



Herms, D.A., and D.G. McCullough. 2014. Emerald Ash Borer invasion of North America: history, biology, ecology, impacts and management. Annual Review of Entomology 59:13-30.

Haack, R.A., E. Jendek, H. Liu, K.R. Marchant, T.R. Petrice, T.M. Poland, and H. Ye. 2002. The Emerald Ash Borer: a new exotic pest in North America. Newsletter of the Michigan Entomological Society 47(3&4):1-5.

Ontario Ministry of Natural Resources (OMNR). 2014. Forest health conditions in Ontario – 2012. Queens Printer for Ontario, Toronto, ON.

Ontario Ministry of Natural Resources and Forestry (OMNRF). 2015. Emerald Ash Borer. [Available at:]

Natural Resources Canada. 2015. Emerald Ash Borer. [Available at:]