Emerald ash borer

The emerald ash borer was first detected in North America in 2002, but probably arrived on this continent a decade earlier. Native to Asia, the beetle has proven to be highly destructive. Since its arrival, it has killed millions of ash trees and continues to spread into new areas, with considerable economic and ecological impacts.

Canadian Forest Service (CFS) scientists estimate that costs for treatment, removal and replacement of trees affected by emerald ash borer in Canadian municipalities may reach $2 billion over a 30-year period. The CFS researchers are studying the ecological impacts of ash tree mortality, including its effects on aquatic organisms, birds and understorey vegetation.


Emerald ash borer was first detected in Canada in 2002, in Windsor, Ontario. By 2005, it had spread into Essex and Lambton counties and the municipalities of Chatham-Kent and Dutton/Dunwich. In 2006, it was detected in London, Ontario, and in 2007, new locations were detected as far east as Toronto. The insect has continued to spread in Ontario, with infestations found as far north as Sault Ste. Marie and, by 2011, as far east as Ottawa and Prescott-Russell and Leeds-Grenville counties. In 2013, the beetle was also detected in Frontenac County and Manitoulin Island.

The Canadian Food Inspection Agency confirmed the presence of emerald ash borer in Quebec’s Montérégie area in 2008. By 2011, the insect had also been detected in Gatineau and Montreal, and by 2012 in Longueuil.

All of these areas are regulated by federal ministerial orders prohibiting movement of potentially infested ash commodities that could spread the emerald ash borer. More information about the regulations and a map of the current regulated areas are available from the Canadian Food Inspection Agency.

Influencing factors

In North America, the emerald ash borer has few effective natural enemies, and native ashes have limited resistance to attack. Surveys have shown that the emerald ash borer damages and kills trees in stands within one to four years of infestation. Typically, within six years of an infestation arriving in a woodlot, more than 99% of the ash trees have been killed. This extensive mortality increases the likelihood of invasion of forests by invasive plants, and poses a significant challenge to affected urban centres.


The area infested by emerald ash borer is expected to continue to expand, mostly through human movement of infested material such as firewood. Extensive areas with a large proportion of native ash trees have yet to become infested; the impact is therefore predicted to continue to increase as these forested areas are colonized by the emerald ash borer.

CFS researchers are investigating the spread (both natural and assisted) and impact of emerald ash borer in these more heavily forested landscapes. In addition, cities throughout central and western Canada often have a high proportion of ash in their urban tree inventories, and will be significantly affected if and when emerald ash borer arrives in those locations.

It is difficult to detect the emerald ash borer at low population levels. The visual survey method, looking for signs and symptoms of attacks, is often used to detect emerald ash borer populations. However, in the early stages of an infestation, signs and symptoms are not readily apparent.

In collaboration with United States Department of Agriculture scientists, CFS researchers have developed a green prism trap system for detecting emerald ash borer infestations. Baited with a green-leaf volatile lure, the green prism traps have been used by the Canadian Food Inspection Agency since 2010, resulting in the detection of new infestations outside of the regulated areas.

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Emerald ash borer. Duration: 3:26

CFS researchers have also demonstrated the attraction of male emerald ash borers to a female-produced pheromone. The pheromone has been shown to increase both trap captures and trap detection rates. It is now available commercially as a lure that can be used in combination with the green-leaf volatile lure on the green prism traps. Researchers are now investigating the use of the pheromone to disorient males and thereby reduce successful mating.

CFS researchers in Sault Ste. Marie have also developed a novel survey method that involves sampling branches pruned from the crown of host trees. This method provides a high rate of detection of asymptomatic infestation, and is currently being used by numerous municipalities and the provincial forest health monitoring group. It can be used to follow up on positive results of trapping survey programs, to determine which trees are infested and to what extent.

Other research is focused on the potential for long-term biological control of emerald ash borer. Some natural enemies, such as native parasitoids (insect parasites that kill their hosts) and insect pathogenic fungi, may help reduce emerald ash borer populations. CFS researchers are studying levels of mortality caused by these pathogens and parasitoids, in order to quantify their potential impact, as well as methods of increasing or augmenting their populations.

Researchers in the United States are continuing to study parasitoids imported from China to battle the emerald ash borer as part of a biological control program. Numerous releases of three species of imported parasitoids have been conducted in areas infested with emerald ash borer throughout the northeastern United States. Populations of these exotic parasitoids have been shown to be established at a number of release locations. Petitions for the importation and release of the three parasitoids in Canada have been submitted to the Canadian Food Inspection Agency for evaluation. If the petitions are successful, the parasitoids will be released at one location in Ontario in 2013.

TreeAzin™, formulated from an oil derived from seeds of the neem tree (a member of the mahogany family), was granted full registration in 2012 for use as a systematic insecticide to protect individual high-value ash trees and trees in isolated infestations. The Canadian Forest Service developed the product in partnership with BioForest Technologies Inc. Now commercially available, TreeAzin™ is being used by numerous municipalities and tree care companies as one component of their emerald ash borer management strategy. Models for estimating the economic costs and benefits of various management options are being developed by CFS researchers.

In collaboration with scientists from the universities of Western Ontario and Waterloo, CFS scientists have been working to understand the overwintering physiology of emerald ash borer, and its potential survival and distribution in Canada’s cold winter climate. Prepupae, the overwintering stage of emerald ash borer, can withstand average minimum temperatures of –30°C by employing antifreeze compounds.

Through the National Emerald Ash Borer Scientific Committee, CFS scientific staff are particularly proactive in supporting the Canadian Food Inspection Agency in establishing sound regulation practices based on the best scientific knowledge available.

In addition, because human-assisted movement is an important vector of emerald ash borer, CFS technology transfer and scientific staff are very active in providing the media with relevant scientific information and informing both the general public and groups including stakeholders, foresters and municipal forest technicians about the insect.