What I can tell you about the emerald ash borer

For the past few months, I've been working as an emerald ash borer specialist at the Invasive Species Centre - a not-for-profit located in Sault Ste. Marie, Ontario. 

Alongside my colleague and mentor, and former Forest Health Specialist at the Ontario Ministry of Natural Resources, I've travelled around Ontario meeting with municipalities, conservation authorities, and local groups in order to share and discuss the science, best practices, and management options around this invasive insect. 

Here is a lot of what I’ve learnt about the infamous emerald ash borer that has been labeled as the “most destructive invasive insect in North America”.

EAB is not native to N.A....

EAB is native to China and eastern Asia and was likely transported to Canada by way of wood packaging materials. It was first discovered in North America in 2002 in the Detroit, Michigan area and shortly after in Windsor, Ontario.

...it attacks ash trees...

EAB attacks all species of ash (Fraxinus spp.). This doesn't include mountain ash, which isn't a true species of ash. In China, the native ash species including Manchurian ash tend to be resistant unless already on a decline. In Canada, all ash trees are attacked, stressed or healthy, although blue ash has shown some resistance and is thought to be genetically closer to Manchurian ash than the native white, green/red, black, or pumpkin ash. Furthermore, there aren't any natural enemies present to keep EAB populations in check.

...and the larvae cut off the trees' circulation.

Even though the adult beetles feed on the leaves, this doesn't really affect the health of the tree. It is the larvae that burrow under the bark and create s-shaped galleries (shown to the left), which cut off the circulation of the tree and eventually leads to mortality. The physical symptoms include dieback (thinning of the crown), epicormic shoots (sprouting at the lower portion of the trunk), cracks or woodpecker damage, tiny D-shaped exit holes, and sometimes pink discoloration.

Within 6 years, all of the ash trees die...

Trees attacked by EAB tend to die within 2-3 years after attack and research has shown that within 6 years, 99% percent of the ash trees in an infested area will have died. This one percent accounts for what are called lingering ash, which may show some resistance to the insect; though this is rare.

...then they fall...

Unlike the persisting elms that were killed by Dutch Elm Disease, ash trees killed by EAB seem to topple over. Their root system rots and the tree loses its support system creating a human hazard especially on streets and in parks. 

...and must be removed.

Since dead ash trees are hazardous due to their weak root system and likelihood of falling over, cities are left with the cost of removing all of the dead ash trees on streets and in open parks. In some urban areas, the percentage of ash trees compared to the rest of the canopy is over 80% and the cost of removal and replacement can be in the millions. It is expected that ash tree replacement, removal, and treatment will cost municipalities $2 billion over 30 years.

However some can be "saved" with an insecticide...

If the ash tree is still in a healthy state and showing minimal stress symptoms, the trees can be treated with an insecticide. Since it is the larvae that kill the tree when burrowing under the bark, the insecticides must be injected at the bottom of the trunk (shown to the right) and they are naturally distributed through the tree by way of the tree's circulatory system. There are three insecticides currently on the market, ACECAP, Confidor, and TreeAzin, although TreeAzin is the safest of the three and is the only one that has been shown to control EAB populations rather than just suppress them. 

...which can cost less than removal...

Removing and replacing a tree can cost well over a thousand dollars; whereas treating a tree with TreeAzin costs approximately $200 per biannual injection. TreeAzin has been shown to provide 2 years of protection from EAB, and over ten years it can be cheaper to inject rather than remove. Another option is to treat and underplant with another non-ash tree, so that when you do stop treating the ash tree, you will have a good-sized tree in its place.

...and buy us more time for science to catch up.

Some people ask whether they will have to inject their ash trees indefinitely. The hope is that within the next ten to fifteen years, there will be large populations of enemies to keep the populations low. Three parasitic wasps that kill EAB in its native land have been released in the United States and are currently undergoing the approvals necessary to be released in Canada. The hope is that the populations of wasps will build up to the point that they can greatly reduce EAB populations. In addition, a native parasitic wasp, Phasgonophora sulcata (shown above) is being released this summer and there is other ongoing research around a native fungus (Beauvaria sp.) that may play a role in reducing EAB as well.

We have come a long way from basic visual surveys...

In 2002 and for years after, the only known way to survey for EAB was to look for the tree decline symptoms (listed above). The problem with relying on physical symptoms of infested trees is that they usually only show up after the tree is already in decline, years after, when the insect population has likely already spread to a much larger area. If you don't know where the population is and where its leading edge is, it is hard if not impossible to eradicate (exterminate) or contain the population. When the infestation was found in Essex County, the federal government tried to contain the population by creating a firebreak or an "ash-free zone" by removing all ash trees within a 10km band between Essex and Chatham-Kent. However, because they were relying on visual surveys, it was only well after the cutting began that an established population had been detected on the other side.

...to green prism traps and branch sampling.

There are now tools like branch sampling that can detect an infestation before any visual symptoms can be seen. EAB adults tend to lay eggs first on branches in the canopy where there is more sun and where the bark is thinner. Only in the later years are eggs laid lower on the bark and the 

larvae create more severe damage in the main trunk. Knowing this, scientists and practitioners now use a method, where they cut specific branches in the canopy and peel back the bark. If the tree is infested, you will see tiny serpentine galleries under the bark along the branch. This is an effective way to know just how infested an area is. Whereas, green prism traps with lures, mostly tell you whether there is EAB present in an area, but not necessarily which trees are infested and should be removed.

  

Humans play a large role in the spread of EAB...

The adult beetles don't fly that far. Although lab research has shown that EAB can fly up 20km/year, this is very uncommon in the field where there are ample ash trees. More likely, the beetle is moved by way of infested wood products, especially firewood. 

...but there are regulations to limit movement...

The Canadian Food Inspection Agency (CFIA), which is the regulatory body responsible for regulating non-native invasive species, has set quarantines around the infested Ontario counties. These quarantines restrict the movement of firewood or ash wood out of infested areas into non-infested areas. In Canada, the majority of southern Ontario is regulated, as well as areas around Ottawa, Gatineau, and Montreal, along with Manitoulin Island and Sault Ste. Marie.

...which are by no means perfect...

Quarantines are currently set by county. This means that as soon as an EAB is found in a trap (in Canada, we use green prism traps with lures), CFIA will regulate and quarantine the whole county. Once an area is quarantined then products can move freely within and from other adjacent regulated counties and in some cases increase the rate in which the insect is spread. There is the case where it could only be one beetle caught and no infested trees identified, as was the case in 2011 on Manitoulin Island, but the whole island or county still gets quarantined.

...and will likely expand next year.

Due to resource issues and a low confidence in their survey method, CFIA is looking to expand the quarantined areas beyond a county-by-county basis to a much larger area up to the French and Mattawa rivers, allowing for a smaller perimeter for surveys. This would include many areas not currently known to be infested by EAB, including Muskoka, Haliburton, and Algonquin Park. This is not a good idea for obvious reasons, and although it still isn't known how EAB will persist in natural forests, this is definitely a good way to find out, fast. The area was based on trade routes, where CFIA thinks EAB has or will move and will be implemented in April 2014.

That is, unless other levels of government work together to take over the surveying for CFIA, then there is the possibility that the agency may not increase the quarantine size. Either way, this will get people at the lower government level and of the public more involved with urban forest management. 

Knowledge will continue to be shared and transferred.

Although this is an unfortunate situation, through my work, I have seen incredible support and transfer of knowledge between different municipalities and other levels of government or non-government organizations. 

Over the next year, many new products are anticipated to be published. These include the Canadian Forest Service EAB best management practices, which will be a comprehensive document of the most recent research and recommended management options, public video announcements about the emerald ash borer and how to manage, as well as a website similar to EAB Info, but more focussed on Canadian content.

For more information about the emerald ash borer, visit the Canadian Food Inspection Agency website.

For emerald ash borer research publications, go to the Canadian Forest Service website and search for "emerald ash borer".

For more information about identifying infested ash trees, see the Visual Guide to Detecting Emerald Ash Borer Damage.

For more information about TreeAzin, visit the Bioforest website.

Photo credits: Canadian Food Inspection Agency, United States Department of Agriculture, BioForest, Ottawa Citizen, and Kare 11.