Ontario Trees at Risk
Two tiny Asian insects could have huge impact
on the environment in North America
Gard Otis holds a piece of bark from a tree that has been
ravaged by the emerald ash borer.
Photo by Grant Martin
Trees in southern Ontario are in danger, says Prof.
Gard Otis, Environmental Biology. Ash, maple, birch, willow,
elm and fruit trees are all at risk because of two exotic
beetle species that have made their way to North America,
One of the pests, the Asian longhorned beetle, was recently
discovered in Toronto, and it's hoped the insect can be
contained to a small region of that city, says Otis. But
another Asian beetle, the emerald ash borer, has already
killed thousands of ash trees in the Windsor area.
Working with graduate student Nicole McKenzie, Otis is
helping to detect and contain emerald ash borers before
they spread across the country.
"When I heard about the borer, I saw it as a research
opportunity," he says. "I was lucky and got linked
with Canadian Forest Service researchers who are spearheading
a number of projects to understand everything we can about
Most people barely notice dead trees, let alone take the
time to stop and look at what may have killed them. That's
why both species went undetected for several years.
"For both these beetles, until the adults emerge and
there is an exit hole in the tree or trees are dying in
large numbers, there is little evidence they are infested,"
says Otis. Only if you look closely for symptoms and peel
back bark will you see their mark.
"The discovery of the Asian longhorned beetle in Toronto
came as a huge surprise," he says.
One of the people called on to help diagnose the bug during
the initial outbreak was Otis's colleague Prof. Steve Marshall,
who has overseen Guelph's insect collection since 1982.
The Canadian Food Inspection Agency (CFIA) is now co-ordinating
a survey of the areas infested in Toronto. "If the
beetles get into the nearby forests along the Humber River,
it's going to be really hard to stop them or detect them,"
He notes that the current development stage of the pests
is buying the CFIA some time. "Luckily, the beetles
are done flying for the year. The CFIA has the winter to
complete the survey and figure out what to do."
There are only two ways to destroy the beetle: cut, chip
and burn affected trees, or inject the trees with insecticides
that kill the beetle larvae as they feed. Otis says the
city of Chicago has been successful in containing the beetle
through cutting and chipping trees, but new infestations
continue to be found around New York City.
It's vital to find a solution to the problem before spring,
when adult beetles emerge from trees and take flight, says
Otis. "Because they're not very host-specific, longhorned
beetles could have a big impact. The effects on shade trees,
forests and the maple syrup industry could be devastating."
In contrast to the relatively slow decline of trees attacked
by the longhorned beetle, trees infected with the emerald
ash beetle have been dying rapidly in Windsor and southeastern
"Trees in Windsor that were healthy in spring were
dead by fall," Otis says.
There has been a general decline in ash trees for a number
of years, referred to as "ash decline." It was
only in May 2002 that unusual D-shaped holes were noticed
in dead ash trees in Michigan.
"As soon as inspectors started looking under the bark,
extensive galleries, distinctive larvae and small bright
green beetles about one centimetre long were found,"
says Otis. "They put two and two together and realized
that these insects were at least partly involved in what
was affecting ashes."
An estimated six to 10 million trees in Michigan have died
as a result of this beetle. Many thousands of trees in Essex
County have died as well.
"By fall, it's difficult to tell a live ash from a
dead ash, so surveying them is really quite difficult and
not very efficient," says Otis. "Inspectors look
for holes, swellings and cracks on the bark as well as crown
dieback. If you find the distinctive galleries under the
bark or D-shaped holes, then the presence of the emerald
ash beetle is confirmed."
One focus of his research has been the ash beetle's mating
"If we knew there was a sex attractant, then it might
be possible to develop lures for more efficient detection
and survey. Although our observations failed to provide
evidence of sex pheromones, they suggest that we may be
able to use green decoys to attract beetles to sticky traps."
Left to their own devices, neither of the Asian beetles
disperses very rapidly. The biggest problem is their almost
instantaneous dispersal through humans moving firewood.
Despite signs on the 401 and at border points stating that
it's illegal to import firewood into Ontario or remove it
from a quarantine zone, people are still moving firewood.
On the 2003 Victoria Day weekend, more than 300 people were
stopped from bringing firewood into just three provincial
parks in southwestern Ontario, says Otis.
"If you translate that to the number of people who
moved firewood to their cottages and other parks, I think
it's pretty hard to believe that there are no outlier populations
far from Windsor."
Although he believes Canada is being proactive in its fight
against these pests, he predicts that in one to two years,
emerald ash borers will be found throughout much of Ontario
as they come across the border from heavily infested counties
in Michigan and as people inadvertently transport them on
Otis says that by killing ash trees, these beetles could
have a huge impact on the environment. "Ashes are very
important along streams and as a food source for wildlife.
Right now, it's unclear how the loss of ashes will filter
down through the system."
As with the destruction caused by Dutch elm disease and
the Asian blight fungus that wiped out American chestnut
trees, U of G researchers will likely play a role in the
recovery of trees. Henry Kock, the Arboretum's interpretive
horticulturist, has been leading an elm recovery project
since 1998. With the public's assistance, he's found more
than 100 surviving mature white elms in Ontario and has
used them to create a living gene bank. Some of the seedlings
from this population are likely to exhibit resistance to
Dutch elm disease.
Profs. Brian Husband, Botany, and Greg Boland, Environmental
Biology, have conducted a survey to locate chestnut trees
growing in southern Ontario as part of the World Wildlife
Fund's chestnut recovery program.
"We hope to find patterns where trees are healthier
in certain areas than others to determine how to bring the
chestnuts back to past levels," Husband says.
As for the beetle pests, other than not moving firewood,
there's little that can be done to contain them, says Otis.
He adds, however, that researchers in China are now searching
for biological agents to control the bugs.
"To find effective biological control agents, you
go to the area where the insect came from to see what organisms
are keeping things in check. Once a pest species has been
established and eradication is impossible, biological controls
offer the best permanent solution."