You should check your hardwood trees for signs of this beetle
by Art Drysdale
by Art Drysdale


Art Drysdale, a life-long resident of Toronto and a horticulturist well known all across Canada, is now a resident of Parksville, British Columbia on Vancouver Island, just north of Nanaimo. He has reno-vated an old home and has a new garden there. His radio gardening vignettes are heard in south-western Ontario over radio station Easy 101 FM out of Tillsonburg at 2 PM weekdays.

Art also has his own website at

August 5, 2018


A streetscape of American elm trees; and a single American elm totally iced over during the winter. Below, a photo of the Asian long-horned beetle; followed by a sketch of same. Author photos.




As I recall, it is well over half a century ago now that the first elm bark beetles (vectors of the now omni--present Dutch elm disease) arrived in North America from Holland. I don't think I need go into much detail about the devastation that the disease has caused to our once glorious and statuesque American elm trees in virtually all parts of Canada.

Now we're faced with a similar problem from a much larger insect known as the Asian long-horned beetle.

Over 20 years ago the first ones in North America were found in New York City. Specifically in Brooklyn, thousands of large trees have had to be destroyed. And 20 years ago, they were found in Chicago where, like in NYC, great damage has been done to a wide range of hardwood trees (maples, horse-chestnuts, magnolias etc.). Entire parks have had to be cleared since the beetle has no natural predators and there is no known pesticide, and if allowed to breed, the additional thousands of beetles would just lead to even more trees dying from the damage caused by the beetles.

But we are not exempt in Canada! A number of Asian long-horned beetles have been found in Vancouver, as well as in Waterloo, Ontario. They enter Canada in the wood used in either packing crates, or pallets that come from a northern Chinese city. To date few have been found in trees in Canada. To try and assure that will remain the case, the Canadian Food Inspection Agency is attempting to have as many Canadians as possible examine their hardwood trees (particularly maples) either for the damage from or telltale signs of the beetles and their larvae.

The Canadian Food Inspection Agency includes the former plant inspection service of Agriculture Canada. CFIA officials have recently visited Chicago where they photographed the damage to trees caused by the burrowing of the larvae into tree limbs, and later the next season, by the emerging beetles.

The key damage to look for is this. The beetles lay eggs in oval, darkened places, about the size of a dime, on relatively smooth, younger limbs. Here you'll find small holes where the larvae have entered the tree. The next season the beetles emerge from holes at least 1.25 cm (1/2 inch) in diameter. These holes look as if they have been precisely drilled with a high-quality tool, or to others, like shot holes from a .44 calibre firearm. The entrance holes generally will not be on old branches or trunks where the bark is thick, rather where bark is thin. But the exit holes, easily identified may be found anywhere on the trees, roots, trunks, or branches.

The key item of identification is sawdust. Generally, large piles of sawdust will be found at the base of trees infected by the beetles. The beetles themselves are distinct. They are large, with even larger antennae. Their body length is about 3 cm (1 1/4"). The backs of their bodies are covered with black and white spots. The antennae are 5 cm (2") long and are likewise banded black and white.

If you should spot anything that resembles these descriptions, you should call the nearest office CFIA immediately. But be warned, if any tree or trees is discovered to be infested, it will be put on a removal list by the local parks department (if in a city or town), or other agency. Since there is no known control, infested trees must be removed as soon as possible so that beetles/larvae within the trees can be destroyed. As mentioned, at least one park in Chicago had to have all of its mature trees removed and chipped up.

Cities and towns are not the only areas where the beetles and their damage could be found. Maple syrup bushes too are vulnerable. Since the beetle comes from a cold part of China, and we know that it has over-wintered in Chicago, there is no doubt it can over-winter here in most parts of Canada.

A final point. There are other boring insects that attack various trees and shrubs. Examples would be the lilac borer that is a serious pest on all lilacs, and locust borer which is a frequent visitor to black locusts. The telltale signs (holes in branches and sawdust trails) from these pests are similar to those of the Asian long-horned beetle, but not as dramatic. Please do inspect your trees!


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