Insect traps help guard Edmonton's urban forest

Hundreds of insect traps have been set up around Edmonton so city pest management staff can monitor any threat to the city's urban forest.

"About half of our street trees are green ash and the other half are American elm so between the two of them there's a lot of vulnerability there," said Mike Jenkins, biological sciences technician with the city of Edmonton.

Two of the most destructive pests in North America go after those two tree species, which are a huge asset to the city, Jenkins said.

"Edmonton has the largest stand of Dutch elm disease-free elms in the world," he said. "We have about 60,000 city-owned trees and about 30,000 privately owned elms."

Summer monitoring program

While a monitoring program has been underway every summer in the city for decades, the problem insects that Jenkins and his staff focus on vary from year to year.

This summer the four main families of insects staff will be searching for includes bark beetles, longhorn beetles, metallic wood-boring beetles and Sirex woodwasps. 

While there are about 14 different species of Sirex, most of them only go after dead trees.

One species, Sirex noctilio, has become an important pest of pines in eastern North America, able to kill healthy, living trees. So far, Jenkins said, there has been no sign of Sirex noctilio west of Quebec.

The mountain pine beetle is among the family of bark beetles staff are checking for.

"Mountain pine beetle has been a major pest in British Columbia and northern Alberta for the last several years  — a huge impact on the forest industry and especially lodgepole pines," he said.

It has been detected, but in very small numbers — only a dozen last year and 13 so far this year, said Jenkins.

"It's not a cause for alarm at this point but yes, it has been detected in the city now."

Early detection is key

The primary reason for the monitoring is early detection. "If you wait until the pest is already established and you start to detect it because of the damage that it's doing, it's way too late, Jenkins said.

"It's already firmly implanted in that area and it's much more expensive to try to get rid of, and much less likely to work."

An example of the success of the monitoring program is the detection three years ago of a newer invasive species, the banded elm bark beetle, a carrier of Dutch elm disease.

While only three of the beetles have been found in Edmonton, it is now on the radar and city staff have ramped up the search for the insect, Jenkins added.

The traps, which vary in size and shape depending on what they are meant to catch,  are put up during the insects' flight period, which is from April through to October.

One of the more obvious traps people are likely to stumble across in the river valley is the Lindgren funnel trap.

Each year, a few of them get vandalized and Jenkins says the destruction of the equipment means the destruction of valuable information.

"Any time it's vandalized we lose all the data from that particular trap and also however long it takes to get it replaced, so it creates a hole in our data," he added.