City crews have discovered a new evil weevil in town that preys upon local elms. But don't worry, say bug specialists, you can fend it off with proper pruning.
City workers have recently confirmed the presence of the red elm weevil in city trees, said city arborist Kevin Veenstra. The tiny bug, known for its voracious appetite, can kill already sick trees and is a possible carrier of Dutch elm disease.
Crews were doing their regular winter pruning of broken branches about a month ago, when they spotted some suspicious branches in Forest Lawn and Grandin.
"They were peppered with holes every one to two inches," Veenstra said of the trees.
When workers stripped the bark, they found the wood contained long galleries (tunnels) that were full of little white grubs.
The crews sent pictures to entomologists at Olds College and a lab in Edmonton that recently confirmed that the bugs were red elm weevils, Veenstra says. This is the first time that this beetle has been spotted in city trees.
"Beetles are the number one spreader of Dutch elm disease," Veenstra said, which makes this a bug to watch.
Residents should make sure to prune any broken branches from their elm trees, as those are prime habitat for these weevils, he said.
Not-so-evil weevil
The red elm weevil is a yellowish to reddish-brown beetle native to North America, according to the City of Edmonton's pest management department. The adults are up to six millimetres long and have a long, curved snout. The larvae are about the same size, and resemble white grubs with brown heads.
This bug has been moving up north through Alberta for many years, said Mike Jenkins, biological sciences technician with the City of Edmonton, and was first spotted in Edmonton in about 2003. It's considered a relatively minor pest as, unlike the European bark beetle, it only kills sick trees, not healthy ones.
Red elm weevils usually move around Alberta in firewood, Jenkins said, as the province doesn't have big elm corridors outside of cities. St. Albert's population definitely could have spilled over from Edmonton, he added.
The red elm weevil is a tough little beetle that has its mouth on the end of its long nose, said Ken Fry, the Olds College entomologist who identified the St. Albert weevils. Females lay eggs in stressed elm trees that hatch into "little eating machines" of larvae that chew wriggly tunnels through the sapwood.
"It looks like someone had little Spirograph drawings under the bark," he said.
Enough of those tunnels can completely cut off the flow of sap, killing the branch or tree.
These weevils help weed out old and sick trees in nature, Fry noted, opening up space for new ones. But road salt and pollution in cities can weaken elms, making them unnaturally vulnerable to the bug.
Red elm weevils are pretty much pesticide-proof, so the best way to deter them is to keep your trees healthy, Fry said.
"It's really the weak trees that attract the beetle," he said.
Make sure the tree gets plenty of water and is in non-compacted soil, Fry said. Prune any broken branches before the April 1 elm-pruning deadline (as they will attract beetles) and check wilting branches for holes.
Weevil questions should go to public works at 780-459-1557.
