An invasive beetle species, infamous for decimating ash tree populations in north America, is marching through Canada with 20 million trees dead in its wake.
Known by its acronym EAB, the emerald ash borer (Agrilus planipennis) attacks all 16 species of ash trees in North America and has killed hundreds of millions of ash trees so far.
The small metallic-green beetle, native to eastern Asia, was first found in Oregon in 2022. Since then, extensive testing to limit the damage has failed.
Ash is prized for flooring, cabinetry and other high value wood products and is the traditional choice for making baseball bats, oars, skis and other sporting goods.
A native tree, the Oregon ash is found throughout the Pacific Northwest’s interior valleys, along streams and in wet sites. In fact, its tolerance to standing water allows this tree to grow on the most poorly drained valley soils, where no other tree species will thrive.
With more than 70,000 ash trees on public land and many more on private property, the insect poses a severe threat to urban canopies.
“No state has been able to eradicate EAB, so since its first detection we have expected it to eventually show up in new parts of Oregon,” said Cody Holthouse, the compliance and regulatory manager at the Oregon Department of Forestry.
“That’s why folks from collaborating agencies have been methodically surveying for the insect, setting out traps beyond the known infestation area and training people to know the signs and symptoms of infestation. This helps us learn where the insect is spreading.”
The borer’s’ larvae burrow into the bark of ash trees, causing canopy dieback and, ultimately, tree death. The half inch beetle, half the size of a $2 coin, is often challenging to detect, especially in newly infested trees.
The extent of dieback suggests EAB may have been present for many years but went unnoticed given the difficult access and dense vegetation, which includes a mix of oak and conifers.
The borer’s’ larvae burrow into the bark of ash trees, causing canopy dieback and, ultimately, tree death. The half inch beetle, half the size of a $2 coin, is often challenging to detect, especially in newly infested trees.
Signs of infestation include thinning and yellowing leaves, bark splitting, D-shaped holes in the tree bark, and basal shoots.
That quarantine, hopefully, restricts the movement of several tree materials, including, but not limited to logs, green lumber, nursery stock, scion wood, bud wood, chips, mulch, stumps, roots, branches, and firewood of hardwood species.
“We want to protect the rest of Oregon for as long as possible to give communities more time to prepare,” said Cody Holthouse.
A favourite among botanists, the emerald ash borer is quite striking. The insect wears a spectacular and shimmering pair of wings that catch the light and reflect an almost unnaturally bright green. Hidden beneath those wings is a magnificent crimson abdomen. And if that weren’t charming enough, the ash borer’s face looks almost exactly like a classic science fiction alien, with big, black eyes taking over half its head.
“Yet by the time you spot this masterpiece of evolution, it’s probably already too late for the ash trees,” says Emma Hudgins, an ecologist at the University of Melbourne. The insects lay their eggs under the tree’s bark, where they’ll hatch about a week later. These larvae chew around underneath the bark, slowly digging curving tunnels just below the surface of the tree.
Eventually, the ash borers pupate, transmogrify into their adult forms, emerge from the tree, and fly off in search of a mate so the next generation can repeat the cycle all over again!
For an ash tree, this process can be fatal. Trees transport nutrients and water through their bark, and by gouging holes through that bark, the ash borers sever the tree’s roots from its branches.
“It essentially cuts off the circulation of the tree,” Dr Hudgins said.
