Coping With Foreign Invasive Species

"It's [emerald ash borer larvae] basically girdling and strangling the tree. It [the tree] can't move water. It can't move nutrients. It's like the circulation system of the tree. By the time you see this, when it's gone all the way around the main trunk, the tree can't survive. It kills 99 percent of the trees [it infects] and most of it happens before you even know it's there."
"Those [introducing parasitoid wasps as biological control agents] are the only real options at this point. Otherwise it's a matter of removing what you can't save, replanting and moving on. It [the beetle] is still a pretty devastating insect."
"It's a very long-term project. It will take a long time for populations of wasps to build up to levels where we can see any impact. But in its native range in China, the [beetle] has a range of parasitoids that keep it under control."
"They're not a kind of [insect to] sting or bite [ash borer-parasitic wasps] you, or [likely to] really want [to have] anything to do with you."
Krista Ryall, ecologist/entomologist, senior research scientist, Canadian Forest Service

Bilberry Creek Ravine forest, Orleans, Ontario

Anyone who ventures into the forest can see what's happening to ash trees. They've been dying; once infected it doesn't take that long. And it's beyond sad. An important part of the forest is being killed off and everywhere one looks in an urban setting or in a woodland there are gaps being created where dead trees abound. Ashes begin to lose their bark when they've been attacked by the emerald ash borer even as boughs distinguish themselves by dead foliage.

Injections used by botanists to try to extend the life of ash trees are expensive, quite an investment if a property owner wants to save a treasured ash shading property and beautifying it, yet the effect is temporary, it wears off and the property owner is back to square one. It's a shoulder-shrugging admission that the temporary solution is just that; temporary, and a waste of time, energy and money, leaving little option but to allow the tree to die.

The oobius agrili parasitic wasp is very small and doesn't have a stinger. It lays its eggs within emerald ash borer eggs, killing the host egg. (Houping Liu/Michigan State University)

But Dr. Ryall and her colleagues from the Canadian Forest Service have embarked on a much larger experimental study which they hope will present a solution in time. They have taken possession of adult wasps grown in ash trees at a U.S. Department of Agriculture station in Michigan. Short sections of trees called mini-bolts are hung on still-living ash trees which have been infested with the beetle larvae in the hope that the mature female wasps will respond to emerald ash borer eggs or larvae, to lay their eggs upon.

The project is four years into its process at about a dozen test sites in Ontario and Quebec. There are two types of wasps, one that attacks the eggs of the ash borers and another which feeds on its larval stage, both native to China, where the borer itself comes from. Site examination has thus far revealed that the egg-eating wasps appear to be doing the work anticipated, while it is as yet unclear whether the larvae-eating wasp has been equally successful in adapting to the work in Canada they are known for in China.

Barry Lyons, a forest entomologist for Natural Resources Canada, stands next to two "oobinators" full of oobius agrili eggs. (CBC News)

 

The emerald ash borer's existence was first noted in 2002 in North America. It has since spread in both provinces and throughout 27 eastern American states. Eggs of the small green beetle are laid in crevices in ash tree bark with the larva burrowing into the tree, cutting channels under the bark that serve to choke off the flow of water and nutrients. The result has been the death of tens of millions of North American ash trees.