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Approved: Tiny Wasps That Kill Emerald Ash Borer

By Tom Spears

Ottawa Citizen June 5, 2013

OTTAWA — Finally, the emerald ash borer has an enemy.

Canada has approved the release of two tiny wasps from China to eat the tree-killing beetles, which otherwise have no natural enemies in North America.

The ash borer is eating its way through our ash trees, which make up about one-quarter of Ottawa's trees.

Now the Canada Food Inspection Agency has approved both a eulophid wasp and a braconid wasp. A third candidate won't be released because there isn't enough information to know whether it would be harmful to insects we want to keep.

"You'll barely even be able to see them, they're so tiny," said insect scientist Bruce Gill at CFIA. And they don't sting humans.

Eulophids are a little over a millimetre long, while braconids very slightly larger. Both lay their eggs inside other insects such as moths, butterflies and beetles.

The young wasps hatch and eat their way out of the host insect, killing it. It's the same system used by the monsters in the Alien movie series.

"Perfect for the long-term strategy to try to control this pest," Gill said.

The wasps won't kill every beetle but should "bring them back to a level where they become a manageable presence in the environment.

"Hopefully they will be at such low numbers that ash trees won't be dying."

The ash borer has killed vast numbers of trees in North America, especially in the U.S. Midwest.

These wasps come from northern China, the region from which the emerald ash borer was probably brought to North America.

There are many types of both eulophids and braconids; the types approved now are called Tetrastichus planipennisi and Spathius agrili.

Until now, the only defence against the ash borer has been to inject a beetle-killing chemical into each tree at two-year intervals, a slow and expensive process.

And there's good news this week from Michigan, which has been battling the ash borer longer than Ontario. The wasps tested there seem to be working.

The researchers sampled trees for wasp broods at six forest sites near Lansing, Michigan. By the fall of 2012, they found a fast-growing population of the eulophid wasps.

As well, the number of ash borer beetles that were "parasitized" by wasps grew from 1.2 per cent in the year when wasps were first released (2007) to 21.2 per cent last year.

The results were published this week in the Journal of Economic Entomology.

Ash borers lay their eggs under the bark of all types of ash tree. The immature beetle tunnels under the bark, destroying the part of the tree that carries water and nutrients.

They were first found in North America in 2002, in Michigan.

Importing one non-native species to kill another is called biological control, but it brings risks. The main one is that the species brought in as a saviour starts feasting on plants or animals that we don't want it to eat, or that its population spirals out of control.

CFIA has approved the importing of parasitic insects in the past to control farm pests such as cereal leaf beetle.

The wasps "were brought in to the United States, went through screening in the U.S., were released (there) and they have just gone through our regulatory system in Canada," Gill said.

 

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