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Woodpeckers to the rescue

Sian Griffiths, Ottawa, CanadaDecember 28, 2015

As scientists in eastern North America have been struggling to find a weapon to use against the emerald ash borer, a tree-murdering beetle, nature may finally have come up with a response - the woodpecker.

Downy Woodpecker m Canada
Image: picture-alliance/dpa/P.Henry

On neighborhood streets and in parks across eastern North America, a battle is being waged between man and a small green bug.

It goes by the scientific name of Agrilus planipennis but is commonly known as the emerald ash borer. Since this invasive species was first discovered in Detroit, Michigan, in the United States in 2002, it has been responsible for the deaths of millions of trees.

This insect targets ash trees and breeds at an exponential rate. Billions of North America's ash trees remain at risk.

However, a recent natural development has offered a glimmer of hope: the arrival of hordes of woodpeckers. But is it too little, too late?

Perfect predator

During the most recent bird count around Ottawa, the Canadian capital, birders were surprised to see that the number of woodpeckers had tripled - smashing previous records. And they were all found on ash trees, the home of the emerald ash borer.

"You see it?" said Ted Cheskey, a bird specialist with Nature Canada, excitedly pointing to a small bird, a woodpecker, tapping away high up on an ash tree in Gatineau Park.

"He's busy foraging. Oh, there's another!"

The park is a large forested conservation area across the river from Ottawa. It was once home to a healthy ash tree population. Now many are dead, dying or have been chopped down. In Ottawa and Gatineau, condemned trees have a red mark.

Ted Cheskey, bird specialist with Nature Canada, standing in front of condemned dead ash tree in Gatineau
Cheskey is hopeful that woodpeckers could play a role in controlling emerald ash borer populationsImage: Sian Griffiths

Cheskey explains that woodpeckers are ideal hunters of tree-dwelling bugs.

"They will drill a hole, get inside," he says. "They have an extremely long tongue. It's like a sticky tongue but it has hairs on it, goes in and pulls them out."

'Houston, we have a problem!'

Bruce Gill, a Canadian government scientist, joined US counterparts in a Detroit park to try to discover why ash trees were dying in such large numbers.

He still recalls the horrific sight after one of his colleagues removed bark from a tree.

"Hundreds of these white larvae came spilling out of the tree and then we just agreed 'Houston, we have a problem!'"

The bright, emerald green beetles, around a centimeter (or less than half an inch) in length, generally feed off the leaves of ash trees and are relatively harmless. It's their larvae that are so toxic to trees.

After mating, the female lays her eggs in the bark. Larvae emerge from the eggs and chew through to the cambium, or inner layers, of the tree in search of nutrients - literally sucking the life out of the trees.

Gill points to evidence of an Emerald ash borer attack on the trunk of a dead ash tree at Ottawa's Central Experimental Farm, a government run farm and research facility.

He points to the open tunnels left by the larvae. "The larvae have stripped all of the cambium away so then the tree dies."

Two Emerald Ash Borers mating on an ash tree, Pinecrest Park, Ottawa.
Two emerald ash borers mating on an ash tree, Pinecrest Park, OttawaImage: Sian Griffiths

An abundance of food and a lack of natural predators have created the ideal conditions for the Emerald ash borer to thrive and reproduce at an exponential rate.

Gill says that an emerald ash borer female lays about 200 to 400 eggs.

From pesticides to biological control

There had been attempts to use a pesticide called TreeAzin to control the emerald ash borer population. But repeated injections into the enormous number of ash trees just proved too expensive.

Scientists have been turning to parasitoid wasps, the natural predator of the emerald ash borer in Asia. Two types are now in use in Canada: one attacks emerald ash borer larvae; the other attacks the eggs.

"But it's always sort of a catch-up game," says Gill of the wasps, newcomers in the North American battle against the bug, now long-established in Ottawa's tree population.

While 6,000 wasps have been released, it's too early to tell how much of an impact these biological control agents will be able to make on the small green beetle.

That's why there has been such excitement around woodpeckers, whose numbers have skyrocketed.

Woodpeckers hunt for both the larvae and pupae, the last life cycle stage before the insect turns into an adult beetle, emerges from the tree and starts all over again.

Though Gill describes this new woodpecker food source as a "great buffet," he is skeptical whether woodpeckers can indeed get rid of the bugs, as the emerald ash borer has been active in the area for nearly a decade.

Clearing the dead

Meanwhile, there is little the City of Ottawa can do but clean up the dead and plant new non-ash species like oak saplings.

Jason Pollard, City of Ottawa Forestry Services Dept, with dead ash tree
Pollard says the city will do whatever it can to slow the insect's murderous marchImage: Sian Griffiths

Jason Pollard of the City of Ottawa's Forestry Services Department says the city only had to remove 200 trees in the first year of the infestation. That number has now soared to 7,000 trees a year.

The city has been forced to increase spending to combat the infestations. The budget for 2015 is 5.4 million Canadian dollars (3.7 million euros) - an increase of 20 percent from the previous year.

Pollard is skeptical that the woodpecker can control Emerald ash borer numbers. "We'll take help wherever we can get it to slow this insect down!" he says.

Woodpecker supporter Cheskey is a little more upbeat and believes the answer may lie in an unconventional union.

"Perhaps parasitic wasps and woodpeckers can get together and deliver that decisive blow to the ash borer!"