Every ash tree in CT to die within the decade

The effects of the emerald ash borer can be seen in this piece from an ash tree in Redding Thursday, Oct. 18, 2018. Redding Highway Department workers and Knapp Tree Service of Wilton, take down ash trees on Sunset Hill Road in Redding Thursday. less The effects of the emerald ash borer can be seen in this piece from an ash tree in Redding Thursday, Oct. 18, 2018. Redding Highway Department workers and Knapp Tree Service of Wilton, take down ash trees on ... more Photo: Carol Kaliff / Hearst Connecticut Media Photo: Carol Kaliff / Hearst Connecticut Media Image 1 of / 14 Caption Close Every ash tree in CT to die within the decade 1 / 14 Back to Gallery

Within the next eight years, every ash tree in the state of Connecticut will be dead.

“It’s not a pretty picture,” said Claire Rutledge. “It’s a little hard to be optimistic about it.”

If you want to know who to blame, look squarely at the emerald ash borer, a non-native, invasive species of beetle that feeds on the trees.

Originally found in Michigan in the 1990s, the first emerald ash borer was confirmed in Connecticut in 2012, though they’ve probably been here a few years longer than that.

Since then, the bugs have been spreading at an exponential rate.

“After they reach a site it’s usually about between eight and 10 years that everything is dead that they can eat,” said Rutledge, an entomologist working with the Connecticut Agricultural Experiment Station. “It’s going to be spreading out in a wave.”

The effects are obvious. At a meeting of the Weston town Board of Selectmen this week, tree warden Bill Lomas said he expects every ash tree in the town to be dead within a few years, as Weston-Today reported.

That’s true in Hamden, New Haven, Prospect (where the first emerald ash borers were found in Connecticut), up and down the coast from Greenwich to Hartford and, recently, to New London.

Exactly how many trees are infected?

“At this point it’s billions and billions,” Rutledge said. “Kind of a Carl Sagan thing.”

It’s a tragic tale, in which the emerald ash borer is clearly the villain, bent on total destruction. But this story also has an unlikely hero, a champion bringing hope to tree lovers across the nation: Parasitic wasps.

To understand how the parasitic wasps could help save Connecticut’s ash trees, it helps to understand how the emerald ash borers thrive and spread.

The beetles live most of their lives inside the trees, laying their eggs under the bark which hatch into larvae.

Those larvae are what cause the damage.

The bugs are specifically interested in the trees’ cambium layer, which state forester Chris Donnelly called “the growth layer for the tree, very rich in nutrients.”

Larvae are also interested in the phloem layer, the trees’ circulatory system, Donnelly said. One larva is not a problem, but too many of them and the tree literally starves to death.

“They are essentially able to mass attack trees,” Donnelly said.

The emerald ash borer has no native predators and, so far, every ash tree is at risk if it hasn’t been treated with insecticide.

“As far as we know it’s all ash trees native to North America,” Donnelly said. “It’s going to be a major, major problem for that genus of trees.”

Enter the parasitic wasps.

“Are you familiar with parasitic wasps? Rutledge asked. “Have you ever seen ‘Alien’? Think of the lifecycle of the aliens. Now make it very small. They lay their eggs inside the body of the emerald ash borer. Eventually it gets eaten from the inside-out and the wasps emerge and hunt for their next victim.”

Actually it’s three kinds of parasitic wasps, each designed to attack the beetles at a different point in their life cycles.

The wasps, bred by the swarm in the midwest and shipped to Connecticut in a variety of interesting ways — some sent as larvae, living in big logs that are nailed to infected trees; others are just in disposable cups — have been here since 2013.

But entomologists don’t expect them to have much effect on the emerald ash borer population until that infestation has run its course.

“It’s called the ‘death curve,’” Rutledge said. “After the wave goes through they really do multiply in crazy numbers. They literally have eaten themselves out of food. The level of infestation actually drops because they’ve moved on to greener pastures.”

At that point, some of the the ash trees will have resprouted or grew from seed, and the beetle population will be low enough for the wasps to keep them in check.

“What we’re hoping is after this initial wave dies down the wasps can then follow them down and keep them suppressed at a level that allows some ecological space,” Rutledge said, though she noted that first the trees have to die.

“Bio-control is not for the faint of heart,” she said.

Neither the wasps nor insecticides will save the state’s ash trees, which Rutledge said make up about 5 percent of the state’s trees (though they’re not evenly spread out).

The only true hope is that between the wasps and insecticides, new ash trees will develop a natural resistance to emerald ash borers.

“The ultimate answer is going to be natural selection,” Rutledge said. “Some of those trees are going to be able to resist them.”