Keeping the emerald ash borer in check

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In the past 15 years, invasive emerald ash borers have killed tens of millions of trees in 31 US states. What options do communities have to combat this voracious beetle?

This adult emerald ash borer began life as a larvae that contributed to the ongoing destruction of America's ash trees.
Minnesota Department of Natural Resources/AP/File

At roughly the size of a pinkie fingernail, the emerald ash borer is almost cute.

But don’t be fooled by the beetle’s small size and metallic green-purple coat, ecologists say. The exotic beetle is one of the worst invasive species to ever infest the United States.

“It is certainly the most devastating pest of deciduous trees that we have ever known,” says Don Cipollini, a professor of chemical ecology at Wright State University in Fairborn, Ohio, who has studied the emerald ash borer, or Agrilus planipennis, for more than a decade.

With hundreds of millions of US ash trees already killed, ecologists are in a race against time to save these beloved trees. Researchers in Pennsylvania have made some headway by developing long-term strategies for dealing with the pest that they hope can empower communities around the country to save their trees.

Native to Asia, the half-inch-long beetle is believed to have hitched a ride to the US on a piece of wood. Since its first sighting in Detroit, the emerald ash borer has claimed hundreds of millions of trees in 31 states.

“If you go to Michigan where everything started, you will see lots of dead trees. But each year we see more states added to the list,” says Houping Liu, an entomologist at the Department of Conservation and Natural Resources in Pennsylvania, where the pests first appeared in 2012. “This beetle will not stop.”

Dr. Liu says that communities need not be resigned to losing their trees – if they act quickly. If the beetles are left to their own devices, cities and towns will have to spend significant funds on dead tree removal. By developing long-term plans, those funds can instead be used to protect trees before they die.

Ash trees offer both ecological and economical value, ecologists say. Green ash is a “pioneer species,” says Professor Cipollini, which means it is often one of the first trees to populate a new open space and sets the groundwork for other species to follow. And economically, ash wood is valuable: it is used to make a variety of everyday products from baseball bats to shovel handles. There are almost 8 billion ash trees on US timberlands, according to a 2014 assessment, valued at more than $282 billion dollars.

Each community needs to decide how highly it values its ash trees, Liu says. From there, decisions can be made about how aggressively urban planners and forest managers will attack the problem and what financial resources will be allocated to combat it.

In Pennsylvania, Liu has helped 12 communities develop individualized 10-year management plans that range in how aggressively the target the problem. 

Aggressive management might include preemptive removal of infested trees to prevent colonization of neighboring trees, targeted pesticide applications, and introduction of predator wasps.

The most effective course of action, according to Liu, is for communities to establish a plan before infestation becomes a problem.

“People tend to not worry about things that are not in their backyard ... but it will soon be in their backyard,” says Liu. “You need to look at your financial situation as a community and say, what can we do?”

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