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Invasive beetle kills ash trees in more towns; wasp species may control it



Monitor staff
Saturday, January 28, 2017

The emerald ash borer, an invasive insect that is killing ash trees throughout the eastern U.S., is continuing to spread throughout New Hampshire, but there are hopes that two wasp species will bring it under control.

The New Hampshire Division of Forest and Lands has recently added Deerfield, Epsom, Gilford and Laconia to the list of towns where the beetle has been found. This makes more than three dozen communities which have been classified as infested areas since New Hampshire’s first EAB was spotted in Concord almost four years ago.

“Those recent towns are adjacent to already infested towns, which is pretty consistent with the spread of EAB,” said Bill Davidson, a forest health specialist with the Division of Forests and Lands.

“Towns that are infested are getting worse. There are areas in Concord where there are whole stands that have already died off or are going to be dead pretty soon, especially along the (Merrimack) River, along I-93,” he said.

The bright green beetle, a native of Asia, probably traveled to the U.S. in wooden packing material. It was found in Michigan in 2002 and has since spread to 27 states, killing millions upon millions of ash trees.

The beetles lay their eggs under the bark, which hatch into larva that eat into the tree, killing it within a few years by disrupting the passage of water and nutrients.

Two species of wasps that prey on the EAB are being tested as a form of biocontrol in New Hampshire and many other infected states.

One species lays its eggs on the EAB eggs and one species lays its eggs on the EAB larva. In both cases, the wasp eggs hatch and the resulting wasp larva kill their host.

Davidson said populations of the wasps have been released in test sites around the state to see if they can establish themselves enough to reduce EAB numbers.

“We’re trying to get them established so they can build up their populations and spread. We don’t expect immediate mediation of damage,” he said.

“In Michigan, they’re starting to see pretty high rates of (wasp) attack on the ash borer,” Davidson said, although the ash population is so devastated in Michigan that even effective biocontrols may be too late there.

In New Hampshire, Davidson said, the larvae-attacking wasps seems to be establishing themselves.

“Last fall we were doing some work and found it up to a quarter mile away from release site, an indication that it’s starting to spread from those released areas,” he said.

The egg-attacking wasp has survived in about half the test locations, he said – although it’s hard to know for sure because it’s extremely hard to find it.

“The (wasp larvae) are incredibly small and very difficult to detect – less than a millimeter. We might be missing it,” he said.

The process of hunting for these wasps involves shaving bark from the outside of the tree, sorting through the sawdust looking for EAB eggs, then seeing if they are infected.

(David Brooks can be reached at 369-3313 or dbrooks@cmonitor.com or on Twitter @GraniteGeek.)