AGENCY INFORMATION

• HWA Overview

Release of Tiny Predators in York County--December 2007

Colleen Teerling, Forest Entomologist

(A version of this article was published in the January 2008 SWOAM newsletter)

If you fight fire with fire, how do you fight bugs?  Sometimes with more bugs.  This is the idea behind some of the work the Maine Forest Service (MFS) has been doing to combat the Hemlock Woolly Adelgid (HWA).  This insect was accidentally introduced to eastern North America from Asia, has spread rapidly and is killing hemlock trees along the east coast.  As of 2007, HWA has been found in Kittery, Eliot, York, South Berwick, and Wells.  These southern Maine towns, in addition to Ogunquit, are currently under quarantine for HWA.

In its native range in Asia and western North America, HWA does not kill hemlock trees, probably due to tree resistance as well as to the presence of several predators of the pest.  Our eastern hemlock doesn’t seem to have much resistance to the adelgid, but we are working on the predator front.

In the months of October and November, with funding from the federal government, we released 1400 predatory beetles called Laricobius nigrinus at three sites in Kittery and York.  Although 1400 beetles will do little to combat the millions of adelgids out there, the hope is that they will become established and reproduce.  This is a long-term project and results may not really be seen for years.  However, we hope that eventually this beetle, along with other predators, will help slow down the spread of HWA through Maine’s forests, and that it will help keep adelgid numbers low enough to allow trees to survive.

This is not the first predator we have released.  Over the past few years, MFS has released another predator in Kittery; a very tiny beetle with the very large name of Sasjiscymnus tsugae.  In trials in Connecticut this beetle has shown the potential to reduce the numbers of HWA and allow partial recovery of hemlocks.   In many states where this beetle was released, researchers have had trouble finding it in subsequent years – it just seemed to disappear into the forest.  However, here in Maine we have had good success in finding the beetle in the years after its release.  Its numbers seem to have increased, and it has spread from the initial release site and moved to the most heavily infested trees it can find.  There it has settled in, eating adelgids.  It’s nice to know it’s doing exactly what it is supposed to be doing.

Some people have expressed concerns about bringing in yet more exotic insects to fight exotic pests.  This is a justifiable concern, and we are very careful about bringing foreign insects into our forests.  Any biocontrol agents for use against HWA or any other foreign pest must first pass through a very stringent federal screening process before Maine will even consider them.  It was found that both of these predators are dependant on adelgids – if they have no adelgids to feed on, they cannot reproduce, and will die out.  So you won’t see them running amok through our forests, feeding on our native insects.  Unfortunately, these beetles are not likely to ever run out of adelgids in eastern North America.  But they’re working on it. 

 

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