New York State IPM Program

Biocontrols for Invasive Pest Help Save Mountain Forests

Biocontrols — organisms that help keep serious pests in check — are a key component of IPM. And sometimes they’re the only hope. Consider the lovely, lacy-needled hemlock tree, a member of the pine family.

“The hemlock is a foundation species in our forests,” says Mark Whitmore, a forest entomologist at Cornell University and a founder of the New York State Hemlock Initiative. “It occupies the base of the food web and is a critical species in the habitat it helps create.” But the hemlock is under threat by a killer pest so tiny it verges on microscopic.

“Take no prisoners” describes the woolly adelgid’s modus operandi.

Whitmore’s checklist? Hemlocks

  • moderate stream water temperatures for trout and many other animals
  • provide a buffer for nutrient inputs to maintain water quality
  • stabilize shallow soils, especially in steep gorges
  • shelter plants and animals — especially important in winter, when they help moderate temperature swings
  • offer critical habitat for migrating neo-tropical birds
  • provide large-scale watershed quality and biodiversity protection

Hemlocks also help ring the registers when fishing season opens. How can that be? Well, trout fishers’ contribution to New York’s economy is nothing to sneeze at. And research in the Delaware Water Gap showed that streams draining hemlock forests support an average of 37 percent more aquatic insect taxa — including many that provide food for trout — than do streams flowing through deciduous forests.

About that pest — it’s the hemlock woolly adelgid, native to Asia. This tiny pest has already done a staggering amount of damage to hemlock stands in the southern Appalachian Mountains, leaving scarred remnants of once-lovely ravines and mountainsides in its wake.

Now it has gained a foothold — in some cases, a stranglehold — in forests throughout the Northeast.

Losing those hemlocks? “Catastrophic” could be the right word to sum up the consequences. “The hemlock is the only tree in eastern North America that can do its job so well,” said Kathleen Shields, project leader for biological control with the U.S. Forest Service in a 2002 article in Forests Magazine. “If we lose the hemlocks, there’s no other tree to fully take its place.”

The waxy white balls that cover every twig mark this tree as a goner. (Photo Forestry Images)

But if you’ve even heard of the hemlock woolly adelgid you’re way ahead of the game, because the hemlock woolly adelgid isn’t much to look at. In fact, you’d have to scrape off the waxy white ball it hides in, then squint into a 10-power loupe — a special type of magnifier — just see it.

And because it rarely travels fast or far (for most of its life cycle, it doesn’t even move), the adelgid might not strike you as a particularly menacing pest. Until, that is, thousands of them suddenly set up shop on every hemlock tree in your neck of the woods.

How can this be? Well, there’s the adelgids’ prodigious reproductive capacity. In fact, a single adelgid’s offspring can, by the season’s end, potentially contribute upward of 5,000 adelgids — and every last one is female — to the hemlock’s pest burden.

Then there’s the adelgid’s life cycle: it breeds during the winter. Most insect predators don’t. And factor in that those predators aren’t looking for a bug that resembles little more than a ball of wax.

Sure, it took 50-plus years for the woolly adelgid to reach upstate New York — but it’s here now. Meanwhile, Whitmore has been working against this day for many years.

The only good thing you could say about the adelgids implacable pace is that it’s given Whitmore time to test and release predators which help provide the backbone of a suite of predators that could soon keep the adelgid at bay in New York.

The first predator out of the box was Laricobius nigrinus, a type of tooth-necked fungus beetle, released in 2009. In 2015, Whitmore released two species of silver fly, both from the genus Leucopis. Altogether, these predators should flank the adelgids for a more complete biocontrol.

This larval silver fly slides into that waxy ball, where it feeds on adelgids — and nothing else.

Of course, work like this has to be a team effort, and Whitmore has worked in concert with colleagues at the U.S. Forest Service and the University of Massachusetts-Amherst on one project; the U.S. Forest Service, University of Vermont, and Oregon State University on a second.

And of course — each new biocontrol must feed on its host prey and nothing else. It takes long, patient vetting over many years to be sure a biocontrol won’t itself become a pest.

Whitmore’s work is built around classic IPM techniques, especially monitoring (are they in your neck of the woods yet?) and biological controls. The countless hours Whitmore has put into this earned Whitmore an “Excellence in IPM” award in 2015.

“Mark’s meticulous research brings together all the strengths of IPM; of truly integrated pest management,” says Jennifer Grant, director of NYS IPM “But it’s his passion for his work that really makes the difference. Whether it’s volunteer citizen-science groups or the New York State Department of Environmental Conservation, people look to Mark for the information and expertise they need.”

“He speaks for the trees.”

Author: Mary M. Woodsen

Pests and pesticides — both can cause harm. How can we protect ourselves the least-toxic way? IPM is the sound, sensible, science-based approach that works wherever you do. The New York State Integrated Pest Management Program develops and offers tested tactics for pests new and old, whether on farms, offices, orchards, schools, parks, vineyards, more.... Wherever you find pests, you find IPM.

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