To Tame A 'Wave' Of Invasive Bugs, Park Service Introduces Predator Beetles

Jun 2, 2016
Originally published on June 13, 2016 3:02 pm

The forest at Great Smoky Mountains National Park is sick, infected by invasive bugs and plants. Matt Moore, Kaleb Lique Naitove and Emily Baird of the National Park Service are some of the field medics trying to keep it alive.

"We're out here trying to save trees," says Moore, a seasonal forestry tech, as he steps over downed logs and through thick patches of rhododendron on the Tennessee side of Great Smoky Mountains National Park. Moore and his colleagues work on the park's vegetation management crew, veg crew for short. They carry plastic buckets filled with their "medical supplies" — a bicycle pump, a tangle of tubing and Kool-Aid-blue and candy apple-red pesticides.

The forest they walk through is mesmerizing. The trees glow green in the Tennessee sun. There are a lot of tree species in this forest, but the one they're looking to treat is an Eastern hemlock, an evergreen conifer that ranges from Canada to northern Mississippi. Hemlocks make up a significant portion of a lot of forests in the eastern U.S., but particularly so in Great Smoky Mountains National Park.

"One out of every five trees in the Smokies is a hemlock currently," says Jesse Webster, head of the veg crew.

Hemlocks are hugely important to those forests and ecosystems. It is "a foundational species," Webster says. They're like lions, wolves or sea otters – keystone species that have an outsized impact on the ecosystem around them. Hemlocks provide a lot of shade, which means "they moderate the highs and lows of air and water temperature," he says. By moderating those temperatures, they provide good habitat for other plant species and for birds, insects and trout.

It's a different landscape without them. And there's plenty of evidence of that in the park. As the crew hikes, they point out a swath of forest across the ridge where the hemlocks were not treated. "They were too far gone," Webster says. Nearly all of the trees are dead and the sun is pouring through and past their skeletal tops to the forest floor below. The ground there would be hot, Moore says. "And then there's these nice spots where most of the hemlocks are still alive, and it's shady and cool."

Without the work of the veg crew, that sunny, hot picture Moore describes would be the norm in the park and across the eastern U.S.

"They'd still exist in an arboretum or in someone's backyard," Webster says. "But outside of that, you know, we're looking at a complete ecological extinction on our landscape."

So the veg crew is out here helping Hemlocks one by one, with pesticides and an invasive insect to help kill the reason these trees are sick: a little aphid-like bug called the hemlock woolly adelgid.

'A Tsunami Wave' Of Adelgids

After about 20 minutes of hiking off-trail in the park, Moore and company reach the tree they've been looking for. It's tall, but not particularly big. You could wrap your arms around its trunk and still clasp your hands. By all outward appearances, it's healthy.

It's time for the crew to start helping the tree by injecting it with pesticide. Moore drills holes around the tree's base and then Lique Naitove and Baird attach tubing. A bicycle pump connected to the tube system begins to fill it and then the base of the tree with the red pesticide.

It's called a tree injection system. "We call them IVs," Webster says. "They're out doing a tree IV."

It's like a flu shot that will help the tree ward off invasive bugs. Most of the trees Webster's crew treat just get sprayed with pesticides that have the same effect. This one's different because it's near a stream and the crew doesn't want pesticides getting in the water.

They can't do it for all of the trees they treat because there are just too many. The vegetation crew here has treated more than a quarter million trees in the Great Smoky Mountains. The treated ones, like the one they hiked to, are easy to spot because they look healthy and are alive. The trees that weren't treated are probably dead "or they're close or on the way out very soon," Webster says. "Probably in the next 10 years."

The reason for this die-off is the hemlock woolly adelgid, which is native to Asia. Scientists believe that the specific kind killing the Eastern hemlock is from southern Japan.

Adelgids were first discovered in the U.S. in the 1920s. They were transported overseas by humans and continue to be spread with human help, mostly through the purchasing, selling and transporting of firewood. Today, the hemlock woolly adelgid is established in 16 states, from Maine to Georgia.

The trees at Great Smoky Mountains National Park have been infested with adelgids for longer than a decade. With no natural predators and no evolved defenses, the adelgids swept through the hemlocks at the park like "a tsunami wave," Webster says. Many of the park's hemlocks died quickly; others are dying more slowly.

Hemlocks aren't the only tree or species in the park that's dealing with such threats. Balsam woolly adelgids are attacking Fraser firs. Ash trees are being killed off by the emerald ash borer. Kudzu, a fast-growing Asian vine, is choking off trees. More than 350 species of invasive plants have been found or identified in Great Smoky Mountains National Park. Most of those don't pose serious threats to native species, but the ones that do, the veg crew manages. Almost none pose the same level of threat as the hemlock woolly adelgid.

The bug's infestations are so widespread that they're easy to find in the park. Webster walks down a path near Gatlinburg, Tenn., and grabs the branch of a young hemlock. "Here's the wee beastie," he says, pointing to a speckling of little white cotton-like globules clustered at the bases of needles on the tree's outermost branches. "Each light, fluffy mass you're seeing is an ova sack," he says. Inside is anywhere from 30-60 adelgid eggs.

Under a microscope, the little light, fluffy mass looks like a cotton ball. The wool is a defense for the adelgid and is where the critter gets its name. Webster picks at one of the balls with a tweezer-like tool, pulling away tufts of wool, revealing a little cluster of eggs that look like tiny grapes.

There's also a full-grown female adelgid, the mother, nested in the wool. She's mostly dead, Webster says. To the naked eye, she'd be no bigger than a speck of dust, but magnified you can see that she's attached herself to the base of the hemlock's needle. From there, she feeds off of the tree's nutrients, keeping them from the tree itself. It doesn't seem like a lot, but if you multiply this across hundreds or thousands of needles, you have a starved, soon-to-be-dead tree. Multiply it by millions, and you have a dying forest.

A Predator-Prey Balance

The pesticide treatment that the park's vegetation crew uses doesn't get rid of the hemlock woolly adelgid. It protects the tree that gets it and only lasts five to seven years. "It's a stopgap solution," Webster says.

Because of that, the National Park Service and scientists have been trying a longer-lasting one: predator beetles. The hemlock woolly adelgid, like most invasive species, thrives in its new environment because it doesn't have any natural predators. To change that dynamic, Great Smoky Mountains National Park has brought in a few species of predator beetles from Asia that they're raising at insectaries, or nurseries for bugs.

Webster knocks on the branches of an infected hemlock at one insectary and holds a canvas sheet underneath. Spiders, needles and little specks fall off. He looks over the canvas and touches at a little shape with a pine needle. "This is the baby predator beetle," he says. "This is a laricobius."

The beetle isn't some fanged, wicked-looking predator. It's the size of a pinhead and looks a bit like a roly poly bug. Webster knows that it doesn't inspire confidence to have such a tiny aspiring equalizer. "Well look at the adelgid," he says. "They're smaller than these."

The National Park Service has been criticized for introducing another non-native species into the park. Some scientists and environmentalists argue that predator beetles could cause more problems than they fix. Entomologists and scientists tested the predator beetles with other native species to see if there would be other effects, but it's impossible to know in a short time-frame. There are many examples of humans introducing one new species to curb the growth of another and it going wrong.

The problem of the hemlock woolly adelgid is so dire though that it was deemed necessary to ensure the survival of the hemlock. "I'd rather do something than do nothing," Webster says. "Really, we're trying to set up that natural predator-prey balance, a sustainable system and then back away."

Predator beetles will never eradicate the hemlock woolly adelgid. They're here to stay. The hope of the Park Service is that by creating that balance between predator and prey and by educating people to not move firewood from one location to another, they can slow the spread of the adelgid enough to give the remaining Eastern hemlocks a chance to survive and adapt.

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DAVID GREENE, HOST:

If you're in North Carolina or Tennessee and you drive into Great Smoky Mountains National Park, you might be awed by the trees. The forest glows in vibrant green. But many of those trees are actually sick, infected by deadly invasive pests. NPR's Nathan Rott met the people who are trying to keep the forest alive.

NATHAN ROTT, BYLINE: So we're looking for a tree?

MATT MOORE: (Laughter) Yeah, several.

ROTT: It's midafternoon, about 70 degrees outside, and we are hiking off-trail on the Tennessee side of Great Smoky Mountains National Park - uphill, over logs and through thick patches of brush.

This is an easy hike for Matt Moore and the park's vegetation crew, veg crew for short. They're wearing backpacks and carrying 5-gallon buckets filled with drills, tubing, pumps and pesticides, some of the many medical supplies of this nationally protected forest.

MOORE: You found it? Oh, Mylanta.

ROTT: The tree we hiked all the way up here for is - well, a tree. It's tall, but not particularly big. You could wrap your arms around it and still clasp hands. We'll get into the specific species and all of that stuff in a bit. But for now, let's do what we're here to do - treat this tree.

For this kind of treatment, the veg crew drills about six tiny holes into the tree around its base.

JESSE WEBSTER: Don't pump too much chemical through one hole.

ROTT: They then push skinny, metal spikes into each of those holes. All those spikes are connected by tubing, and a bicycle pump is connected to the other end of the tube system. It gets a few pumps, and a Kool-Aid blue pesticide works its way through the tubes into the base of the tree. Jesse Webster, the head of the veg crew, says this is what's called a tree injection system. Basically, they're giving the tree a shot to keep it healthy.

It really does look like an IV system that's hooked up to the tree.

WEBSTER: Oh, it's - we call them IVs. I mean, they're out doing a tree IV.

ROTT: Few trees get this intense of a treatment. Most just get sprayed with chemicals, which is less time-consuming. That's important logistically because there are a whole lot of trees in this forest that need treating.

Overall, the veg crew has treated more than a quarter million trees in Great Smoky Mountains National Park. They're easy to spot, Webster says, because they're the ones that are still alive.

WEBSTER: Any tree that wasn't treated in this park and has never seen a treatment is probably dead or closely or on the way out very soon, within the next 10 years.

ROTT: OK. So let's get off this hillside for a bit and talk a little more with Jesse Webster about the tree in question. It's an eastern hemlock. But we're just going to call it a hemlock from here out. Hemlocks range from Canada to northern Mississippi. They can live longer than 500 years. And they're known as the redwood of the East because of their size, height and gnarled tops.

They make up a significant portion of a lot of forests, but particularly so at Great Smoky Mountains National Park.

WEBSTER: One out of every 5 trees in the Smokies is a hemlock currently.

ROTT: And hemlocks serve a very important role in these forests.

WEBSTER: It's a foundational species. You know, people real familiar with keystone species.

ROTT: Like lions, wolves, sea otters - species that have a huge impact on the ecosystem around them - that's the hemlock in eastern forests.

WEBSTER: They moderate the highs and the lows of air and water temperature.

ROTT: Because of the shade they provide, they are nesting sites for birds. The list of things they do is long. But because of one nefarious little critter, hemlocks are dying off at a scary rate. Webster says without treatment...

WEBSTER: You know, we're looking at complete ecological extinction on our landscape.

ROTT: The reason for this die-off is a little aphid-like bug called the hemlock wooly adelgid. Native to Asia, the bug was first reported in the Eastern U.S. in the 1950s, but it spread primarily through the buying and selling and moving of firewood to 16 different states. Now in Great Smoky Mountains National Park, they are not hard to find.

WEBSTER: Here's the wee beastie.

ROTT: Oh, man. That's it.

WEBSTER: Yeah, so each light, fluffy mass you're seeing is an ova sac.

ROTT: It's like the end of a Q-tip, only way smaller, at the base of the outermost needles on this tree. And really, they look pretty harmless.

So we take an infected branch into a nearby research center to get a closer look under a microscope.

WEBSTER: So here's one.

ROTT: Webster takes a little metal tool and starts picking away at one of the white, woolly masses. There's a close-up image on a video display.

WEBSTER: Here's a mass. OK. Now you can look at this - a female that's still - was relatively still alive.

ROTT: Whoa.

WEBSTER: They haven't darkened. These eggs haven't darkened.

ROTT: Inside is a cluster of eggs in a full-grown female adelgid. To the naked eye, she would be no bigger than a speck of dust. But up close...

WEBSTER: It's gnarly even up close.

ROTT: (Laughter) It is gnarly, man.

The female has attached herself to the base of the needle, where she's been feeding off of the tree's nutrients, keeping them from the tree itself. Multiply this by thousands, and you have a starved soon-to-be dead tree. Multiply it by millions - well, you have a dying forest. So how can you possibly deal with something like this?

Webster takes us to a place that might hold the answer, an insect nursery.

Those pesticide injections we heard about earlier only last five to seven years. These scientists are looking for something longer-lasting.

WEBSTER: So this is the baby predator beetle.

ROTT: Scientists have brought over a few different species of predator beetles from Asia that prey on hemlock wooly adelgids.

WEBSTER: This is a laricobious.

ROTT: They raise them at insectaries, insect nurseries like the one we're at now. And for those of you like me hoping to hear about some vicious, fanged-looking predator, sorry.

WEBSTER: These beetles, you know, they're pretty small.

ROTT: Really, they're no bigger than a pinhead and almost look like a roly-poly bug.

WEBSTER: How much of an effect can they have on this problem? Well, look at the adelgid. They're smaller than these.

ROTT: And one predator beetle can lay eggs on scores of adelgid egg sacs, killing all of them. Now, introducing any predator species to a national park is not an easy decision. But it's one that was made out of necessity. Hiking into the forest, treating trees every five years with pesticides really isn't a sustainable or practical practice, and it doesn't work at scale.

WEBSTER: Really, we're trying to set up that natural predator-prey balance, a sustainable system and then back away.

ROTT: The predator beetles will never eradicate the hemlock woolly adelgid. Webster knows that. But hopefully, it will help to slow the adelgid spread and give the Eastern hemlock and these forests a chance to adapt. Nathan Rott, NPR News, Great Smoky Mountains National Park. Transcript provided by NPR, Copyright NPR.