Balance & Barrier

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Episode 6: The Future of Forest Threats

Produced and hosted by Jonathan Yales - 17 min.

Research Biologist Rob VenetteResearch Entomologist Melody Keena in a greenhouse

In addition to studying and monitoring the non-native insects already here, scientists are monitoring pests that have potential to become problems if they ever do arrive, whether from overseas or from other parts of North America.

Jonathan Yales
This is “Balance & Barrier,” Part 6. I’m Jon Yales. On today’s final episode: future threats.
Rob Venette
We talked about the chalara disease of ash, we talked about pine processionary moth, but there's Japanese oak wilt, there's Siberian silk moth, there's platypus quercivorus, there's the two spotted oak borer. So, in our conversation, we’ve really just scratched the surface on some of the threats, but there are plenty more that are out there.
Jonathan Yales
This is Rob, a research biologist. His own unit thinks about what the next new threats to our trees could be, and what to do about them.
Rob Venette
The best solution to dealing with the invasive species problem is really prevention. Once invaders get into the United States and begin to become problematic, it becomes increasingly expensive to deal with them, and so, the earlier that we can respond the better off that we are. Now, that's a pretty big undertaking, and so part of the challenge that I've undertaken in my program is to do a bit of horizon scanning, and what that means is it's looking at what are potential threats to trees and forests in different parts of the world, and what threat do they pose here in the upper Midwest? Some of that though is also looking at new insects that have invaded other parts of the United States and asking a very similar question: could they become a problem here?
Jonathan Yales
But, with hundreds of thousands of insects out there, how does one guy keep tabs on the emerald ash borers and gypsy moths of tomorrow?
Rob Venette
That's probably the most nerve-wracking part of my job because I really need to try and keep an eye on a pretty wide array of different pests. And so, things don't really jump onto my radar until there's some sign that they're causing tree mortality in some part of the world. So, you know a couple of examples of issues that I'm concerned about: there's the pine processionary moth, that's a problem in portions of Europe, as well as a new disease of ash that's really problematic in the United Kingdom, it’s called chalara disease. Neither of those occur in the United States, but where they do occur, they're causing really severe mortality of trees. And so, those are examples of pests and diseases that we definitely don't want to have in this country. In other cases, we may be dealing with something that already has a foothold somewhere in North America, and then we begin to ask the question, ‘Well, what's it doing there?,’ in other words, ‘Is it causing trees to die, and should we be concerned?’ So, a really good example of that is the walnut twig beetle. I've got good collaborators out in California, and they were noticing how extensive the mortality of black walnut was pretty widely around the West. And, black walnut is native to eastern North America, and so, we need to know what would it do if it arrived here. And so that's where we began to work more on the walnut twig beetle.
Jonathan Yales
All four of the pests in this series — Part 2 through 5 — originally came from either Asia or Europe, but as Rob said, there are insects already here in North America that could spread to new parts of the country and act like those foriegn invaders.
Rob Venette
So the walnut twig beetle, we think, is an example of what we would call, a domestic invasive species. And so what that means is that it's native to parts of the United States, but it's being spread into other ecosystems where it has never occurred before. And so, we believe, that populations are native to the southwestern United States, and its hosts are all walnuts, and its close relatives. So, another example, is butternut — that's a really important species here in the Northeast. The walnut twig beetle has been found pretty widely throughout the West. So it's pretty widely distributed throughout California now, all the way up into the Pacific Northwest. Some of its most dramatic, initial impacts were first reported from Colorado. And then there have been pockets in the East where it's also been found, so areas around Tennessee for example, were some of the first finds of the walnut twig beetle in the eastern side of North America.
Jonathan Yales
This beetle is just one species in a broad group we all call ‘bark beetles.’ There are 600 different species in that group and they’re all native to the U.S. During the past decade, in western forests, tree deaths have increased due to these guys, correlated with shifts in temperature and increased water stress, which creates conditions within trees that are favorable to these beetles.
Rob Venette
And it's a tiny little bark beetle. In fact, if you had one in your hand, you would perhaps confuse it with a mouse turd, to put a less than delicately. But what's important about that tiny little insect is that it carries a pathogen that can kill parts of the tree. So, the pathogen is called Geosmithia morbida — sort of implying the death that it can cause. And so, as that bark beetle attacks a tree it carries the fungus with it and then that fungus begins to grow and it kills parts of the tree tissue causing what we call a canker. And the cankers don't necessarily develop a lot, but there are so many attacks from the walnut twig beetle that there are literally thousands of these cankers that develop and will ultimately kill the tree. And that's why walnut twig beetle is part of what we call thousand cankers disease.
Jonathan Yales
When you were originally describing the walnut twig beetle, you used words, like, ‘believe’ and ‘we think’ and ‘it seems.’ At what stage of our knowledge of this insect are we at?
Rob Venette
So when I say, 'we believe,' that's partly because, as a scientists, ultimately, we are empiricists. We really want to see what happens, in reality, firsthand. And so, the ideal circumstance that would give us the confidence to say things more specifically would be to actually watch a walnut twig beetle land on one of these walnuts in the East and watch its behavior and see how its populations develop and how does the tree respond. But, at the same time, that's an experiment that we never want to happen, and we're really working hard to keep it from happening. So, when I use fudge factors like 'we believe' or 'we think' that's because, by and large, we haven't had the chance to see how will this beetle really react to a living tree in the field in these unique circumstances.
Jonathan Yales
So, how do you, personally, get around that kind of conundrum of, we want to be able to study a spreading invasive insect, yet our whole job — and a lot of what the [Forest Service] does — is stop invasive insects from spreading? You know...
Rob Venette
Well, so, there are a couple of different elements to that. So, one is that we always want to be keenly aware of what we know and what we don't know, and we want to be sure that we don't communicate more certainty than we really do have. But, the second part is that there are some things that we can do to try and address some of these issues. And so, one of the things that's really fantastic — that the Forest Service and some of our partners maintain — are a number of quarantine laboratories. And what those allow us to do are to bring the insects from, either other parts of the country or other parts of the world, into an enclosed environment where we can physically get our hands on these insects and begin to study them in a very directed way.
Jonathan Yales
Melody, from last episode, is the head of the Northern Research Station’s quarantine lab.
Melody Keena
All the work that I do with invasive insects that are under eradication or that aren't present here in Connecticut, is done in the Forest Service quarantine
laboratory that we have here in Connecticut. It's 3,100 square feet under quarantine, and insects... we bring them in, but they can't get out.
Jonathan Yales
It's a state-of-the-art facility with a lot of safeguards.
Melody Keena
It's down an obscure lane, nestled away in a residential area — chain link fence, barbed wire above it, access only for people that are authorized. Once you enter the facility you have to go through a couple of airlocks that are dark. Because insects are attracted to lights, there's a light trap in there, should anything get close. Once you go inside the facility, the air pressure is negative, so that you open the door, air rushes in, again, push insects back if they get close. We wear Tyvek suits and booties so that we can see an insect on us if we have one on us. You know, there are screens in our sinks. All the air goes through a 100-mesh screens before it leaves, so nothing can get out that way. Triple-pane windows. All kinds of safeguards to make sure these insects don't get out.
Jonathan Yales
From the outside, it looks like a standard single-story white office building, but inside, things are a bit different.
Melody Keena
We have multiple rooms inside. We have a room that is cleaner, where we use artificial diet that mimics trees or leaves that we feed the larvae of the insects on, and then that diet is in a container and the insect is in it, and then that goes in a chamber that mimics whatever temperature that we need to have them at, whether it be summer or winter or fall or spring. And then we have another room adjacent to that that we do the work with the host plant materials, so, Asian longhorn beetle, we have to cut small saplings and pieces of sapling that she can — the female — can have to lay her eggs in and twigs for them to feed on. Then off of that room, we have a room where we can work with live insects and observe their behavior in a more natural setting — bring in potted trees, change the lighting, the temperature, things like that. And, we have an even dirtier room, that we can work on the microbials that attack the insects. So, I've had people from, say, Cornell, come and work on, entomophaga maimaiga, the fungus that attacks gypsy moth. So, it's a separate room, its own air handling system, so we don't contaminate the colonies.
Jonathan Yales
And, in this lab, Melody’s also working on researching a future threat of her own: the spotted lanternfly.
Melody Keena
Well, actually, today we are starting to set up our study, the first of two, to look at how the different stages of spotted lanternfly respond to temperature, to get a better handle on what parts of the United States it might be able to do well in.
Jonathan Yales
This is a new pest and a new threat.
Melody Keena
So, it arrived in Pennsylvania — or at least it was first noticed — in 2014, and it was immediately put under a state quarantine and they've been attempting to eradicate it. Its infestation is spreading. It’s been found now in a couple other states in small pockets and it's been found —single specimens — in New York state, Connecticut, and a bunch of other places.
Jonathan Yales
And it’s a concern to both forests and agricultural. If allowed to spread, it could seriously impact our country’s grape, orchard, and logging industries.
Melody Keena
It has over 70 species of mostly woody hosts that it can attack. It ranges from apples, birch trees, cherries, grapes, lilacs, maples, poplars, and — probably it's preferred host in China — tree of heaven, but it's also gotten on hops and a bunch of other agricultural crops.
Jonathan Yales
But, what does it look like?
Melody Keena
The young ones, before they get their wings, are black bodies with white spots. And then as they become the instar right before they're an adult, they have a red body with spots. And then the adults kind of look like a grayish moth with spots on the wings and with dark black or brown legs, but when they open their front wings you'll see the lower part of their underwing is bright red with spots and their upper part of the under wing is black and white. Then you have the body has black and white stripes and some yellow.
Jonathan Yales
And, the spotted lanternfly, with its threat to both forest and agriculture, is part of a group of insects, that Rob says, is a new concern.
Rob Venette
So, one of the things that I really would like people to know about is the fact that the Forest Service is also concerned about a new group of insect pests that traditionally aren't just an issue for trees or forests. And these are insects that move across the landscape and spend a big chunk of their time in a forest, but may ultimately be a bigger problem in agriculture.
Jonathan Yales
And, he’s got an example of his own.
Rob Venette
So, a really good example of that is the brown marmorated stink bug. This is an insect that’s invaded many parts of the country, at this point. But what we know is that it spends its winters, naturally, in a forested environment, often times beneath the loosened bark of dead and dying trees. In the spring, when things warm up, it'll leave those overwintering sites and it’ll move into a wide variety of agricultural areas, where it can be really problematic. So in the Northeast, apple growers have had a pretty severe bout of brown marmorated stink bug. But, what we're trying to do is to be aware of this deeper connection between forests and agriculture, and thinking about new pests that are moving across those different systems.
Jonathan Yales
And, one last point.
Rob Venette
The other, broader, point that I’d also like to emphasize is that, as you can tell this work on invasive insects and diseases is incredibly hard, and it takes a lot of talent and perspectives. So, it's not just forest pathologists and entomologists who work on this, but we're also working very closely with climatologists, we're working with folks who are doing the actual forestry and pest management, a lot of folks involved with trends in international trade, trying to bring all of that information together. So, it's definitely a very multidisciplinary effort, and we really rely on partners both within and outside the Forest Service to help make that happen.
Jonathan Yales
So, there you have it, that does it for the Northern Research Station’s six-part series on non-native forest pests.
Even with the series ending, the podcast will go on. In the coming months, I’ll be bringing you another series, from a different research unit who are reintroducing trees back into forests after decades of decline due to insects and pathogens. We’ve just learned ways we stop and slow the insects from attacking trees, but scientists have also been developing trees that are specially designed to be resistant to their pests and pathogens. How we do that and how that works, I have no idea, we’ll find out. I hope you stay tuned.

Thanks again for listening. And see you soon.

This episode — and this six-part series — was produced and edited by me, Jon Yales. My editors at the Northern Research Station were, as always, Jane Hodgins, Sharon Hobrla, and Gina Jorgensen. Thanks for all the help, guys. For this final episode, special thank you to Melody Keena and Rob Venette of the Northern Research Station; and to the Department of Entomology at Michigan State University; and the MSU student radio station WDBM.

If you enjoyed this podcast, or have questions, or have topics that you want to hear more about, let us know on Twitter at @USFS_NRS.
And, as always, this podcast is produced by the U.S. Forest Service. The Forest Service is an agency of the U.S. Department of Agriculture, which is an equal opportunity provider, employer, and lender.

Thank you for listening. See you soon.

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