Balance & Barrier

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Episode 5: The Hornless Asian Longhorned Beetle

Produced and hosted by Jonathan Yales

Research Entomologist Melody Keena in a greenhouse Research Ecologist Talbot Trotter

The Asian longhorned beetle has the makings of a disaster pest poster — a wide possible geographic and climatic range, a number of host trees, and few control options. Lucky for us, it just doesn’t seem to spread far on its own. There are biocontrol and predator options, but nothing is ideal, or especially effective. At this time, there isn’t much we can do other than chop down and chip infested trees.

Jonathan Yales
This is “Balance & Barrier,” Part 5. I’m Jon Yales. On today’s episode: the Asian longhorned beetle.
One of the most recent poster pests to enter the United States is the Asian longhorned beetle. In the late 90s, a Brooklyn resident was in front of his house standing on the street, when he looked up and noticed that all the maple trees lining the street were riddled with dime-sized holes. He thought the holes were from pesky humans, but they were actually from this pesky beetle.
Melody Keena
Well, the first report was of a homeowner that thought somebody had vandalized their trees with a drill, because when this beetle comes out it chews a perfectly round exit hole that you can stick a pencil in and it'll stick straight out.
Jonathan Yales
This is Melody, a research entomologist.
Melody Keena
Most likely they came from China, and the reason that we got them is that in China they had used up their trees for the most part. And so they had very small patches of forest left, and this beetle was just doing normal beetle things there, not very obvious, nobody cared about it. But, China went into a big period of planting trees to try to produce lumber that they needed, and then this beetle decided that it liked those trees that China planted and came out of the forest and started putting holes through their trees. Once their trees were holey, there was nothing they could do with them, but turn it into solid wood packing material or pallets, and if those aren't treated, this insect as a large larva can survive in that wood and move around the world and finish up its development, come out, and if there's trees close by that it can use, an infestation starts.
Jonathan Yales
And when those beetles did come out, they were quite large — bigger than a cricket. But, don’t worry, they don’t have horns — as the name suggests — just long antennae.
Melody Keena
So, ‘longhorn’ just means that they have long antennae. And they use those to sense their environment: tapping on the trees, and moving around looking for mates, and things like that. This particular insect is half an inch to an inch and a half long. It has a black body with white spots, and it also has antennae that have white bands around [the] black base of the antenna. They can also have iridescent blue feet, which is kind of cool.
Jonathan Yales
And how big are the antenna — compared to the body size?
Melody Keena
Yeah, on females, they're usually the size of the body or just a little longer. Males can be one and a half times the body length.
Jonathan Yales
And they do seem to prefer a certain tree here in the U.S., but like the gypsy moth, they can use various hosts.
Melody Keena
So, Asian longhorned beetle can use a lot of different hosts. And it does prefer maples, but it also uses poplars and willows, etc.
Jonathan Yales
And, do we know why that is?
Melody Keena
It probably has something to do with how they smell, because they are attracted to the smell of their host. And females also will chew a pit in the tree, as if they're going to lay an egg, but just taste and see if it tastes right. So, they may be attracted to the sweet from maples just like we are.
Jonathan Yales
And, where are maples located in the U.S.? What is their range, in a sense? Are they everywhere? Are they only in the Northeast? Do they grow in the South?
Melody Keena
Most of the maples are located here in [the] eastern part of the United States. As far north as the southern part of Canada, down to Florida, and as far east as Minnesota and Texas is the range for red maple, for example — it has one of the broader ranges. But the problem with maples is that they're not just in the forest. We plant a lot of maples in our cities, exotic ones too, like, Norway maple. And, we plant them around our yards. So, there are maples places that isn't part of their natural range. So, most of the maples are concentrated here in the East/Midwest, but you're still going to have maples out West and in big cities across the nation.
Jonathan Yales
Being our second wood borer of the series, this beetle is a lot like its companion, the emerald ash borer, in how they do damage to the tree.
Melody Keena
It's the larvae. As they feed in the tree, not only are they consuming part of the tree, but they can actually completely go around a branch and do what we call ‘girdling’ it and that will kill an entire branch because there's no food or water can move through that branch any longer. So, you might see some trees that are infested that will have a branch dead here or a branch dead there. So, it's the larval feeding. The adults, you wouldn’t even notice what they do.
Jonathan Yales
Back in the 90s, back in Brooklyn, after those first beetles were identified, it was recommended that the infestations be eradicated. And the only practical way to eradicate the beetle was to completely destroy the trees. Within a year, 1,500 infested trees had been cut, chipped, and burned.
Being in an eradication mode — as we still are to this day — the beetle hasn’t really spread across the country like emerald ash borer, or hemlock woolly adelgid, or gypsy moth. Relatively small pockets pop up in the spread map now and again, but agencies swoop in and eradicate the beetle keeping it confined to these small pockets — if not totally wiping them off the map. And, over the last 20 years, A.L.B. has popped up in just a few new locations outside of Brooklyn.
Melody Keena
So, you have Worcester and the towns that surround it in Massachusetts; you've got, Brooklyn and parts of Long Island; you've got, Bethel, Ohio and the neighboring area; we had a pocket in Chicago; there was a very small pocket in Boston. And some of these have already been eradicated, others are still under eradication. So, it's little pockets here and there. We caught this beetle early enough to be able to eradicate it, and also it doesn't spread very fast on its own. It likes to reinfest the same tree that came out of; it only flies when it has to — things like the tree is getting bad so that it's no longer useful for its larvae; it landed on a host that's not an appropriate host that has fly to another tree find something that works; aggressive behaviors between the same sex on the tree like two males they fight like crazy if they find each other; to find a mate if there's no mates on its tree, things like that. So, it doesn't move a lot, and that all helped us be able to eradicate this beetle.
Jonathan Yales
And is there a reason why Asian longhorned beetle, as of today, is in that stage versus biocontrol? Why is the tactic, in a sense, to get rid of every last one?
Melody Keena
Because of the potential for loss that is associated with the maples in particular. The street trees alone, you're looking at 12-61% of all the cities’ trees being killed by this beetle if they are allowed to run unfettered through cities. And that doesn't count all the trees we have out in our forests that we’re using for maple production of syrups, and bats, and all kinds of wood products, etc. So, there's a lot of potential loss, and so you weigh that against the cost of eradication, and it far outweighs the cost of eradication.
Jonathan Yales
Now, remember Talbot from the last episode?
Talbot Trotter
Melody, is a research entomologist, so she's focused on the insects themselves. My background and training is in ecology, so it's more focused on, sort of, systems and processes.
Jonathan Yales
He has more on the potential loss due to A.L.B.
Talbot Trotter
You know, besides looking at the map, the distribution of what's at risk, we can also just put a dollar sign on it. You know, about 1.2 billion urban trees — so these are trees just in urban environments, these aren't small towns, these are not forest trees, these are just basically trees in cities, and they make up about a third of the urban tree cover — and the value that's been assigned to those trees is $669 billion, with a ‘b.’ This is just the cost that would be borne by these cities if the beetle were to spread across the landscape. You compound that with losses to timber, to fiber production, to potentially recreation/tourism, you know, it sort of goes up from there.
Jonathan Yales
He also works with Melody’s data to model ecological processes associated with A.L.B.
Talbot Trotter
So, she has worked extensively with A.L.B. and a number of other species with lab studies identifying the parameters under which that they grow and reproduce, and then what I will do is take that information and try to apply it to the outside world, to the landscape. What environments is it going to be suited to? Where might it be able to spread to? How quickly might it grow? Those sorts of things. So...
Jonathan Yales
And do you have any recent examples of that? Just...
Talbot Trotter
Yeah, actually the one of the most recent things is we've been able to take a lot of the laboratory data that she has that's very specific to the Asian longhorned beetle and use that to build a computer model that allows us to evaluate how the beetle develops in different locations and under different conditions, and so we can then start to ask ‘what if’ questions. So, if we have a new location with a new infestation, we can evaluate whether or not that location is suitable, how fast a population might grow, those sorts of things.
Jonathan Yales
Just like how a physical model — like a model airplane or sailboat — simplifies something down to help us learn about what it’s made up of and how it functions, a computer model does the same for all those things we need to understand that we can't build out of miniature plastic parts. Things like the weather, or how swarms of insects might move.
Talbot Trotter
The tools that we use are based on graph theory, which is just the idea of understanding how points on a landscape are connected. So, you can think of it as just dots and lines that connect the dots. So, that component of it is quite old. The way that we're using it now is fairly new because what we're doing is we're taking large-scale databases that are collected by the eradication programs that document where all these infested trees are and roughly how infested each tree is, and using that information to build a series of rules — a model — where we say, okay, if the beetle is going to move, it can only move from certain trees, and it can only move to, say, trees that are nearby. And if we apply these rules, and change these rules — and we know where all the infested are on the landscape — we can basically connect the dots. We draw lines between all of these infested trees and those lines represent the dispersal of the beetle. And the only way that we can really do this, of course, is with computer programs because if you have 15,000 trees you have 15,000 dots that have to be connected. Doing that by hand would be pretty time consuming. So, having the computer do it, of course, does it in a few minutes. But, the advantage that this gives us is that it allows us to play games with the rules. We can essentially say, if the beetle moves according to these rules, what does dispersal look like, and then we can change the rules and say, well if those rules don't make sense or we find new information, now what do we think the dispersal looks like? And so, we're actually using these conceptual constructs to predict — or to reconstruct — the pattern of infested trees that we already know on the landscape. So, that’s a really, really long-winded way of saying, that, essentially what we're doing, is playing connect the dots.
Jonathan Yales
In addition to modeling the beetle’s movement around infestations, Talbot and Melody — along with a grad student Alex Kappel — wanted to see how much of the entire country could be suitable for the beetle even though A.L.B. isn’t rapidly spreading. How far could this thing spread if it went unchecked?
Talbot Trotter
We ended up taking the phenology model that we built with Melody and applying that to a lot of geographic data sets based on climate for the continental U.S. and building a set of maps that show two things: One, where can the beetle complete its life history based on having suitable hosts and the right climate conditions. And also, if we look across that landscape, how fast can it complete its life history — how fast can it get from an egg to an adult? And that matters because when you find a population and you're trying to eradicate it, the faster that population grows, the harder it is to eradicate.
Jonathan Yales
And what they found out was:
Talbot Trotter
Basically, most of what we would consider hardwood landscapes in the U.S. are absolutely suitable for the Asian longhorned beetle. And so, it's very fortunate that right now the Asian longhorned beetle populations are so small and in these three specific locations. And the fact that again most of the hardwood forests of the U.S. are susceptible, kind of puts into context how important it is to stop these little pockets of infestation before they get loose on the landscape, because what's at risk is huge.
Jonathan Yales
And, remember the hemlock woolly adelgid and how the cold in the northern U.S. has been helping us out and slowing it’s spread? Melody knows that this beetle, if it was to face cold, wouldn’t have as much of a problem.
Talbot Trotter
Asian longhorned beetle is very plastic in its biology, it can go through multiple instars that allow it to adapt to different climates. So, for instance in Europe it's been found as far north as Finland and as far south is Italy, so it's got a very broad temperature range that it can grow in and it just adapts to these different climates and, you know, takes 3 to 10 years to develop in Finland and maybe one to two years in the warmer places. And, part of its ability to adapt is that the larvae can actually freeze inside of the tree and then thaw, complete development, and become normal adults that can mate and reproduce. So, it's freeze tolerant, whereas a lot of other insects aren't.
Jonathan Yales
And, unfortunately, at this time, there just isn’t much else we can do to hold off this beetle then to take down the trees, like we originally did in Brooklyn. There are biocontrol and predator options, but nothing is ideal, or especially effective.
Melody Keena
There's not a whole lot we can do to eradicate it other than finding all infested trees, cutting them down, and chipping them up. Chipping them would destroy any larvae that might be inside. There are some natural controls that are possibly available, or going on. There are some fungi that are commercially available — and also some naturally available ones — that could kill the adults. There are some predators and parasitoids that are effective against it — the nematodes that we use to kill grubs in the lawn, will actually kill the larvae. And, in China they’ve done — they’ve tried inserting some of those into the tree and they will follow the tunnels and find the larvae, but it’s not economical. There are some biocontrols, some parasitoids, and some predators in China that do a little bit against [A.L.B.], but many of them have characteristics that we wouldn't want here. For example, one of them will even go after honey bees, which we obviously wouldn't import into the United States. They’re also looking at some natural controls of some other longhorn beetles that have switched over from A.L.B. to the.. or from these other insects to A.L.B. That’s happened both in Europe and in North America, and some of them are promising, but again, they won't eradicate it. And as long as it's under eradication, we're not going to move into a biocontrol mode.
Jonathan Yales
So, this beetle has the makings of a disastrous poster pest: a wide possible geographic and climatic range, a number of host trees, few control options. Yet, lucky for us, it just doesn’t seem to spread much on its own.
Melody Keena
I don't think this insect would be a dramatic spreader — under most conditions. It doesn't like to fly very much, it wants to reinfest the same tree it comes out of, and it takes a long time to kill the trees that it's infesting. So, it's going to stick around and not move a lot.
Jonathan Yales
Next up, in the last part of this series, Part 6, we’ll talk with Rob, who’s in charge of looking for the pests that aren’t even here yet, future insects that could threaten our forests.
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
And, we’ll chat again with Melody to go inside the quarantine lab where we study the non-native insects that haven’t yet invaded..
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
Thanks for listening! See ya soon!

This episode was produced and edited by me, Jon Yales. My editors at the Northern Research Station were Jane Hodgins, Sharon Hobrla, and Gina Jorgensen. A special thanks to Melody Keena and Talbot Trotter of the Northern Research Station; and as always, to the Department of Entomology at Michigan State University; and the MSU student radio station.

If you liked this podcast please leave a review on Apple Podcasts. If you have any questions, we’re 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.
Thanks for listening.

Asian longhorned beetle (Gillian Allard, FAO of United Nations, Bugwood.org)

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