This tiny beetle could threaten Minnesota's forests
A dead pine in the Black Hills of South Dakota, June 2013. The pine has the characteristic popcorn-like pitch tubes indicating beetle infestation.
Courtesy of Brian Aukema
Can you picture a sturdy stand of tall green pine trees across a flat mossy landscape? Tiny insects called the pine beetle may have a big impact on that beautiful stand of trees.
Brian Aukema is professor of Forest Insect Science at the University of Minnesota – St Paul campus. He has been studying the Mountain Pine Beetle and the threat it poses to our forests.
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Audio transcript
CATHY WURZER: It's Minnesota Now here on MPR News. I'm Cathy Wurzer. Can you picture this? It's a sturdy stand of tall, green pine trees. It's something that's a pretty common sight in Minnesota. Well, I have some concerning news. Tiny insects called pine beetles may have a big impact on Minnesota's forests and the pine trees in your own yard.
Brian Aukema is Professor of Forest Insect Science at the University of Minnesota Saint Paul campus. He's been studying the mountain pine beetle and the threat it poses to our forests. He's on the line right now. Professor, good to have you here.
BRIAN AUKEMA: Thanks for the invitation.
CATHY WURZER: Sounds kind of interesting, this-- concerning, as I say. What is the mountain pine beetle?
BRIAN AUKEMA: The mountain pine beetle is a bark beetle. It's about the size of a grain of rice, and it's a little tiny insect that lives inside of pine trees. The females will land on the tree, and they'll chew through the bark. And as they chew through the bark, they release a tiny chemical known as a pheromone that you or I can't smell, but it attracts many of the other mountain pine beetles.
And so the males will land on the bark and try to get in underneath and join the female and mates. Other females are also coming to the tree and chewing in, and so you can get this massive attack from thousands of mountain pine beetles on a tree.
And as they tunnel in, I liken it to death by 1000 paper cuts. The tree can maybe fend off a few bark beetles by emitting some resin that tries to plug up those holes. But in the face of thousands of bark beetles attacking a tree, the tree can lose very, very quickly.
CATHY WURZER: Oh. Do you know if your tree is being attacked?
BRIAN AUKEMA: Yeah. Mountain pine beetle likes to breed in big mature pine trees, and it will feed on just about every species of pine in Western North America. And we're not quite sure yet how it might do in Eastern North America. And that's our major concern, because it's undergoing a little bit of a range expansion, and we're very concerned about mountain pine beetle arriving in Minnesota and our neighboring states.
CATHY WURZER: Where have they been so far?
BRIAN AUKEMA: The farthest east that they currently are are ponderosa pine forests of South Dakota in the Black Hills.
CATHY WURZER: I've been there, and those pine forests look a little tough.
BRIAN AUKEMA: Yeah, mountain pine beetle undergoes outbreaks every few dozen years, and it can kill massive amounts of pines in a very short period of time. There was a major outbreak in Western Canada about 20 years ago when mountain pine beetles-- there were so many of them, they got over the Rocky Mountains into an area called Northwestern Alberta where lodgepole pine, its ancestral host, hybridized with jack pine.
And jack pine is a new species of pine to mountain pine beetle, and it's reproducing in that hybrid zone in Alberta, Canada, between jack pine and lodgepole pine. And we have concern that mountain pine beetle could continue through that jack pine corridor through the Canadian boreal forest into Minnesota and Wisconsin and Michigan and even farther out to the east coast.
CATHY WURZER: Of course, Minnesota's known for the white pine and the red pine, too. Do these beetles munch on those?
BRIAN AUKEMA: That's correct. We have red pine, white pine, jack pine, Scots pine-- all different species of pines here in the state that mountain pine beetle has not previously been exposed to. We're not sure how they would do in these species of pines. And that's what really concerns us, because we see how it does out west, and we know that the threat is very real here.
CATHY WURZER: What environmental or climate conditions have spurred the pine beetles expansion east?
BRIAN AUKEMA: Well, in Western North America, it was ameliorating winter temperatures. Mountain pine beetle will typically die if it gets to -40 degrees Fahrenheit. And a number of winters in a row, that temperatures didn't quite reach that low level allowed populations to increase and led in part to that major outbreak that I was just talking about, which unleashed this range expansion eastward.
CATHY WURZER: So it sounds like they prefer a climate that's not going to be too harsh-- which, of course, climate change is kind of making that happen during the wintertime. The winters are not as cold. What are you doing to study these insects?
BRIAN AUKEMA: We're working at three different areas right now, Cathy. The first is looking at how they might do in Minnesota's pines. What we've done is we've taken trees from Minnesota to the Black Hills of South Dakota where there are populations of mountain pine beetle.
We do not want to do experiments where we bring mountain pine beetle to Minnesota. We just cannot risk unleashing an epidemic here. So we harvest jack pine, red pine, white pine, Scots pine, we bring it to South Dakota, and we expose them to mountain pine beetle populations.
And what we have found is that the beetles can recognize the trees. They can tunnel into the trees. They can release pheromones that attract other beetles. They can mate lay eggs. So they seem to be quite suitable for mountain pine beetle reproduction. What we don't know is how live trees would potentially be susceptible. So that's one area of focus that we have.
Secondly, we're looking at the climate and how a change in climate might affect populations of mountain pine beetle. We see, actually, when we bring our Minnesota pines out west, that sometimes mountain pine beetle can reproduce just a little bit faster than we expected.
And it might seem to be on the surface very bad news that, oh, our pines are very nutritious, and the beetles are developing very, very, very rapidly in these pines, more so than they would out west in their typical host, like lodgepole or ponderosa pine.
In fact, though, mountain pine beetle does the best in the winter. If it goes through the winter as a larval form, it needs to be those tiny little grubs underneath the bark, because that's the most cold hardy stage for mountain pine beetle.
And so if they reproduce too quickly and go through the winter in a life stage other than wriggling little grubs under the bark, they may be more susceptible to winter temperatures. So we might actually see a scenario where our pines are actually too good for mountain pine beetle, and it risks exposing them to temperatures that they're not accustomed to at different life stages.
The third area that we're working on is looking at how it would interact with our native bark beetles and insect predators that we already have here in Minnesota. Minnesota has many different types of bark beetles, actually, and mountain pine beetle would have to share the forest resource with those bark beetles.
We have bark beetles that are much less of a problem. They do not kill live trees on the scale of mountain pine beetle does. But many bark beetles, when they chew through the bark and they start emitting these chemical pheromones to attract other bark beetles, they also advertise themselves to other insect predators that are eavesdropping on that chemical signal.
And so that smell attracts not only bark beetles, but other insect predators. What we have done is deployed some of those pheromones to insect traps to see what would come in to these mountain pine beetle pheromones. What is out there in the forest that can cue in on them? Some good news is that we have never ever found mountain pine beetle here in the states, so we have some confidence that mountain pine beetle is not here yet.
Some news that's perhaps not so good is that we haven't found that the insect predators recognize the pheromones of mountain pine beetle. So we put that smell out, and we're just not seeing many of our native insect predators coming into these traps. And in fact, our native bark beetles just seem to avoid the pheromones of mountain pine beetle.
CATHY WURZER: OK. If it does show up here, though, what would your team and other foresters do at that point?
BRIAN AUKEMA: Right now, we are we are simply scrambling to learn absolutely as much as we can. Another area that we're still working is the risk of dispersal. We realize that the Black Hills of South Dakota are only 500 miles from our pine forests here in the state of Minnesota.
We've done a number of experiments working with outbreaks of mountain pine beetle in Montana and South Dakota and Wyoming where we have taken lines of traps starting in the forests where we have mountain pine beetle out 100 of miles into rangeland where there are no trees. And we feel perhaps even a little bit silly putting traps baited for mountain pine beetle in the middle of a cow pasture where there just aren't any trees for as far as the eye can see in some of these Western states and rangelands.
And what we've tried to do is quantify how many mountain pine beetle might be blowing off the infestation fronts away from the forest as they seek new hosts. And we know that a certain proportion just get caught in these attractive updrafts, and they can blow dozens and dozens of miles.
Some good news is that we have not found mountain pine beetle more than maybe 50 miles from infested forests, and that's a fraction of a percentage. And while it's somewhat alarming when we look at some of these traps with no trees around and we can actually find some mountain pine beetles, it is reassuring in the fact that we don't see the risk of mountain pine beetle blowing into Minnesota as a very high risk any time soon.
CATHY WURZER: All right. Professor, thanks. Good information. I appreciate your time.
BRIAN AUKEMA: Thank you, Cathy.
CATHY WURZER: That was Brian Aukema. He's a Professor of Forest Insect Science at the University of Minnesota in Saint Paul. To learn more about the mountain pine beetle, there's a lot of information on the State Department of Agriculture website. That's mda.state.mn.us.
Brian Aukema is Professor of Forest Insect Science at the University of Minnesota Saint Paul campus. He's been studying the mountain pine beetle and the threat it poses to our forests. He's on the line right now. Professor, good to have you here.
BRIAN AUKEMA: Thanks for the invitation.
CATHY WURZER: Sounds kind of interesting, this-- concerning, as I say. What is the mountain pine beetle?
BRIAN AUKEMA: The mountain pine beetle is a bark beetle. It's about the size of a grain of rice, and it's a little tiny insect that lives inside of pine trees. The females will land on the tree, and they'll chew through the bark. And as they chew through the bark, they release a tiny chemical known as a pheromone that you or I can't smell, but it attracts many of the other mountain pine beetles.
And so the males will land on the bark and try to get in underneath and join the female and mates. Other females are also coming to the tree and chewing in, and so you can get this massive attack from thousands of mountain pine beetles on a tree.
And as they tunnel in, I liken it to death by 1000 paper cuts. The tree can maybe fend off a few bark beetles by emitting some resin that tries to plug up those holes. But in the face of thousands of bark beetles attacking a tree, the tree can lose very, very quickly.
CATHY WURZER: Oh. Do you know if your tree is being attacked?
BRIAN AUKEMA: Yeah. Mountain pine beetle likes to breed in big mature pine trees, and it will feed on just about every species of pine in Western North America. And we're not quite sure yet how it might do in Eastern North America. And that's our major concern, because it's undergoing a little bit of a range expansion, and we're very concerned about mountain pine beetle arriving in Minnesota and our neighboring states.
CATHY WURZER: Where have they been so far?
BRIAN AUKEMA: The farthest east that they currently are are ponderosa pine forests of South Dakota in the Black Hills.
CATHY WURZER: I've been there, and those pine forests look a little tough.
BRIAN AUKEMA: Yeah, mountain pine beetle undergoes outbreaks every few dozen years, and it can kill massive amounts of pines in a very short period of time. There was a major outbreak in Western Canada about 20 years ago when mountain pine beetles-- there were so many of them, they got over the Rocky Mountains into an area called Northwestern Alberta where lodgepole pine, its ancestral host, hybridized with jack pine.
And jack pine is a new species of pine to mountain pine beetle, and it's reproducing in that hybrid zone in Alberta, Canada, between jack pine and lodgepole pine. And we have concern that mountain pine beetle could continue through that jack pine corridor through the Canadian boreal forest into Minnesota and Wisconsin and Michigan and even farther out to the east coast.
CATHY WURZER: Of course, Minnesota's known for the white pine and the red pine, too. Do these beetles munch on those?
BRIAN AUKEMA: That's correct. We have red pine, white pine, jack pine, Scots pine-- all different species of pines here in the state that mountain pine beetle has not previously been exposed to. We're not sure how they would do in these species of pines. And that's what really concerns us, because we see how it does out west, and we know that the threat is very real here.
CATHY WURZER: What environmental or climate conditions have spurred the pine beetles expansion east?
BRIAN AUKEMA: Well, in Western North America, it was ameliorating winter temperatures. Mountain pine beetle will typically die if it gets to -40 degrees Fahrenheit. And a number of winters in a row, that temperatures didn't quite reach that low level allowed populations to increase and led in part to that major outbreak that I was just talking about, which unleashed this range expansion eastward.
CATHY WURZER: So it sounds like they prefer a climate that's not going to be too harsh-- which, of course, climate change is kind of making that happen during the wintertime. The winters are not as cold. What are you doing to study these insects?
BRIAN AUKEMA: We're working at three different areas right now, Cathy. The first is looking at how they might do in Minnesota's pines. What we've done is we've taken trees from Minnesota to the Black Hills of South Dakota where there are populations of mountain pine beetle.
We do not want to do experiments where we bring mountain pine beetle to Minnesota. We just cannot risk unleashing an epidemic here. So we harvest jack pine, red pine, white pine, Scots pine, we bring it to South Dakota, and we expose them to mountain pine beetle populations.
And what we have found is that the beetles can recognize the trees. They can tunnel into the trees. They can release pheromones that attract other beetles. They can mate lay eggs. So they seem to be quite suitable for mountain pine beetle reproduction. What we don't know is how live trees would potentially be susceptible. So that's one area of focus that we have.
Secondly, we're looking at the climate and how a change in climate might affect populations of mountain pine beetle. We see, actually, when we bring our Minnesota pines out west, that sometimes mountain pine beetle can reproduce just a little bit faster than we expected.
And it might seem to be on the surface very bad news that, oh, our pines are very nutritious, and the beetles are developing very, very, very rapidly in these pines, more so than they would out west in their typical host, like lodgepole or ponderosa pine.
In fact, though, mountain pine beetle does the best in the winter. If it goes through the winter as a larval form, it needs to be those tiny little grubs underneath the bark, because that's the most cold hardy stage for mountain pine beetle.
And so if they reproduce too quickly and go through the winter in a life stage other than wriggling little grubs under the bark, they may be more susceptible to winter temperatures. So we might actually see a scenario where our pines are actually too good for mountain pine beetle, and it risks exposing them to temperatures that they're not accustomed to at different life stages.
The third area that we're working on is looking at how it would interact with our native bark beetles and insect predators that we already have here in Minnesota. Minnesota has many different types of bark beetles, actually, and mountain pine beetle would have to share the forest resource with those bark beetles.
We have bark beetles that are much less of a problem. They do not kill live trees on the scale of mountain pine beetle does. But many bark beetles, when they chew through the bark and they start emitting these chemical pheromones to attract other bark beetles, they also advertise themselves to other insect predators that are eavesdropping on that chemical signal.
And so that smell attracts not only bark beetles, but other insect predators. What we have done is deployed some of those pheromones to insect traps to see what would come in to these mountain pine beetle pheromones. What is out there in the forest that can cue in on them? Some good news is that we have never ever found mountain pine beetle here in the states, so we have some confidence that mountain pine beetle is not here yet.
Some news that's perhaps not so good is that we haven't found that the insect predators recognize the pheromones of mountain pine beetle. So we put that smell out, and we're just not seeing many of our native insect predators coming into these traps. And in fact, our native bark beetles just seem to avoid the pheromones of mountain pine beetle.
CATHY WURZER: OK. If it does show up here, though, what would your team and other foresters do at that point?
BRIAN AUKEMA: Right now, we are we are simply scrambling to learn absolutely as much as we can. Another area that we're still working is the risk of dispersal. We realize that the Black Hills of South Dakota are only 500 miles from our pine forests here in the state of Minnesota.
We've done a number of experiments working with outbreaks of mountain pine beetle in Montana and South Dakota and Wyoming where we have taken lines of traps starting in the forests where we have mountain pine beetle out 100 of miles into rangeland where there are no trees. And we feel perhaps even a little bit silly putting traps baited for mountain pine beetle in the middle of a cow pasture where there just aren't any trees for as far as the eye can see in some of these Western states and rangelands.
And what we've tried to do is quantify how many mountain pine beetle might be blowing off the infestation fronts away from the forest as they seek new hosts. And we know that a certain proportion just get caught in these attractive updrafts, and they can blow dozens and dozens of miles.
Some good news is that we have not found mountain pine beetle more than maybe 50 miles from infested forests, and that's a fraction of a percentage. And while it's somewhat alarming when we look at some of these traps with no trees around and we can actually find some mountain pine beetles, it is reassuring in the fact that we don't see the risk of mountain pine beetle blowing into Minnesota as a very high risk any time soon.
CATHY WURZER: All right. Professor, thanks. Good information. I appreciate your time.
BRIAN AUKEMA: Thank you, Cathy.
CATHY WURZER: That was Brian Aukema. He's a Professor of Forest Insect Science at the University of Minnesota in Saint Paul. To learn more about the mountain pine beetle, there's a lot of information on the State Department of Agriculture website. That's mda.state.mn.us.
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