A Bit of Background on Bark Beetles
MICHELE NORRIS, host:
Joining us now to talk about bark beetles and climate change is Diana Six. She's a professor of Forest Entomology at the University of Montana and she's an expert on bark beetles. She joins us now.
Welcome, Professor Six.
Professor DIANA SIX (Forest Entomology, University of Montana): Hi.
NORRIS: We've just heard the sounds of this infestation. What does that actually look like?
Prof. SIX: Well, that's a pretty amazing sound. It was great to hear. When you see it out in the forest though, you really don't see it till about a year after the tree is dying. They stay green and then all of a sudden you'll see the trees began to turn yellow and red. And it can happen very, very rapidly.
NORRIS: So could you help make that link for us? Explain this link between this infestations and climate change.
Prof. SIX: Ah, that's a good one. With temperature increases, you have some pretty strong and immediate effect on insect populations. Insects are what we call cold-blooded and so they pretty much develop at the rate of the temperature around them. And so, if you increase temperatures even a couple of degrees, you can increase development very rapidly and of course, as you increase development, you get faster population growth. Couple that with the fact that we aren't having these real cold winters anymore that typically kills a lot of the insects off during the winter, now we have big populations, growing very fast and a lot of tree mortality.
NORRIS: So the bark beetles feed on the trees. Is there anything out there that feeds on the bark beetles?
Prof. SIX: Yeah. There's lots of things that feed on bark beetles. There's lots of other insects that feed on bark beetles - and woodpeckers. Woodpeckers are incredibly good natural enemies of bark beetles.
NORRIS: Large enough appetite to keep the pest in check?
Prof. SIX: No. You can't get enough woodpeckers out there in the woods to control the bark beetle outbreak. For one thing, they're fairly territorial and so you'll only get so many woodpeckers. So once populations get over a certain point, they pretty much outgrow their natural enemies.
NORRIS: How was it that the bark beetle, of all the insects that are out there, that this one bug winds up being the harbinger pest, the pest that tells us the most about climate change?
Prof. SIX: Well, it's a strong responder to temperature and to tree stress. And the fact that it can kill trees.
NORRIS: Tree stress.
Prof. SIX: Yeah. If you look at the effects of climate change on bark beetle populations or insect populations, in general, it comes basically from two places. One, temperature, warming supports faster development and greater survival but also, as an area warms and quite often gets drier, the trees become much more stressed. And stressed trees have very few defenses.
NORRIS: If the tree was healthy, what could it do to send off the bark beetle?
Prof. SIX: Oh, they have a couple lines of defense. First, they have resin and if they're very healthy and vigorous, they can produce a lot of resin. And as the beetle begins to try to bore in, it will push the beetle out or even drown it with the resin. If the beetle gets passed the resin, they actually have an induced response where they produce a lot of really nice toxic chemicals that can kill the beetle or even just push it again back out of the tree. In fact, if you walk through a pine forest and you smell that wonderful pine odor, those are actually toxins or natural pesticides the trees produce to protect themselves against the beetles.
NORRIS: You know, a walk through the forest may never be the same.
Prof. SIX: I know. My student really hate when I tell them that story.
NORRIS: Well, Professor Six, thank you so much for talking to us.
Prof. SIX: Sure, thank you.
NORRIS: That's Diana Six. She's a professor of forest entomology at the University of Montana.
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