This common garden plant summons wasps as bodyguards

In our latest science news roundup: how nature adapts, for better or worse. When faced with pests, plants may not be able to run away – but that doesn’t mean they’re defenseless. Some have thorns or spines, others have poisonous leaves or berries, and still others have…elaborate chemical defense alarm systems? In a recent study https://doi.org/10.1126/sciadv.aec3229, researchers discovered that the common bean plant, P. vulgaris, has a particularly innovative response to hungry caterpillars: a compound in the caterpillar's spit causes the plants to release a chemical signal that attracts wasps. Those wasps then eat the caterpillars or lay eggs in their bodies, effectively removing the threat. Today on the show, we’re diving into plant science and a round of other new scientific studies with All Things Considered host Sacha Pfeiffer. If you're interested in the fibermaxxing episode Han mentioned, check it out here http://lnk.to/PcSZyC. Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:00Speaker 00

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• 0:15Speaker 00

  You're listening to Short Wave from NPR.

• 0:20Regina Barber?

  Hey, Short Wavers. Regina Barber here.

• 0:22Speaker 02

  And Hannah Chin with our biweekly Science News roundup.

• 0:25Regina Barber?

  And we're lucky enough to have Sasha Pfeiffer back on the show, third time in a row.

• 0:29Speaker 03

  Hi, Regina. Hi, Hannah. Fun to be back with you.

• 0:32Speaker 02

  All right, Sasha, our first topic is about beans and bean plants, surprising chemical counterattack against caterpillars, which are a common garden pest.

• 0:40Speaker 03

  Ah, you know, given that fiber has become such a wellness trend with everybody fiber-maxing, I'll be very interested to hear about this one.

• 0:46Speaker 02

  I mean, we also have an episode about fiber-maxing.

• 0:48Regina Barber?

  Just came out.

• 0:49Speaker 02

  Yeah.

• 0:49Speaker 03

  Great.

• 0:50Regina Barber?

  Then we're going to talk about another pest. We're going to be talking about how best to teach mice.

• 0:55Speaker 02

  And lastly, we've got one more story about pests. This time, it's how the bug repellent D could have a major Achilles' heel.

• 1:02Regina Barber?

  You know, Han, I think today's episode is actually about nature adapting.

• 1:07Speaker 02

  It's true. Today on the show, adaptation for better and for worse. You're listening to Short Wave, the science podcast from NPR.

• 1:22Speaker 00

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• 2:42Regina Barber?

  Okay Sasha, we have so much to get through, but you talked about fiber maxing, so let's start with beans.

• 2:47Speaker 03

  Let's do that. The more fiber for the world, the better.

• 2:50Regina Barber?

  Yeah, so this story is an amazing example of plant versus animal warfare. And it might make you think a little differently about how crafty plants can be in defending themselves. And it all centers around the common bean plant. So this is the one I feel like a lot of grade schoolers grow in classrooms. It's a garden staple, the bush bean or pole bean. And it turns out it has an elaborate chemical defense mechanism.

• 3:14Speaker 03

  Ah, and what's it defending itself against? I assume some pest or some blight or something?

• 3:18Speaker 02

  In this case, it's caterpillars. So Sasha, in a study out this week in the journal Science Advances, researchers described how when caterpillars munch on bean plants, a compound in the caterpillar's spit causes the bean plants to release a chemical signal into the air. Think about it as a kind of distress flare that calls in a fleet of wasp bodyguards.

• 3:41Speaker 05

  The types of chemicals we were able to measure were known to be attractants to predatory wasps, parasitoid wasps that lay eggs in caterpillars.

• 3:51Speaker 02

  So this is Adam Steinbrenner. He's a plant biologist at the University of Washington, and he's one of the authors on the study. He says some of the wasps eat the caterpillars. Others lay eggs inside the caterpillar's bodies so their babies can eat them, really effectively removing the threat to the bean plants.

• 4:06Regina Barber?

  And Sasha, this kind of chemical signal isn't rare. Plants release them all the time. Like, cut grass smells a specific way. That's the plant's chemical response to being wounded.

• 4:16Speaker 03

  Oh, interesting. The cut grass smelling a specific way reminds me of flowers smelling sweet because they're trying to attract bees.

• 4:22Speaker 02

  Yeah. And these are both chemical responses, right? But the specific compound that attracts wasps is really only triggered via caterpillar spit. So the bean plant doesn't call wasps in if, say, you cut a leaf or if you damage the plant in a different way. And Sasha, this is just one of multiple ways that plants have really evolved to defend themselves. If you think about the thorns of a rose, or the spines of a cactus, or bitter, poisonous leaves. Or, I guess in this case, the strategy, right? Calling in some aileron reinforcements from the insect world.

• 4:52Speaker 03

  It's like calling in the drones.

• 4:54Speaker 02

  Yes, exactly.

• 4:55Speaker 03

  All right. You also mentioned, for your second topic, new ways to speed up learning in mice. Tell us about that one.

• 5:01Regina Barber?

  Yeah, so I brought you a study just published in the journal Science. In lab experiments, researchers typically give mice little rewards to help them learn tasks. But in this study, they found that giving them bigger rewards less frequently actually helped the mice learn a lot faster. Here's Josh Dudman, one of the authors of the study.

• 5:19Speaker 06

  We discovered that we had been substantially underestimating how efficiently animals can learn. We could essentially take some of the slowest learners and move them all the way up to the fastest learners.

• 5:30Speaker 03

  I really want to know what the rewards were. I'm thinking about cheese or peanut butter we put in a mousetrap. What did they use as rewards for these mice?

• 5:37Speaker 02

  So, in this case, the reward was artificially sweetened water, which, for what it's worth, is also something that humans appreciate.

• 5:44Speaker 03

  And what sort of things were the mice trying to learn?

• 5:47Speaker 02

  Well, one was the classic Pavlovian cue. They were learning that certain sounds meant a reward was coming. And they also had to learn harder things, like pulling a joystick or turning a tiny steering wheel right or left to get a reward.

• 6:00Speaker 03

  So I'm interested in this idea that a bigger amount of reward given less frequently resulted in faster learning rather than smaller, more frequent rewards. Tell us more about why that worked better.

• 6:12Speaker 02

  Yeah, well, we don't know the whole picture, but Josh and his colleagues think it has something to do with dopamine and engagement, right? Dopamine is a chemical that makes you feel good, and then your brain is like, oh, I want to do that again. And when the mice got these big rewards, they got a bigger burst of dopamine. And the scientists say that lasted longer and kept them more engaged than these little rewards. They also pointed out there might be other factors at play, not just dopamine.

• 6:37Speaker 03

  Since this is just a mouse study, what does it tell us potentially about human learning?

• 6:42Speaker 02

  Yeah, so these experiments give insight into what keeps the brain engaged, which might be helpful for future animal experiments. We aren't quite at the point of comparing these experiments to human learning, but it's a step in the right direction.

• 6:54Speaker 03

  All right, so topic three, we move on to another type of pest in some people's eyes. And that is how our strongest mosquito repellent may have a weakness we didn't know about before. What repellent and what weakness?

• 7:07Speaker 02

  Yeah, so many people know DEET is an important chemical in many mosquito repellents, but it may have an Achilles' heel. Mosquitoes can learn to associate its smell with dinner. Which is a pretty big deal, right? Because having an effective mosquito repellent isn't just good for avoiding itchy bites, it also saves lives. Mosquitoes can spread really deadly diseases like malaria.

• 7:27Speaker 03

  Yeah, so tell us more about this, because of course, the reason we wear DEET is to keep mosquitoes away. So remind us, what is it that DEET does that repels mosquitoes?

• 7:38Speaker 02

  Yeah, so that's the part that's wild to me. We still don't fully know how exactly DEET works because...

• 7:44Speaker 07

  It is not as easy as one might think to ask mosquitoes, you know, how does it feel? How do you smell or taste that?

• 7:51Speaker 02

  So this is Clement Viderger. He's a neuroethologist at Virginia Tech who worked on the study, which was published recently in the Journal of Experimental Biology. He says the reason DEET generally works is because it repels mosquitoes. We just know they don't like it for some reason or another. Here's the thing. Previous research shows that repeatedly exposing mosquitoes to DEET made them less repelled by it. And Clement and his colleagues wanted to take it a step further and find out if mosquitoes could learn to actually be attracted to DEET.

• 8:20Speaker 03

  This all seems so counterintuitive. So how do you teach a mosquito?

• 8:25Regina Barber?

  Like one of the experiments in the mice study about rewards, these researchers went back to Pavlov, you know, that study where you ring a bell, you make the dog salivate because they think they're going to get fed.

• 8:36Speaker 02

  And the researchers used the same concept, but instead of a bell, they used the smell of deet. And as a reward, they used a bag of blood or sugar that the mosquitoes could bite and feed on.

• 8:46Regina Barber?

  And the training worked. They found that in a little over half of the trials, mosquitoes actually began to associate deet with feeding time. And they would actively approach it, even if the reward wasn't there. And when they tested with actual humans, they found that trained mosquitoes would also gravitate towards a person's hand sprayed with deet, more than their other hand without the repellent.

• 9:07Speaker 03

  All right, so I feel like I'm confused by this. You put deet on and it's going to attract a mosquito, even though we want deet to repel mosquitoes. So what does this tell us about deet's use and effectiveness in the real world?

• 9:18Speaker 02

  This study shows it's possible for mosquitoes to learn to be attracted to deet. And that surprised Ali Afifi. He's an entomologist and a neuroscientist at Drexel University. He wasn't involved in the study. But he pointed out that it's unclear whether this sort of thing could happen in the wild. Because, remember, this required a lot of training mosquitoes. And usually, wild, untrained mosquitoes will fly away from deet.

• 9:40Regina Barber?

  Because mosquitoes are not attracted to deet in real life. So it's very difficult for mosquitoes to experience deet while blood feeding. So for now, the researchers say, please don't stop using deet. They emphasize that it's still a very effective repellent in real world situations.

• 9:58Regina Barber?

  For more science stories just like these, follow Short Wave on the NPR app or wherever else you're listening from.

• 10:04Speaker 02

  Speaking of which, on the app, we've got podcasts, broadcasts, digital stories, a bunch of stuff to help you know what's going on with the world and keep up with the news. So download the NPR app and sign up for push notifications so you can know when the latest Short Wave episode drops.

• 10:20Regina Barber?

  So Sasha, did you enjoy our pest control adaptation episode?

• 10:25Speaker 03

  I did.

• 10:27Regina Barber?

  Makes you think differently about beans, I think.

• 10:29Speaker 03

  Everybody needs more fiber, right? Does anybody get enough?

• 10:31Regina Barber?

  Not in America. Yeah, over 90% of us are not getting enough.

• 10:36Speaker 03

  Not good.

• 10:36Regina Barber?

  Well, come back anytime, Sasha. Thank you so much.

• 10:39Speaker 03

  Thank you.

• 10:40Regina Barber?

  This episode was produced by Mallory Yu and Arun Nayar. It was edited by Christopher Intagliata. Tyler Jones checked the facts. David Greenberg and Tiffany Vera Castro were the audio engineers. I'm Regina Barber.

• 10:53Speaker 02

  And I'm Hannah Shin. Thanks for listening to Short Wave, the science podcast from NPR.

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