This common garden plant summons wasps as bodyguards

Summary

Short Wave Podcast Summary

Episode Title: This common garden plant summons wasps as bodyguards
Date: June 3, 2026
Hosts: Regina Barber, Hannah Chin
Guest: Sascha Pfeiffer

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Overview

This episode of Short Wave explores the remarkable ways in which nature adapts to threats, focusing on plant defenses against pests, innovations in behavior training for mice, and a surprising limitation in the effectiveness of DEET, the popular mosquito repellent. Through a lively, curiosity-driven discussion, the hosts and guest Sascha Pfeiffer unpack how plants and animals fight, learn, and evolve alongside each other.

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Key Discussion Points & Insights

1. Bean Plants: Calling in Wasp Bodyguards (02:17–04:28)

• Main Idea: Common bean plants (bush or pole beans) have developed a unique chemical defense when attacked by caterpillars.

• When caterpillars eat the plants, compounds in their saliva trigger the beans to emit airborne chemical signals—essentially a distress call.

• These signals attract parasitoid wasps, which prey on the caterpillars or lay eggs inside them, directly protecting the beans.

  "A compound in the caterpillar 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."
  — Hannah Chin (02:54)

  "The types of chemicals we were able to measure were known to be attractants to predatory wasps, parasitoid wasps that lay eggs in caterpillars."
  — Adam Steinbrenner, University of Washington (03:16)

• This plant defense is highly specific: general damage (like cutting the plant) does not release the same wasp-attracting chemical. Only caterpillar saliva has the effect.

• Plants have a variety of strategies for defense: thorns, toxins, and now—in this case—"calling in the drones" (wasps).

2. Mice Learn Faster with Bigger, Less Frequent Rewards (04:28–06:29)

• Main Idea: New research shows mice learn tasks faster when given larger but less frequent rewards, as opposed to the traditional small and frequent model.

  "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."
  — Josh Dudman, study author (04:54)

• The study suggests that larger rewards provide a stronger, longer-lasting dopamine boost, keeping the mice engaged for longer periods.

• Tasks learned included both simple Pavlovian cues and complex tasks such as manipulating joysticks and steering wheels.

• Implications: While direct comparisons to humans are limited, the research opens avenues for better understanding engagement and learning in animal models.

3. DEET's Achilles Heel: Mosquitoes Can Learn (06:29–09:39)

• Main Idea: Mosquitoes, after repeated exposure, can learn to associate the smell of DEET (the most common active ingredient in mosquito repellents) with a blood meal, potentially undermining its effectiveness.

  "Mosquitoes can learn to associate its smell with dinner, which is a pretty big deal."
  — Hannah Chin (06:52)

• The research mirrors Pavlovian conditioning: mosquitoes exposed to DEET along with a blood or sugar meal began to associate DEET's scent with food, eventually seeking it out even without the reward present.

• In experiments, "trained" mosquitoes sought hands sprayed with DEET more often than unsprayed hands (08:21).

• However, scientists stress this conditioning is unlikely to occur naturally; it took repeated, concentrated training in the lab. In the wild, most mosquitoes are still repelled by DEET.

  "It's very difficult for mosquitoes to experience DEET while blood feeding."
  — Ali Afifi, entomologist, Drexel University (09:16)

• Takeaway: DEET still works well for most users; don't stop using it based on these findings!

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Notable Quotes & Memorable Moments

• On plant defense evolution:
  "It's like calling in the drones."
  — Sascha Pfeiffer (04:28)

• On the versatility of plant behavior:
  "Cut grass smells a specific way. That's the plant's chemical response to being wounded."
  — Regina Barber (03:41)

• On American fiber intake:
  "Over 90% of us are not getting enough."
  — Regina Barber (10:06)

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Important Timestamps

• 02:17: Start of bean plant chemical defense segment
• 03:26: Adam Steinbrenner explains how wasps are attracted
• 04:37: Mouse learning study introduction
• 04:54: Josh Dudman describes breakthrough in mouse learning
• 05:48: The dopamine connection in learning
• 06:29: Introduction to DEET research and mosquito adaptation
• 07:26: Clement Vidanger on how DEET confounds mosquito senses
• 08:21: How researchers "trained" mosquitoes to associate DEET with food
• 08:53: Ali Afifi comments on real-world implications
• 09:23: Researchers emphasize DEET still works

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Tone and Style

The conversation is lively, engaging, and filled with curiosity. The episode balances cutting-edge science with accessible explanations, humor, and practical takeaways.

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Conclusion

This Short Wave episode highlights the incredible adaptability of plants and insects, revealing hidden dramas in our gardens and new insights into animal learning. It ends with a reassuring reminder: while nature is constantly evolving, many of our current tools—like DEET—remain effective, and our understanding continues to grow.

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Transcript

[Announcer]

This message comes from Avalara. What's it like running a business with Avalara? No thinking about tax and compliance. It's handled calculating, filing validating accurately, and audit defensibly. Avalara agentic tax and compliance with confidence. You're listening to Short Wave from npr.

[Regina Barber]

Hey, shortwavers.

[Hannah Chin]

Regina Barber here and Hannah Chin with our bi weekly science news roundup.

[Regina Barber]

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

[Sascha Pfeiffer]

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

[Hannah Chin]

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

[Sascha Pfeiffer]

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

[Hannah Chin]

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

[Regina Barber]

It just came out. Yeah, great. Then we're gonna talk about another pest. We're going to be talking about how best to teach mice.

[Announcer]

And.

[Hannah Chin]

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

[Regina Barber]

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

[Hannah Chin]

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

[Announcer]

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[Regina Barber]

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

[Sascha Pfeiffer]

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

[Regina 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 defense mechanism.

[Announcer]

Ah.

[Sascha Pfeiffer]

And what's it defending itself against? I assume some pest or some blight or something.

[Hannah Chin]

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 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.

[Sascha Pfeiffer]

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

[Hannah Chin]

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 caterpillars bodies so their babies can eat them, really effectively removing the threat to the bean plants.

[Regina Barber]

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

[Sascha Pfeiffer]

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

[Hannah Chin]

Yeah, 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, this strategy. Right. Calling in some aerial reinforcements from the insect world.

[Sascha Pfeiffer]

It's like calling in the drones. Yes, exactly. All right, you also mentioned, for your second topic, new ways to speed up learning in mice. Tell us about that one.

[Regina 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 help the mice learn a lot faster. Here's Josh Dudman, one of the authors of the study.

[Hannah Chin]

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.

[Sascha Pfeiffer]

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?

[Hannah Chin]

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

[Sascha Pfeiffer]

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

[Hannah Chin]

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.

[Sascha Pfeiffer]

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.

[Hannah Chin]

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.

[Sascha Pfeiffer]

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

[Regina Barber]

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.

[Sascha Pfeiffer]

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?

[Regina Barber]

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

[Hannah Chin]

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. Yeah.

[Sascha Pfeiffer]

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?

[Regina Barber]

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

[Announcer]

easy As I think, to ask mosquitoes, you know, how does it feel? How do you smell or taste that?

[Hannah Chin]

So this is Clement Vidanger. 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.

[Sascha Pfeiffer]

This all seems so counterintuitive.

[Regina Barber]

Yeah.

[Sascha Pfeiffer]

So how do you teach a mosquito,

[Regina 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?

[Hannah Chin]

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.

[Regina 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.

[Sascha Pfeiffer]

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?

[Hannah Chin]

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 because mosquitoes are not attracted to DEET in real life. So it's very difficult for mosquitoes to experience DEET while blood feeding.

[Regina Barber]

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

[Hannah Chin]

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.

[Regina Barber]

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

[Sascha Pfeiffer]

I did.

[Regina Barber]

Makes you think differently about beans.

[Sascha Pfeiffer]

I think everybody needs more fiber, right? Does anybody get enough?

[Regina Barber]

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

[Sascha Pfeiffer]

Not good.

[Regina Barber]

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

[Sascha Pfeiffer]

Thank you.

[Regina Barber]

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

[Hannah Chin]

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

[Sascha Pfeiffer]

This message comes from Bombus. Upgrade your summer staples with soft socks, cushy sandals and breezy basics. One purchase means one donated. With over 200 million donations and counting, go to bombus.com NPR and use code NPR for 20% off your first purchase.

[Announcer]

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