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Christophe Duplais on what scent can communicate - Research Matters S2E10

• Cornell University • Season 2 • Episode 10

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In this episode of Research Matters, entomologist Christophe Duplais explains how scent molecules can identify stressed plants, help farmers detect crop problems early and even offer clues about human and animal health. Decoding these airborne messages reveals a hidden communication network that connects ecosystems, agriculture and medicine. Watch here.

Christophe Duplais:

We're trying to learn a new language, the language of the plant chemistry or the insect chemistry. We try to decode each words and try to understand what the sentences they try to put out there.

Laura Reiley:

Hi, I'm Laura Reiley, and this is Research Matters, a show about the Cornell researchers who are finding solutions for the world's biggest problems. What if the key to understanding the health of our bodies, our environment and the crops that feed us was floating all around us? What if the invisible world of scent — those chemicals whispering in the air — held clues waiting to be decoded. Today we're diving into that world with Christophe Duplais, associate professor in the Department of Entomology at Cornell AgriTech. His work asks a surprisingly bold question: Can we collect and analyze smells to understand the world around us? Welcome, Christophe.

Christophe Duplais:

Hello. Hi.

Laura Reiley:

So I would love to start with kind of a big idea. Most of us think of scents as kind of, you know, this personal, like. Oh, that's a lovely cologne. Or, you know, who burnt the toast? That kind of thing. But your your research treats smell as kind of an information system. Something almost like a language. What does it mean to read smells in nature?

Christophe Duplais:

So reading smell in nature means really, it's really about trying to understand the words that help us to communicate, right? When we communicate, we use words to make sentences, but the smells can — each molecule can be associated with a word, something, sing. And so if you put different chemicals together, you can start to have a sentence. And so I think that since the beginning of, the evolution, any organism has been trying to interact with each other by communicating, whether using smell or other ways. But the smell is a very easy one to communicate.

Laura Reiley:

So who is signaling whom? Like give us like the array. I mean, we hear about pheromones. It's a very mysterious kind of, you know, thing in humans. But what are the... who are the signalers and who are they signaling?

Christophe Duplais:

So I think that I will say that there is a topic called multi-trophic interaction, where you go from the plant to the herbivore to the parasitoids of the herbivores. So it's like the good way of, like, starting this conversation because when an herbivore is chewing on a plant, the plant is going to start to release a bunch of molecules. Some of the molecules, they have no function at all. But some of them, they actually, trigger for parasitoid, who's going to try to — The parasitoid is going to figure it out that some plant is being attacked by a herbivore, that the parasitoid can put, lay, lay eggs inside. So so that's the ...

Laura Reiley:

This is so the plant is deterring their, their predator by attracting a predator for that animal.

Christophe Duplais:

The plant is calling for help for some organisms that can help the plant to defend against the attacker. So the question is, like, words of selection has been made here. Is it the olfactory receptor of the parasitoid or is it the chemicals being released for the plants that's being the selection pressure? This is very hard when you've got the emitter and a receiver to see the dynamic of evolution of like who's studying it first, the communication.

Laura Reiley:

Are you developing ways of kind of eavesdropping on those on the plants that are sending out these messages?

Christophe Duplais:

Exactly. We're trying to learn a new language, the language of the plant chemistry or the insect chemistry. We try to decode each words and try to understand what the sentences they try to put out there.

Laura Reiley:

Okay. So this is sounding very kind of, almost psychedelic right now. So but how do you I, you know, woo. But how do you collect the scents? What does that look like in the field?

Christophe Duplais:

So in the field it's very hard. And most of the time there is, like, this technique that we've been using for a very long time. We use absorbent. So we use kind of like, dispenser that absorb the smell. So sometime when you try to filter your water use a charcoal, right? But actually charcoal is a very good absorbent for lots of volatile. So even in environmental studies when we try to figure out toxins in the air, we use these kind of absorbent like charcoal to trap the molecule. And then we can dissolve them either by using absorbent or by just, like, heating. So you, we release gases that are being absorbed into this, dispenser, but it's still very biased. There's lots of biases when we collect volatile. And so some of the, we there is one instrument that we can bring in the field, but it is a very expensive instrument. And the when I try to buy this instrument, which cost like half a million dollars, when I ask if I can see one in New York State, they say, like, the last time someone buy it in New York state, actually, he was struck by lightning because you put a piece of metal and electronics in the middle of the field. And it's so you get burnt. But I feel like now that we've got a new technique, that is being, driven by the actually the food science and the food industry. And we've got, like, very, very tiny, piece of plastic that we can drop around and they absorb very efficiently.

Laura Reiley:

That sounds way less expensive than that half a million dollars —

Christophe Duplais:

Very less expensive. We still... but it's still no real-time monitoring. So we still need to bring back the sample in the lab analyzing it. So we... It's crazy that we 2025 we can have probes everywhere on Earth. It's still very hard to have the detection of smell in real time in any place.

Laura Reiley:

Is that an indicator that smell is something we haven't taken as seriously as the other senses?

Christophe Duplais:

Not we haven't taken seriously. I think he's a very one to work through and to decode carefully, because I think that we know that humans have smells. Pheromones. We haven't figured it out. And we have —

Laura Reiley:

I thought that was like what Axe body spray was for. Or, you know, I thought that that's how we kind of attract each other. Is this pheromones?

Christophe Duplais:

There are a few experiments that test, how we behavior for pheromones. And we know we have behavior for pheromones. We haven't figured out the chemicals behind that.

Laura Reiley:

Okay, so for for humans, a smell, you know, goes from the nose to the olfactory bulb to the amygdala and the hippocampus, I guess, is that for all vertebrates? Do all vertebrates smell the same way.

Christophe Duplais:

So I don't even think that we humans smell the same way. I think there is lots of variation, even for us. So then across different species, definitely something that smell — Think about, I can think about, the, the corpse flower. So they've got this plant who smells like corpse to attract pollinators. For us is going to be the smell of the corpse. So it could be deterrent. But from some of pollinator is true smells like heaven for them because it's an attractant. So depending — I think it goes beyond the, the type of brain decoding function we have, it's, it's about what is the, the smells make how this makes change of behavior. And what's the driving force of that.

Laura Reiley:

So are we all... I mean across invertebrates, are we all driven by smell?

Christophe Duplais:

We are all driven by many cues. Smell is one of them. But I'm not quite sure that, you know, we are the only species who... But I'm not quite sure about that. We are the only species who use smell for perfume. Right? But, other, other species would take benefits of the smell to camouflage or to even, like, do courtship. I think this is, this is not belonging only to humans. I think lots of some other species do that.

Laura Reiley:

Yeah. Makes sense. All right. Let's talk a little bit about agriculture and kind of the application of this. So you know, we've we've been through, I don't know, 80 years of very chemistry-intensive agriculture. And it's gotten us in a little bit of a pickle in some ways, depending on who you talk to. Large-scale commodity, row crop, you know, pesticide intensive. Are there ways that, that your research can bring a different kind of paradigm to how agriculture, how pests are dealt with in the field?

Christophe Duplais:

So I'm always trying to make this analogy between personal medicine and and precision medicine and personal agriculture and precision agriculture, because we in medicine, we try to detect the disease before it spread out. Or even if the first cancer cell appear, we try to detect that. It's the same challenge in, in, in agriculture. Every time we've got a new disease, we want to make sure that we can detect it before it's spread all around. And so smell is one of the good things to track down, because when we are sick, we smell differently. Whether any organisms with some kind of disease will have some cues going to be different when they are not affected. So figure it out when one single plant is getting infected by any disease, help us to tackle down this issue and spread less pesticide because instead of spreading the whole field, if we can localize precisely where the infection is, then we would use the, the, the, the chemicals we put in the field.

Laura Reiley:

Well, I know that dogs have been used — obviously, you know, we've, we have a long history of pigs being used to hunt truffles, but we've also had dogs that in recent years have hunted things like they're in Florida, there's a, a boring beetle in avocados that... It's like drones have have identified parts of fields that have, like, canopy damage. And then dogs have been sent out to, to scent, essentially, where the disease is or where these boring beetles are. Is that an asset or, strategy that could be used more broadly?

Christophe Duplais:

It is. But the, the dog training has limitation. I can tell you an example of the, the leaf wall virus, which is a virus that affects grape vine and it changes the taste of grapes. So they have zero tolerance in California to have this virus, they have to remove the whole vine. Right now we have really big trouble detecting that because we have to use PCR tests. And we train dogs right now to detect the vine. They can smell when the grape vine has this virus, but you still have limitations. So I'm working with some different companies right now who can develop a new type of detector that can provide real testing on site, and we try to train the device right now using AI to differentiate the smell of the plant when they have the virus or not.

Laura Reiley:

So some kind of, this isn't dogs doing this. This is a device that detects scent.

Christophe Duplais:

Exactly. We try to have the same sensitivity as a dog nose, basically.

Laura Reiley:

All right, so you're — so the goal is to detect these diseases before they become cataclysmic for a particular crop or widespread. Are there ways of introducing smells as a protectant for crops? And what would that look like?

Christophe Duplais:

So absolutely, because sometime you just try to put the pest outside your field. And so there is, like, this very — actually not very recent. We've been using that in Africa for a long time. It's called the push-pull system. So you put in the middle of the crops some plant going to be a deterrent. And you put outside of the crop of the field some attractant plant. So you get these push-pull system that push the pest out of the field, attract them outside the field. So this push-pull system is being used and we keep using it because it's a very good alternative to pesticide. Absolutely.

Laura Reiley:

So it's kind of like, you know, I've always been told to plant marigolds at the edge of your garden to keep certain pests away.

Christophe Duplais:

Yes, exactly.

Laura Reiley:

So the pull part, are there ways of... I know that in a lot of biodynamic gardening or farming situations, they're trying to attract good predators for the bad bugs? Like, are there things that, you know, attract these? I don't know whether it's ladybugs or whatever.

Christophe Duplais:

Yes, and that's, that's the the difficult part of this challenge of which molecule attract which insects or which beneficials, whether you microbes or nematodes, and how much eavesdropping you're going to have from species you don't want, who's going to adapt to the flavor you put in a field.

Laura Reiley:

Yeah, yeah. I can see.

Christophe Duplais:

So being selective and make sure that these molecule attract only one species or just the good ones, it's very, very hard.

Laura Reiley:

Yeah. The adaptation the learning of these, these animals. Sure. Well so I'd love to talk a little bit about kind of human health. And are there ways of using these kinds of strategies in diagnostics for human illness or in, you know, thwarting human illness. Like how could smell be brought to bear in that situation?

Christophe Duplais:

So when I was a baby in French Guiana, I remember like a skin doctor telling me that you can recognize lots of skin disease because of the just the smell, the, the, the the patient is going to have when they just enter into his office and he will scan — He knew that this one's got Leishmania, this one is malaria. And even the smell of each disease. Again, the challenge is some of the diseases are going to have the same smell, going to produce the same smell. And so in this case is can like... it's kind of hard to tease apart which one's going to be. So we now going to be very selective. But some, some disease is going to be very selective of the smell. Right now, I know that some different companies are trying to, get diagnostic for, for Covid-19. And they've been very successful in UPenn, for example, they designed a a sensor that can using the, the smell of the blood, of the smell of urine, and now they're going to smell the skin, they can discriminate if you've got Covid-19 or not. And so now the the big battle are for example, cancer that when we detect them it's already a stage four, stage five. So ovarian cancer, prostate cancer — when we detect them it's already too late. So having to, like, proactively be able to have early detection of them will be a breakthrough in medicine, for sure.

Laura Reiley:

So I know I, I think there was a piece in the New Yorker maybe last year about a woman who detected Parkinson's, I believe, by smell and I am assuming this is just an anomalous, like, freaky sense of smell. Are there people who... like a super taster kind of thing... who have unique abilities to perceive things like that?

Christophe Duplais:

Absolutely. I think it's like the the absolute ear thing, absolute ear, right? Some musician can detect any notes. Some people have gustatory receptors, like way beyond also there is some super power humans out there. Some time, I'm not quite sure they aware of the ability. In other questions, like now that they are aware of the ability, what they can do with them. And I think this person who can smell Parkinson, I would love, you know, to understand how she can decode that and how she can figure out which smell is associated with the disease itself.

Laura Reiley:

Yeah. All right. Well, so in terms of next steps for you in your work, what are the big questions that you're asking right now?

Christophe Duplais:

So it's funny, you know, like this morning I was actually, with my good colleague Scott McArt and Dani Dryer, working on the small hive beetles. So we got lots of problem with honeybees, and there's lots of of pests. One of them is actually small hive beetles that infest the hives. And we just want to ask this question of not being, I mean —

Laura Reiley:

Are these Varroa mites or —

Christophe Duplais:

They are not Varroa mites. They are small beetles, and they eat the brood, they eat lots of things. And when you get the infestation, it's, it's really, really bad. And right now, they are — we are not quite sure the prevalence of these pests in, in North America. We know the, the, they here for sure. And it's a big problem in the South. Not so much in the North but is coming up. Now the question is like... a simple question, how did you take the hive? What is the smell of the hive? Do they prefer the hive when it's infested or not? Are they preferring honey, honey bees? Or they're going to go for bumblebees? So we try to figure it out what the cue they're looking for, whether it's a long distance cue or a short distance cue to see if we can do better trapping system, because right now we don't know how to deal with them.

Laura Reiley:

Can you run interference? Can you introduce olfactory kind of, bait and switches that, that, make these pests go somewhere else?

Christophe Duplais:

Exactly. Like try to make sure that the the trap is very close. And so they think they go to the hive and they go to somebody else to send a different trap.

Laura Reiley:

Yeah. Oh my gosh. That's that's fascinating. All right. Well so obviously in agriculture the big money is there are five crops that the big... Well let's just call it corn and corn and soy primarily. And then you have wheat and rice. And I guess cotton is probably the number 5 or one of the field crops. Yeah. For field crops. So I mean those are like well, corn I think is something that has a number of, of predators and pests that are problematic, pretty consistently. Are there anything... are there any ideas there that, that, that could be brought, could have, could be erased or eradicated by, I mean, approaches like this?

Christophe Duplais:

So one thing we try to deal with right now, when we talk about precision agriculture, is making sure that we know when the pest or the disease is right here, right. And to do that for, for, insect pests, we track them down by using sex pheromones. So we've got traps. We put the sex pheromones for the, for the of the female that will attract the male. So we trap the male and we know exactly when the population to build up. And then when there was a threshold, when we know that the population is too high, we have to spray. So this timing is very important because some of the crops for fresh market for, for, for corn, for example, because for only one time these pesticides, this insecticide. So they really have to be very careful when to spray exactly. They don't want to have the — they want to have the perfect timing. And to do that we have to make sure that, we can trap the insects based on the sex pheromones very accurately. And we do that only not only for corn, for apple it's the same thing. We're coming up — with lots of crops, we have to track down the insect to make sure that we can monitor the dynamics of either it's the insect that is overwintering here or whether the insect that migrating from the south.

Laura Reiley:

So I know that, that Cornell has kind of a long history in, in this kind of research in, in Geneva. Can you talk a little bit about kind of your predecessors in the Cornell environment?

Christophe Duplais:

So I will say that the big names that we know at Cornell are Jerry Meinwald and Thomas Eisner, one was an entomologist, one was a chemist. They were friends because they were playing music together, and together they are one of the founders of the chemical ecology, the field of chemical ecology. But there's so many other names. We got lots of new generation that comes right after May Berenbaum was one of the first PhD students who cracked down the co-evolution of toxins and adaptation in plant insects. She's a member of Academy of Science. So we got the generation after generation of chemical ecology in Cornell, which is amazing. But again, for agriculture specifically, can can talk about someone that is also, a major figure that not everyone really knows about because it was more the field of agriculture, which is Wendell Roelofs. He was a chemist like me, was like doing organic chemistry and shift completely to, to agricultural chemistry. One thing that he created back then in the 70s, which is like outstanding, he... because of his skills of analytical chemistry and all the entomology physiological part we have, he created something that can help detect the... what the insects smell. So he created a device where you can mount the antenna to electrical wire. And when we put smell in front of this antenna, there is a signaling going through the antenna. So we can record the signal, the electrical signal, and we can figure it out which molecule are detectable by the antenna. By doing that, he was able to detect over 17 insect pest pheromones that are still being used right now in the field to detect insect pests dynamics of migration.

Laura Reiley:

Wow. So it sounds like the idea that organisms communicate chemically has been around for a long time and kind of have been building towards this, you know, defense...defenses and, lures, essentially, you know, the stick or the carrot, I guess. So what are the next, logical questions in this in this field?

Christophe Duplais:

So I'm very interested in chemical ecology, but I'm also very interested in chemical evolution. So understanding like the evolution of the chemistry, the evolution of these pheromones. What does it constrains, the evolution of the, the receptors. What come first? And we can we track down how many these olfactory receptor and molecule combination are the same. Do you always use the same receptor to detect the same smell? All this evolutionary trade off and constrain are very interesting to have a broader understanding of how we can decode better and faster any smell.

Laura Reiley:

Christophe, before we go, if our listenership today has a real interest in this topic and wants to learn more about our sense of smell, do you have any book recommendations?

Christophe Duplais:

Yes, absolutely. I got an amazing book that is not only about smell, but it's about all the cues in the world by any organism. And this book is by Ed Yong. The name of the book is An Immense World, and he's really put yourself in the skin of an organism and how you smell, how you taste, how you see, what you hear. And it's a really amazing book about the perception of any organism in the world and give you an idea of, like, how you can figure it out, how something else smell and see.

Laura Reiley:

Wow. Well, we have whipped through a bunch of minutes here, and I, I could I could go on and on because I just find this such a fascinating topic. But, thank you so much for joining us today. You have been listening to Research Matters from Cornell University. If you'd like to learn more about Christophe Duplais' research, visit the Cornell AgriTech website. If you like this episode, subscribe wherever you get your podcasts and share it with a friend who loves facts as much as you do. Thanks for listening. And remember, when research meets purpose, we move closer to a healthier, fairer world. Thank you.