MADDIE SOFIA, HOST:
You're listening to SHORT WAVE from NPR.
Hi, everybody. Maddie Sofia here with NPR food and farming reporter Dan Charles. Hiya, Dan.
DAN CHARLES, BYLINE: Hi, Maddie.
SOFIA: Dan, I'm hoping you are here with more bug-related reporting. It has been a while since we've tackled the invasive species beat together.
SOFIA: You've told us all about invasive lanternflies, other insect pests that eat farmers' crops. You've answered our listeners' questions about invasive species.
CHARLES: Yes, Maddie. And I am here with another bug story.
CHARLES: But this one is totally different.
SOFIA: Oh, my God. I'm so ready, Dan. Let's go.
CHARLES: It's an incredible battle. In this corner, we've got billions of little, pink caterpillars, tiny things from across the Pacific...
CHARLES: ...Love to chow down on seeds inside bolls of cotton - incredibly destructive. And on the other side, in the other corner, we've got cotton farmers in the southwestern U.S. They've cooked up a wild scheme to wipe out the bug, eradicate it from Arizona, Texas, New Mexico and Mexico.
SOFIA: Dan, are you sure you're not a wrestling announcer?
CHARLES: Oh, yeah.
SOFIA: OK. OK.
SOFIA: All right. That does sound like a wild battle, Dan, and also, like, kind of impossible to eradicate it.
CHARLES: Yeah. Like, who actually completely gets rid of an invasive species?
CHARLES: So that is what Bruce Tabashnik thought. He's an entomologist. And he studies exactly this sort of thing at the University of Arizona.
BRUCE TABASHNIK: I guess, as a biologist, as an evolutionary biologist, someone who studies evolution of resistance in insects, the first thought is always that the insect will adapt. There's something missing in your process if you think you're going to overcome the insect.
SOFIA: I say that every day when I wake up, Dan, you know, you know?
SOFIA: OK. OK. So who won this battle, the farmers or the bugs?
CHARLES: Patience, Maddie, we'll get there.
CHARLES: But I'm going to tell you the whole story from the beginning. And it involves genetically engineered crops. It involves scientists dumping billions of sterile bugs out of airplanes, sex pheromones.
CHARLES: And Bruce Tabashnik is still kind of amazed at how it turned out.
TABASHNIK: I think it's stunning. And that's one of the reasons I want people to know this story. Right now, very few people know about it.
SOFIA: So today on the show, the fight to eradicate a tiny, pink caterpillar decimating cotton crops in the southwestern United States. You're listening to SHORT WAVE from NPR.
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SOFIA: All right, Dan, what is this little, pink bug? What's it about?
CHARLES: OK. It's called the pink bollworm. And I found a guy who has seen more of these little creatures than he ever wanted to.
KARL BUTTON: My name is Karl Button (ph).
CHARLES: Karl is a cotton farmer in Arizona. He rents land from people in the Gila River Indian community. Now, 30 years ago, he would go out to his fields. He would pick out some cotton bolls, which are the little pods where the cotton fiber grows. He would cut them open looking for these tiny, little, red worms.
BUTTON: And you could find three or four worms in the same boll. And they were all different ages, different generations. And that was a really, really serious problem.
SOFIA: Dan, why is that such a problem, just because they're going to do so much damage to his crops?
CHARLES: Right. There's so many of them. But also, because these different generations, he knows that in order to kill them, he was going to have to keep spraying this field with some pretty nasty chemicals for weeks into the future. See; those pesky little insects, they spend the first part of their lives tucked away inside these cotton bolls and then, right after that, in cocoons in the soil. And that whole time, Karl could not get at them. You know, they were protected. His only chance to kill these pests was later when they emerge as moths flying around looking for mates.
BUTTON: This one here will be out in a week. This one here will be out in 14 days. This one here will be out in 21. This one here is going to take until the 28th. I got to have this hill painted, you know, for 28 days with enough to kill a frigging dinosaur.
SOFIA: Wow. OK. So at this point, his choice, Dan, is either spray like crazy or flat out lose his crops?
CHARLES: Yeah, pretty much. I called his pest control adviser, a guy named Tom Montoya (ph). He is the person who works with a lot of different farmers like Karl Button and tells them what they have to do to control their insects. And he was saying the pink bollworm was a terrible problem all across this region for cotton farmers, especially in the 1980s and the 1990s.
TOM MONTOYA: It was ugly. Basically, it was - people were spraying 12, 13, 14 times. Some guys were spraying more than that, some guys were less.
CHARLES: That's 12 or 13 times in one growing season.
CHARLES: And, you know, fun fact, Maddie, a lot of them were doing this with airplanes flying in the middle of the night (laughter) because that's when the moths come out.
SOFIA: So on top of needing chemicals for just this one pest, they're flying at night, which seems, you know, maybe kind of dangerous to me, not to mention pretty expensive?
CHARLES: Right. And the thing is, it didn't even work very well.
MONTOYA: People went to bed, lost farms, took a lot of financial damage. And there wasn't an end in sight.
CHARLES: No end in sight until about 25 years ago. The tide starts to turn because cotton growers got a new weapon against the pink bollworm. And the weapon is called Bt Cotton.
SOFIA: Oh, yeah, Dan, we talked about this the last time you were on the show, this cotton that's been genetically modified. It has a gene that's been taken from a kind of bacteria, Bacillus thuringiensis. And it makes the cotton plants poisonous to certain insects, right?
CHARLES: Yeah, exactly. The original GMO, right? And it - for the cotton farmers, it worked so well.
MONTOYA: It was a salvation.
SOFIA: But, Dan, last time, you were telling us that Bt crops aren't working so well anymore, that the insects are becoming resistant to Bt because farmers have been overusing it in a lot of places.
CHARLES: Right. And that is still true. And it was a risk for the pink bollworm. In fact, in India, a new strain of the pink bollworm emerged that is immune to Bt. But this story I'm telling you today is a kind of counterexample because in the southwest, cotton growers really did the right thing. Along with the Bt cotton, they planted these so-called refuges of non-Bt cotton just so they wouldn't have a situation where the Bt was everywhere, and then the only bollworms that survived were those few rare ones that were immune to it.
SOFIA: Right, because if there's still plenty of non-Bt cotton, lots of regular pink bollworms are surviving. And that resistant strain won't have the opportunity to become, you know, the only bug in town.
CHARLES: That's right. That's right. Now, the thing is, even though farmers were planting those refuges and there was no resistant pink bollworm emerging, Karl Button says some of these farmers were not happy about it because, you know, first of all, they're paying for the Bt cotton, which costs them a lot of money. And then they still had to plant these refuges, which were basically pink bollworm nurseries, you know, keeping some of the enemy alive so they didn't all become resistant.
BUTTON: So there was a push on to find, you know, a way to just eradicate the pest.
CHARLES: They said, we think we can wipe it out entirely. And part of their plan for doing this was planting completely Bt cotton.
SOFIA: I mean, Dan, that sounds like a recipe for creating a strain of insects that's resistant to Bt.
CHARLES: Yeah, exactly, the thing that, you know, the refuges were supposed to avoid. So this is what Bruce Tabashnik is thinking, you know, that entomologist at the University of Arizona.
TABASHNIK: My stomach was turning. And I was trying to figure out how I was going to tell these guys, no, no, don't do this.
CHARLES: But here, we get to a twist in the story because the cotton growers had another weapon in their arsenal, sterile pink bollworm moths.
SOFIA: Oh, yeah. I know a little bit about this because we did an episode about it. It's an insect control technique that a couple of scientists from the USDA pioneered decades ago to control another tricky insect, screwworms.
CHARLES: That's right, Maddie. And the thing is, they already had some practice doing this with pink bollworms, too, to keep the pest from spreading to other parts of the country. So the farmers in Arizona were saying, look; Bt has reduced our pink bollworm population so much, now we can just overwhelm them with these sterile insects and wipe them out. So they came to Bruce Tabashnik, our skeptical scientist. And they asked him to do some computer simulations of this, calculate how likely it would be to succeed.
TABASHNIK: We ran the simulations. And pretty much, no matter how we tweaked it, it always worked.
SOFIA: So these computer models showed that they could completely eradicate the pink bollworm if they planted all Bt cotton and also released these sterile moths?
CHARLES: Right. Yeah. Basically, in his simulations, no resistant strain of pink bollworms emerged because the sterile moths basically had replaced the refuges. Any of those rare resistant moths, you know, that emerged able to survive the Bt cotton, instead of mating with other survivors and producing resistant offspring, they mated with these sterile moths instead and produced no offspring.
SOFIA: Right. Right.
CHARLES: So eventually, you know, Bruce said, OK. I guess it'll work. And he went along with the farmers' eradication plan. And it got launched in 2006.
So as this gets underway, what are you thinking?
TABASHNIK: Honestly, even though - I should tell you, even though the simulations said it would work, I guess, in my heart of hearts, I still didn't think it would work.
SOFIA: I get that, Dan. I mean, I've had these days thinking, all right, this is what my calculations say will happen. But I must have screwed this up somehow. I must be missing something. It's like a classic scientist mentality.
CHARLES: Right. So - you know, with doubt in his heart...
CHARLES: ...They went ahead with this. The cotton farmers planted all Bt cotton. The USDA's insect factory rolled out as many sterile moths as it possibly could.
TABASHNIK: Over the course of the eradication program, more than 11 billion sterile pink bollworm moths were released by airplanes over every cotton field in the state of Arizona.
CHARLES: Yeah. And to see whether it was working, they set up a network of pheromone traps. You know, these are traps with a scent that female pink bollworms release to attract males. You know, so basically, you know, the pink bollworms flock to these traps if they're there. And if you were making a graph to show the number of insects caught in these traps over the years, the line dropped like it was falling off a cliff.
TABASHNIK: So it went from over 600,000 to one from 2006 to 2012. And then 2013, '14, '15, '16, '17 and '18, I can say '19 and '20 now, all zero - zip, zilch, nada, bupkis.
SOFIA: (Laughter) The scientific terms, Dan, the scientific term.
CHARLES: (Laughter) Technical, yeah.
SOFIA: OK. So his computer simulations were right. But, I mean, Dan, come on, is it really gone, gone?
CHARLES: (Laughter) It seems like it. In 2018, the USDA declared the pink bollworm eradicated in the southwest. Cotton growers basically don't have to worry about it anymore. The campaign wound down. They're not dropping sterile moths anymore. But the traps are still out there to detect any of the insects that might have survived or somehow, you know, caught a ride in from somewhere else because, you know, that pest control adviser we heard from, Tom Montoya, he is still on guard.
MONTOYA: There's got to be one out there. I mean, you just can't forget about it. I mean, it's a horrible pest.
SOFIA: I'll tell you what, Dan, I identify with Tom's anxiety, for sure, for sure. So is there a lesson in this apart from, you know, don't trust your heart, trust the computer?
CHARLES: (Laughter) Well, Bruce thinks there is. He and some colleagues just published a paper about it in the journal PNAS. And he says this really only happened because they were able to combine these two different powerful tools, the Bt cotton and the sterile moths because neither one of them by itself would have worked.
SOFIA: Scientific collaboration, Dan, that's what it's all about, you know?
CHARLES: Absolutely, Maddie - and in journalism, too.
SOFIA: That's right. That's right. All right, Dan, thank you so much for coming on the show to give us some good news today. We appreciate you, as always.
CHARLES: Thank you, Maddie. It's always fun to be here.
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SOFIA: This episode was produced by Thomas Lu, edited by Gisele Grayson and fact checked by Ariela Zebede and our new intern Rasha Aridi. Welcome, Rasha. The audio engineer for this episode was Patrick Murray.
I'm Maddie Sofia. And you're listening to SHORT WAVE from NPR.
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