Bruce Tabashnik, head of the University of Arizona's entomology department, says his own intestinal distress at a conference led to collaboration with Mexican researchers on a new "designer toxin" that kills pink bollworms by attacking their guts.

Kelly Presnell / arizona daily star

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There aren't many stories about south-of-the-border intestinal distress that end with a scholarly paper about cotton pest eradication published in the journal Science.

Bruce Tabashnik has spent much of his entomology career studying insects' ability to resist human efforts to kill them.

He is the head of the entomology department in the University of Arizona's College of Agriculture.

Tabashnik says he loves bugs, he really does. They're fascinating, he says. But he also knows some of them are destructive. And, being part of the College of Agriculture and Life Science at a public university, a good bit of work in the entomology department has to do with killing those fascinating subjects if they are annoying taxpayers in the state's private sector.

As old-time Arizonans know, copper was king and cotton was not far behind.

So the most destructive insect on Arizona's cotton crops, the pink bollworm, was pretty much public enemy No. 1.

The tiny first stage of this cotton monster creature is so small you'd probably miss it if it were on the back of your hand. But, once on the cotton boll — the hard, fibrous shell from which a puff of cotton should pop when it's mature — it destroys much of the cotton, preventing it from forming and drastically reducing the boll's yield.

And so it was for years the leading cause of damage to Arizona cotton, says Larry Antilla, director of the Arizona Cotton Research and Protection Council.

Thanks to genetically modified cottonseed, the pink bollworm was increasingly turned into a rare pest since the mid-1990s, says Antilla. Today most of the state's 180,000 acres of cotton are planted in Bt cotton, Antilla says.

The modified seed causes cotton plants to produce a bacterium — Bacillus thuringiensis, aka "Bt" — that produces a toxin that attacks a protein in the gut of pink bollworms and kills them. At least most of them.

Tabashnik says old-style pesticides were effective, if you literally "drenched" the cotton plants, but that was expensive financially and environmentally.

So, the Bt cotton approach to wiping out the pink bollworm was a winner — cutting down on crop loss, reducing pesticide expenses and doing it without hurting most beneficial insects.

But every entomologist knows it's only a matter of time before any bug killer meets a better bug.

Cotton growers and agricultural entomologists expected resistance, and quickly, Antilla says. But it didn't happen with Bt cotton. Resistant pink bollworms were rare.

It was something of a miracle seed. Still, Tabashnik said, a member of a UA entomology team working on resistance collected some of the resistant pink bollworms and kept the breed alive in the lab as they became more and more scarce in the field.

Then, Tabashnik was in Mexico for a conference on Bt toxins. He was there to listen to other experts' presentations and to give his own talk.

He recalls being deathly ill with the dreaded traveler's intestinal ailment, waiting for what seemed like forever to give his presentation — his guts doing flip flops, he barely knew where he was, thanks to a 105-degree fever.

In a cruel twist, he recalls, speaker after speaker talked in excruciating detail about fascinating bacteria and how they raise hell in the guts of insects.

Tabashnik toughed it out until he could do his presentation and then, he says, "I pretty much collapsed."

To the rescue came a couple of Mexican researchers who offered to take him to a doctor. His professional duties done, he said, "Yes." They not only took him to a doctor, but saw him back to health.

"They took care of me," he says. "I felt grateful. What can I do for you? Anything."

His rescuers were working on understanding how the mysterious Bt actually does its deadly work on insects at the molecular level.

And they learned that Tabashnik and his colleagues on the UA team — Tim Dennehy and Yves Carriere — had some Bt-resistant pink bollworms they had rescued from a cotton field in 1997 and continued to breed in the lab, many generations later.

They struck a deal to use the UA resistant pink bollworms to try out a new treatment they had developed and hoped the resistant pink bollworms could not work around.

To put it in laymen's terms, Tabashnik says, the pink bollworms work with the Bt toxin like a lock and key. Normally, the key — the toxin — fits the lock — in the bug gut, destroying the tissue. But in the resistant pink bollworms, the lock doesn't fit the key.

The Mexican researchers — Mario Soberón and Alejandra Bravo at the Universidad Nacional Autonóma de México — have come up with a "designer toxin" that does an end run around the resistant bugs' defense.

Tabashnik says there's talk of commercial applications, possibly an even better way of fighting the cotton pest.

The researchers have applied for an international patent on the development, in cooperation with the UA and Tabashnik.

Antilla says southwestern U.S. states and those in northern Mexico are trying to eradicate the pink bollworm from cotton crops.

He says their death sentence won't fall to the Endangered Species Act because the pink bollworm is not a natural resident of this part of the world.