What's So Hot About Chili Peppers?- page 5 | Science | Smithsonian
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Joshua Tewksbury and colleagues study whether the hot stuff in chili fruit deters bugs that may carry fungus. (Tomás Carlo)

What's So Hot About Chili Peppers?

An American ecologist travels through the Bolivian forest to answer burning questions about the spice

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After Tewksbury paces off the census plot, the team spreads out and begins scouting chilies. Carlo points a laser rangefinder at Tewksbury, who is hovering over a chili plant, so that Carlo can add the plant to a map he's drawing. Tewksbury counts fruits, both ripe and unripe, and assesses their pungency, which is a bit like playing Russian roulette. "I think it's going to hurt," the human capsaicin meter says as he pops a fruit in his mouth. "Ah!" he yelps. (They will test samples more rigorously back in the lab in Seattle.)

Tewksbury scans the plants for fruit-sucking bugs, using his own nicknames. "Red-shouldered beetle mimic," Tewksbury yells, referring to a true bug (order Hemiptera) he once thought was a beetle (order Coleoptera) until an entomologist set him straight. "One, two, three—oh—and red butts!" he says, noticing another insect species that hangs out on the underside of the chili leaves.

During a previous expedition, Levey realized that such bugs may be spreading the seed-killing fungus from chili plant to chili plant. While the rest of the team was out sampling chilies, Levey was stuck in camp, recovering from a bout of intestinal distress. As a distraction, he says, he spent a lot of time examining chilies with a magnifying glass, "and I discovered that a lot of them were pitted with holes from these bugs. When I opened them, I could see traces of fungal infection on the seeds themselves." This fungus was either hitchhiking from fruit to fruit on the proboscis of these bugs, or else the bugs' piercings were simply making it easier for the fungus to infiltrate the flesh.

In any event, the critical test of the theory that capsaicin is an adaptation to fight fungus would come from growing pungent and nonpungent chilies next to each other in the wild to find out if one type does better than the other. Last field season, Tewksbury had hired a man named Don Odon to tend a thousand chili plants at his remote ranch in preparation for the test. But only three plants survived. The rest may have fallen victim to Don Odon's enthusiastic watering regime. If Tewksbury was discouraged when we visited the ranch, he didn't show it.

As we traced our zigzag path southward, he found a huge crop of young wild plants with mild chilies in the town of Yuqueriti. Then we drove on for hours. But when the team woke up the next morning in Charagua, Tewksbury had a "slick" idea. We could race back to Yuqueriti, dig up the mild chili seedlings and haul them several hundred miles to a ranch in the Andean foothills where the plants are all spicy, to learn which are hardier. Tewksbury's enthusiasm can be hard to argue with, and six hours later I would find myself bouncing along in the back of the truck, trying to keep myself and 89 uprooted chili plants from being crushed under a pile of luggage.

Two days later, when we arrive at the ranch in the foothills, Tewksbury observes that the native chili peppers have been "hammered" by drought and cattle grazing. He doesn't think his experimental seedlings would survive in these conditions. He finds another ranch where the owner will allow the team to plant the seedlings on the edge of a cornfield. For a small fee, the owner agrees to tend them. Tewksbury is in high spirits as the team plants each mild chili next to a wild spicy one. When the plants begin fruiting next year, they'll see how many fruits survive and how much fungus they have. Ideally, the team would also dig up spicy plants in the foothills and transplant them near mild plants in Yuqueriti. But this is seat-of-your-pants science, and Tewksbury will have to wait a year to get a more substantial experiment going. "I hope to be working on this system for another 10 to 20 years," he says as he pats soil around the last chili plant. "I can't see myself running out of questions in less than that."

Brendan Borrell wrote about cassowaries in the October, 2008 issue of Smithsonian. He lives in Brooklyn, New York.

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