Show-Me State Times

Rex Cocroft’s groundbreaking research on insect communication is leaping off the pages of academic journals, recently inspiring an episode of a BBC documentary series. His fellow researchers have even taken the rare step of immortalizing his contributions by naming a new species of plant-feeding insects known as treehoppers in his honor.

For more than 30 years, the University of Missouri biologist has studied treehoppers—found on every continent except Antarctica—and how they signal each other by sending vibrations through a plant’s leaves and stem.

“Treehoppers have vibration sensors that detect when their legs move up and down, and they are extremely sensitive to that kind of motion,” Cocroft said. “Sound and vibration are very closely allied in treehoppers, and they experience vibration in the way we experience sound.”

Humans cannot detect the mechanical sound treehoppers make. But Cocroft uses sensors that amplify the signal similarly to how guitars are amplified in musical performances.

“Piezoelectric materials produce an electrical current when under mechanical stress,” Cocroft explained. “A piezo disk is commonly attached to an acoustic guitar's soundboard. The guitar's vibrations become an electrical signal in the piezo, which can be amplified by a speaker to produce sound.”

Treehoppers communicate by vibrating part of their bodies, usually the abdomen, with those vibrations transmitted to the plant stem via their legs. They can mimic cicadas by buckling a part of their thorax to make a clicking sound or shake their abdomen to create songlike sounds that vary in pitch, tone, and volume.

“Treehoppers typically have several different types of signals in their repertoire, and they are good at distinguishing between those and responding appropriately,” Cocroft said. “It’s not what we traditionally think of as an insect sound because the mechanics of producing and transmitting sounds are different. To some people, they sound more like the clicks, chirps, and whistles of birds, frogs or whales.”

Cocroft was first introduced to treehoppers during graduate school after borrowing a recording device originally used for caterpillar sounds. Attaching it to a plant with treehoppers marked his first time hearing them; he described it as incredible.

“With more than 3,000 species of treehoppers worldwide, every species has different songs,” Cocroft noted. “So you don’t know what you’re going to hear until you begin to listen.” He added that plants transmit these vibrations effectively due to their thin, strong, and flexible stems.

Arriving at Mizzou in 2000, Cocroft appreciates teaching while conducting research. “Our students are great,” he said. “The best part about teaching is getting to know them as individuals... It’s fun and satisfying for me to help someone else get to a point where they can make their own discoveries.”

Cocroft’s interest in music began in high school when he learned piano on his grandmother’s instrument. This led him initially toward a music degree before his passion for biology took over after volunteering at the Smithsonian National Museum of Natural History.

His work there allowed him to visit South America where he identified frogs by their sounds—a skill inspired by his musical background. "Communication is such a key part of any animal's behavior," he remarked.

Switching from frog communication studies to insect communication during graduate school aligned with his interest in natural history exploration: "There’s a lot we can still discover about how insects like treehoppers communicate," he concluded.

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