Insects are making sounds the human ear can’t hear. One Midwest scientist is listening

Most people probably hear buzzing and chirping when they imagine what a bug sounds like, but there are thousands of insects that humans can’t hear.

Rex Cocroft has made a career out of capturing the live performances of one species – treehoppers – to better understand how they communicate. The University of Missouri professor of biology, who studied music before science, attaches tiny microphones to a silk plant stem on his desk to demonstrate.

“So this plant is humming with tree hopper sounds,” he said. “Most of those are actually males singing to each other.”

With the microphones connecting to a small speaker, a melody of low drones and crackling becomes audible. It’s coming from the vibrations of thorn-like bugs that live on the plant’s stem.

For the past 30 years, Cocroft has been a pioneer in the study of insect vibrational communication and the larger field of biotremology – which focuses on the overall production, reception, and behavioral effects of animal vibrations. His work has helped scientists better understand how these insects communicate. And with more than 3,000 species of treehoppers across six continents, there might be a lot being said.

“Most of the sounds out there have never been heard by humans, and you can literally go into a backyard in Missouri and hear a sound that no one has ever heard before,” he said. “And it might be something rather strange and interesting that no one has ever heard before.”

Now more researchers are studying insect vibrations to find new and practical applications. Researchers at Oregon State University, for instance, are using robots to mimic insect sounds to protect vineyards from pests. Washington State University researchers have looked into protecting pear trees from a pest species called pear psylla by disrupting their mating vibrations and reproduction rates.

While Cocroft is not solely responsible for the growth of his research field, many of those scientists have credited Cocroft for his contributions and personal impact.

Influence both near and far

At St. Louis University, Kasey Fowler-Finn and her colleagues are trying to understand how climate change could impact insect populations.

“We look at how it affects the rates of mating, how it affects how they sound, and whether they can still detect each other, even though temperature makes animals sound different,” said Fowler-Finn.

They do this by using the chirping rates of crickets as a sort of thermometer, since muscle vibrations are faster at hotter temperatures.

Biotremology has grown over the years, but it’s still a relatively small research community. “We all kind of know each other,” said Fowler-Finn.

Fowler-Finn’s post-doctoral research advisor was Cocroft. She also considers him a mentor; one who’s helped develop inexpensive equipment and software to make the field more accessible for researchers in countries where resources and funding are limited.

She said Cocroft has even helped her students build equipment to record and process their own research.

“Truly some of my projects would not have been possible without his assistance and feedback,” she said “He just has a real mind for figuring out the exact way to design experiments to get at the questions he is asking.”

Rafa Rodríguez also studied with Cocroft, nearly 30 years ago. He now researches insect communication, along with the memories and predatory behavior of spiders at the University of Wisconsin at Milwaukee. That research was inspired in part by the first time he heard treehoppers, said Rodríguez.

“That just blew my mind,” he said. “It was like the first time you go snorkeling underwater and then this whole new universe, this whole new dimension of color and corals, kind of opened up. It was like that, but in sound.”

Like Fowler-Finn, Rodríguez said Cocroft has been generous with his time and expertise. He’s done a lot of outreach with researchers in Central and South America, where many species of treehoppers can be found, to share simple methods to access their signals and other information.

“That dissemination that’s happening here in the Midwest is also beginning to happen throughout Latin America, mainly thanks to Rex’s efforts,” said Rodríguez.

Cocroft’s work has also inspired researchers far beyond the Midwest. That includes Sam J. England, a postdoctoral scientist at the Natural History Museum in Berlin, Germany.

Like others, England has learned a lot from Cocroft – from his research contributions to even sharing his specimens. “There’s very few people that rival him,” he said.

When England and his team discovered a new species of treehopper in Costa Rica, they named it Cladonota rex in honor of Cocroft.

“He’s really fleshed out this field in a way that certainly deserved acknowledgment. So it was kind of my way of saying thank you to him for providing me with all this background information,” said England.

Cocroft is humble about the recognition. And he points out that, so far, researchers have only found the one, single Cladonota rex.

“I don’t know if there’s any chance for me to go out and see one, but it’s a beautiful insect,” he said. “And it was an honor to have it named after me.”

This story was produced in partnership with Harvest Public Media, a collaboration of public media newsrooms in the Midwest. It reports on food systems, agriculture and rural issues.

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