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Warmer Temperatures Remix These Insects' Love Songs — But Females Still Find Them Sexy

Researchers at SLU eavesdropped on treehopper love songs to better understand how climate change might affect mating in this insect species.
David Kovaluk | St. Louis Public Radio
Researchers at SLU eavesdropped on treehopper love songs to better understand how climate change might affect mating in this insect species.

The insects in your backyard are having conversations at this very moment — but you can’t hear most of them.

Many communicate by producing tiny vibrations that travel through plant leaves and stems, like Morse code. 

St. Louis University researchers are studying treehoppers, insects common to Missouri and Illinois, to understand how climate change might affect their mating songs. Based on years of research, they report male treehoppers change their songs depending on temperature, but females still find the new songs attractive. 

Kasey Fowler-Finn has spent the past decade studying these curious insects, which resemble little dinosaurs. The assistant professor of biology at St. Louis University is particularly interested in the ways treehoppers talk to each other. 

“There’s this whole world of communication out there that we’re not privy to,” Fowler-Finn said. “The sounds that treehoppers produce using these vibrations are really beautiful.”

When a male treehopper is hunting for a mate, he serenades females with vibrations that move through the plant. If a female is interested, she’ll vibrate back—essentially, an insect game of Marco Polo. 

Treehoppers congregate on a plant stem in this file photo from 2015.
Credit Kasey Fowler-Finn | St. Louis University
Treehoppers congregate on a plant stem in this file photo from 2015.

Fowler-Finn suspected treehopper love songs might change depending on temperature, which could affect whether the species survives as the climate changes.

If the songs did change, she wondered, would females even recognize them?

‘We’re having a conversation with the insect’

Fowler-Finn and SLU master’s student Dowen Jocson decided to put these questions to the test by building a series of custom incubators using plywood, $10 Ikea shelves and salvaged paving stones. 

But those incubators were just one piece of their setup. To eavesdrop on treehoppers, you need lasers. 

The insect sits on a piece of reflective tape inside the incubator and produces his mating song. The research team then shines a laser beam on the tape, which measures the velocity of the plant stem’s vibrations. 

The equipment is extremely sensitive, Fowler-Finn said.

“It turns out if you talk on one end of the room, even if you whisper, you can hear it in your recording,” she explained. “It needs to be really quiet if you want to hear everything the insects are saying to one another.”

All their hard work eventually paid off. 

Males produced different songs as the temperature changed, just as Fowler-Finn suspected. At high temperatures, males produced higher-frequency songs and vice versa. 

The research team recorded those songs and played them for female treehoppers — then noted how many times the females responded. 

“Essentially, we’re having a conversation with the insect,” Fowler-Finn said. “We play back a bunch of different signals and ask her how much she likes each one.”

As male treehopper songs changed across temperatures, females still recognized them as their own species and vibrated in response.

“When we saw that, we were like, ‘Wow, this is awesome,'” said Dowen Jocson, who is now a Ph.D. student at Washington State University. “I was just surprised that it worked.”

Credit File photo | Veronique LaCapra | St. Louis Public Radio
Kasey Fowler-Finn, left, records treehoppers in the lab with master's student Dowen Jocson in this file photo from 2015.

But recognizing a potential mate is just one piece of the puzzle, Jocson said. At higher temperatures, for instance, treehoppers might not be able to mate or produce viable eggs.

Still, she said the results suggest the treehoppers—and possibly other insects that communicate with vibration—may still be able to mate successfully as the climate changes. 

“If females are able to recognize the males across fluctuating temperatures in the field and lab, then they may be able to adapt as the environment warms up,” Jocson said. “That gives us hope.”

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Shahla Farzan was a reporter at St. Louis Public Radio. Before becoming a journalist, Shahla spent six years studying native bees, eventually earning her PhD in ecology from the University of California-Davis. Her work for St. Louis Public Radio on drug overdoses in Missouri prisons won a 2020 Regional Edward R. Murrow Award. 

Send questions and comments about this story to feedback@stlpublicradio.org.