Katydids, also known as bushcrickets, are known for their acoustic communication, with the males producing sound by rubbing their wings together to attract distant females for mating.
Now scientists from the universities of Lincoln, Strathclyde, and Toronto have located a new genus and three new species of katydids in the rainforests of Colombia and Ecuador that were found to produce the highest ultrasonic calling songs known in nature, with males reaching 150 kHz. The calling frequencies used by most katydids range between 5 kHz and 30 kHz. The nominal human hearing range ends at around 20 kHz. For this reason, the new genus has been named Supersonus.
“To call distant females, male katydids produce songs by ‘stridulation,’ where one wing (the scraper) rubs against a row of ‘teeth’ on the other wing,” said Dr. Fernando Montealegre-Z from the University of Lincoln. “The scraper is next to a vibrating drum that acts like a speaker. The forewings and drums are unusually reduced in size in the Supersonus species, yet they still manage to be highly ultrasonic and very loud.”
“Using a combination of state-of-the-art technologies, we found that Supersonus creates a ‘closed box’ with its right wing in order to radiate sound,” he said. “Human-made loud speakers also use this system to radiate sound. Large speakers radiate low frequencies, while small speakers emit high frequencies. So, these reduced wings are responsible for tuning their calling songs at such high frequencies.”
These insects have lost the ability to fly due to their reduced wing size, so the adoption of extreme ultrasonic frequencies might play a role in avoiding predators, such as bats. Bats can detect the movement of their prey by using echolocation, but they can also eavesdrop and detect the calls of singing animals like katydids and frogs. Rainforest katydids have learned to avoid bats by reducing the time spent singing and by evolving an ear that can detect the ultrasonic echolocation calls of the bats. Although some bats can detect 150 kHz, by singing at extreme ultrasonic frequencies, the katydid calls degrade faster with distance so that a flying bat will find it harder to hear the signal.
“These insects can produce, and hear, loud ultrasonic calls in air,” said Dr. James Windmill from the University of Strathclyde. “Understanding how nature’s systems do this can give us inspiration for our engineered ultrasonics.”
The news species are called Supersonus aequoreus, Supersonus piercei, and Supersonus undulus.
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