A group of entomologists headed by Dr Fernando Montealegre-Z from the University of Lincoln, UK, reported the discovery of a new genus and three species of bushcrickets from Colombia and Ecuador in which males produce the highest frequency ultrasonic calls so far recorded from an arthropod.
Supersonus piercei, female. Image credit: Natasha Mhatre.
Bushcrickets are insects known for their acoustic communication, with the male producing sound by rubbing its wings together to attract distant females for mating.
A new genus of bushcrickets, named Supersonus, with three new species (S. aequoreus, S. piercei and S. undulus), has been discovered in the rainforests of Colombia and Ecuador.
The calling frequencies used by most bushcrickets range between 5 kHz and 30 kHz. The nominal human hearing range ends at around 20 kHz. Supersonus bushcrickets have been found to produce the highest ultrasonic calling songs known in nature, with males reaching 150 kHz.
“To call distant females, male bushcrickets produce songs by stridulation where one wing (scraper) rubs against a row of teeth on the other wing,” explained Dr Montealegre-Z, who is the senior author of a paper published in the open-access journal PLoS ONE.
“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. 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 of flight 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 their prey’s movements using echolocation but can also eavesdrop and detect the calls of singing animals like bushcrickets and frogs.
Rainforest bushcrickets 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. Understanding how nature’s systems do this can give us inspiration for our engineered ultrasonics,” said co-author Dr James Windmill of the University of Strathclyde, UK.
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Sarria-S FA et al. 2014. Shrinking Wings for Ultrasonic Pitch Production: Hyperintense Ultra-Short-Wavelength Calls in a New Genus of Neotropical Katydids (Orthoptera: Tettigoniidae). PLoS ONE 9 (6): e98708; doi: 10.1371/journal.pone.0098708
