Lots of hawkmoths rub genitals to jam bat sonar

"Before now people thought ultrasound usage in insects was very restricted to certain groups, but it looks much more complex than that," says Akito Kawahara. (Credit: Johan J.Ingles-Le Nobel/Flickr)

Hawkmoths have been using their genitals to jam the calls of bats for millions of years. Now, research shows that sonar jamming, one of the insect world’s most sophisticated defense mechanisms, is more widespread than previously thought.

Radar jamming is commonly used in human warfare, allowing pilots to render themselves invisible. By unraveling the evolution of a similar defense from hawkmoths, researchers hope to get a better understanding of nocturnal biodiversity and improve human uses of sonar.

Close up of Hogweed hawkmoth (Hippotion boerhaviae) perching on old wood.
Close up of Hogweed hawkmoth (Hippotion boerhaviae). (Credit: iStockphoto)

Until now, the function and evolution of sonar jamming remained largely a mystery, says lead author Akito Kawahara, assistant curator of Lepidoptera at the Florida Museum of Natural History at the University of Florida.

“Before now people thought ultrasound usage in insects was very restricted to certain groups, but it looks much more complex than that.”

For a new study published in the Proceedings of the National Academy of Sciences, researchers scoured jungles and forests from Borneo to the Amazon, collected moth specimens at 70 sites in 32 countries, and conducted field-based echolocation and lab experiments using more than 700 moths. Of 124 species, nearly half generated ultrasonic sounds with their genitalia.

Researchers also built an evolutionary tree for hawkmoths based on the fossil record, which reveals that the first ultrasound-producing hawkmoths arose in the late Oligocene period about 26 million years ago, after the origin of tiger moths.

Tiger moths, too

Originally thought to be the only major moth group to use sonar against bats, tiger moths produce ultrasonic sound using tymbals, a vibrating membrane located on the thorax, rather than their genitals.

“Our evolutionary tree demonstrates that sonar jamming and the ability to hear bat attack calls evolved twice during the Miocene after the radiation of insectivorous bats,” Kawahara says.

For the study, researchers Kawahara’s hawkmoths against big brown bats in field and lab experiments that tested the function of hawkmoth antibat ultrasound. In one experiment, study researchers played pre-recorded bat attack calls to study how moths responded.

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The findings show that the moths’ acoustic defense was immediately and consistently effective, while bats that failed to capture sound-producing hawkmoths often performed catching behavior without subduing prey.

The evolution and maintenance of ultrasound production in these groups might be driven by response to predators other than only bats, such as ultrasonically sensitive rodents, shrews, and primates, Kawahara says.

“This is just the beginning—we are trying to chip away at what goes on with nocturnal insect biodiversity.”

Jesse Barber, assistant professor of biology at Boise State University, is coauthor of the study.

Source: University of Florida