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Fall 2013

Biologist to Study Eavesdropping Parasites

by John Davis

Biologist to Study Eavesdropping Parasites

Ximena Bernal receives $508,000 NSF grant to study how midges locate their victims.

Midges Swarm Around Frogs

According to Bernal’s research, the midges use sound to find their food source, swarming around the frogs and toads as they call out to potential mates.

The minute they croak for love, swarms of bloodsuckers attack.

Male frogs and toads in Panama call out to potential mates during the rainy season. Frog-biting midges eavesdrop on the party line and have evolved the ability to track their hosts through sound. Now a Texas Tech University biologist will use a $508,000 grant from the National Science Foundation for a four-year research project to study how midges use sound to locate their victims.

Ximena Bernal, an assistant professor of biology and a research associate at the Smithsonian Tropical Research Institute, said that while mosquitoes use carbon dioxide and other chemical cues to find hosts, the midges use sound to find a food source.

Questions remain whether the insect is actually hearing the frog’s call, and Bernal hopes to solve this mystery with her research. The study likely will reveal an evolutionary innovation for hearing in this group of insects, she said. Understanding the midge's tiny ear could lead to advancements in hearing aid technologies for humans.

“When animals send signals to attract mates, these signals make them highly vulnerable to eavesdropper predators and parasites,” she said. “So, male frogs signal to attract females, but the midges are listening in. This is an excellent system that shows how some animals exploit other species’ communication systems.”

bernal collecting midges on frogs

Bernal hopes the study will explain how these insects evolved the ability to hear the frog call as well as which midges hear which frogs’ calls.


Along with understanding the midge’s tiny ear, Bernal hopes to explain how these insects evolved the ability to hear the frog call as well as which midges hear which frogs’ calls. Preliminary evidence suggests that some species of midge only hear the calls of two or three species of frog, while other midges are generalists and attack any frogs or toads making noise.

At the site of her study in Panama, Bernal said about 12 species of frog-biting flies live in the same area, listening in on the calls of about 25 species of frogs and toads.

“All ears of the midges are different,” she said. “How each ear is different may be related to the type of frog on which the midges feed. Overall, this project will provide insights into eavesdropping on other species of animals, a common and widespread behavior that has received little attention.”

By examining evolutionary innovations in insect hearing, this study could also have implications for microphone design, bioacoustics, and the co-evolution of sexual and exploitive communication.

Ximena Bernal

About the Researcher

Ximena Bernal is a professor in the Department of Biological Sciences in the College of Arts and Sciences.

Bernal’s main research goals are to understand the evolution of heterospecific eavesdropping and establish the role of natural selection in constraining the evolution of mating signals.

Learn more on the Bernal Lab website.


John Davis is a Senior Writer in the Office of Communications & Marketing at Texas Tech University.

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Nov 24, 2015