Biologist to Study Eavesdropping Parasites

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

Biologist Ximena Bernal believes that the blood-sucking midges use sound to locate a meal. Her recent NSF grant will help her uncover how the midges locate food through sound.

NSF grant will help biologist Ximena Bernal uncover how blood-sucking midges locate food through sound.

The minute they croak for love, swarms of blood-suckers 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 to study how midges use sound to locate their victims.

Ximena (Hee-May-Nah) 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. Since the midge has such a tiny ear, 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 uses plastic tubing and a jar to retrieve midges from croaking frogs for further study.

Bernal uses plastic tubing and a jar to retrieve midges from croaking frogs for further study.

(Photos provided by Ximena Bernal)

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 two or three different species of frog calls, while other midges are generalists and attack any frogs or toads making noise.

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

“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.”

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Biological Sciences

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