Fruit Flies Use Not Just Eyes, But Antennae To Control Air Speed
April 11, 2014

Fruit Flies Use Not Just Eyes, But Antennae To Control Air Speed

Brett Smith for - Your Universe Online

Geneticists may know the fruit fly genus Drosophila as go-to organisms for their research, but a new study focused instead on how these insects go into a sort of “cruise control” while in flight.

Using bursts of air and sophisticated software, the new study revealed that fruit flies use a combination of vision and their wind-sensitive antennae to maintain a constant flight speed relative to the ground. The new study, published in Proceedings of the National Academy of Sciences, is based on previous research from the 1980s, according to study author Sawyer Fuller.

"In the old study, the researchers simulated natural wind for flies in a wind tunnel and found that flies maintain the same groundspeed—even in a steady wind," said Fuller, a post-doctoral bioengineering researcher currently at MIT.

For the new study, researchers said they wanted to use potent blasts of air instead of the subtle breezes used in the earlier experiment. The quick gusts, which moved down the tunnel at the speed of sound, were designed to see how the fly deals with rapidly changing winds.

The researchers saw their flies act in a counter-intuitive manner – speeding up when the wind was coming from behind and slowing down into a headwind. In each case the flies gradually recovered to reestablish their original groundspeed, but the first response was a bit mysterious, according to the researchers.

"This response was basically the opposite of what the fly would need to do to maintain a consistent groundspeed in the wind," Fuller said.

The scientists said they presumed that flies, like people and most other animals, used their eyesight to gauge their speed in wind, speeding up and slowing their flight based on what they saw. However, the researchers were also wondering about the in-flight purpose of the fly's wind-sensing antennae.

To find their answer, they delivered powerful gusts of wind to both normal flies and flies without antennae. The flies devoid of antennae still raised their speed in the exact same way, but they only sped up half as much as the flies whose antennae remained intact. Furthermore, the flies without antennae were not able keep a constant speed, drastically switching between acceleration and deceleration. The findings indicated that the antennae were offering wind data that was essential for speed control, the researchers said.

To determine the role of eyesight, the study team projected visual images to trick the flies into thinking there was no increase in wind speed, despite what the antennae were sensing. When the researchers delivered strong winds to flies in this situation, the insects slowed and were unable to recover to their original speed.

"We know that vision is important for flying insects, and we know that flies have one of the fastest visual systems on the planet," said study author Michael Dickinson, a bioengineering professor at Caltech. "But this response showed us that as fast as their vision is, if they're flying too fast or the wind is blowing them around too quickly, their visual system reaches its limit and the world starts getting blurry."

"A challenge here is that vision typically takes a lot of computation to get right, just like in flies, but it's impossible to carry a powerful processor to do that quickly on a tiny robot,” he added. “So they'll instead carry tiny cameras and do the visual processing on a tiny processor, but it will just take longer. Our results suggest that little flying vehicles would also do well to have fast wind sensors to compensate for this delay."