Scientists crowded into Corson/Mudd Auditorium to listen to the physicist lecture about, ironically, insects. On Monday, Jan. 25, 2010, Prof. Itai Cohen discussed the results of his research with Cornell entomologists in a seminar, entitled “Flight of the Fruit Fly.” In a blend of physical and biological science, Cohen described the physics of insect flight.
“In full disclosure, I know very little about insects,” the physicist admitted.
Cohen’s physics lab studies the movements of Drosophila melanogaster, the typical fruit fly. In other concentrations, scientists utilize the fruit fly as a model organism. In genetics, the fruit fly provides model examples of reproduction, crossing over, and mutation. For this reason, biologists have successfully mapped the entire fruit fly genome.
However, Cohen the physicist studies the physical science of the fruit fly, particularly, how the fruit fly obtained, maintains, exercises, and regulates flight.
According to Cohen, since the 1950s, many biologists have studied insect flight, but “still to this day we have a very poor understanding about the mechanism of how insects maneuver.” Early attempts to study insect flight utilized impractical approaches, including, as Cohen described with a laugh, a fruit fly on a tethered cord.
“We’re trying to understand the relationship between the wings and the aerodynamics,” he related. “We have three fast video cameras.”
Cohen and the team release individual fruit flies into sealed test areas, surrounded by three cameras attached to laser initiation systems. When a fruit fly crossed a laser, the system triggered all three cameras, capturing 100 frames per second of fruit fly flight.
“So we just collect films, lost of films,” he joked, recognizing that his research leads to exceedingly long hours of flight footage. “Then we study the films to study the maneuvers.”
Cohen offered an example of flight footage, asking the audience, “Can you see the difference how these wings move?” When none of the entomologists answered, he responded, “And that’s the problem.”
Unlike early experimenters, Cohen’s team uses computer programs to study of “ballet” of fruit fly flight, measuring infinitesimally small variations in wings shape and speed. From the data and visual observations, the team can infer the effects consequences of minor changes.
Cohen fancies himself a prisoner in Plato’s “Allegory of the Cave,” which describes a metaphor about the perception and understanding of what is reality. Using the cameras, Cohen’s team isolates images of flight silhouettes to interpret the structure of the flight. Like the prisoners in the famous allegory misinterpret their shadows, Cohen’s team may misinterpret the shadowy images, but when successful, the group produces a three-dimensional, computerized model, “FrankenFly.”
According to Cohen, FrankenFly is not as graceful or attractive as the real thing, but in terms of physics, FrankenFly correctly describes the maneuvers of fruit fly flight.
Using FrankenFly, the group determines how the insects perform their flight patterns. For instance, aero-planes must bank to move right or left, but according to Cohen, fruit flies move left or right in a hovering motion. One wing cuts through the air; one wind pushes in the opposite direction. The coordination of these actions allow the fruit fly to hover left to right without turning its body.
In addition, Cohen’s research shows that insects utilize a fundamental “rowing motion,” like oars on a ship or like the fins of a fish. This observation supports the Swimming-to-Flight Transition Hypothesis, which suggests that insect flight actually originated in water. Moreover, Cohen’s data indicates that the type of air (or fluid) surrounding the insect does not affect the rate of flight.
While much remains unknown about the physics of fruit fly flight, Cohen and his FrankenFly are analyzing the mysteries of of living flight on a scale that no other lab is.