Scientists at the University of Oxford in the U.K. have developed a CT scanning technique that lets them view the inner workings of insects' muscles while in flight.
The intricate movements of a blowfly's muscles—as it flaps its wings 150 times per second—is shown in super slow motion, thanks to a very fast and powerful x-ray machine, the team reports today in PLOS Biology.
"The blowfly's flight mechanism is among the most complex in all of nature," said Oxford associate professor Graham Taylor. "It moves incredibly fast and works on a very small scale. The fly controls its flight using muscles that in some cases are as thin as a human hair. So it presented a real challenge to view and understand."
For a blowfly, like most flying insects, the main muscles that move its wings don't attach directly to the wings. Instead, they attach to the inside walls of the thorax. Two sets of abdominal muscles called "power muscles" (orange and red in the video) can deform the thorax's shape and change its height. This in turn is transmitted to the wing hinge, which amplifies the motion and causes the wings to move up and down and through a range of angles. Smaller steering muscles (green and blue) are designed to fine-tune and tweak the movement of the wings for course and altitude.
These tiny steering muscles, crucial to the fly's maneuverability, are only 3 percent of total flight muscle mass.
So how do you capture these internal motions in something as small and fast as a fly? Answer: By using a large particle accelerator called a synchrotron, in this case one located at the Paul Scherrer Institute in Switzerland. The Oxford scientists worked in close collaboration with scientists from the institute and Imperial College London to develop the scanning technique.
"The fly is placed in a beam of high-powered x-rays and spun on a rotary stage at a high rate of speed," explained Taylor, a co-author of the study. "That allowed us to take x-ray images from all different angles."
The high-powered x-rays provide the very short exposure times required to record the movements of a fast-flapping fly. By capturing different stages of the wingbeat in rapid succession, the scientists could piece together the images to produce a 3-D rendering of the fly's insides.
"It's the same principle as when you go to a hospital for a CT scan, only you remain still and the x-rays are rotating around you," said Simon Walker, who took part in the research as an Oxford postdoctoral researcher. "But in our experiments, the x-ray machine is fixed and the fly rotates instead."
The x-ray images are not the first to capture muscles in motion. CT scanners have long been able to record motion, such as a mouse's lung moving as it breathes. "The key advance is the speed of the motion that we are able to capture," said Walker. "Before, we'd done only things that were moving a hundred times slower than an insect's wings move."
While the scientists studied the high-resolution video to learn about a fly's flight muscles, it will also be used for advanced engineering applications. "The problem the common fly long ago overcame is essentially the same one that engineers now face: producing a large, complicated motion using actuators that are capable of only small, simple motions. This sets up a first step in replicating that."