X-ray Video Gives Inside 3D Look at Insect Flying Muscles

S. Walker/University of Oxford

A stunning technique involving x-ray imagery has given an insider’s look at the muscles involved in the mechanics of blowfly flight. The research was led by Graham Taylor from the University of Oxford using x-ray equipment at the Paul Scherrer Institute (PSI). The results were published in the open access journal, PLOS Biology.

The blowfly (Calliphora vicina) is able to beat it wings a remarkable 50 times in the blink of an eye. As the wings themselves do not contain any muscle, all of the power is generated from muscles located in the thorax. Some of these muscles are quite thin; no wider than a human hair.

Using the Swiss Light Source at PSI, the researchers were able to penetrate through the tissue in the thorax and distinguish individual muscles associated with flight, focusing on the movements associated with steering. This has not been accomplished previously, as visible light was unable to reach inside the thoracic tissue. Radiographs were taken and were able to see the fly in all directions as it flapped its wings at 150 beats per second.

Professor Taylor stated in a press release:

“The key question is how the fly's tiny steering muscles, which make up less than 3% of its total flight muscle mass, influence the output of the much larger muscles that power its flight. We found that blowflies have evolved a mechanism rather like the differential in a car; whilst the power delivered to the fly's wings on each side remains the same, the fly effectively "brakes" on one side by diverting excess power into a steering muscle specialized to absorb mechanical energy.”

The wing hinge joint, which is arguably one of the most complex in nature, allows the blowfly to perform incredible acrobatics that are far more sophisticated than any manmade machinery. The researchers hope that these videos will provide inspiration for the next generation of flying machinery. 

This video shows the insect thorax reconstructed from tomograms and highlights the external movements of the thorax and the location of the indirect power and steering muscles. This is Movie S1 from the article.

The muscles are shown for the high-amplitude (left) and low-amplitude (right) wings through ten stages of the wingbeat, starting at the beginning of the downstroke. The steering muscles are viewed from the inside of the thorax looking out toward the wing hinge, and other parts of the thorax have been removed for clarity. The view of the low-amplitude (right) wing muscles has been mirrored about the sagittal plane of the insect for ease of comparison. The basalare sclerite is not visible directly in the reconstruction, but its position can be inferred by the intersection of the b1 and b3 steering muscles. See article for labelling of muscles. This is Movie S2 from the article.

Differences in the deformations of the thorax and the movement of the basalare sclerite are shown for the high-amplitude (left) and low-amplitude (right) wings through ten stages of the wingbeat, starting at the beginning of the downstroke. The low-amplitude (right) view has been mirrored about the sagittal plane of the insect for ease of comparison. See article for anatomical details. This is Movie S3 from the article.

Citation for all videos and their captions: Walker SM, Schwyn DA, Mokso R, Wicklein M, Müller T. et al. (2014) In Vivo Time-Resolved Microtomography Reveals the Mechanics of the Blowfly Flight Motor. PLoS Biol 12(3): e1001823. doi:10.1371/journal.pbio.1001823

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