WESTNEAT, M.W.; BETZ, O.; BLOB, R.; FEZZAA, K.; COOPER, J.; LEE, W.K.: A new view of insect biomechanics: Using synchrotron phase-enhanced x-ray imaging to study insect respiration, locomotion, and feeding

Biomechanical studies of living animals are often limited by the inability to see inside the animal during a behavior of interest. X-ray cine allows visualization of skeletal mechanics in mid-sized vertebrates, but the motion of internal structures of small animals during activity has largely remained a mystery. We used 15-25 keV x-rays from an undulator at the Advanced Photon Source at Argonne National Laboratory to obtain x-ray phase-enhanced videos of insects during tracheal respiration and movements of the limbs and jaws. The x-ray source is a 3rd generation synchrotron facility that has a small source size, allowing phase-enhanced imaging. Insects remained alive for up to 10 min during the x-ray exposure. A CdWO4 scintillator (for x-ray to visible light conversion) was placed 400 mm behind the samples to enable the phase related edge enhancement effect. A cooled CCD video camera with a telescopic lens focused on the scintillator was used to capture video at 60 Hz. The field of view was 2.4 mm x 3.1 mm. We found that insects ranging from beetles to crickets, ants, and flies used a rapid tracheal pumping mechanism for respiration. Respiration was observed in which major tracheae were collapsed and reinflated in 1-2 sec in the thorax and head. Current models of circulatory hemolymph flow do not explain this mechanism of respiration. We also analyzed the detailed motions of mouthparts to test hypotheses of mouthpart function in beetles and ants, and studied the internal mechanisms of the limb joints in beetles. U.S. D.O.E. Office of Science Contract No. W-31-109-Eng-38, ONR N000149910184 and NSF DEB- 9815614.