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Insects are known to exchange respiratory gases in their system of tracheal tubes by using either diffusion or changes in internal pressure that are produced through body motion or hemolymph circulation. However, the inability to see inside living insects has limited our understanding of their respiration mechanisms. We used a synchrotron beam to obtain x-ray videos of living, breathing insects. Beetles, crickets, and ants exhibited rapid cycles of tracheal compression and expansion in the head and thorax. Body movements and hemolymph circulation cannot account for these cycles; therefore, our observations demonstrate a previously unknown mechanism of respiration in insects analogous to the inflation and deflation of vertebrate lungs.
Respiratory mechanisms in insects are important to our understanding of the physiology, behavior, and evolution of this diverse animal group. Most insects respire through a system of tubes called tracheae that connect to the air via spiracles that can be actively opened or closed (1). Tracheal tubes form a complex network of gas-filled vessels that divide throughout the body segments, legs, and wings. The tiniest tubes, called tracheoles, may be 1 (mu)m in diameter, and they function to exchange gas with tissues of the body. Mechanisms for insect respiration include passive gas diffusion (2, 3), changes in internal pressure due to hemolymph pumping by the heart or by muscle contraction in the abdomen (4, 5), and autoventilation, during which body movements change the volume of tracheal tubes or air sacs associated with the tracheae (68). Despite recent insights into these active mechanisms for changing the volume of the tracheal system (8, 9), the internal mechanics of insect respiration are largely unknown.
To directly observe changes in volume of the insect tracheal system, we obtained highresolution x-ray videos of living insects using 15- to 25-keV synchrotron x-rays [supporting online material (SOM) Text]. The high flux and partial coherence of the x-ray source allow for real-time, phase-enhanced imaging (10) in which edge enhancement of the images enables clear visualization of insect anatomy. X-ray videos were recorded for the anterior thorax and head regions of ground beetles (Platypus decentis), carpenter ants (Camponotus pennsylvanicus), house crickets (Achaeta domesticus), and other insects...