WATERS, J.S.*; SOCHA, J.J.; The University of Chicago; Argonne National Laboratory: Mechanics of tracheal compression in the bessbug, Popilius disjunctus

Recent studies conducted with phase-enhanced synchrotron x-ray imaging have discovered that a range of insect orders exhibit a novel mode of gas exchange, active tracheal compression, in which multiple tracheae collapse and inflate in rhythmic fashion. In one species of beetle, the carabid Platynus decentis, compressions generally occur synchronously throughout the head, thorax, and legs. In this study, we use synchrotron x-ray imaging at the Advanced Photon Source (ANL) to examine a larger beetle, the bessbug Popilius disjunctus (Passalidae), in order to explore the diversity of this mechanism among beetles and as a first step toward understanding the influence of size on tracheal compression patterns. In the bessbug, the most prominent compressions occur in the prothoracic ventral tracheae. In contrast to Platynus decentis, lateral compressions in the largest tubes (diameters up to 0.8 mm) do not occur synchronously along the length of tube, but instead pass in a wave, which may indicate different underlying mechanisms of compression. Furthermore, compression does not always occur simultaneously among different tubes. Although some compressions appear to be correlated with movements of the ventral mesothoracic exoskeleton, they also occur in the apparent absence of external body movements. We will examine tracheal morphology to determine if regions of compression are associated with specific features such as taenidial density, tracheal wall thickness, and cross-sectional shape. In addition, we are currently conducting complimentary studies of the material properties of major tracheae in order to determine if regional differences in properties such as stiffness are responsible for variations in local compression patterns. Use of the APS was supported by the U.S. D.O.E., O.S., B.E.S., under Contract No. W-31-109-Eng-38.