Meeting Abstract
Insects possess a complex network of tracheal tubes throughout the body used for transport of gases to and from the tissues. In some species, parts of the network are rhythmically compressed, facilitating active ventilation in the insect. Previous work suggests that hemolymph pressure pulses may induce tube collapse, but it is not understood how tracheae respond mechanically to a pressure difference across the wall. Tracheal tubes vary in diameter, wall thickness, cross-sectional shape, and taenidial density, which should influence patterns of collapse. To study how tracheae respond to hemolymph pressure, we artificially induced pressure rises in the thorax of 11 intact, sacrificed beetles (Zophobas morio) by manually compressing the abdomen, creating hemolymph pressures of similar magnitude to those observed in live animals (>2 kPa). Simultaneously, we captured synchrotron X-ray video to monitor tracheal tube diameter in several locations in the body, and measured internal pressure using a Fabry-Pirot pressure sensor (Samba Preclin) inserted into the thorax. We found that pressure rises produce collapse patterns that are qualitatively similar to those found in the live animals. Preliminary analyses indicate that large tracheal tubes (diameter ~400 µm) begin to collapse at an average pressure of 0.32 ± 0.02 kPa (n=3), whereas small tubes (diameter ~100 µm) required nearly twice the pressure (0.63 ± 0.02 kPa, n=3). However, smaller tubes collapsed completely at lower average pressures (1.79 ± 0.02 kPa, n=3) than did larger tubes (2.32 ± 0.05 kPa, n=3). These results support the hypothesis that an increase in hemolymph pressure is a mechanism of tracheal tube collapse used for active ventilation in insects.
