Meeting Abstract

30.5  Wednesday, Jan. 5  Patterns of pressure in the thorax of a carabid beetle COX, L.M.*; SOCHA, J.J.; Virginia Tech; Virginia Tech lecox@vt.edu

Many insect species are known to breathe using active ventilation of the tracheal system. Rhythmic tracheal compression (RTC) is one form of active ventilation in which parts of the insect’s tracheal system collapse and reinflate multiple times per minute, producing bulk flow of air. Although the biological mechanism of RTC is unknown, one hypothesis is that an increase in hydrostatic pressure in the hemolymph induces tube collapse. As an initial test of this hypothesis, we measured pressure changes directly in the hemolymph of carabid beetles of the genus Pterostichus using a fiber-optic sensor. Beetles were loosely constrained in chamber that allowed fore-aft locomotion; only data from stationary periods were analyzed. Results showed that pressure pulsations on the order of 0.5 to 4.5 kPa occurred rhythmically in the beetles’ hemolymph at frequencies ranging from 3 to 24 pulses per minute. The duration of pressure pulses was between 2 to 5 seconds, with the period of rising pressure typically occurring faster than period of falling pressure. The frequencies and durations of these pressure pulses are comparable to rhythmic tube collapse previously observed directly with x-rays. These data support the hypothesis that a global, rhythmic pressure increase is the cause of RTCs. Research supported by NSF 0938047, the Institute for Critical Technology and Applied Science (ICTAS), and the Jeffress Memorial Trust.