PhD Candidate Arizona State University Tempe, Arizona
While it is well-known that most insects move air unidirectionally through their tracheal systems, we have few measures of the volume of air moved, hampering development of quantitative models of insect gas exchange. We developed a new method for quantifying unidirectional air flow in insects using the adult darkling beetle, Zophobas morio, which are especially useful for such work as the metathoracic and abdominal spiracles all open into a subelytral cavity. A septum located cranially to the subelytral cover allowed us to separately monitor the CO2 emission rate from the prothoracic and the posterior spiracles. To trace net unidirectional airflow, hyperoxic (30% O2, balance N2) gas was perfused over the prothoracic or posterior spiracles, and oxygen emission was simultaneously monitored from the alternate spiracles. Most CO2 was emitted from the posterior spiracles, and the tracer gas demonstrated that that air flows mostly unidirectionally in the prothoracic and out the posterior spiracles. Individuals with higher unidirectional airflow had higher CO2 emission rates. Beetles flushed their tracheal systems about once every three seconds with fresh air. Comparing ventilation to metabolic rates showed that these beetles maintained levels of oxygen and carbon dioxide in the large longitudinal tracheae near atmospheric, demonstrating that beetles are capable of high unidirectional air flow that very effectively flushes their tracheal systems. Comparison to water loss rates demonstrates that expired air is far from saturated with water vapor, contradicting a common assumption. Supported by NSF IOS 1558052.