Wasserthal, L.T. 2001. Flight-motor-driven respiratory air flow in the hawkmoth Manduca sexta. Journal of Experimental Biology. 204:2209-2220.
During high-speed or hovering flight, the metabolic rate of Manduca sexta can increase 148 times above the resting level; however, the oxygen levels in the flight muscles are known to increase above resing levels during periods of flight. How is the tracheal system of M. sexta able to provide the levels of oxygen observed during flight?
By tethering moths inside a two-specimen flight chamber so that th anterior mesothoracic spiracles opened into the anterior chamber and the posterior metathoracic spiracles opened into the posterior chamber, Wasserthal was able to monitor the direction of Co2 emissions from the moths. During shivering a tidal flow was generated in the tracheal system, but during flight a unidirectional flow from the anterior mesothoracic spiracles ot the posterior metathoracic spiracles was observed. By combining data on pressure within the tracheal system, data on wing beat, and visual examination of the metathoracic spiracle, Wasserthal determined that the wing's down stroke generates low pressure inside the tracheal system while simultaneously closing the metathoracic spiracle. On the up-stroke, pressure inside the tracheal system is increased and the valve covering the posterior spiracle is opened.
M. sexta generates a unidirectional flow of air from its mesothoracic spiracle to its metathoracic spiracle that is powered by its flight mechanism. This efficient respiratory system allows M. sexta to meet its oxygen demands during flight.
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