Ventilatory Mechanism and Control in Grasshoppers

SYNOPSIS. Grasshoppers exhibit a diversity of ventilatory patternsdepending on activity status. For each pattern, the mechanismand control of gas exchange is analyzed in terms of a two-stepmodel, consisting of tracheolar and trans-spiracular steps inseries. During the intermittent gas exchange that characterizesthe most quiescent grasshoppers, spiracles open and close inresponse to changing carbon dioxide, and trans-spiracular resistancecontrols gas exchange. In resting but alert grasshoppers, abdominalpumping occurs, and gas exchange is controlled equally by tracheolarand trans-spiracular resistances; tracheal oxygen and carbondioxide are regulated by variation in abdominal pumping andspiracular opening. During hopping, abdominal pumping does notoccur, and bulk gas flow is driven by cuticular deformationsassociated with locomotion. Increased cellular oxygen consumptiondepends on use of internal oxygen stores and increased partialpressure gradients. After hopping ceases, abdominal pumpingincreases dramatically and restores tracheal gas composition;however, the rise in abdominal pumping after hopping is notaffected by tracheal gas levels. During flight, bulk flow tothe flight muscles is driven by tidal thoracic auto-ventilation,while the remainder of the body is ventilated by abdominal pumping.During both hopping and flight, the greatest resistances togas transport exist in the tracheolar rather than the trans-spiracularstep.