ACTIVITY PHYSIOLOGY OF THE 2-STRIPED GRASSHOPPER, MELANOPLUS-BIVITTATUS - GAS-EXCHANGE, HEMOLYMPH ACID-BASE STATUS, LACTATE PRODUCTION, AND THE EFFECT OF TEMPERATURE

We examined the effect of locomotion on the respiratory and acid-base physiology of the grasshopper Melanoplus bivittatus. Escape hopping was characterized by high initial power output and gradual fatigue over 5 min. Increased O2 consumption was at least 10 times as important as lactate production to energy production during locomotion. Increased gas exchange during hopping was due to increased partial pressure gradients for gas diffusion rather than to increased tracheal conductance. Hopping was accompanied by a respiratory extracellular acidosis. During recovery grasshoppers ventilated rapidly, flushing accumulated CO2 and restoring depleted O2 stores. This resulted in gas exchange rates that were 14%-80% higher during recovery than during activity. A substantial portion of the O2 consumed during hopping (estimated as 35% at 20-degrees-C and 18% at 35-degrees-C) is obtained from tracheal O2 stores rather than from environmental air. Body temperature had relatively little effect on locomotor performance, aerobic scope, lactate accumulation, or hemolymph pH changes during activity (Q10's ranged from 1.0 to 1.4). However, recovery from hemolymph acidosis was faster at 35-degrees-C than at 20-degrees-C. The low tracheal conductances in active hoppers suggest an intrinsic constraint on ventilation during jumping.