CO2 and heat have different effects on directed ventilation behavior of grasshoppers Melanoplus differentialis.

We tested the hypothesis that CO2 and heat have different effects on the ventilatory pattern of grasshoppers Melanoplus differentialis. Eight grasshoppers were sealed between rostral (inspiratory) and caudal (expiratory) spiracles in separated, airtight, chambers and pressure changes were measured. Normal breathing patterns decreased pressure in the rostral chamber and increased pressure in the caudal chamber (i.e. unidirectional pumping rostral to caudal). Insects exposed to ventilatory stimulation by CO2 or heat significantly increased pumping frequency from 26+/-2 (+/-S.E.M.) at 0% CO2 to 54+/-6 breaths/min at 8% CO2 (at 30 degrees C), and from 27+/-3 at 30 degrees C to 44+/-4 breaths/min at 45 degrees C. Unidirectional pumping failed to change with increased CO2 concentration and increased significantly with heat exposure. Thus, while CO2 only increased pumping frequency, heat increased pumping frequency and unidirectional pumping.