ACID-BASE STATUS AND SPIRACULAR CONTROL DURING DISCONTINUOUS VENTILATION IN GRASSHOPPERS

摘要

Many insects ventilate discontinuously when quiescent, exhibiting prolonged periods during which little or no gas exchange occurs, We investigated the consequences of discontinuous ventilation (DV) on haemolymph acid-base status and tested whether spiracular opening during DV is due to changes in internal gas tensions in the western lubber grasshopper Taeniopoda eques, At 15 degrees C, resting T. eques exhibited interburst periods of about 40 min, During the interburst period, haemolymph P-CO2 rose from 1.8 to 2.26 kPa, with minimal acidification of haemolymph, Animals in atmospheres in which C-O2 was 2 kPa or below continued to exhibit DV, while atmospheres in which P-CO2 was 2.9 kPa or above caused cessation of DV. These data indicate that accumulation of internal CO2 to threshold levels between 2 and 2.9 kPa induces spiracular opening in grasshoppers, In contrast to the situation in lepidopteran pupae, variation in atmospheric P-O2 had no effect on interburst duration, Relative to lepidopteran pupae, the internal P-CO2 of grasshoppers during DV is threefold lower, the P-CO2 required for triggering spiracular opening is also threefold lower, and the open phase spiracular conductance is at least tenfold higher, demonstrating that considerable diversity exists in these aspects of insect respiratory physiology. [References: 32]