JOHN BUCK 



73 



opening has l)een linked to an increase in hydrogen ion concentration (i6, 14) 

 but Case (7) has recently shown rather convincingly that the action of C"()2 is 

 independent of hydrogen ion concentration. 



By altering ambient Ov and C O^ concentrations (^ase (6) has shown that 

 spiracular movement in adult tlies can be graded. Sustained intermediate valve 

 positions are also seen in various insects in atmospheric air, particularly during 

 and after exercise. However, in many species at rest there appears to exist a 

 rhythm of spiracular activity involving relatively long periods of closure alter- 

 nating with brief periods of wide opening. This is seen well in adult lampyrid 

 fireflies, for example, and has been described also in fleas (16, 11). The pos- 

 sible all-or-none nature of this activity is obviously of interest in connection 

 with triggered-type responses, but it has been little studied in adult insects 



2 

 < 

 a: 

 o 



35 

 30 

 25 

 20 



CM 

 0,5 



12 3 4 5 6 



HOURS 



Fig. I. CO3 release pattern in diapausing Agapema pupae. (Buck and Keister, 1955, 

 fig. I, p. 146.) 



under reasonably normal conditions. There is, however, a considerable amount 

 of quantitative information on possibly analogous behavior in certain diapaus- 

 ing moth pupae, forms which offer special advantages because of their bodily 

 inactivity, large size and relative insensitivity to handling (12, 15, 4). 



The phenomenon in question is seen very dramatically in Warburg measure- 

 ments of CO2 release rate by the pupae (fig. i), and appears also in continuous 

 recordings by a method with much better time resolution (fig. 2). For technical 

 reasons it has not been possible to study the spiracles during actual respirom- 

 etry, but a direct causal connection between spiracular opening and the 

 CO2 'bursts' can hardly be doubted in view of the facts that a) all pupal gas 

 exchange occurs via the spiracles (15, 4), b) there are no relevant ventilatory 

 or other body movements (15, 4), c) the discontinuity of the COo release cycle 

 is reversibly abolished by intubating some of the spiracles so that the tracheal 



