ENDOCRINOLOGY OF INSECT DIAPAUSE 139 



indeed present during diapause, although in somewhat reduced 

 amounts. But the most sisnificant change is the virtual dis- 

 appearance of cytochrome r^^. 



The action of dinitrophenol on the diapause respiration is 

 important in this context. Dinitrophenol is known to increase 

 the turnover of respiratory carriers, probably by uncoupling 

 oxidative phosphorylation from electron transfer, and so in- 

 creasing the demand for oxygen. In the cecropia pupa dinitro- 

 phenol injections may cause a seventeen-fold rise in oxygen 

 uptake. Moreover, the dinitrophenol-stimulated respiration is 

 CO-sensitive. showing that dinitrophenol increases the satura- 

 tion of cytochrome oxidase-^. 



These results have led to the suggestion that CO- and CN- 

 insensitivity arises as a result of the great excess of cytochrome 

 oxidase in the diapausing tissues relative to cytochrome c. A 

 high proportion of the enzyme is therefore unsaturated and 

 can be immobilized with inhibitors without affecting electron 

 transfer from cytochrome c. Thus cytochrome oxidase may well 

 be the terminal oxidase in diapausing as well as in growing 

 insects. 



The cecropia pupa is a rather extreme example of the insensi- 

 tivity often shown by dormant insects to respiratory inhibitors. 

 Other species are much less resistant — the weevil Sitona. which 

 hibernates as an adult, is an example-^. Such differences are 

 probably related to the amount of muscle present in the dia- 

 pausing insect. In the cecropia pupa there is little of this tissue 

 save for the small intersegmental muscles which serve to flex 

 the abdominal segments. These muscles do in fact retain an 

 intact cytochrome system, but their total volume is small relative 

 to the pupa as a whole. Dormant larvae or adult insects are 

 more mobile and retain a correspondingly large proportion of 

 muscles. These of course contain the sarcosomes with which the 

 cytochrom_e system is associated. 



A very interesting finding which is still incompletely under- 

 stood concerns the striking stimulation of respiration which 

 takes place when a diapausing insect (for example, the cecropia 



References p. 140 



