ENDOCRINOLOGY OF INSECT DIAPAUSE 143 



Harpaz: In experiments we have conducted, diapause was 

 terminated by cold shock treatment, consisting of chilling to 

 — 10° followed by immediate transfer to 25°. This procedure 

 probably has no ecological equivalent, as nowhere are such 

 conditions extant. 



Lees: I think I must disagree with you here. There are some 

 investigators who believe that this finding does have an ecologi- 

 cal application. These include Danilyevsky who found that in 

 the moth Satumia pavonia very low temperatures can terminate 

 diapause; and Way has made similar observations on the fly 

 Leptohylemyia. These authors point out that in continental 

 regions of the north temperate zone, the warmest part of the 

 winter comes first, really cold conditions being delayed until the 

 early months of the year. It is possible that this final stimulus is 

 required to complete the processes which result in the release 

 from diapause. 



Hestrin: In view of the long time period which elapses until 

 the effect of temperature change on the eggs becomes manifest, 

 one might wonder whether the effect might not involve crystalli- 

 sation or solubilisation of components present in the cytoplasm. 

 Has it been possible to see alterations by microscopic examina- 

 tions of the tissues? 



Lees: Yes, cytological changes in the neurosecretory cells of 

 a few diapausing insects have been described, but their signi- 

 ficance is doubtful. So far, such changes have merely been taken 

 as indicating that the particular cells are actually involved in 

 diapause control. 



