so 



PHYSIOLOGICAL TRIGGERS 



moting some synthetic reaction in the brain, this synthetic reaction — pre- 

 sumably requiring energy — ought to be inhibited when the insect's metaboUsm 

 is decreased. An effective method of inhibiting metabolism during low tem- 

 perature exposure is to chill animals anaerobically. To this end, groups of 40 

 diapausing Mormoniella larvae were enclosed in chambers containing pure 

 nitrogen and an oxygen absorbent (10) and were maintained in this anaerobic 

 state at 5°C for periods up to 16 weeks. Parallel control groups were main- 

 tained in air at 5°C. After treatment, the larvae were returned to air and placed 

 at 25°C along with the controls. 



8 10 12 



CUMULATIVE WEEKS OF CHILLING 



s-c 



Fig. I. Effects of alternating periods of chilling and warming in terminating larval dia- 

 pause in Mormoniella. Data for 7-4 are substantially the same as those for 7-2; data for 2-2 

 are substantially the same as those for 7-7. For further details see text. 



Prolonged anaerobiosis at low temperature had little effect on the viability 

 of the animals, and within a day of being placed in air at 25°C they regained 

 their motility. Although they remained alive and apparently healthy for many 

 months, not one of the anaerobically-chilled larvae ever pupated, while the 

 air-chilled control grou[)s broke diapause and developed normally. Thus an- 

 aerobiosis prevented chilling from terminating diapause. In terms of our hy- 

 pothesis, the simplest explanation is that the synthetic reaction occurring at 

 low temperature requires oxidative metabolism. There was no permanent 

 damage to the endocrine system of the anaerobic animals for, when subse- 

 quently rechilled aerobically, they initiated development and develo[)ed nor- 

 mally. 



