INSECT DIAPAUSE IN RELATION TO 

 THE ENVIRONMENT 



A. D. LEES 



Agricultural Research Council, Unit of Insect Physiology, Cambridge 



(Great Britain) 



The phenomenon of dormancy is a famiUar one to entomolo- 

 gists. Indeed, so striking are the instances afforded by insects 

 and mites that Henneguy, as long ago as 1904, appropriated the 

 special term diapause ('interruption of work') to describe the 

 condition. His intention was to emphasise one of the most 

 noteworthy features, namely the failure of growth (embryonic, 

 larval, pupal or reproductive according to species) even under 

 circumstances which would be expected to favour it. Although 

 the employment of the term has served to draw attention to 

 ecological and physiological problems associated with dor- 

 mancy, its use has not been an unmixed blessing since it has led 

 some investigators to conclude that 'diapause' is a single 

 phenomenon and is therefore explicable in terms of one com- 

 prehensive hypothesis. Yet the examination of almost any group 

 of closely related species reveals that their dormant stages occur 

 at different times in the life cycle — a sure indication of their 

 independent evolution. And recent studies on intraspecific 

 variations have further emphasised the extraordinary plasticity 

 of the diapause-controlling mechanism. With such a background 

 we should be prepared for differences rather than similarities. 

 'Diapause' must indeed be recognised as a portmanteau term 

 covering many types of physiological arrest. 



Keihn'si classification of 'hypobiotic' forms of life is based 

 on metabolic considerations. The distinction is made between 

 'ametabolic' organisms which remain viable without detectable 

 respiration and 'hypometabolic' organisms in which respiration 

 remains appreciable, although below the level characteristic of 

 active growth. In arthropods nearly all our examples of quies- 

 cence and diapause fall under the latter heading. One of the rare 



