146 



Temperature 



when in the dormant winter condition. Plant dormancy is induced 

 by lowered autumn temperatures often accompanied by desiccation. 

 Dormancy during the summer, when high temperatures, excessive 

 dryness, and /or shortage of food may occur, is called aestivation, and, 

 although less common than hibernation, it is found widely among 

 insects and some other invertebrates, as well as among plants and 

 certain mammals. In many insects dormancy takes the form of a 

 diapause, that is, a stage in the development of the animal during 

 which morphological growth and development are suspended or 

 greatly retarded. Species having the capacity for diapause usually 

 display a rhythm in the life cycle that is related to the seasons. 

 During periods of unfavorable climate the greater part of the popu- 

 lation is in the resistant, diapause stage. Andrewartha ( 1952 ) re- 

 ports that in the absence of diapause the grasshopper, Austroicetes 

 cruciata, which maintains high numbers over a wide area in southern 

 Australia, would almost certainly die out in most of this area, or at 

 best become a very rare species. Since in general dormancy is cor- 

 related with severe environmental conditions, insects of the same 



After Bodenheimer, 1938 



Fig. 5.7. Variation in the seasons of dormancy and in the number of complete 

 and partial generations in the ladybird beetle, Coccinella septempunctata, in 



different parts of its range. development; aestivation; 



. . . hibernation. 



