REPORT OF THE SOCIETY 



21 



boHsm and it is probable that the insect dies of exhaustion. The rate of 

 metaboHsm, humidity, and the thickness of the cuticle, the size, and the 

 amount of water in the tissues of the insect have an influence on the vital 

 maximum temperature. 



At low temperatures sortie interesting differences appear before torpid- 

 ity ensues. First an infra-optimum zone is reached, leading to cold torpidity 

 at 15°C. This zone is quite variable in different species. Aphis hrassicae 

 has been observed in copulation at -7°C. and active Pemphigus plant lice 

 -3°C. It appears, therefore, that insect tissues can be cooled below zero 

 without freezing. The degree of sub-cooling depends to a large extent 

 on the speed of cooling. 



The lowest point of cooling is called the critical point. Then the tem- 

 perature suddenly rises to 1.5°C. when the tissues begin to freeze. On 

 further cooling the freezing advances until all the tissues are frozen, and the 

 insect enters the lifeless condition. If a hard frozen insect in this condition 

 is warmed it will come to life again. An insect in the lifeless condition is 







Relation of insects to high and low temperatures. (After Bachmetjew) 



