MEASURES OF INSECT COLD HARDINESS. 



455 



aquatic insects where there is practically none, Payne (1926). 

 This periodicity in cold hardiness is shown in Fig. 5. The 

 relation between undercooling and survival temperatures is show r n 

 in Fig. 6. Cold hardiness greater than is usually found in their 



-18 



-10 



-14 



U 

 -12 C 



-10 



-6 



-6 



| 



> 



CO 





-4 



RELATION BETWEEN UNDER- 

 COOLING AND SURVIVAL 

 TEMPERATURES IN 

 POPILLIA JAPONICA 



Undercooling pom! 



Survival temperature 



-2 -4- -6 -8 -10 



UNDERCOOLING POINT 



-\Z 



-14 



FIG. 6. Relation between undercooling and survival temperatures in Popillia 

 japonica. Undercooling point - ; survival temperature - . 



soil habitat can be induced in this insect by dehydration. Con- 

 ductivity measurements of the blood of dehydrated insects were 

 made. The greatest cold hardiness was found in the dehydrated 

 insects and the least in those infected with wilt disease or 

 30 



