MEASURES OF INSECT COLD HARDINESS. 



451 



of the weight loss curve (Fig. i) these insects can survive freezing. 

 When the curve is plotted with rate against weight loss the 

 point of inflection is brought out more clearly (Fig. 2). Up to 



100 



FALL DEHYDRATION OF 

 ISIA ISABELLA AND 

 DIACRISIA VIRGINICA 



xx Isia Isabella 



Diacrisia virginica 



O 

 3OO 



800 



700 600 500 400 



WEIGHT IN MGMS 



300 



200 



FIG. 2. Fall dehydiation of Isia Isabella and Diacrisia virginica. 

 plotted against weight. 



time 



too 



or rate 



the point of inflection of the weight loss curve the undercooling 

 point of the blood is the minimum survival temperature. Beyond 

 that point the undercooling point no longer measures the total 

 cold hardiness which reaches to below - 40 C. There is no 

 free body fluid on which a conductivity reading can be made. 



The oak-borers, Synchroa punctata Neum., Dendroides cana- 

 densis Lee., Romaleum rufulum Hald. also are normally self 

 dehydrating but never to the extent of losing all their free water. 

 Although very cold resistant, having survival temperatures of 

 below - 40 C., at no time even in the deepest \vinter, is it 

 impossible to obtain blood samples. But conductivity is found 

 to be proportional to the survival temperature (Fig. 3). The 

 water content of these insects, obtained by heating them in an 

 oven for four hours at + 50 C., is only relative but does appear 



