MEASURES OF INSECT COLD HARDINESS. 



NELLIE M. PAYNE, 

 NATIONAL RESEARCH FELLOW IN THE BIOLOGICAL SCIENCES. 



Different measures of insect cold hardiness used by different 

 workers may usually be reduced to the empirical survival test. 

 Bachmetjew (1901) used the "vital temperature maximum" or 

 the second time an insect reached the undercooling point. 

 Duval and Portier (1922) considered that there was a freezing 

 point below that ordinarily determined, the higher freezing point 

 being that of the body fluids, the lower that of the body cells. 



In strong contrast to the scarcity of measurements of insect 

 cold hardiness, stand the many determinations by plant physi- 

 ologists. Osmotic pressure as determined by freezing point 

 lowering has been widely used from the time of Sachs and 

 Pfeffer. Water content has been of value as a criterion of cold 

 hardiness in plant groups far separated taxonomically. For 

 example, Johnson (1923) used water content of peach buds as 

 a measure of cold hardiness, and Steinbauer (1926) employed 

 it for clover seeds. Newton and Gortner (1922) and Newton 

 (1924) emphasize the importance of bound water to cold hardi- 

 ness. Muller-Thurgau (1886) proved conclusively that some 

 plants could survive freezing. The ability of a plant to survive 

 freezing was defined by Harvey (1918) as cold hardiness. 



The two kinds of insect cold hardiness (i) hardiness to the 

 quantity factor of low temperature or ability to withstand long 

 periods of relatively mild low temperature and (2) hardiness to 

 the intensity factor of low temperature, or ability to withstand 

 extremes of low temperature have been discussed in a previous 

 paper. In the present paper cold hardiness to the intensity 

 factor alone will be considered. 



Closely associated with changes in cold hardiness are changes 

 in moisture content. Insects dehydrated but not to the period 

 of injury, can withstand temperatures far lower than unde- 

 hydrated individuals. This is strikingly true for insects that are 



449 



