TEMPERATURE 



217 



70 



(other conditions being average), as shown by the difference in 

 time required to complete the stage. Shelford's work is with 

 special reference to the Codling moth, for which he gives tables of 

 developmental units under all combinations of temperature and 

 humidity, and based upon data 

 covering ten years of observation 

 and experimentation. Such a 

 method, however, is obviously 

 too laborious to allow of its ^„ 



60 



general adoption. 



The influence of temperature 

 on the duration of life has been 50 

 shown, in a general way, to 

 exercise a shortening effect in 

 proportion to its rise. The most ^^ 

 exact study of this phenomenon 

 is found in the work of Alpatov 



^ 30 



and Pearl (1929) on Drosophila. 

 Their experiments showed that, 

 in this insect, length of life is 

 doubled in the 10° of temperature 

 reduction between 28° and 18°, 

 which were the temperatures 

 used. Females proved to be 

 longer lived than males, and 

 individuals of both sexes were 

 used in the double series of 

 experiments. In one series they 

 were reared from the egg at 18° 

 and in the other series at 28°. 

 The adult flies were then tested 

 as regards their viability at temperatures of 18 



20 



Fig. 70. Average duration of life in 

 days : males (two lower curves) 

 and females (upper curves) of 

 Drosophila. Black lines indicate 

 development at 18° and broken 

 lines at 28°. (From Alpatov and 

 Pearl.) 



25° and 28°, and 



the results are shown in Fig. 70. It will be noted that the survival 

 of individuals reared at 18° was marked longer than those at 28°. 

 Alpatov and Pearl's conclusion that, at the higher temperatures, 

 the increased rate of energy expenditure during growth and 

 imaginal life shortens survival is what would be expected. 



