VARIABLE TEMPERATURES 



213 



conditions unless previously subjected to low temperature, and 

 the same principle is well known to the commercial rearers of 

 eggs of univoltine silkworm moths. 



In further illustration of this same phenomenon the work of 

 Cook (1927) may be cited. This experimenter used first instar 

 larvse of the Noctuid moth Porosagrotis orthogonia which were 



•018 



10' 15' 20' Z5' 30- 35' 



Fig. 69. Influence of temperature on the growth rate of Porosagrotis 

 orthogonia. (From Cook, Journ. Econ. Ent., XX.) 



subjected to constant temperatures of 12°, 16°, 22°, 27°, 32° and 

 37° as controls, and the time which elapsed before the first ecdysis 

 took place was noted. Simultaneously other batches were sub- 

 jected to alternating temperatures. For high temperatures 22°, 

 27°, 32° and 37° C. were used, while 8° was the low temperature 

 in each instance. Four batches of larvse were placed at each 

 high temperature, one batch each for two, four, eight and sixteen 

 hours per day, while for the remainder of the twenty-four hours 

 they were placed at 8° C. (Table III.). The growth rate, or the 



