214 



SOME ASPECTS OF ECOLOGY 



reciprocal of the time required to complete the first instar, is 

 shown in Fig. 69. It must be pointed out that growth at a 

 temperature of 8° is exceedingly slow, but as the time spent under 

 this condition was large, in some cases a considerable amount of 

 growth must have occurred. Inspection of the curve labelled 

 constant in Fig. 69 indicates that a value 0-001 is the approximate 

 growth rate at 8°, and assuming this value Cook gives the following 

 sample calculation : — 



Larvae exposed at 22° for sixteen hours daily underwent ecdysis after 

 97-6 hours at that temperature, followed by 40-8 hours at 8° (Table III.). 

 Total development . . . =100000 



40-8 hours at 8° (value 0001) . . = 00408 



By subtraction this leaves 0-9592 for the value of 97-6 hours at 22°, 

 and the value of one hour at that temperature is consequently 0099, 

 which is taken as the growth rate for the batch of larvae in question. 



The growth rates are thus calculated for each lot in the series and 

 are shown in Table IV., together with those of larvae maintained 

 at constant temperatures. 



Table IV. Growth Rate for First Instar of Porosagrotis 

 orthogonia at Constant and at Alternating Temperatures. 

 (From Cook.) 



Cook also gives data with respect to the rate of COg production 

 by the nearly mature larvae of another Noctuid, Chorizagrotis 

 auxiliaris during similar combinations of temperatures. Both 



