339 



standard time tor the stage. This calculated number of days m each 

 case was then compared to the actual number of days recorded for the 

 stage in question. (For more detailed discussion of these methods of 

 calculation, sec PART THREE, pp. 381-400.) 



a. Pupae. 



Standard time for the pupal stage was calculated on a basis of 6,480 

 as the normal developmental total, this total being divided by the mean 

 daily number of developmental units for the actual period of the stage as 

 recorded by Glenn. For convenience, since most of the data were 

 expressed in days, this calculation was generally done by dividing one- 

 twentv-fourth of the dailv mean into 270, which is one-twenty-fourth 

 of 6,480. 



The results in detail for a part of the 1015 pupae, with means for 

 groups of 30 individuals, are shown in Table VII ; and the results by 

 30-individual means for all the pupae of 1915-1917 are shown in Table 

 VIII and Fig. 3. The detailed data on the first-generation pupae shown 

 in Table VII are similar, in general, to those on the pupae of all gener- 

 ations ; the differences are of a minor character and will be considered 

 later. 



The accuracy of this method of measurement of development, as 

 well as the validity of these standard velocity values, is indicated by the 

 fact that the actual time for all the Olney data averaged only 0.1% over 

 the calculated time. The deviation was — 0.67p for 1915, — 1.4% for 

 1916, and 2.1% for 1917.* These deviations from calculated time are 

 the averages of the 30-individual groups for the whole of each year. 

 Averaging the means of the three generations for each year gives the 

 following deviations: 1915, —1.5%; 1916, —2.8%; 1917, —1.8%; total 

 average deviation, — 2%. 



The Urbana data on pupae showed the following ratios of actual to 

 calculated time: 1917, all generations, 99% ; 1918, first generation, 119%. 

 The average ratio is 103.6% ; with the 1918 set omitted, it is 99.8%. The 

 ratios for individuals vary from 91% to 119.0%. The actual time for 

 the latter part of the first generation shows the largest positive 

 deviation from standard time ; it is about standard in the beginning and 

 increases to the end of the generation. The actual time for the second 

 generation is at first shorter than the standard ; it then increases and 

 finally falls off again ; while that for the third generation is short through- 

 out. This type of deviation is apparently characteristic, though it is due 

 in some measure to factors other than temperature and humidity (see 

 Fig. 28), which are discussed in Part III. 



b. Adult Moths. 



Isely and Ackerman ('23) ascribed the abundance of codling moths 

 in a given season partly to favorable conditions of light and temperature 

 during the oviposition period. They found that a temperature of 62° F, 



♦ This 1917 time is high because of a lacls of a large part of the data for the 

 second generation. The loss of one hygrothermograph sheet necessitated large omis- 

 sions at a period when the actual time is usually less than the calculated time. 



