356 



Modification of Normal Developmental Totals. 



Corrections of developmental totals must be made relative to rainfall, 

 variability of temperature, and individual variation. Rainfall corrections 

 are given in Tables III and IV. Rising and falling mean daily tempera- 

 ture and hvimidity affect the development of pupae and eggs. When the 

 mean daily temperature rises from day to day, the length of the pupal 

 stage is increased to as much as 10 per cent higher than average ; that is, 

 the developmental total may be 110 per cent of the normal number of 

 developmental units. When temperature begins to fall from day to day 

 in the middle of August, the developmental total decreases steadily until 

 in the third generation. The decline is about 2 per cent per week, begin- 

 ning with the first week of falling temperatures in August. The third 

 generation normally requires only 5,952 developmental units for the 

 pupal period and 3,360 developmental units for the incubation period. 

 Pupal and incubation time for the central portion of the second genera- 

 tion in 1915 and 1916 was about standard. For such condiuons, Table VI 

 shows corrections to be made. 



All estimation is on the basis of average data. Individual variation, 

 however, makes the developmental total for some of the first-generation 

 larvae in the apple 16 per cent less than normal. Corrections of this kind 

 may be niade for other stages by subtracting 8 per cent from the normal, 

 when the date of first appearance is desired. When maximum emergence 

 is to be predicted, the correction for individual variation is, of course, 

 unnecessary. 



Correction of Low Temperatures Applicable to Glenn's Method. 



It would involve considerable calculation to bring Glenn's corrections of 

 high temperatures into accord with the findings by our methods. His correc- 

 tions, however, proved very valuable and his original data indispensable. His 

 normal pupal total of 265 "degi'ee-days" above 50° F. as the "starting point", 

 or 241 "degree-days" above 52° F., is useful for the medial range of temper- 

 atures. The "maximum rate" for pupae and eggs should probably be set at 

 89° instead of 87° F. At the lower temperatures, between 44° and 60° F., cor- 

 rections may be applied to his calculations as follows: 



(60 — X) 

 To each two-hour reading, add 0.7 



2 

 (60 — 46) 



Thus, it the reading is 46° P., add 0.7. , or 4.9°, making a corrected 



2 



temperature of 50.9° F. to be used in getting an effective sum. Such a sum 

 should correspond fairly closely to the suhstitution-quotient, or one-twenty- 

 fourth of the normal developmental total. 



