403 



alpha value and, therefore, a larger and presumably more nearly correct 

 product of time and temperature above alplia. It will be noted that the 

 maximum velocity appears to be at a higher temperature than in the case 

 of the pupae. This introduces a slight error when the pupal velocities 

 are used for incubation at high temperatures. In Fig. 23 this might have 

 been corrected by adding 2 to each velocity value for all temperatures 

 above 89° F. Such a correction is unnecessary in prediction work, as 

 the duration of such high temperatures is usually very short. 



Time from Hatching to Leaving the Apple. (Data by C. S. Spooner.) 

 Newly hatched larvae were placed in small cuts in apples. All experi- 

 ments at 53° and 83° F. were failures. The number successful at each 

 temperature was small (Table XXIII). The small series suggests a 

 relatively smaller effect of temperature increases than is shov^'n by the 

 other stages. One item (temperature 81.0° F and time 32.1 days) was 

 omitted in the calculation of time-temperature products, as its longer time 

 suggested that 81.0° may be above the straight-line limits. The other 

 temperatures and velocities were averaged together in two groups. The 

 lower temperature, with a mean of 67.9°, gave a mean velocity of 24.1. 

 The higher temperatures, with a mean of 78.8° were associated with an 

 average velocity of 26.3. These two points are shown and marked A on 

 Fig. 24. A continuation of the line passing through them would reach 

 velocity at about 40 degrees below the Fahrenheit zero, making it obvious 

 that reasonable thresholds cannot be determined from such a few data 

 with so much variation. 



Glenn's data, however, proved much more workable. A comparison 

 of the tangents and alpha values of Glenn's reciprocal (i. e., relative 

 velocity) curves for the pupal and larval periods shows that the pupal 

 velocity is 2.8 times that for the larval period. Thus, when the substi- 

 tution-quotient for the pupa is 270, that of the entire larval period should 

 be about 756. Glenn found an average of 673 "degree-days" for this 

 period. An examination of his Table III, by the Von Oettingen method, 

 gives an alpha value of 47.5° F., an uncorrected sum of 763 "degree-days" 

 and a substitution-quotient of 744. A curve was drawn (see circles in 

 Fig. 24) to fit Glenn's data when his reciprocals were multiplied by 763 

 and plotted on mean temperatures above 47.5° for the larvae from hatch- 

 ing to pupation, and the upper curvature was copied from the curve for 

 the larval development after hibernation (see Fig. 26). Velocities were 

 read from this trial curve and applied to Glenn's original data, in order 

 to correct the upper curvature. (When the upper straight-line limit is too 

 high, the calculated time becomes smaller as the number of high tempera- 

 Pig. 24. Curve for velocity of development of the larva in the apple. The 

 curve was estimated from experimental data (shown by crosses) and from 

 Glenn's observations shown by circles. The dotted peak is for hibernated larvae 

 under average weather conditions. The velocities are based on dividing the 

 mean number of days into 650 for the period from hatching to leaving the 

 apple, and into 750 for the period from hatching to pupation. The latter figure 

 was obtained from Glenn's corrected temperatures by applying the Von Oettin- 

 gen method. 



