252 
the zero of development is 265, and the variation due to causes other 
than the use of the day as the unit gives 256 as the minimum and 274 as © 
the maximum. 
CONCLUSIONS FROM THE FOREGOING DISCUSSION 
1. There is a fairly constant relation between temperature and the 
rate of development of different stages of the codling-moth. 
‘2. Only temperatures above the zero of development are effective. 
3. The rate of development increases as the temperature rises 
above the zero of development until a temperature is reached at which 
the maximum rate of development takes place. 
4. For the first few degrees, at least, above the degree of the maxi- 
mum rate of development the rate of development decreases approxi- 
mately as the temperature rises above this point. 
5. The average daily effective day-degrees are found by subtract- 
ing from the average daily day-degrees above the zero of development 
twice the average daily day-degrees above the degree of maximum rate 
of development. 
6. The product obtained by multiplying the average daily effective 
day-degrees by the period, expressed in days, or other convenient unit, is 
fairly constant for all temperatures. 
7. Variations in the total accumulation of day-degrees recorded foul 
individuals from the average accumulation, may result from the follow- 
ing causes:—l. Use of too large a unit of time. 2. Differences in hu- 
midity. 3. Individual differences. 4. Errors in observation. 5. Slight 
differences of temperature between the individual under observation and 
the recording instrument, due to difference of locality. 6. Abnormal 
environment and treatment of the individual. 
8. The zero of development for the egg stage is about 50 degrees 
F. and the degree of the maximum rate of development is about 88. The 
equation of the curve of development is PE = 163, in which P = period 
in days, and E = average daily effective day-degrees. 
9. The zero of development for the larva is about 50 degrees and 
the degree of the maximum rate of development is about 85 degrees. 
The equation of the curve of development for larve reared in apples on 
the tree is PE =- 673; that for larve reared in picked applies is PE = 587. 
10. The zero of development for the pupa is about 52 and the de- 
gree of maximum rate of development is about 87 degrees. The equation 
of the curve of development is PE=241. For practical purposes 
it will be more convenient to use 50 as the zero of development for the 
pupa when applying the data to the whole life cycle, and the error that 
will result from so doing will amount to only a fraction of a day in the 
length of the period. The equation when 50 degrees is used, is 
PE. —— 200) 
