222 
Temperature is the predominating factor, so far as weather condi- 
tions are concerned, in determining the rate of development and the time 
of the appearance of the various stages. 
Development begins in the spring as soon as the temperature in the 
warmer parts of the day rises above 52 degrees F., and the rate of devel- 
opment increases as the temperature rises,* until the degree of the 
maximum rate of development is reached, which for the egg is about 88, 
for the larva 85, and for the pupa 87 degrees F. The pupa will not 
develop at temperatures below 52 degrees, but the egg and larva will 
develop at temperatures: above 50. 
Temperatures above the degree of maximum rate of development 
retard development, and the retardation appears to be proportional to the 
number of degrees above the degree of the maximum rate, so that the 
rate of development at one, two, three, etc., degrees above the degree of 
the maximum rate is the same as one, two, three, etc., degrees below 
that degree. 
There is a fairly constant relation between the accumulation of 
effective day-degrees and the time of appearance of the different broods. 
For practical purposes, 50 degrees F. may be used as the zero of develop- 
ment and 86 degrees as the degree of maximum rate of development, 
and the effective day-degrees for any day may be determined by finding 
the average temperature above 50 degrees and subtracting from it twice 
the average temperature above 86 degrees. 
It requires an average of 163, 673, and 265 effective day-degrees to 
complete the development of the egg, larval, and pupal stages, respectively, 
and an average of 1101 for the development of an individual through the 
three stages when 50 is taken as the zero of development and 88, 85, and 
87 as the degrees of maximum rate of development for the egg, larva, and 
pupa, respectively. The number of effective day-degrees which accumu- 
late from a certain stage in the development of one generation to the same 
stage in the development of the succeeding generation varies in round 
numbers from about 1000 to 1600, the average being about 1195, when 
50 is taken as the zero and 86 as the degree of maximum rate. 
The first larve of the first, second, and third generations enter the 
fruit when the accumulations of effective day-degrees have reached 
about 550, 1550, and 2550 day-degrees, respectively. 
The seasonal history of the codling-moth for a normal year may be 
determined approximately in any locality by ascertaining the normal total 
accumulation of effective day-degrees for each day in the season in that 
locality. 
* This statement is not strictly true, for with each unit of change in temperature, the 
rate of development is affected more at temperatures near the zero of development, and 
less at temperatures near the degree of maximum rate of development than at intermediate 
temperatures, but these variations from the rule are so slight that they may be disregarded 
for the purposes of this paper. _ 
+ The statements with regard to temperature relations may possibly not apply to 
places differing widely in latitude or altitude from Olney, Illinois. 
