253 
disregarding the slight differences in the units due to the use of 88, 85, 
and 87 as the degree of the maximum rate of development of the egg, 
larva, and pupa, respectively, we have for the equation of development 
‘of the three stages PE = 1101. 
Since the larval period is about equal to the egg and pupal periods 
combined, the use of 86 degrees as the degree of maximum rate of de- 
velopment for all three stages will give about the same results and will 
give units of the same value for all three stages. 
OBSERVATIONS ON THE Lire History oF THE CODLING-MOTH 
in 1915, 1916, anv 1917 
Continuous observations were made on the life history of individuals 
j throughout the seasons of 1915, 1916, and 1917. The methods employed 
| 
: 11.. Taking 50 as the zero of development for all three stages and 
: 
: 
in making these observations are described on page 228 of this article. 
The following tables give the principal facts as to length of the 
periods, oviposition, and number of effective day-degrees which accumu- 
lated during the entire period of development. In computing the effective 
day-degrees for the stages, 50 degrees F. was taken as the zero of develop- 
ment and 88, 85, and 87 as the degree of maximum rate of development 
of the egg, larva, and pupa, respectively. By reason of the slightly dif- 
ferent degrees of the maximum rate of development used for the dif- 
ferent stages, the effective day-degrees of the different stages are units of 
not quite the same size and strictly speaking can not be added, but they 
differ so slightly that their sums, which are recorded in next to the last 
column in the tables, will serve as a basis for comparison. 
In order that we might have a common unit in terms of which to 
express the accumulated effective day-degrees of the whole period from 
the deposition of the eggs to the emergence of the adult, it was necessary 
to use as the degree of the maximum rate of development a single point 
instead of 85, 87, and 88, and 86 was selected as the nearest integral 
r degree to the weighted average of the three. Using 50 as the zero of 
: development and 86 as the degree of maximum rate of development, 
the effective day-degrees which accumulated during the combined egg, 
larval, and pupal periods were computed and recorded in the last column 
3 in the tables. All of the tables bearing on the life history of the insect 
- (Tables 9—25) follow. 
Erratum: P. 253, last line, for “follow” read “precede this page.” 
