Mar. 34,ms Temperature and Evaporation on Aphis pomi 
985 
Table V shows the relation of temperature to the rate of development of 
Aphis pomi . The actual mean temperatures of the developmental periods 
of the several series were first plotted as shown by the circles on the 
graph, figure 8. It was found that these points lie approximately along 
Fig. 8 .—Curve showing theoretical relation of temperature to rate of development of A Phis pomi. 
a hyperbolic curve having the formula x = 
a 7 
y — b* * 
This formula may be 
expressed by the formula: Length of developmental period in days 
__180_ 
~ Temperature in degrees Fahrenheit — 41 ' 
If the curve thus plotted be extended it will be found that as the tem¬ 
perature is lowered the development of the aphids becomes less rapid, 
until at a temperature of 41° F. or less development ceases entirely. In 
other words, only temperatures above 41 0 are “ effective” 8 in the develop¬ 
ment of Aphis pomi. By subtracting all temperatures of 41 0 or less and 
by computing the mean of the remaining temperature readings the mean 
effective temperatures (Table V) were obtained. By subtracting from 
the developmental period the time during which the temperature was 41 0 
or less the duration of effective temperature was determined. These 
data were then plotted on the graph (fig. 8) as indicated by the crosses. 
7 The writer is indebted to Prof. E. B. Beaty, of the Department of Mathematics, Oregon Agricultural 
College, for the computation of the formula for this curve. 
• Sanderson, E. Dwight, the relation of temperature to the growth of insects. In Jour. 
Econ. Ent., v. 3, no. 2, p. 113-139, fig. 6-26. 1910. Authors cited, p. 138-1,39* 
