3 
depositing eggs, and it is in the egg state only that, under normal 
weather conditions as to temperature, the “green bug” passes the 
winter, and it is from these eggs that it originates in the spring. 
But from spring to fall there are neither eggs nor males; all are 
females, and these give birth to living young in a series of genera- 
tions. With the normal cold of early winter these females gradu- 
ally disappear and only the winter eggs remain; but if the winter 
temperature is mild, and the temperature of the following spring 
abnormally cold, the summer method of reproduction continues 
throughout the winter and during spring. 
The “ green bug” will breed freely in temperatures ranging from 
100° F. down to below 32°. As the young mature in eight days and 
themselves begin to give birth to young, it will be seen that an excep- 
(a) 
¥ 
Fic. 3.—Lysiphlebus tritici, principal parasite of the spring grain-aphis or ‘‘ green bug:” 
Adult female and antenna of male. Highly magnified (original). 
tionally mild winter followed by an abnormally cold spring offers 
the best possible conditions for the excessive increase of the pest, 
which would ordinarily begin breeding only in spring, and from the 
eggs. 
With excessive reproduction and the destruction or aging of its 
food plants, this insect develops a corresponding abundance of winged 
migrating females, which are the means of the spread northward 
or outward from original centers. 
The “ green bug” in normal years—that is, when its breeding be 
gins in spring—is effectively held in check by its natural enemies, and 
notably by a minute, black, wasplike insect, Lysiphlebus tritici 
Ashm.) (fig. 3) that deposits eggs singly in the “ green bugs,” the 
grub hatching from the egg feeding internally on the bug and de- 
[Cir. 93] 
