3 
THE RELATION OF TEMPERATURE TO DESTRUCTIVE OUTBREAKS. 
This insect, as with other closely allied species of aphides, repro- 
duces in two ways. As cool weather approaches in autumn there 
occur in greater or less numbers both males and females, the latter 
depositing eggs (see fig. 4), and it is in the egg state only that, under 
normal weather conditions as to temperature, the “ green bug ” passes 
the winter, and from these eggs 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 generations. With the 
normal cold of early winter these females gradually disappear and 
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. Indeed, it is not improbable that males and egg-laying fe- 
males may be found in spring, especially in the South. 
The “ green bug ” will breed freely in 
temperatures ranging from above 100° 
to below 46° F. As the young mature 
in eight days and themselves begin to 
give birth to young, it will be seen that 
an exceptionally 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 W 
in spring, and from the eggs. Fic. 4.—Spring grain-aphis (Tor 
rT: TRNCI ST ACLS E : optera graminum): Egg-laying 
With excessive reproduction and the feiale withtaeeGatt boawiercate 
destruction or aging of its food plants, enlarged ; at right, egg, still more 
this insect develops a corresponding a er me eu ste 
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. (see fig. 5) that deposits eggs singly in the “ green bugs,” the 
grubs hatching from the eggs feeding internally on the bug and de- 
stroying it (see fig. 6). Other natural enemies are the larvee of cer- 
tain predaceous flies, and the larvee and adults of lady-beetles. The 
little wasplike parasite first mentioned, however, is the one that keeps 
the “ green bug” in control in normal years, and in years when the 
latter is most abundant finally overcomes it, as was the case in 1907 
in Kansas, North Carolina, and other States in the more northern 
part of the range of the pest. 
[Cir. 93] 
