588 
Journal of Agricultural Research 
Vol. XIV, No. 13 
The winged migrants give birth to viviparous females (virgogenia) 
which start colonies on the roots of crucifiers, upon which they feed. 
The infestation at the roots of crucifiers, which is usually made appar¬ 
ent by the white, cottony material which the aphids excrete, gradually 
becomes more severe, owing to the increase in the number of the sub¬ 
terranean forms. It appears that, under certain conditions, the smaller, 
wingless viviparous females occurring in the soil are able to migrate to a 
considerable distance from their place of birth and there begin new 
colonies. 
Fig. i.—D iagram illustrating the seasonal history of Pemphigus populi-transversus at Baton Rouge, I*a. 
Winged migrants (sexupara) appear in the subterranean colonies 
during the winter. They have been found at the roots of cabbage, tur¬ 
nip, Brussels sprouts, rape, Coronopus didymus , and Roripa sp. Colo¬ 
nies of a species of Pemphigus have also been found at the roots of mus¬ 
tard, cauliflower, broccoli, and Lepidium virginicum. No winged mi¬ 
grants were present in these colonies, but it appears probable that the 
aphids were of the same species. 
In the spring the winged migrants fly from the crucifers to poplar 
trees where they give birth to the true sexes (sexuales), usually in crev¬ 
ices on the trunks and branches. 
The sexed individuals take no food and, after pairing, the female 
deposits a single egg. 
