584 
Journal of Agricultural Research 
Vol. XIV, No. 13 
Upon examination of the soil about plants attacked by the subter¬ 
ranean forms colonies may be found upon any portion of the root system, 
but the small rootlets appear to be preferred. Where dead leaves, or 
other trash, occur on the surface of the soil, there is often a growth of 
rootlets immediately beneath, and colonies are often found in such 
locations. 
Mr. J. L. E. Lauderdale made an interesting observation at Baton Rouge 
on March 19, 1917, while examining roots of Coronopus didymus in a field 
of stock beets {Beta vulgaris ). The beets were growing on ridges where 
the soil was less moist and less compact than that midway between 
the rows. Of 25 plants of C. didymus growing on the ridges, 24 were 
infested with Pemphigus populi-transversus y whereas only 6 of 25 plants 
growing in the low ground between the rows had aphids present on 
their roots. This would indicate that either the compactness of the soil 
between the rows, or its higher moisture content, or both, was disad¬ 
vantageous to the development of the aphids. 
The white, flocculent material which the aphids secrete is of material 
aid in locating them. This secretion often occurs in considerable abun¬ 
dance about the colonies (PI. 85). The light-yellow color, character¬ 
istic of the bodies of the wingless females, except in their early stages, 
usually makes it easy to locate them when the soil about the roots on 
which they are feeding is carefully examined. 
INJURY CAUSED BY THE SUBTERRANEAN FORMS 
Where the aphids occur in small or moderate numbers at the roots of 
plants, it is difficult to estimate the amount of damage done by them. 
The following extracts from correspondence received by the Louisiana 
Experiment Stations give information as to injury to crucifers by Pem¬ 
phigus spp. in Louisiana. As only wingless forms were forwarded by 
the correspondents, it can not be stated positively that the root aphid 
causing the injury was P. populi-transversus , although that is probable. 
On November 13, 1915, a correspondent living at Rhoda in St. Mary 
Parish wrote: 
I am sending you under separate cover a cabbage plant that is badly infected with 
a small yellow louse, and would ask if you can recommend anything that can be 
done. The bug or louse is found at the root of the plant, and seems to suck the sap 
or eat off the roots, as the plant is badly wilted during the warm part of the day, but 
revives a little at night, until it finally is killed. 
On November 22 of the same year a letter was received from New 
Iberia, Iberia Parish, in which the writer stated: 
Enclosed please find stalk of cabbage with insect at the root that is destroying all 
my plants. 
