Sept. 33, 1918 
Pemphigus populi-transversus 
585 
A report has also been received from Dr. C. E. Mauldin, in charge of 
the Iberia Live-Stock Experiment Farm of the Bureau of Animal Indus¬ 
try, at Jeanerette, La., that— 
It has been necessary for us to abandon the planting of rape and kale at this station 
on account of the root-louse. 
At Baton Rouge the subterranean forms apparently cause more severe 
injury to turnip than to any other cultivated cruciferous crop that has 
been under observation. Not only have they been found in greatest 
numbers on turnips but plants have been frequently noted which, when 
pulled, came up easily. The roots of these plants were mostly dead, 
apparently because of the attack of the aphids. 
FOOD PLANTS OF THE SUBTERRANEAN FORMS 
Wingless specimens of the genus Pemphigus have been taken in 
Louisiana from the roots of the following Cruciferae: Cabbage, turnip, 
mustard ( Brassica nigra), cauliflower, and broccoli ( Brassica oleracea 
botrytis), Brussels sprouts {Brassica oleracea gemmifera), rape {Brassica 
napus), Coronopus didymus , Lepidium virginicum , and Roripa sp. The 
last three host plants are weeds, the first being common in uncultivated 
fields at Baton Rouge during the winter months, when the plants are 
sometimes gathered and used as “greens.” 
Winged migrants (fundatrigenia) of the species of Pemphigus under 
consideration have been found at the roots of cabbage, turnip, Brussels 
sprouts, rape, Coronopus didymus , and Roripa sp. It is quite possible 
that further observations will disclose the fact that the species occurs 
also at the roots of plants not belonging to the family Cruciferae. Mr. 
Lauderdale has found individuals on the roots of stock beet. Adjoin¬ 
ing infested roots of Coronopus didymus apparently explained their 
presence on the beet roots, as examination of the roots of many beets, 
near which no crucifers were growing, failed to disclose additional 
instances of infestation. 
SPREAD OF SUBTERRANEAN FORMS 
Observations made in the field and under laboratory conditions indi¬ 
cate that at least the smaller wingless viviparous females (virgogenia) 
that are present in the soil during the winter months are capable of con¬ 
siderable locomotion, and that when conditions become unsatisfactory, 
these individuals seek more suitable locations. During December they 
have been found in great abundance crawling over the surface of the soil 
and upon the plants in a field of Brussels sprouts. While carrying on 
some experiments in the greenhouse about a year later, individuals were 
found to have left flowerpots in which they were feeding on turnip roots, 
apparently because the turnips had begun to die as the result of being 
severely infested with the aphid Myzus persicae Sulzer. They were 
