Sept. 23, 1918 
Pemphigus populi-trcmsversus 
583 
Of 200 galls collected on September 15, 17 per cent contained winged 
females, while they were present in all of 150 galls taken on September 28. 
The number of winged females in a single gall also showed a gradual 
increase as the year advanced. In June usually only one was found in a 
gall, while on November 7 as many as 76 were present. 
DATES WHEN WINGED MIGRANTS (FUNDATRIGENIA) LEAVE GALLS 
Although winged females appeared in the galls at Baton Rouge during 
1916 as early as June 1, there is no evidence to show that migration to 
crucifers took place until late summer. The earliest collection of winged 
female migrants on crucifer leaves was on August 31, and not until early 
October were crucifer roots found infested to any considerable extent. 
On October 2, 1917, during a period of clear, cool, autumn weather, the 
migrants from the galls were common on turnip leaves at least 500 feet 
from poplar trees. As many as five were found on the underside of a 
large leaf. The greatest migration probably occurs during October. 
While the writer has no definite data regarding the maximum distance 
they may traverse while in flight, it is probable that they, as well as the 
sexupara, may be carried long distances by winds. 
NUMBER OF WINGLESS VIVIPAROUS FEMALES (VIRGOGENIA) TO 
WHICH WINGED MIGRANTS (FUNDATRIGENIA) GIVE BIRTH 
On October 25, 1916, 25 winged females taken from galls were placed, 
without food, in vials and kept under observation indoors. All of these 
began almost immediately to give birth to young, and by October 30 
all had died. The average number obtained from each individual was 
26, the number ranging from 14 to 37. In one instance a female brought 
forth 30 young in about 24 hours. 
The young viviparous females locate on the roots, feed, and when 
mature bring forth other wingless viviparous females. In this way the 
subterranean colonies become established. 
INJURY TO AND APPEARANCE OF PLANTS INFESTED WITH SUBTER¬ 
RANEAN FORMS 
While severe Pemphigus infestation on the roots of crucifers may be 
indicated by the wilted condition of the leaves, a slight or moderate 
infestation does not usually affect, to a noticeable degree, the portions of 
the plant above the ground. For this reason such infestation usually 
goes unnoticed. In other words, this insect, while it may cause as much 
damage as many of those species which feed upon the leaves or other 
parts of the plant above the surface of the soil, does not attract as much 
attention as such species because it works out of the sight of the ordinary 
observer. Inasmuch as these aphids feed upon the roots, it is to be 
presumed, however, that any infestation is detrimental to the plant. 
