Sept. 23,1918 
Pemphigus populi-transversus 
587 
plaee. The female is larger than the male and deposits only a single egg. 
In a well-ventilated insectary at Baton Rouge, during 1916, eggs were first 
noted on March 6 in vials in which the true sexes had first appeared 12 
days before. 
OVIPOSITION 
The egg is often found resting in a small amount of white, cottony 
material secreted by the female. The true sexes apparently do not, as 
a rule, move far from their places of birth, eggs being found in the field 
in crevices on the trunks and limbs of poplar trees where living winged 
migrants (sexupara) and the dead bodies of others were present. In 
the insectary at Baton Rouge stem mothers were first seen on March 22, 
1916, in vials where eggs had first been noted on March 6, giving a period 
of 16 days for the incubation of the egg. 
FORMATION OF GALT 
Of necessity the young, active stem mother (fundatrix), after issuing 
from the egg, must make its way to the developing leaves, ^yhere it 
settles down on the petiole and becomes responsible for the formation 
of a gall. While there is no absolute proof that such is the case, it is 
believed from field observations that one stem mother is responsible for 
one gall only and that a gall is only formed when a young stem mother 
locates on a leaf petiole. 
SEASONAL HISTORY OF PEMPHIGUS POPULI-TRANSVERSUS IN BRIEF 
The following summary has been prepared from observations made 
in the field and laboratory at Baton Rouge (fig. 1). The dates when the 
various stages appear and migration takes place probably depend to 
some extent upon the weather. It would be interesting to know the 
seasonal history of the species in the northern portion of its range where 
climatic conditions, especially as regards temperature, are so different 
from those existing in Louisiana. 
The galls begin to develop on the petioles of the young leaves of Populus 
delioides in the spring. They increase in size during the summer and by 
the time the leaves fall in the autumn some have reached a diameter 
of nearly an inch. 
Of 1,175 leaves gathered from a poplar tree on July 26, 1916, 26.2 
per cent had galls on their petioles. They occur on both small and 
large trees. 
Winged migrants (fundatrigenia) have been found in the galls as 
early as June 1. The percentage of galls containing winged migrants, 
as well as the number found in anv one gall, increases as the season 
advances. 
Winged migrants from the galls fly to various cruciferous plants. 
They have been found on the leaves of such plants as early as August 
30 and as late as October 31. 
