Sept. 23, 1918 
Pemphigus populi-transversus 
579 
In lists and synopses of North American aphids the species has been 
mentioned by several authors. It is included in the “ Host-plant list 
of North American Aphididae” by Williams (4, p . 6, 9), published in 
1891, and in a bulletin entitled “The Aphididae of North America” 
by Hunter (ro, p . 7<?), issued in 1901. In a synopsis of the genus Pem¬ 
phigus Jackson (14, p. 182 , 183 , 206-208) in 1908 referred to the species 
somewhat in detail and stated that the life history was “very imper¬ 
fectly known.” Further references to its life history have been made 
by Davidson (r6, p. 372) and Gillette and Bragg {22, p . 98). Davidson 
stated that the stem mothers had been observed “founding their colo¬ 
nies” in the vicinity of Stanford University, California, in March. 
Gillette and Bragg ( 22 , p. 98) in “ Notes on some Colorado aphids having 
alternate food plants,” published in 1916, gave “winter host, Populus 
species; alternate host unknown.” 
EXPERIMENTS IN TRANSFERRING THE SPECIES FROM CRUCIFERS TO 
POPLAR AND FROM POPLAR TO CRUCIFERS 
Soon after investigational work on this root aphid was begun, winged 
viviparous females (winged migrants or sexupara), collected from the soil 
about cruciferous roots, were sent to Dr. Gillette and to Mr. J. R. Parker. 
Both stated that they did not recognize the individuals as belonging to 
any described species of the genus Pemphigus, but suggested that it 
was possible that they might be identical with Pemphigus populi-trans - 
versus . In view of this, experiments were begun in an attempt to ascer¬ 
tain whether there was a migration of the species from crucifers to poplar 
at one season of the year, and a return migration at another season. 
In 1916 cuttings were taken from trees of Populus deltoides , before the 
buds began to swell, and stuck in moist sand in flowerpots, which were 
kept in a greenhouse. When leaves began to appear on these cuttings, 
young individuals of the stem mother (fundatrix) were placed on them. 
These stem mothers had recently issued from eggs obtained in the labo¬ 
ratory from the true sexes, which had in turn been produced by winged 
females (sexupara) taken from about the roots of crucifers in the field. 
Swellings soon began to appear on the petioles where the stem mothers 
had located, and these swellings, increasing in size, gradually took on 
an appearance typical of the gall of Pemphigus populi-transversus (PI, 
82). Unfortunately the stem mothers died after the galls had reached 
a diameter of about inch. Galls were again formed about stem mothers 
on leaf petioles of poplar in the greenhouse in the spring of 1917, and 
these, developing to a greater size, appeared identical to those of P. 
populi-transversus . 
During the fall of 1916 winged migrants (fundatrigenia) from the galls 
of Pemphigus populi-transversus were placed under cheesecloth in a cage 
where turnips were growing. Later, examination of the soil showed the 
roots of the turnips to be heavily infested with aphids of the genus 
