57 
or they may migrate definitely, by means of a fixed generation, 
from one species to another, requiring thus for their continu¬ 
ance two plant species often extremely unlike * 
Finally, the sexual, oviparous generation (commonly the last 
to appear in fall) may leave its eggs on the exposed parts of 
the plant last infested, or it may deposit them in the earth 
among or on the roots of its host. In the former case the de¬ 
struction of the plant, or of its remains, will destroy the lice; 
in the latter, the eggs rest like a seed in the earth to stock the 
ground the following spring with a horde of young, ready to 
infest the succeeding crop if suited to their tastes and habits. 
All the plant, lice of our present list of species infesting the 
roots of corn are, so far as known,t subterranean only, producing 
no galls, but leaving their eggs in the earth over winter. They 
infest more than one plant, spreading from one to another 
species in an indefinite manner, not definitely migrating. The 
corn and grass root lice ( Aphis maidiradicis and Schizoneura 
panicola) develop early in the season winged forms by which 
they easily spread from field to field. 
Six species of plant lice belonging to as many different genera,! 
have been found by us habitually infesting corn roots in Lllinois. 
They are Aphis maidiradids, Schizoneura panicola, Tram a erip;. 
eronensis , Forda occidentalis, Tychea hrevicornis , Rhizohius spi- 
catus and Geoica squamosa. By far the most important of these 
is the first mentioned, commonly known as the corn root aphis. 
This is, in fa.ct, the only one on the list which infests corn primari¬ 
ly as a principal food plant, the others being essentially species 
of the meadow and pasture, attacking corn but lightly, and 
most commonly only when it follows grass. 
The association of all these species with ants, which care for 
them in many ways, some of them indispensable, and feed in 
turn on excretions of their insect charges, is a fact of special 
*The apple louse ( Aphis mali), for example, passes from the apple to various grasses 
in midsummer, returning to the apple leaf in fall, and leaving upon the twigs eggs from 
which young hatch the following spring. The hop louse ( Phorodon hamuli) alternates in 
a similar manner between the hop and the plum; and a grass root louse ( Schizoneura corni) 
between the grasses and the dogwoods. 
+ It has long been a general opinion that the corn root louse, presently to tre discussed* 
is a subterranean form of the leaf louse (Aphis maidis), a surmise which I have failed to 
verify after many efforts extending through several years, and so ha\ e declined to accept. 
+ The following brief table may serve in a general way to indicate the correct genus and 
species of each of our corn root lice: 
Cornicles well developed. t . Aphis maidiradicis. 
Cornicles reduced to dark rings. Schizoneura panicola. 
Cornicles wanting. 
Last two joints of beak not longer than basal portion. 
Anal plate subglobose, strongly prominent. . 
Third antennal joint about as long as first two combined, an additional joint 
usually more or less distinctly formed from it, making the antennae 6- 
jointed.. Trama eriqeronensis. 
Third antennal joint very long, nearly twice as long as first two combined, 
antennae uniformly 5-jointed. Forda occidentalis. 
Anal plate short, transverse, not at all prominent. 
Antennae normal, as large as rostrum, third and fifth joints more than twice 
longer than thick. Tychea hrevicornis. 
Antennae minute, much smaller than rostrum, joints less than twice as long as 
thick. Iihizobias spicatus. 
Last two joints of beak much longer than basal portion, anal plate retracted into 
dorsal segments. Geoica squamosa. 
