never being seen on the roots of the grain even where these and the — 
grass roots were closely interlaced. 
The relation of this louse to other plants than corn has an im- 
portant economic bearing. For example, in fields on old corn ground, 
the.first generation of plant lice are very noticeably more abundant early 
in spring in the lower parts of the field than elsewhere, especially in — 
those parts so situated as to receive the wash from the remainder. I can 
at present only account for this unquestionable fact by the very much 
greater abundance here of young smartweed plants, doubtless due to the 
washing down of the seeds left on the ground in fall. This seems — 
especially likely to be the true explanation, since the difference in the 
number of plant lice on low and high ground in the same field dimin- — 
ishes greatly or entirely disappears with the advent of later generations 
and the scattering of the winged lice abroad. 
LIFE HISTORY 
General Statement—The corn root aphis passes the winter as an 
egg in the earth, in corn fields or, rarely, in other grounds where purs- 
lane grows late in fall, always, so far as known, only in the nests of a 
small brown ant about an eighth of an inch long, known to science as — 
Lasius niger or its variety, L. niger alienus. This ant is the constant 
companion of the root louse throughout the year, living in burrows 
among the roots of the corn. The aphis egos begin to hatch about the 
time of the opening of the seed leaves of the smartweed or heartweed 
(Polygonum persicaria), abundant in cultivated ground. This first of 
the spring generations is readily distinguished by characters of form | 
and color from all that follow. Appearing usually before the corn is 
planted, it is dependent at first, in our region, almost wholly upon the 
young smartweed plants. The roots of these are laid bare by the bur- 
rows of the ants, and upon these roots, within their narrow tunnels, the 
lice will usually be found thickly clustered. Later, if the field be not 
planted to corn, our common species of pigeon-grass (Setaria) divides 
the attention of the lice, offering in fact, for a little time, a more succu- 
lent herbage than the rapidly growing smartweed. 
The second generation begins to: appear about the 1st of May,—we 
have one breeding-cage record of the 28th of April_—and by the middle 
of that month may be itself mature. Many of this generation are 
winged, while others are without wings,* the winged form first occurring 
about May 10.+ These “migrant” root lice may live at first, like those of 
the preceding generation, upon smartweed and pigeon-grass, but more 
commonly they are transferred to corn by the little brown ink already 
mentioned, either in the same field or after they have flown to another. 
These ants not only carry from weeds to corn the root lice already in 
their possession, but burrow hills of corn in advance, eagerly seizing and 
conveying to their subterranean galleries winged root lice which come 
their way. 
*Two young of this generation, born of the same mother in a glass tube en- 
closing a corn root, were kept by us until adult, when one proved to be a wingless 
aphis and the other winged. 
+ This generation is at its best from May 15 to 20 in average years in Central 
Illinois. 
