The appearances described may, nevertheless, be due either to the 
corn root blight—a disease not caused by insects, and hence not treated 
in this report—or to the grass root louse, a species likewise attended 
by ants, but far less injurious to corn than the aphis under discussion. 
If the damage be due to the root blight, the root lice themselves will be 
few or wanting;* and if to the grass louse, the fact may readily be as- 
certained by an examination of the roots of the corn. 
The root aphis of the corn is of a bluish green color, slightly whit- 
ened by a waxy bloom. The form of the body is oval, and on the hinder 
part of the back are two short, slender, but conspicuous, tubes, standing 
erect or projecting slightly backwards, which may be seen by the glass 
to have open ends externally. These are called the cornicles of the 
aphis, or, sometimes, the “honey tubes,” it having been formerly supposed 
that they were the source of the abundant excretion upon which the ant 
attendants of the lice eagerly feed. The grass louse, on the other hand, 
is white in color, with a blackish head and other blackish markings, but 
without any tint of green; and it has no trace of cornicles, their place 
being taken by two minute openings in the corresponding segment of the 
body, each surrounded by a delicate brownish rim. 
The evidences of serious injury by the corn root aphis are, in short, 
an unusual dwarfing and discoloration of the corn, an abundance of 
small brown ants in the field, nesting among the hills, and, finally, the 
presence of the bluish green insects themselves upon the larger roots of 
the corn, especially near the base of the stalk. 
The amount of injury may vary from a searcely noticeable check 
upon the growth of the plant to a total destruction of the corn over 
considerable patches, up to half an acre or more. This more serious 
effect is, however, rarely, if ever, produced by the root louse alone. Like 
most insect enemies, especially those of suctorial habit, which abstract 
the sap of the plant they feed upon,—the corn root aphis serves to in- 
tensify the effect of drouth and other unfavorable influences, and it is 
often difficult to say how much is to be ascribed to the action of the in- 
sect pest and how much to other causes codperating. 
There is some evidence to the effect that a too serious check to the 
growth of the corn results in the early evolution of a great number of 
winged plant lee of the second spring generation, whose escape from 
the fields in which they start so breaks the force of the attack that in a 
favorable season very badly damaged plants may rally and make good 
corn; but if the insect injury is followed or reinforced by drouth, the 
corn may grow sluggishly the whole season through, and either fail to 
ear, or bear small imperfect nubbins only. Sometimes a field not in- 
fested the year before is permanently damaged in June, or even late in 
May, as the result of an early accidental concentration of the w inged hee 
originating in other fields. te 
INJURY TO OTHER PLANTS. 
No other crop plants are especially liable to injury by this aphis, 
unless possibly we should except broom corn and sorghum. Although 
not at all uncommon on these plants, it does not commonly thrive on 
* See also page 46, b. 
