80 
of the field—as to prevent so far as practicable the seeding of 
pigeon-grass and smartweed among the corn; (2) that infested 
fields should be plowed deeply and thoroughly harrowed late in 
fall or during some suitable early winter interval; and (3) that 
a somewhat rapid rotation of crops should be systematically 
followed, corn usually being allowed to grow on the same ground 
but two years in succession. While some work remains to be 
done with reference to the precise value of these methods in 
practical application, there is no longer any doubt of their sub¬ 
stantial usefulness, at least as a means of holding in check the 
injuries of the corn root aphis. 
DESCRIPTION OF CORN ROOT APHIS. 
Wingless Viviparous Female. (Plate VIII., Fig. 1).—Body 
broad-oval. Head and prothorax blackish, remaining segments 
p ile green, the first three with a transverse dusky mark at 
middle. Abdomen with blackish marginal patches on the second, 
third, and fourth segments, also numerous smaller spots of vari¬ 
able number and extent. The seventh and eighth segments have 
transverse blackish marks at middle. Antennae dusky towards tip 
and slightly so at base. Cornicles black, cauda and anal plate 
dusky. Beneath nearly uniform pale green, except the usual oblong 
transverse chitinous plate on the seventh segment ; beak black 
at base and tip; coxae, most of femora, tips of tibiae, and tarsi 
black. Antennae rather short, reaching about to the hind coxae, 
I and II short and thick, both combined about two thirds as 
long as III. IV, V, and basal part of VI about equal, the latter 
about three fifths as long as the spur, IV and V combined about 
equal to III. Four outer joints imbricated throughout, more dis¬ 
tinctly on the spur, a group of sensoria on VI at the base of 
its spur, and one near the tip of V, as usual, rarely also one 
near tip of IV or III. Beak passing middle coxae, usually at¬ 
taining hind coxae. Lateral thoracic tubercles large and distinct, 
directed somewhat forward. Similar conical tubercles occur on 
the abdomen, each surrounded by a dark ring; one on each 
side of the first segment, between the first two spiracles, and 
another pair on the seventh segment, each side of the chitinous 
plate. The cornicles are about as long as the third joint of the 
beak, rather slender and nearly cylindrical, often broad at base, 
the outlines straight or concave. The cauda is a little longer 
than its breadth at base, where it is widest, tapering to apex, which 
is broadly rounded. 
Length 1.4 mm., width .93 min., antenme .57 mm., cornicles 
.10 mm. The young are paler in color, and have proportion¬ 
ally longer beaks and shorter cornicles. The chitinous space of 
the seventh segment is almost wanting, and the cauda is shorter 
and broader, as in the pupa. 
Pupa of Winged Viviparous Female. —(PlateVIII., Fig. 3.) Head 
obscure dusky, thorax pale reddish brown, abdomen dull pale 
green, without marking; beneath greenish. Cornicles blackish, 
cauda subtriangular, dusky. Beak dark at base and tip; tarsi 
