Diabrotica longicornis (The Northern Corn Root Worm). 
(Plate XIV., Fig. 6-8; and Plate XV., Fig. 1-8.) 
Page 135. 
DETAILED Discussion oF INJURIES TO THE Roots. 
1. Some of the roots deadened, hardened, or dwarfed, without loss of 
substance. . 
a. Small brown or yellowish ants abundant in the hills, and very 
small, bluish green or whitish, oval, thick-bodied root 
lice on the larger roots. 
PLANT LICE AND MEALY BUGS. 
(APHIDIDA AND CoccID.®) 
Associated with ants in hills of corn, the observer may find any one * 
or more of eight species of minute, soft, thick-bodied, six-legged insects, 
sometimes winged, but usually without wings, and always of very slug- 
gish habit and slight power of locomotion. When exposed, they may 
show little or no signs of disturbance, but if shaken off the roots into 
which their stout jointed beaks are thrust, they will probably crawl 
slowly and clumsily about, making movements almost too sluggish and 
aimless to look like efforts to escape. The ants which have ‘nested in 
the hill will, however, commonly seize these little insects in thelr man- 
dibles and hurry away with them into concealment. 
By far the greater part of those answering to the above description 
to be found in the corn field, will usually be plant lice (aphides) ; and 
will mostly belong, in fact, to a single species, the corn root aphis; but 
a few may be ‘‘mealy bugs” (genus Dactylopius, family Coecide), ree- 
ognizable as such by their general resemblance to the kinds of “mealy 
bugs” common in greenhouses. They may be readily distinguished 
from the plant lice by their thicker, clumsier bodies, and by the almost 
rudimentary size of their legs and antenne. They are always covered 
with a mealy or powdery excretion of minute particles of wax, and never 
have honey tubes, or cornicles, on the back of the abdomen—both char- 
acters in which they agree, however, with some of the lower plant lice. 
From all the corn-infesting plant lice they may be technically separated 
by the fact that their tarsi are single jointed, and bear a single tarsal 
claw, while the plant lice of this group have two tarsal joints and a pair 
of tarsal claws. 
Plant lice are among the most prolific of insects,* producing sev- 
eral generations annually, but they are commonly held severely in check 
by climatic, meteorological, and biological conditions; that is, by sea- 
son, weather, and plant or animal parasites. They are, consequently, 
* Slingerland has bred twenty-five generations of a plant louse (Myzus achy- 
rantes?) in a single year (Science, Vol. XXI., 18938, p. 48); and Buckton shows (A 
Monograph of British Aphides, Vol. L., p. 80) that a single rose aphis (Siphonophora 
rose might give origin, at its normal rate of unchecked multiplication, to over 
thirty-three quintillions of plant lice in a single season, equal in weight to more than 
a billion and a half of men. 
