24 
General Program of Prevention 
In the light of what we now know concerning the corn root-aphis, 
the following measures of precaution are to be recommended as a 
practical program. 
1. A short rotation period in corn, especially during relatively dry 
years. A single year in corn is better than two years, and a period 
of two years is better than one of three. Especially if the crop was 
visibly injured by the root-aphis the preceding year, or if more than 
twenty ants' nests to the mile are turned up by the plow, it is best 
that the field should be put into some other crop than corn — which 
other is a matter of indifference, since no other is liable to injury by 
the corn root-aphis. 
It must be remembered, however, that even a field in corn for 
the first time may become infested during the season by means of 
winged root-lice coming into it from other fields in its neighborhood, 
this infestation perhaps beginning as soon as the corn is up ; and that 
the rate of multiplication of these insects is so enormously rapid, under 
favorable conditions, that such a new infestation sometimes reaches 
destructive numbers before the first season is over. Even the shortest 
rotation is consequently not a complete preventive where the root- 
aphis has become so generally prevalent as it now is in most parts of 
the Illinois corn belt. This is, however, the most reliable of all known 
measures of prevention, and has the very great additional advantage 
that it affords complete protection against another of the great insect 
pests of the corn field, the notorious northern corn root-worm (Dia- 
brotica longicornis. 
2. A deep, thoro, and repeated stirring of old corn ground in fall 
or spring {or, better still, in zvinter, where possible) as a preparation 
for corn-planting. So quick a rotation as that advised in the preceding 
paragraph is perhaps not always practicable, and is at any rate often 
unwelcome and will not always be practiced. If corn is to be planted 
on ground more or less infested by the root-aphis the preceding year, 
injury by this insect may be greatly diminished by such a preparation 
of the soil as will repeatedly break up the underground nests of the 
ants and scatter the contents of these nests, consisting of the eggs and 
young of the ants together with the root-lice and their eggs, thoroly 
and repeatedly thru the dirt. The burrows of these ants do not often 
reach to a depth of more than six inches, and if plowing to this depth 
is followed by a deep stirring of the ground with a disk harrow, or 
better, with a corn cultivator set into the ground as far as possible, 
the attempts of the ants to recover their propery and to reconstruct 
their nests are greatly disturbed and rendered largely fruitless. The 
more thoroly, frequently, and deeply the ground is stirred in the in- 
terval between the first plowing and the corn-planting, the fewer will 
be the root-lice in the field in the beginning of the season. By this 
means a check will also be placed upon the increase of the ants them- 
selves, by the destruction of their helpless maggotlike young which 
they have brought thru the winter in their nests. Furthermore, the 
