66 — 
time when this is likely to be most injurious. (3) Since the small 
brown ant cares assiduously for the eggs in winter and spring, we may 
assume provisionally the necessity of such care and strive to find means 
of so disturbing the nests of the ants or of breaking up and dispersing 
their contents in late fall or in winter that their stores of aphis eggs 
cannot be recovered by them, and so shall be left to perish. (4) Taking 
account of the early hatching of the eggs in spring.—several days, as a 
rule, before the usual time for planting corn,—and the dependence of 
the young lice for food at that time on sprouting weeds in the field— 
especially smartweed and pigeon-grass,—we may seek to handle the 
ground in such a manner that there shall be no sufficient start of vegeta- 
tion to keep the lice alive. We may also delay somewhat, if necessary to 
this end, the planting of the field to corn. 
Rotation of Crops.—There can be no doubt that a judicious rota- 
tion of crops has the effect at least to diminish injury by the corn plant 
louse by distributing its attack; and there is also considerable reason to 
believe that it must result in the destruction, direct or indirect, of a 
certain proportion of the insects themselves. Corn planted on ground 
not previously stocked with plant-louse eggs must escape at any rate 
until invaded from without by winged individuals of the second genera- 
tion, and then, as a rule, it will be no more subject to injury than the 
other fields in its neighborhood. On the other hand, as the corn root 
aphis has never been known to infest to an injurious extent any other 
crop following corn, there is very little probability that the escape of 
the corn will be balanced by damage to other crops. 
We have many observations going to show that wheat and oats and 
the smaller grass-like plants in general are commonly soon deserted by 
such corn root lice as commence to breed on them—a fact which indi- 
cates that these plants are less suitable than corn to the maintenance and 
multiplication of these insects. We have also considerable reason to 
believe that many winged plant lice flying about in search of feeding 
and breeding grounds must be destroyed by some of the innumerable 
accidents to which these feeble and helpless insects are necessarily ex- 
posed. This measure of rotation may consequently have the effect to 
diminish to an important extent the number of corn root lice in later 
generations. Precise proof on these points is, however, very difficult to 
secure. Artificial breeding experiments are altogether too variable in 
result to serve the purpose, as our own attempts at a solution of this 
question show; and evidence must be sought in the field especially by 
making detailed comparative observations of parts of the same previously 
infested fields, planted here to corn and there to small grain. The rela- 
tive abundance of the lice late in May and early in June will go far to 
show the comparative utility of these crops as a food resource to the 
eorn root aphis. 
Applications of Fertilizers and Insecticides.—Various field observa- 
tions have given us reason to conclude that fertilization of the soil will 
serve to support corn under the drain of aphis injury, especially by 
enabling a stunted plant to rally more rapidly and completely after the 
insects have begun to seatter. The rapidity and vigor with which, in 
rich ground and in a fairly favorable season, corn will outgrow an 
apparently fatal injury by the root aphis is, in fact, often quite sur- — 
