EXPERIMENTS WITH REPELLENTS AGAINST 
THE CORN ROOT-APHIS, 
1905 AND 1906 
The corn root-aphis, a minute, bluish green, skiggish, soft-bodied 
insect found on the roots of corn, is one of the most destructive and 
dangerous insect pests of the corn plant. Beginning as soon as the 
kernel sprouts to suck the sap from the young roots, it may continue 
its injury without interruption until frost, unless the infested plant 
in the meantime perishes. It has an enormous power of multiplication, 
producing, under favorable circumstances, as many as sixteen genera- 
tions in a season, and it is capable of spreading from field to field 
rapidly on the wing, many of each generation, except the first of the 
year, having the power of flight. 
Altho a peculiarly sluggish and stupid insect, wholly unable to 
make its own way unaided, it has always in its service one of the most 
capable, abundant, active, and persistent of our common insect species. 
This is the so-called corn-field ant (Lasius alieniis americanus), in 
whose charge the corn root-aphis is usually found, and by which its 
eggs, laid in fall, are carried thru the winter. This corn-field ant 
has no power of injuring the corn directly, except as it may occasion- 
ally, or under peculiar circumstances, devour the softened kernel in 
the earth, and the root-aphis, left to itself, can not even get access to its 
food in numbers to do any noticeable harm ; but the two in partnership 
check the growth of the plants, and even kill outright whole fields of 
corn, the aphis making the destructive attack, and the ant protecting, 
transporting, and guarding the aphis, and collecting, preserving, and 
hatching its eggs. 
The practical control of this pair of insects is especially important 
because the injury done to corn, already very heavy, is sure to increase 
with time. The more generally and continuously corn is grown, and 
the more the soil deteriorates under continuous cropping, the greater 
this aphis injury must become. It is hence most serious and threaten- 
ing in those very parts of our area best adapted to corn, and is much the 
greatest now in Illinois in the central part of the state, where corn is 
the principal crop. 
Neither of these insects is subject, so far as known, to destruction 
by parasites or by contagious diseases, the principal natural checks on 
the multiplication of most other injurious species. About the only 
natural agency which can be depended on to reduce the numbers of 
the corn root-aphis is a long-continued soaking of the ground by fre- 
quent heavy rains, especially if these come in a slow, cool spring. The 
very wet spring of 1907, for example, seems to have had the effect to 
