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LI B R.AFIY 
 
 OF THE 
 
 U NIVER.5ITY 
 
 or ILLINOIS 
 
 570 
 
 no.l-24 
 cop. 6 
 
 NATURAL HfSTORV 
 SURVEY 
 
 NATURAl 
 HISTORY SURV 
 
Digitized by the Internet Archive 
 
 in 2011 with funding from 
 
 University of Illinois Urbana-Champaign 
 
 http://www.archive.org/details/cornrootaphis06flin 
 
y:^~*<T 
 
 STATE OF ILLINOIS 
 DEPARTMENT OF REGISTRATION AND EDUCATION 
 
 DIVISION OF THE 
 
 STATE NATURAL HISTORY SURVEY 
 
 STEPHEN A. FORBES. Chief 
 
 Entomological Series 
 
 CIRCULAR 4 
 
 THE CORN ROOT-APHIS 
 
 BY W. P. FLINT 
 Chief Field Entomologist 
 
 PRINTED BY AUTHORITY OF THE^STATE OF ILLINOIS 
 
 URBANA. ILLINOIS 
 
 1919 
 
 ILOFOLUB. 
 
 Nstwf «) History Sui^«f 
 
ScHNEPP & Barnes, State Printers 
 
 Springfield, III. 
 
 1919 
 
 17707— lOM 
 
610 
 
 ^^■^ 
 
 THE CORN ROOT-APHIS 
 
 By W. P. FLINT, Chief Field Entomologist 
 State Natural History Survey 
 
 If our crops were being destroyed because one of our neighbors 
 turned his stock into our fields, we would naturally go to the owner 
 and not to the stock to have this practice stopped. But if for some 
 reason he claimed that his stock had a right in our fields and persisted 
 in trying to get them there, we should find it much more difficult to 
 keep them out than if the animals had strayed in of their own accord; 
 for, generally speaking, at least, the owner would have more intelli- 
 gence than his stock. This is much the same condition that we have 
 to face in dealing with the corn root-aphis. If the old adage holds true 
 that possession is nine points of ownership, the corn root-aphis has 
 an owner, and it is this owner, the little brown ant of the corn fields, 
 that we must combat if we are to keep our corn roots free from the 
 aphis. 
 
 Were one to dig, during some warm period in winter, around the 
 hills in a field that has been in corn for several years, he would almost 
 certainly find, at a depth of eight or ten inches, a nest or burrow of 
 the corn-field ant. In the chambers of this nest would be found num- 
 bers of the maggot-like young of the ants, and in some of them small 
 piles of the dark-green, shiny eggs of the corn root-aphis. If the day is 
 warm enough so that the ants are active, they will make as great an 
 effort to protect the aphis eggs as they do to protect their own young.; 
 and if this nest could be watched through the winter we should find 
 the ants giving most careful attention to the aphis eggs, moving them 
 about in the nest that they might not become too damp or too cold. 
 When the ground becomes warmer in spring the ants move nearer the 
 surface, and as soon as their aphis eggs begin to hatch (which is gen- 
 erally about the time the first smartweeds begin growing in the fields) 
 they place the young aphids on the roots of these and other corn-field 
 weeds. Here the aphids suck the sap from the roots, growing rapidly, 
 and in a few weeks begin giving birth to living young. The ants seem 
 to know that corn is one of the best of food plants for this insect, and 
 if there is any corn growing near the ant colony they are very sure 
 to find it and to place the aphids on its roots. There they remain 
 through the summer, attended by the ants and reproducing at a very 
 
Plate I 
 
 The Corn Root-Louse (Aphis maidiradicis). B, the common wingless, and A, the 
 Winged viviparous female; F, the pupa of the winged female; C, the oviparous 
 female occurring in autumn, and D. its egg ; E, the root-louse ant (Lasius mger). 
 
rapid rate by giving birth to living young. These young are all wing- 
 less at first, but some of them develop wings and, making their way 
 to the surface of the ground^ take flight. When they settle to the 
 ground they wander aimlessly about until found by some ant which 
 at once takes them to its burrow and places them on the roots of a 
 food-plant. It is mainly in this way that new colonies of the aphis 
 are started. On the approach of cold weather a change takes place in 
 the manner in which the aphids reproduce, and they then deposit eggs 
 which are gathered by the ants and cared for during the winter. 
 
 It is not to be supposed that the ants give all this care to the root- 
 aphis and receive nothing in return. The root-aphis gives oflf a fluid 
 which we call honeydew, and it is to get this substance as food that 
 the ant cares for the aphis. 
 
 So our fight to prevent injury by the corn root-aphis must be 
 made against its owner — the corn-field ant. 
 
 The best means we have found for destroying ants' nests in an 
 infested field is to break them up and scatter them through the soil by 
 thorough and repeated deep cultivation before the corn is planted. If 
 a heavily infested field is plowed four and a half to five inches deep 
 and the plow is followed through the field, it will be found that a 
 large number of the ants' nests have been split in two, a part turned 
 out in the furrow slice and a part remaining undisturbed in the bot- 
 tom of the furrow. The ants will soon reestablish their nest about 
 the unbroken part, and as we can not hope to break this up by later 
 work with the disk but little has been accomplished towards clearing 
 the ants from this field. If the field is plowed six and a half inches 
 deep, nearly all the ants' nests will have been turned out entire in the 
 furrow slice, and if this sort of plowing is followed by three deep 
 diskings at intervals of two or three days, the ants' nests will have 
 been very thoroughly broken up, and their young, eggs, and aphids 
 scattered through the soil and lost or destroyed. 
 
 Field experiments with this method have repeatedly proved this 
 to be the most effective practical method we know of for destroying 
 the aphis and reducing the numbers of the corn-field ant. 
 
 Where the land dries out slowly or the spring is so late that the 
 corn must be planted as soon as possible after the ground is broken, 
 ants may be kept from the corn for a time by the use of some sub- 
 stance which is repellent to them. These substances are best applied 
 by mixing them with some finely ground material or fertilizer and 
 dropping in the hills with a fertilizer attachment on the corn-planter. 
 The best substances for this purpose are, in the order named, oil of 
 tansy, oil of lemon, anise oil, and tincture of asafetida. The results 
 
Plate II 
 
from the use of these will not be as good as from the deep cultivation. 
 
 By following the plow for a short distance when the ground is 
 being broken in spring, one can easily determine how abundant the 
 colonies of the corn-field ant are in the field. If their nests average 
 over twenty to the mile of furrow, give as thorough and deep cultiva- 
 tion as possible before planting the land to corn. 
 
 Rotation of crops is one of the best methods of dealing with the 
 corn root-aphis problem, but in some cases injury to corn will follow 
 the first year after some other crop, where this crop was foul with 
 some of the weeds or grasses on the roots of which the corn root-aphis 
 lives. 
 
 Urbana, Illinois, March 7, 1919. 
 
iii 
 
 570IL6C 
 
 CIRCULAR 
 
 1-24 
 
 UNIVERSITY OF ILLINOIS-URBANA 
 
 C006 
 
 3 0112 017541175 
 
 
 HiM-iS.