THE CORN ROOT-APHIS. 9 



summer months ; indeed, throughout life they are ^Yholly dependent 

 on the ant, which obtains in return for its work a sweetish fluid, the 

 " predigested " sap of the corn or other plant, which is given off in 

 considerable quantities by the aphids. Since the relationship between 

 ants and aphids is so intimate, and since the aphids are entirely 



Fig. 5. — Diagram showing how ants foster the corn root-aphis. These aphids, which are 

 cared for by the ants in their nests during the winter, are carried through tunnels to 

 the corn plants and placed on the roots. 



dependent on the ants, it is evident that any method which will dis- 

 turb, demoralize, or destroy the ant colonies will reduce the numbers 

 of aphids, and this fact will be explained further in the paragraphs 

 dealing with the means of control. 



PAST HISTORY. 



Previous to 1891 the corn root-aphis was generally supposed to be 

 the subterranean form of the corn leaf-aphis,^ which is everywhere 

 present on corn, usually occurring beneath the leaf and ear sheath 

 or the stalks of the unfolding tassel. As early as 1822 root-aphids, 

 which were probably the corn root-aphids, were reported damaging 

 corn in Pennsylvania, and in 1862 this species was definitely observed 

 attacking, corn roots and injuring the crop in Illinois. This pest has 

 increased gradually in destnictiveness until now it is recognized as 

 one of the four or five most generally injurious insects affecting corn, 

 for it occurs, with few exceptions, wherever this crop is grown in 

 the United States. 



^ Aphi-i inatdis Fitch. 



