INSECTS INJURIOUS TO CORN. 



257 



while the corn plant is small. The fact that these aphids are frequently 

 more abundant upon the roots of corn in the low places in the field is 

 simply due to the fact that the rains have washed the seed of smart-weed 

 and fox-tail or pigeon grass to the low places, and the presence of 

 large numbers of plants of this weed appearing there early in the spring 

 has attracted the ants, and they have placed the aphids in these situations, 

 and when the corn is planted the ants simply removed the aphids a 

 short distance to the corn. 



When the corn plant becomes too old for the aphids to derive 

 nourishment from its roots, the ants, which have during the entire season 

 obtained practically all their food by feeding upon the so-called honey- 

 dew, which has been excreted by these aphids, then carry the aphids 

 from the roots of the corn plant to the roots of purslane, which by this 

 timic has developed throughout the corn field. The aphids stay upon 

 the roots of the purslane through the fall, and it is usually about the roots 

 of this plant that the eggs are deposited in the burrows of the ants. 



In the fall of the year there are developed from these wingless 

 agamic females, which .have been bringing forth living young during 

 the entire summer, generation'after 

 generation, without laying eggs and 

 without the appearance of males, in 

 the same way now bring forth cer- 

 tain individuals which are true 

 males and true females. A picture of 

 one of the males is shown in figure 

 16, enlarged twenty-five diameters, 

 and a female in figure 17, enlarged 

 fourteen diameters. These true 

 males and females pair, and the fe- 

 male soon deposit eggs, which com- 

 pletes the life cycle of this insect, 

 the eggs remaining over winter, 

 while all the other individuals per- 

 ish. 



It is an absolute fact that the Fig. is. — Com-Root-Aphls, ApMs maidlr- 



adicis, male ; enlarged twenty-five diara- 

 corn-root-aphis depends entirely up- ^ters ; a, antenna. 



on these small red ants for its existence. The aphids by themselves 



would not be able to move through the soil and seek the roots of their 



food plants. In fact, it has been demonstrated by experiments that these 



aphids will starve to death when left within an inch or two of the roots 



of their normal food plant. They must be carried by the ants and 



A— 17 



