THE CORN EOOT-APHIS. 5 



aphids usually attack corn that is grown on cornland, although occa- 

 sionally other ground may develop heavy infestations if it has har- 

 bored certain weeds and likewise the aphids. (2) Injury, resulting 

 in a stunting of the plants and yellowing of the leaves, usually occurs 

 in early summer, when the plants are from 6 to 18 inches high. (3) 

 Ant hills and the common brown cornfield ants are to be found at or 

 near corn plants attacked by root aphids. (4) Plants infested with 

 root-aphids have a complete root system, but when uprooted the 

 bluish-green aphids will be found thickly clustered on the roots and 

 on the underside of the crown at the base of the roots. 



SEASONAL HISTORY AND HABITS. 



There are four distinct forms of the corn root-aphis. The true 

 sexes — that is to say, the males and the egg-laying females (fig. 3) — 

 occur only in the fall. These females 

 lay the pale yellowish-green eggs which 

 later turn to jet black. Ants take the 

 aphid eggs to their nests and care for 

 them during the winter months. In 

 spring, and continuing throughout the 

 summer, only winged and wingless fe- 

 males are to be found, and these give 

 birth to living young. (See title-page 

 illustration and fig. 1.) 



The seasonal history of this insect, 

 which is graphically shown in figure 4, 

 is as follows: The eggs, which are kept ^'^ 3 -The corn root-aphis: 



..*=*=' . i Egg-laying female. Greatly 



by the ants m their nests over winter, be- enlarged. (Redrawn from 

 gin to hatch about the time smartweed Forbes.) 

 seeds begin to germinate — usually the latter part of March or the first 

 of April — and the young, frail aphids are transferred by the attentive 

 ants to the roots of convenient weeds along which tunnels previously 

 have been made. The aphis is able to live and reproduce on a large 

 variety of weeds, but is most frequently to be found on such common 

 field weeds as smartweed or knotweed,^ crab grass,- purslane,^ and 

 foxtail or pigeon grass.* The young that hatch from eggs mature 

 in about 15 days or longer and give birth to a second generation. 

 Members of this and the succeeding generations until fall give birth 

 to living young, which they produce without fertilization by a male. 

 On an average about 16 or 17 generations occur from the date of 

 hatching in the spring until fall, and the length of each generation 

 varies according to the season, being longer in the spring and fall 



^Polygonum sp. ^ Portulaca olcracea. 



-Digitaria sanguinaUs. * Setaria sp. 



