These are small (1/16" long) bluegreen to graygreen sucking insects that feed on corn roots. They are tended by ants and are generally present in a field based on weed growth. Curly dock is a frequent host for this insect.
Leaves of infested plants will wilt and may turn brown and die. These aphids are tended by ants and ant mounds and activity may be visible on the soil surface. Plants are rarely killed but may be stunted for a time. Damage is most severe under dry soil conditions.
There are no rescue treatments. Soil insecticides will provide some control when applied at planting.