Corn Root Aphid
Egg - The dark green, oval-elongate egg is less than 1 mm long.
Nymph - The pale green nymph has red eyes, resembles the adult in shape, and measures from 0.3 to 2.0 mm in length.
Host Plants - Corn, cotton, and smartweed roots seem to be the most common hosts of the corn root aphid. Other hosts include broomcorn, crabgrass, dock, foxtail, knotweed, mustard, pigweed, plantain, purslane, ragweed, sorghum, sorrel, squash, and wheat roots.
Damage - The corn root aphid pierces roots with its needle- like mouthparts and extracts sap. As a result of aphids' feeding, the foliage soon develops a characteristic yellowish to reddish tinge. Heavily infested seedlings become stunted, rarely growing taller than 25 cm (10 inches). In addition to these symptoms, infested fields are likely to harbor many anthills; however, the presence of anthills does not necessarily imply infestation by the corn root aphid.
Life History - Throughout their life cycle, corn root aphids are highly dependent upon ants, especially cornfield ants. In most areas, the aphids overwinter as eggs deep within the ant nest. In late March or April, ants carry newly hatched nymphs to the roots of corn or weeds, particularly dock and smartweed. If corn seedlings are available, aphids are transferred to them either from the over-wintering nest or from weeds. Later the ants feed on the aphids' honeydew secretions. First-generation aphid nymphs feed on roots for 2 to 3 weeks before developing into wingless female adults. By-passing the egg-laying stage, these mature aphids soon give birth to 40 or 50 live nymphs. As summer approaches and temperatures increase, nymphs may mature in as few as 8 days. After several generations, winged female aphids often appear and fly to nearby fields, especially corn or cotton. After landing on anthills, they are carried to the roots by ants. Here the aphids continue to feed and reproduce as before until the approach of cold weather. In the fall, wingless male and female forms develop, mate, and are responsible for the production of overwintering eggs. These eggs are protected from the cold by the ants which carry them deep into their nests. The number of annual aphid generations varies greatly with latitude and environmental conditions. In no- till corn, 10 to 22 generations per year are possible.
