Both species have the potential for developing large populations on carrots. Fall infestations on seedlings can seriously set back growth and development. Spring and summer populations may also require control. Damage results from direct feeding by the aphids in the phloem of plants.
Large numbers remove sap and effect quality and yield of seed.
Seedling carrots become twisted, stunted and may show yellow-red discoloration. Honeydew secreted by aphids looks like glistening varnish on the plants. W-CA is also known to vector motley dwarf virus. The small black, football-shaped eggs are clustered around dormant buds. They hatch as buds open.