Corn Leaf Aphid
Rhopalosiphum maidis (Fitch), Aphididae, HEMIPTERA


DESCRIPTION

Adult - The oval wingless adult, about 2.0 mm long, is usually pale bluish-green with black antennae, legs, and cornicles and a dark area around the base of the cornicales. The head is marked with two longitudinal dark bands, and the abdomen with a row of black spots on each side. The body often seems to have a powdery coating. The winged form is about the same size.

Egg - Unknown.

Nymph - Similar to the wingless adult, the nymph is smaller and has no wings.


BIOLOGY

Distribution - The range of the corn leaf aphid extends throughout the tropical and temperate regions of the world. In the continental U.S. it occurs in all areas except the Rocky Mountain region. It is rarely a problem in the northern states.

Host Plants - The corn leaf aphid shows a preference for barley, sorghum, and corn, in that order. It also infests many other wild and cultivated grasses.

Damage - Feeding by colonies of these aphids causes mottling and discoloration of leaves. Heavily infested leaves turn red or yellow, shrivel, and die. The important damage usually occurs during and after flowering. At this time the aphid population peaks and feeds on corn tassels and silks. Areas fed upon become covered with sweet, sticky honeydew secretions. Black mold grows on the honeydew and may result in poor corn pollination, interference with photosynthesis and, in severe cases, reduced grain development. Entomologists have speculated that the honeydew attracts corn earworm moths and, therefore, induces heavy earworm egg deposition.

Life History - Little is known about the biology of this pest in North Carolina. Since the relationship between corn and this aphid is not well understood, it has been difficult to estimate damage and to determine thresholds. This aphid generally is not considered a serious threat.

Corn leaf aphid adults overwinter each year in southern states, including North Carolina. On warm winter days, females actively continue to feed and reproduce on winter grain crops or other grasses. The first spring adults are winged females which fly in search of suitable host plants, sometimes migrating far northward. Shortly thereafter, they give birth to live nymphs which usually develop into wingless females. Under favorable conditions, more winged females develop and migrate. Males are rarely found but females continue to reproduce without mating. No egg stage is known. Reproduction slows down in winter and summer and is most rapid during cool weather. Therefore, corn leaf aphids tend to be a problem on winter grains in spring and on late-planted corn in fall. The number of generations per year varies from 9 in Illinois to 50 in southern Texas.


CONTROL

Heavy corn leaf aphid infestations usually are restricted to late-planted corn; therefore, early planting and other cultural practices which hasten maturity help prevent aphid problems. Corn leaf aphids rarely require control in North Carolina because high temperatures and natural enemies reduce aphid populations in summer. Should damaging aphid populations develop, consult the current North Carolina Agricultural Chemicals Manual.

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