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

DESCRIPTION

Adult - The wingless adult is oval and about 2.0 mm long. It is usually pale bluish green with black antennae, legs, and cornicles and a dark area at the base of the corn cles. The head is marked with two dark, longitudinal 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 as the wingless form.

Egg - Unknown.

Nymph - The nymph is smaller than but similar to the wingless adult.

BIOLOGY

Distribution - The corn leaf aphid is common wherever small grains and corn are grown in the United States and Canada, being especially abundant in the South. Its range extends throughout the tropical and temperate regions of the world. In North Carolina, there appears to be no geographic difference in population.

Host Plants - The corn leaf aphid is commonly found on corn, barley, millet, broomcorn, sorghums, Sudan grass, and many other wild and cultivated grasses. It shows a preference for barley and sorghums. Although this aphid has been reported to attack wheat, oats, and rye, economically significant infestations on these crops are uncommon.

Damage - The corn leaf aphid causes injury to small grains in the southern United States by the removal of plant sap and the introduction of diseases. Feeding by colonies of this aphid causes mottling and discoloration of the leaves. Infested plants become covered with sweet, sticky honeydew secretions. Sooty mold fungi grow on the honeydew causing reduced grain development and interfering with photosynthesis. These aphids also transmit a mosaic disease of sweet corn and the barley yellow dwarf virus of small grains.

Life History - Little is known about the biology of this pest in North Carolina. Apparently it overwinters as an adult and actually does much of its damage during the winter. Ovoviviparous females, both winged and wingless, form the bulk of the population. Males are rarely found, and no eggs have ever been seen. This suggests that the aphid can reproduce parthenogenetically. The female aphids are found in large clusters on the leaves, where they feed and reproduce. 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 fall, on warm winter days, and in spring. The number of generations per year varies from 9 in Illinois to 50 in southern Texas.

CONTROL

Resistant varieties, early planting and proper growing conditions reduce this insect's impact. Pasturing infested winter barley is recommended to free the crop of this pest. In North Carolina, 25 aphids per head of grain or 100 foliar-feeding aphids per 30 cm (1 row foot) are recognized as economic thresholds. For further control recommendations, consult the current North Carolina Agricultural Chemicals Manual.