English Grain Aphid
 Macrosiphum avenae (Fabricius), Aphididae, HEMIPTERA

DESCRIPTION

Adult - The wingless adult, about 2.5 mm long, is pale green with long, black antennae. Extending backward from the rear of the abdomen are two long, black cornicles. The winged form is about the same size and color as the wingless adult, though the lobes on its thorax are brown or blackish. The wingspan is about 6 to 9 mm.

Egg - The newly laid, pale yellow egg is 0.3 mm wide and 0.7 mm long. Within a few days, it becomes green or black in color.

Nymph - Although similar in shape and color to the wingless adult, the nymph is slightly smaller.

BIOLOGY

Distribution - The English grain aphid is found throughout the United States and southern Canada wherever small grains are grown. In North Carolina, they are widespread throughout the state, commonly occurring where grain is grown in mixed or pure populations.

Host Plants - English grain aphids feed on all small grains and many wild cultivated grasses. They have been found in small numbers on corn but are not important pests of this crop.

Damage - The English grain aphid is one of the most common and destructive aphids attacking the foliage and heads of wheat and other small grains. Colonies of this aphid feed upon the leaves until the grain begins to head; they then collect on the heads among the ripening kernels. When sufficiently large populations develop, their feeding shrivels the growing kernels. Extensive early spring feeding can kill grain plants. This aphid species is also a known vector of the barley yellow dwarf virus disease of small grains in the eastern United States.

Life History - These insects overwinter as eggs, late instar nymphs, or adults. The overwintering forms are all females, which in the spring give birth to live young. These progeny mature into wingless females which produce live offspring without mating. In early spring, the aphids feed on growing grains. As these plants mature and become less succulent, winged aphids develop and migrate to wild or cultivated grasses, where they spend the summer. In the fall, after the winter grains are planted, the aphids return to the grains or gather in large numbers in clumps of volunteer grain. Males appear during the fall or early winter and mate with the females, which then lay eggs on the grains where they have been feeding. Each female lays only about eight eggs. As many as 17 generations occur each year.

CONTROL

Normally these aphids are held in check by their natural enemies, which include parasites, predators, and fungal diseases. Grains are usually injured when the parasites have been destroyed and the aphids are allowed to multiply unchecked. Because an outbreak is often preceded by several dry seasons, it has been speculated, but not scientifically proven, that such seasons hinder the development of fungal diseases.

Properly managed fields are more vigorous and far less susceptible to injury from this pest. When populations of aphids reach 25 per head of grain or 100 foliar-feeding aphids per 30 cm (1 row foot), chemical control is warranted. For current control recommendations, consult the current North Carolina Agricultural Chemicals Manual.