APHID

also called Plant Louse, Greenfly, or Ant Cow, any of several species of sap-sucking, soft-bodied insects (order Homoptera) about the size of a pinhead, with tubelike projections (cornicles) on the abdomen. It is a serious plant pest. Aphids not only stunt plant growth, produce plant galls, and transmit plant virus diseases but also deform leaves, buds, and flowers. The life cycle of the aphid is complicated. Wingless females, called stem mothers, produce living young without fertilization (i.e., by parthenogenesis) throughout the summer. Eventually the plant containing the stem mother and her offspring becomes overcrowded; when this occurs, some aphids develop two pairs of large membranous wings and seek new plants. In late summer, both males and females are produced; after they mate, the female lays eggs that survive the winter. In warm climates there may be no egg stage. The white, woolly-ball appearance of many aphids is the result of wax-gland secretion. Aphids are controlled by chemical sprays and natural enemiese.g., ladybird beetles, aphid lions, and lacewings. Ants may take care of aphids, protecting them from weather and natural enemies and transferring them from wilted to healthy plants. In this way they ensure their source of honeydew, a sweet excretory product of aphids. Ants obtain honeydew by stroking, or milking, the aphids. Common types of aphids include the following: The apple aphid (Aphis pomi) is yellow-green with dark head and legs. It overwinters as a black egg on its only host, the apple tree. It produces honeydew that supports growth of a sooty mold. The cabbage aphid (Brevicoryne brassicae) is small and gray-green with a powdery, waxy covering. It is found in clusters on the underside of leaves of cabbage, cauliflower, Brussels sprouts, and radishes. It overwinters as black eggs in northern regions but has no sexual stage in southern regions. It is controlled by dusts or sprays. The cooley spruce gall aphid (Chermes cooleyi) causes formation of conelike galls about 7 cm (3 inches) long on the tips of spruce twigs. In midsummer when the galls open, adults migrate to Douglas firs to lay eggs; the life cycle may proceed on either spruce or Douglas fir. Control is by spraying with insecticide, removing galls before aphids emerge, and planting spruce and Douglas fir apart from each other. The corn root aphid (Anuraphis maidi-radicis) is a serious pest dependent on the cornfield ant; the ants store aphid eggs in their nests during the winter, and in spring the aphids are carried by the ants to weed roots and then transferred to corn roots. The aphid stops growth of corn and causes plants to turn yellow and wilt; it also infests other plants. The eastern spruce gall aphid (Chermes abietis) produces pineapple-shaped galls 1 to 2.5 cm long composed of many cells, each containing about 12 aphid nymphs; galls open in midsummer, releasing mature aphids that infect the same or another spruce. New galls are green with red or purple lines; old galls are brown. Infested branches often die, but individual trees vary in susceptibility. The best control is by poisonous spray. The greenbug (Toxoptera graminum) is one of the most destructive pests of wheat, oats, and other small grains. It appears as patches of yellow on the plant and may wipe out an entire field. Pale green adults have a dark green stripe down the back; each female produces between 50 and 60 young per generation, and there are 20 generations annually. It is controlled by parasites and chemical sprays. The green peach aphid (Myzus persicae), also called the spinach aphid, is pale yellow-green with three dark lines on the back. The life cycle involves two hosts; the female reproduces parthenogenetically during summer and produces sexual males and females in autumn. It is a serious pest, transmitting many plant mosaics. The melon, or cotton, aphid (Aphis gossypii) is green to black. In warm climates live young are produced all year, while in cooler areas there is an egg stage. Among the dozens of possible hosts are melon, cotton, and cucumber. It is usually controlled by parasites and natural predators. The pea aphid (Macrosiphum pisi) is pale green; it kills pea plants and carries yellow bean mosaic. It overwinters on clover and alfalfa, migrating to peas in spring. Each female produces 50 to 100 young in each of 7 to 20 generations a year. It is controlled by sprays and weather conditions. The potato aphid (Macrosiphum euphorbiae) begins as black eggs on rose plants, which hatch into pink and green young that feed on rosebuds and leaves. In early spring they migrate to the summer host (potato plant). One generation occurs every two to three weeks. It is the carrier of tomato and potato mosaic virus diseases and kills vines and blossoms. The rose aphid (Macrosiphum rosae) is large and green with black appendages and pink markings. It is common on its only host, the cultivated rose. Natural predators are ladybird larvae and aphid lions. The rosy apple aphid (Anuraphis roseus) deforms fruit, producing aphis apples. It causes leaves to curl about it, forming a protection from insecticide sprays. The life cycle involves an alternate host, plantain; the aphid returns to the apple tree to deposit eggs in the fall. It also attacks pear, hawthorn, and mountain ash. It is controlled by sprays and by natural enemies, chiefly syrphid flies, lady beetles, lacewings, and parasitic wasps. The woolly apple aphid (Eriosoma lanigerum) lives on roots and may stunt or kill apple trees. White cottony masses enclose the young aphids. It is controlled by parasites. See also grape phylloxera.