APHID (probably from Gk. cicpet5is, aphei des, unsparing, from el, a, priv. e ide st ha i to spare). A bug of the family Aphidithe, commonly known as plant-lice, which live either free on the foliage, bark, or roots of plants, or inclosed in galls. They nourish themselves on the sap of their plant-hosts, which they suck up through a long, slender rostrum. They are mi nute, the largest being one-fourth of an inch long. The color is usually green or brown, and the shape like that of a pear. Most of the forms that live on the roots of plants underground have neither compound eyes nor ocelli. Several forms secrete a cottony, protective coat. At the pos terior end of the abdomen of most aphids there are two tubes, or perhaps mere perforations, through which a sweet liquid, called honey-dew, comes out, a drop at a time. Upon this the young feed for the first day or two. The flow may be so abundant as to render the stems and leaves sticky, or, when the wind is blowing, the liquid may even fall to the ground in a sweet spray. The leaves and bark are not infrequently covered by fungi, which thrive on the honey-dew, and insects, especially ants, are attracted to it. The ants protect from year to year the makers of this food supply. and also feed eagerly upon the honey-dew itself, and cherish the aphids for its sake. See ANT.
Dimorphism, or even polymorphism, is very common among aphids. Thus the forms that live on the roots of plants and those that live on their foliage possess certain structural differenees. When all the foliage forms perish, the under grotuid ones may make good the loss, as is the case with the Delaware peach species. Again, the sexes may be winged or wingless, and the females may bring forth the young alive, or they may lay eggs. From the eggs parthenogenetic females alone hatch. These produce living young for many generations. At times of drought or on the approach of winter, males, usually winged, appear, which fertilize the eggs of the wingless females. These eggs hatch in the following
spring into the "stem mothers," and the cycle begins again. It has been estimated that the progeny of a single "stem mother" of the cot tony apple aphis may be one quintillion in a season. See Hop-LousE.
Aphids stunt or kill growing tips, weaken the entire tree by impoverishing it of sap, and pro duce galls and other abnormal growths. Entire crops of cereals may be destroyed by them. Let tuce, beans, indeed nearly all vegetables, suffer from their ravages, and house-plants are particu larly infested by them. The price of hops from year to year varies largely according to the abun dance of the hop-vine aphids; and to this fam ily belongs also the grape-vine pest (Phyllox era) of Europe. Inundation of the ground in cold weather is fatal to this pest. Carbon hisul phide is also used. In the greenhouse, tobacco smoke, soapsuds, and ladybird beetles are effect ive cheeks. Young fruit and shade trees in the open may also be treated with soapsuds. as well as with hydroeyanic-acid gas applied under closed tents. Birds and spiders feed on plant lice. ichneumon and syrphus-fly lame destroy great numbers of them, both the adults and the young of all sorts of ladybird beetles feed ravenously upon them, and they are persecuted by deadly parasites. indeed, were it not for the insect foes of plant-lice. there would be little or no vegetation. The winter eggs of aphids may endure any amount of cold, but a cold, wet spell in the spring is fatal to the newly hatched aphid. See SCALE INSECTS, and the names of va rious trees and plants upon which they prey; and of works on injurious insects and economic entomology, especially for the United States, see Thomas, Eighth Report State Entomolo gist of Illinois (Springfield, 1879) ; and for Europe, Buekton. Monograph of British Aphides, Ray Society (Loudon, 1879-S3).