APHID, a plant-louse of the family Aphidida., order Hemiptera. Aphides are among the most abundant of insects and do much in jury to vegetation by their habit of sucking the sap of leaves and stems of plants. They are usually very small, never over a quarter of an inch in length. Their mouth-parts form a slen der beak adapted for puncturing leaves and sucking the sap. Their antennae are from three to seven-jointed, and generally longer than the The ocelli are usually present, and the is three-jointed and developed in both sexes. The legs are long and slender, with two jointed tarsi. The males and females are winged, and also the last brood of asexual in dividuals, but the early summer broods are wingless. Their bodies are flask-shaped, being cylindrical, the abdomen thick and rounded, and in aphis and lachnus provided with two tubes on the sixth segment for the passage of a sweet fluid (honey-dew) secreted from the stomach, which attracts crowds of ants (see ANT). The wings are not net-veined, having few veins, which pass outward from the costa. They are usually green in color with a soft powdery bloom exuding from their bodies. Bonnet first discovered that the summer brood of wingless individuals were born of virgin parents, hatched from eggs laid in the autumn, and that the true winged sexes composed the last generation, which united sexually, and that the female laid eggs in the autumn which produced the spring brood of asexual wingless individuals.
In the early autumn the colonies of plant-lice are composed of both male and female individ uals. These pair, the males then die, and the females begin to deposit their eggs, after which they die also. Early in the spring, as soon as the sap begins to flow, these eggs are hatched, and the young lice immediately begin to pump up sap from the tender leaves and shoots, in crease rapidly in size, and in a short time come to maturity. In this state it is found that the whole brood, without a single exception, con sists solely of females, or rather, and more properly, of individuals which are capable of re producing their kind. This reproduction takes place by a viviparous generation, there being found in the individuals in question young lice which, when capable of entering upon individual life, escape from their progenitors and fonn a new and greatly increased colony. This sec
ond generation pursues the same course as the first, the individuals of which it is composed being, like those of the first, sexless, or at least without any trace of the male sex throughout. These same conditions are then repeated, and so on almost indefinitely, experiments having shown that the power of reproduction under such circumstances may be exercised, according to Bonnet, at least through nine generations, while Duval thus obtained 11 generations in seven months, his generations being cur tailed at this stage not by a failure of the re productive power, but by the approach of winter, which killed his specimens. Huber ob served that a colony of Aphis dianthi, which had been brought into a constantly heated room continued to propagate for four years in this manner without the intervention of males, and even in this instance it remains to be proved how much longer these phenomena might have been continued.
Certain species feed on the roots of plants, as asters, lettuce, grasses etc., and these also attract numerous ants. The corn plant-louse has been found by Forbes to hibernate in the wingless, asexual form in the earth of previ ously infested corn-fields. In the spring an ant (Lasius alienus), which runs its tunnels along the principal roots of the corn, collects the aphides and conveys them into its galleries, where they are watched and protected. The aphis (Lachnus strobi) is destructive to young white-pine trees. Another aphid is the grape Phylloxera (q.v.). The woolly aphids (Schisoneura tessellate) flock on the stems of the alder, their bodies concealed by a flocculent mass of wax. Another destructive species is the apple woolly louse (S. lanigera). Aphides can be exterminated by frequent spraying.
Buckton, ( Monograph on British Aphides' (Ray Society, London 1879 83) ; Miall, L. C., (Injurious and Useful In sects) (London 1908) ; Osborn, Herbert, 'Agri cultural Entomology) (Philadelphia 1916) ; Thomas, (Eighth Report of State Entomologist of Illinois> (Springfield 1879).