Aphis

Collier's New Encyclopedia (1921)

a genus of insects, the typical one of the family aphidæ. It contains those soft pulpy little animals, winged or wingless, and with long antennæ, which are seen beneath the leaves, or in curled-up leaves, or in the axils of many plants, or even on the roots of some. Sometimes, as in the case of the elm, their destructive operations upon a leaf raise a gall of considerable size. The species are very numerous, and are gen rally called after the plants on which they feed, as A. rose, the aphis of the rose; A. fabæ, the bean aphis; A. brassicæ, the cabbage fly; A. humuli, the hopfly. They are exceedingly prolific, but are kept within bounds by various insects, especially by the coccinellidæ, or lady birds, of which they are the appropriate food. They drop a fluid called honey-dew, which is so grateful to the ants that the latter, to receive it, tend them like milch cows. The mode of propagating their race is the abnormal one described as alternation of generations, metagenesis, and parthenogenesis. The winged aphides, confessedly perfect insects, sects, bring forth a wingless race, apparently mere larvæ, and which therefore, it might be thought, would be incapable, while thus immature, of bringing forth young. In certain cases they do it, however, and their offspring are winged, and as perfect as their grandparents. This alternation of generations, or metagenesis, with its attendant parthenogenesis (or birth from virgins) in every second generation, goes on for nine or ten generations by which time the season is over. The last aphides of the year are fully formed and winged, and deposit eggs, which are hatched in spring.