If, however, the
food-plant is grown in a conservatory where protection against cold is
afforded, the aphides may go on reproducing agamogenetically without
cessation for many years together. Not the least interesting features
connected with this strange life-history are the facts that the young
may be born by the oviparous or viviparous methods and either
gamogenetically or agamogenetically, and may develop into winged forms
or remain wingless, and that the males only appear in any number at the
close of the season. Although the factors which determine these
phenomena are not clearly understood, it is believed that the appearance
of the males is connected with the increasing cold of autumn and the
growing scarcity of food, and that the birth of winged females is
similarly associated with decrease in the quantity or vitiation of the
quality of the nourishment imbibed. Sometimes the winged females migrate
from the plant they were born on to start fresh colonies on others often
of quite a different kind. Thus the apple blight (_Aphis mali_) after
producing many generations of apterous females on its typical food-plant
gives rise to winged forms which fly away and settle upon grass or
corn-stalks.

Closely related to the typical aphides is _Phylloxera vastatrix_, the
insect which causes enormous loss by attacking the leaves and roots of
vines. Its life-history is somewhat similar to that of _Aphis rosae_
summarized above. In the autumn a single fertile egg is laid by apterous
females in a crevice of the bark of the vine where it is protected
during the winter. From this egg in the spring emerges an apterous
female who makes a gall in the new leaf and lays therein a large number
of eggs. Some of the apterous young that are hatched from these form
fresh galls and continue to multiply in the leaves, others descend to
the root of the plant, becoming what are known as root-forms. These,
like the parent form of spring, reproduce parthenogenetically, giving
rise to generation after generation of egg-laying individuals. In the
course of the summer, from some of these eggs are hatched females which
acquire wings and lay eggs from which wingless males and females are
born. From the union of the sexes comes the fertile egg from which the
parent form of spring is hatched.

See generally G.B. Buckton, _British Aphides_ (Ray Soc. 1876-1883);
also ECONOMIC ENTOMOLOGY. (R. I. P.)

APHORISM (from the Gr. [Greek: aphorizein