From October to April the Phylloxera hybernate, or rather, such of them do as have laid no eggs during the period of their active existence, for the egg-laying females die, and young phylloxeræ only are preserved during the winter months.
With the return of April they awake from their winter sleep, and recommence their devastating career. They then increase rapidly in size and begin to lay unimpregnated eggs, for there are at that time no males. “These bring forth females which in their turn develop and lay unimpregnated eggs, and the virginal reproduction continues for five or six generations, the development increasing in rapidity with the heat, but the prolificacy or the number of the eggs decreases.
“In July some of the individuals show little wing-pads at the sides, and begin to issue from the ground and acquire wings. These winged individuals become very numerous in August, and continue to appear in diminishing numbers thereafter till the leaves have all fallen. They are all females and carry in their abdomen from three to eight eggs of two sizes, the larger ones about 2⁄100ths of an inch long and half as wide; the smaller 3⁄4th as long. These eggs are also unimpregnated and are laid by preference on the under side of the more tender leaves, attached by one end, amid the natural down. They increase somewhat in size, and give birth in about ten days to the true sexual individuals, the larger producing females, the smaller, males.
“Anomalous as it may seem these creatures are born perfect, though without mouth, and with no other than the reproductive function.
True female Phylloxera; a, ventral view, showing obsolete mouth and solitary egg, occupying nearly the entire body; b, dorsal view; c, tarsus; d, contracted anal joints after the egg is laid; dot in circle showing natural size.
“A most remarkable fact, discovered by
Babiani, is that some of the females never acquire wings, but always remain on the roots, also produce the few different sized eggs from which these true, mouthless males and females hatch. The sexes pair soon after hatching, and the female is delivered on the 3rd or 4th day of a solitary egg, and then perishes. This egg is never laid on the leaf, but always on the wood, either under the bark, or in sheltered situations above ground, or on the roots underground. The young hatching from it is the normal agamous mother, which, with increased vigour and fertility, lays a large number of eggs, and recommences the virginal reproduction and the cycle of the species’ curious life. The impregnated eggs laid early in the season doubtless hatch the same year, though some of the later deposited ones may pass the winter before hatching.”[104]
[104] Riley.
The parts of the vine attacked by the Phylloxera are the rootlets, which in a diseased plant, may be seen more or less covered with what appears to the naked eye, a yellowish powder, but upon a microscopic examination reveals itself as a mixture of phylloxeræ of different sizes, and of their eggs.