Page:Popular Science Monthly Volume 5.djvu/23

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13
THE GRAPE PHYLLOXERA.

oviposition. Two or three days after this operation the mother dies; but the males live as long again.

This solitary egg, which Balbiani calls the winter-egg, soon takes on a dark color, which indicates its fecundity and distinguishes it from parthenogenetic eggs of both the winged and wingless females. It is surmised that this egg passes the winter to give birth in spring to the form destined to recommence the cycle of development belonging to the species.

These discoveries are truly remarkable, and appear to me all the more so since Balbiani [1] likewise found that the individuals which never become winged attain maturity without laying eggs on the leaves on which they were born, but crawl on to the branches and in the interstices of the old scales at the base of the new year's growth. There they lay a number of eggs, which are absolutely like those deposited by the winged females, and, like them produce the sexual individuals i. e., both males and females. Now, this does not correspond with what I have seen myself of the species, or with what has been described by others; for the apterous individuals of quercus surround themselves with eggs on the leaves where they are born.

M. Max-Cornu has already announced having found a sexual individual, without mouth-parts, of the Grape Phylloxera; and it is quite likely, now that Balbiani has paved the way, that we shall next year have its natural history complete. But whether the Grape Phylloxera produces this fecundated and solitary egg or not, such an egg is neither essential to its winter life, nor to that of an American species (Phylloxera Rileyi Lichtenstein), which will be described farther on, and which is, in every respect, very closely allied to the European quercus.

While, therefore, there is much yet to learn in the life-history of our Grape Phylloxera, the facts which I have already unequivocally stated, as well as those which I shall now proceed to give, remain indisputable, and do not seem fully to accord with Balbiani's discoveries.

As fall advances the winged individuals become more and more scarce, and as winter sets in only eggs, newly-hatched larvae, and a few apterous egg-bearing mothers, are seen. These last die and disappear during the winter, which is mostly passed in the larva state, with here and there a few eggs. The larvæ thus hibernating (Fig 4, b) become dingy, with the body and limbs more shagreened and the claws and digituli less perfect than when first hatched; and, of thousands examined, all bear the same appearance and all are furnished with strong suckers. As soon as the ground thaws and the sap starts in the spring, these young lice work off their winter coat, and, growing apace, commence to deposit eggs. All, without exception, so far as I have seen, [2] become mothers and assume the degraded form (a) already described.

  1. Auctore Dr. Fr. Cazalis, as reported in the Messager du Midi, November 16, 1873.
  2. I have examined thousands in the vineyard in early spring, and other thousands reared artificially in a warm room in winter.