Page:Popular Science Monthly Volume 5.djvu/26

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16
THE POPULAR SCIENCE MONTHLY.

of such a delicate and frail-winged fly to traverse the air to any great distance. "On a calm, clear day, the latter part of last June, it was my fortune to witness a closely-allied species (Phylloxera caryæfoliæ Fitch), of the same size and proportions, swarming on the wing to such an extent that to look against the sun revealed them as a myriad silver specula. They settled on my clothing by dozens, and any substance in the vicinity that was the least sticky was covered with them. With such a sight before one's eyes, and with full knowledge of the prolificacy of these lice, it required no effort to understand the fearful rapidity at which the Phylloxera disease has spread in France, or the epidemic nature it has assumed. Imagine such swarms, mostly composed of egg-bearing females, slowly drifting, or more rapidly blown, from vineyard to vineyard; imagine them settling upon the vines and depositing their eggs, which give birth to fecund females, whose progeny in five generations, and probably in a single season, may be numbered by billions, and you have a plague (should there be no conditions to prevent that increase) which, though almost invisible and easily unnoticed, may become as blasting as the plagues of Egypt."[1]

Since the above-quoted passage was written, I have fully proved the same ability to fly in the winged grape-root lice, and am satisfied that they can sustain flight for a considerable time under favorable conditions, and, with the assistance of the wind, they may be wafted to great distances. These winged females are much more numerous in the fall of the year than has been supposed by entomologists. Wherever they settle, the few eggs which each carries are sufficient to perpetuate the species, and thus spread the disease, which, in the fullest sense, may be called contagious. Whether in a state of nature these winged females show a preference for any one part of the vine in the consignment of their eggs, is not yet known. It is quite certain, however, that they do not reënter the ground. Neither do we know whether—in the light of Balbiani's discoveries regarding the European Oak Phylloxera—the young hatching from these eggs produce the diminutive sexual individuals already described. In confinement I have had such eggs deposited both on the leaves and on the buds, and from the preference which, in ovipositing, these aërial mothers showed for little balls of cotton placed in the corners of their cages, I infer that the more tomentose portions of the vine, such as the bud, or the base of a leaf-stem, furnish the most appropriate and desirable nidi. On this hypothesis it is quite possible for the insect to be introduced from vineyard to vineyard, or from country to country, as well upon cuttings as upon roots.

  1. "Entomological Report of Missouri," vol. v., pp. 72, 73.