Page:Popular Science Monthly Volume 5.djvu/19

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9
THE GRAPE PHYLLOXERA.

Type Radicicola or Root-Inhabiting.—We have seen that, in all probability, gallæcola exists only in the apterous, shagreened, non-tubercled, fecund female form. Radicicola, however, presents itself in two principal forms. The newly-hatched larvæ of this type are undistinguishable, in all essential characters, from those hatched in the galls; but in due time they shed the smooth larval skin, and acquire raised warts or tubercles which at once distinguish them from gallæcola. In the development from this point two forms are separable with sufficient ease, one (a) of a more dingy greenish-yellow, with more swollen fore-body, and more tapering abdomen; the other (ß) of a brighter yellow, with the lateral outline more perfectly oval, and with the abdomen more truncated at tip.

Fig. 4.
PSM V05 D019 Type radicicola.jpg
Type Radicicola.a, roots of Clinton vine, showing relation of swellings to leaf-galls, and power of resisting decomposition; b, larva as it appears when hibernating; c, d, antenna and leg of same; e, f, g, forms of more mature lice.

The first or mother form (Fig. 4, f, g,) is the analogue of gallæcola, as it never acquires wings, and is occupied, from adolescence till death, with the laying of eggs, which are less numerous and somewhat larger than those found in the galls. I have counted in the spring as many as 265 eggs in a single cluster, and all evidently from one mother, who was yet very plump and still occupied in laying. As a rule, however, they are less numerous. With pregnancy this form becomes quite tumid and more or less pyriform, and is content to remain with scarcely any motions in the more secluded parts of the roots, such as the creases, sutures, and depressions, which the knots afford. The skin is distinctly shagreened (Fig. 4, h), as in gallæcola. The warts, though usually quite visible with a good lens, are at other times more or less obsolete, especially on the abdomen. The eyes, which were quite perfect in the larva, become more simple with each moult, until they consist, as in gallæcola, of but triple eyelets (Fig. 4, k), and, in the general structure, this form becomes more degraded with maturity,