THE PHYLLOXERA
(Continued)
“The yellow plant-louse found on the roots of the grape-vine,” resumed Uncle Paul, “has no bent for traveling: wingless, sluggish, and big-bellied, it is ill adapted to locomotion. Where once its sucker has implanted itself, there the creature is glad to abide as long as the place is tenable. But when the rootlet dies and begins to decay, then a new refectory must be sought out, with a better-furnished table. Accordingly the louse has to move. A persistent explorer, it knows how, with patience and in course of time, to make its way through cracks in the soil from one root to another, and dares even to climb to the surface, where, proceeding in the open air, it emigrates from the exhausted vine-stock to the neighboring one rich in sap; and there it pushes down to the roots through some fissure in the ground.
“To this slow-goer a single one of our steps would be a journey of excessive length. Therefore, to propagate its kind far and wide, it must have other and quicker means than the extremely deliberate method of locomotion just described. This other method for planting colonies at a considerable distance has already been illustrated for us by the [[289]]green louse of the rosebush. Like that species, the phylloxera has a special division of winged travelers, and it is these that propagate the race throughout the grape-growing district.
“At the time of the greatest midsummer heat there make their appearance, amid the throng of yellow lice covering the roots, certain individuals with longer bodies, which soon change their skin and then bear on their sides two pairs of black stumps, the sheaths of four future wings. These are the nymphs destined for emigration. These nymphs leave their subterranean abode and climb up to the foot of the vine-stock, or sometimes even out upon the surface of the ground. There another change of skin takes place, whereupon we behold the winged insect, superior in form to its underground relatives.
“It measures a little more than a millimeter in length, not including the wings. These latter, transparent and iridescent, extend far beyond the length of the body, and the upper ones are wide, rounded, and slightly smoke-colored at the end, the lower ones narrow and shorter. They are supported by strong sinews that denote great power of flight. With its large, diaphanous wings, its broad head and big eyes, its belly ending in a blunt point, and its yellowish color, the traveling insect bears some resemblance to a very small cicada. Such, in brief, is the phylloxera commissioned to propagate the race at a distance.
“We have here no longer to do with the sluggish pot-bellied creature that needs all its strength to [[290]]move from one root to the next adjoining; we behold an agile denizen of the air, capable of covering with the swiftness of an arrow a distance of several leagues, especially when aided by a favorable wind. During the warm season of July and August these winged insects take flight and settle in swarms on the vineyards not yet ravaged. They alight on the leaves, where their suckers perform their function in sober moderation.
“To stuff themselves like gluttons, after the manner of their kindred that live on the roots, is not their way. Hence their own depredations are of no importance. Unfortunately, however, it is their mission to do us a most disastrous disservice by infesting, one after another, the adjacent vineyards, peopling the still unaffected districts with underground ravagers. All take part in this; all, without exception, set to work laying eggs.
“These eggs are few in number, it is true, each insect laying at most but half a score amid the cotton-like down of the buds and young leaves. But the aggregate is none the less enormous, since in this strange family we have thus far encountered none but mothers. We have just seen that all the wingless phylloxeras on the roots lay eggs, and now we find that all their winged kindred on the leaves do likewise.
“This excessive fecundity would in the end exhaust the insect and result in its extinction if there were no seasons of quietude for renewing the vitality of the race. Yellowish in color like the eggs of [[291]]the underground phylloxera, those of the winged insect are of two kinds: one of a larger size, the other only about half as large. The first produce females, the second males. Here, at last, we have the two sexes, whose coöperation will assure indefinite prosperity to the race. That is the normal order governing all animal life.