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
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 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
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.
“But what queer little creatures! Yellow, wingless, stubby, they look
like the lice on the roots, but even smaller. These phylloxeras of the
third kind are dwarfs in a family of dwarfs. They have no stomachs for
digesting, no suckers for puncturing the leaves and extracting their
sap. Self-nourishment, however slight, is not at all their affair. The
laying of eggs that shall renew the vigor of the race, the placing of
them where they will be safe, and then a speedy death—that is the sole
purpose of their brief span of life.
“For some days these dwarfs, male and female, wander over the vines and
mate, one with another; then, in the fissures of the wrinkled bark, the
mothers lay each an egg, a single egg, of enormous size in comparison
with the smallness of the layer, greenish in color and sprinkled with
fine black spots. This egg takes the name of ‘winter egg,’ being
destined to pass the cold season fastened by a little hook to the
vine’s bark. After this the layer of the egg shrivels up into a reddish
point and dies.”
“But how do these eggs manage to get through the winter without
freezing?” asked Louis. “Hens’ eggs or birds’ eggs would be good for
nothing after being left out-doors from autumn till spring.”
“That is true,” assented Uncle Paul; “nevertheless these minute germs
of future insect life seldom fail to hatch when warm weather returns.
From them come plant-lice like those on the roots of the vine. Each
new-born louse crawls down the natal vine, hunts around on the ground
until it finds a crack in the soil, and then makes its way through this
fissure to settle at last on a rootlet, into which it plunges its
sucker. At ease thenceforth beneath the surface of the ground and in
the bosom of abundance, it does not long remain alone. Close to its
fixed position it deposits its little heap of yellow eggs, whence there
quickly issues a new generation. In like manner each member of the
family surrounds itself with a family of its own; and so on by several
successive repetitions of the process until, from having but a single
occupant at first, a root speedily becomes covered with a legion of
destroyers. To this population of recent origin we must not forget to
add the older inhabitants that have passed the winter under ground and
have only waited for the return of the warm season to resume their own
laying of eggs on the roots of the vine.
“Let us recapitulate these singular ways of the phylloxera. The species
comprises three forms of insects, each having its own peculiar
structure, its manner of life, its separate function. The customary
animal unity is here a trinity: three different insects are grouped in
a single species.
“The sedentary members are wingless and live on the roots. All lay eggs
and are followed by several generations likewise capable of laying
eggs. Under the pricking of their collective suckers, numberless in the
aggregate, vineyards are ruined. There we have the formidable foe, the
ravager whose sucker, hardly visible to the naked eye, has already cost
us more than ten milliard francs.
“The migrating members are furnished with large wings. They live on the
leaves and lay each a small number of eggs in the down of the buds.
Like their sedentary kinsfolk, they all lay eggs. Their peculiar office
is to disseminate the race from one vineyard to another.
“The members endowed with sex come under the operation of the general
law: they are divided into male and female. Unprovided with wings,
sucker, or stomach, they wander over the vine without taking any
nourishment. Each mother lays a single egg, the winter egg, whence
issues in the spring a sedentary phylloxera, which makes its way down
to the roots, establishes itself there, and becomes the head and center
of a new colony.
“How contend against this foe which, by reason of its numbers and its
underground abode, defies our attempts to exterminate it? Three
principal methods are employed. In the lowlands the vineyards are
flooded and kept under a good depth of water throughout the winter.
This submersion causes the death of the phylloxera at the roots of the
plant. As a second method, through holes bored to the roots the soil is
injected with an asphyxiating fluid called sulphur of carbon, the fumes
of which instantly kill all insects that they reach. The difficulty is
to do a thorough job and leave no survivors. A third device is employed
by those who import from America certain wild vines much hardier than
our cultivated ones, but producing inferior fruit. These American
plants resist the attacks of the phylloxera, and continue to flourish
where our vines would succumb. On these wild stocks, as soon as they
are well rooted, are grafted our native vines, and thus is obtained a
grape-vine of two-fold quality, resisting by the hardy nature of its
root the phylloxera’s assaults, and bearing, on its engrafted shoots,
the incomparable fruit of our old vineyards.”