THE PHYLLOXERA
“In our talks on ants a few words were said concerning their
milch-cows, plant-lice. You haven’t forgotten those curious herds with
udders in the form of two little tubes that emit, from time to time, a
sweetened liquid. The ant comes and milks these cows, caressing them as
it does so with its two antennæ. It fills itself with their milk,
making its stomach serve the purpose of a milk-pail, and then runs
back, all bursting with the delicious fluid, to disgorge it into the
nurslings’ mouths.
“These ant-cows are watched over with jealous vigilance; in case of
need they are pastured within enclosures, for fear of marauders. So far
all is for the best: the ants’ cattle afford us some passing amusement,
and apparently they are open to no serious reproach. But if we pursue
our inquiries further the plant-lice will reveal themselves to us under
a far more serious aspect.
“Let us speak first of rosebush lice. You wish to pluck a rose. Its
perfume fills the air, its form and color rejoice the eye. But just as
you are about to break the stem what do you find under your fingers? At
the base of the flower and all over the branch that bears it, the
superb plant is contaminated with a legion of green lice; a host of
odious vermin has taken possession of it; the magnificent has
associated with it the disgusting. The eye is offended; the fingers
recoil before this species of animated bark which the slightest
pressure turns into a sticky mush. Let us pluck the rose nevertheless,
and before shaking the lice from it let us examine them a moment.
“They are light green in color, big-bellied, and wingless. With a
little attention we distinguish the two minute posterior horns whence
oozes the liquid on which the ants regale themselves. They have,
underneath, a sucker, straight and very slender, a sort of bore which
they push into the tender bark to extract from it the juices on which
they live. The sucker once implanted at any convenient point, the
animalcule seldom stirs from that spot. If it does decide to move a
little, it is because its well has run dry and it must bore another
close beside it. A promenade of merely the length of the branch is a
liberty that only the most adventurous dare allow themselves. As a
rule, the plant-louse sticks to the spot where it was born, to the very
end.”
“But how can the stem of a rose get so completely covered with those
little green lice?” asked Emile.
“That is easily explained,” answered his uncle. “Plant-lice multiply
very rapidly, since each one, without exception, from the first to the
last, whatever their number, becomes capable in a few days of
procreating a family. The newly born settle down beside their mothers,
and are themselves soon surrounded by their own progeny. These in turn,
in a little while, have offspring of their own; and so on,
indefinitely, as long as the season lasts. Thus the stem, the branch,
the entire plant, become covered with lice so closely packed one
against another that in places the real bark is hidden by this bark of
vermin.
“Have you ever seen a garden-patch of broad beans overrun by black
lice? There, better than anywhere else, may be seen the rapidity of
propagation. On that green expanse appears at first a small black
stain, announcing the beginning of the invasion. It is a family of lice
installed at the top of a beanstalk, the tenderest part of the plant,
where the insects’ suckers can work to best advantage. The gardener, as
soon as he is aware of what is going on, hastens to cut off this part
of the stalk and crush it under his heel. He hopes to exorcise the evil
by destroying this nest of vermin.
“His hope is short-lived. A few days later, instead of one plant
invaded there are dozens. He lops off again; he turns up the remaining
leaves and examines them one by one; he crushes what vermin he finds,
taking all pains to make the extermination complete. Will he make an
end of it this time? Not at all: the black hordes reappear in greater
numbers than ever; the invaded stalks can no longer be counted. A few
lice that escaped the slaughter were enough to infest the whole patch
of beans. The foliage hangs down, foul and withered; the young pods,
riddled with punctures and corrugated with scars, shrivel up and can
grow no larger. For this ill there is no remedy; the harvest is ruined.
“The gardener pulls it all up and throws it on the dung-hill. His care
and vigilance have been unable to arrest the invasion. In vain he
crushed legions at a time under his angry heel: in a few days the
half-dozen survivors had propagated a larger colony than ever. Man is
hardly in a position to contend successfully against this lowly vermin
which braves extinction by virtue of its countless numbers.
“As I told you, the plant-louse does not like to change its place. It
plants its sucker on the very spot where it has just been born, and
thenceforth sticks to that spot, filling its stomach with sap and
surrounding itself with a family. This love of repose explains to us
very well how the twig of a rosebush or the top of a beanstalk
undergoes a progressive colonization; but it does not account for the
distant propagation of the species.
“With its home-keeping habits the insect ought to be confined within
narrow limits, on a single leaf and not on all leaves, on one rosebush
and not on the neighboring rosebushes. But as a matter of fact it is
disseminated everywhere. When one patch of beans becomes infested,
those in the neighborhood are equally unfortunate; when one rosebush
shows a colony of plant-lice, all those around it are similarly
visited. No vegetable growth can defend itself from the pest. How,
then, is it that this obese animalcule, which totters with fatigue
after one step forward, succeeds in passing from rosebush to rosebush,
from garden to garden? By what means is it able to spread in all
directions without limit?
“Let us examine a number of rosebushes, and we shall have a prompt
answer to our question. In addition to the wingless plant-lice, big of
belly and all grouped on the tender twigs, we shall see others, green
like the first ones, but more elegant in form, of greater freedom of
movement, and provided with four wings, very beautiful wings too,
diaphanous and gleaming with rainbow tints. These creatures are no lazy
sap-bibbers forever squatting over the well their sucker has bored.
They are seen to come and go, circulating briskly among the stationary
herd, inspecting the foliage, passing from branch to branch, and even
taking flight for some distant goal. They are the travelers of the
family. Their function is to propagate the race in the surrounding
district, with the aid of their wings, and even at considerable
distances when a puff of wind carries them thus far.
“Two classes, then, dissimilar though related, are to be noted among
the green lice of the rosebush and the black ones of the beanstalk, as
also among countless others. The members of one class have no wings;
they pass their lives where they were born, and multiply in serried
legions. Those of the other class, which is relatively small, are
equipped with wings. Confined to no one spot, they fare forth as some
passing breeze or their own strength of wing may determine, and deposit
in favorable localities the germs that are to serve each as the
beginning of a community of wingless plant-lice. The first kind
procreate on the spot with a fecundity almost beyond belief; the second
take leave of the stationary family and go out to start new centers of
population in various quarters. The first propagate without limit; the
second colonize.
“To soil the stem of a rose with a coating of lice is not exactly a
capital offense; but to lay waste a field of beans, the hope of the
farmer, is a far more serious matter. Yet even that is as nothing when
compared with other depredations committed by plant-lice. There is a
species of these insects that lives underground, subsisting on the
roots of the grape-vine. Oh, the hateful creature! Never has
agriculture known anything to equal the ravages it commits; no floods
or droughts or inclement seasons have ever wrought such woes. Its
terrible sucker has, up to the present time, caused us losses estimated
at the fabulous sum of ten milliard francs. What a mouthful for a
miserable little louse hardly visible to the naked eye! And to think
that the combined efforts of nations cannot succeed in exterminating
this pest! Alas, how feeble is mere force when confronted with the
exceedingly minute infinitely multiplied!
“This destroyer of the vine is known as the phylloxera, a name strange
to our tongue, but losing nothing of its impressiveness in translation.
‘Phylloxera’ means ‘witherer of leaves.’ The plant-louse thus
denominated does indeed cause the foliage of the vine to wither up—not
acting on the leaves directly, it is true, but attacking the roots.
These, done to death by the insect’s sucker, cease to draw from the
soil the nourishment needed by the vine. The vine-stock wastes away,
and with it the leaves, which become yellow and withered.
“It is not merely the foliage, then, that the phylloxera dries up; it
withers and kills the whole vine. Moreover, the name it bears was not
invented expressly for it, but was borne by another before the ravager
of vineyards became known. The louse that was first called phylloxera
lived at the expense of the oak-tree and took up its station on the
leaves, sucking the sap from them. There you have the true witherer of
leaves. The vineyard louse has therefore inherited an old appellation
which fails to indicate fully the seriousness of the creature’s
depredations.
“This last-named insect is a tiny yellowish louse, plump of body, but
hardly discernible to untrained eyes, its length being barely three
quarters of a millimeter. It lives in clusters on the minute
ramifications of the roots wherever the bark is tender enough to enable
it to push in its sucker. Its ranks are so dense that the infested
rootlets wear a continuous coating of vermin which stains the fingers
with yellow. It lays its eggs in little heaps in the interstices that
occur in the swarming colony; and these eggs are oval in shape and
sulphur-yellow at first, but turn brownish as the moment for hatching
approaches.
“From these eggs there come, in a few days, new layers of eggs, which
settle down beside the earlier comers and add their own progeny to the
already overgrown family. Thus, as long as the season continues
favorable, these myriad numbers of successive generations are added to
the existing myriads, until the thread-like rootlets become completely
hidden by the accumulated layers of eggs and the eggs themselves.
“Riddled with punctures, the rootlets swell up at intervals and present
the appearance of a string of elongated seeds. Thus deformed, fatally
injured in their delicate suckers, the roots cease to imbibe the
nutritive juices of the soil, the famished vine languishes for a time,
putting forth only feeble shoots that are incapable of bearing fruit,
and at last the whole plant dries up and dies. To secure its own
prosperity the louse has killed its nurse.”