Phylloxera (Gr. , a leaf, and , parched), a word coined in 1834 by a French entomologist, Fonscolombe, to designate a genus of plant lice, founded on the phylloxera qvercus, a species living on the under side of oak leaves in Europe, and causing them to wear a withered appearance. The genus is more particularly distinguished structurally by having three-jointed antennas, the terminal joint longest, by the simple venation of the wings, and by the wings when at rest being folded flat upon the back. It is also peculiar from occupying an osculant position between two great families, the plant lice (aphidce) and the bark lice (coccidce), agreeing in some respects with the insects of the latter, but in most of its affinities being decidedly aphidian. The genus, though discovered in Europe, has its greatest representation in America; for while there are but two or three discovered species indigenous to that continent, all occurring on oak, there are 16 described species in America, most of them inhabiting galls upon the leaves and twigs of different species of hickory (carya), one inhabiting the grape vine, and one only, on oak (phylloxera Rileyi), being an external feeder.
None of these species except that on the grape vine seriously affect man's interests. - In 1865 a disease of grape vines in the vineyards of France began to attract general attention. It was first noticed in the lower valley of the Rhdne, a little above Avignon, upon the plateau of Pujault, department of Gard. In 1866 the disease had not only spread north of Avignon, but was observed at different localities in the S. part of the department of Bouches-du-Eh6ne. In 1867 it continued to spread and to gain in intensity, and in 1868 the whole of the country along the left bank of the Rh6ne, from its mouth to the environs of Donzere, was infected. In 1869 the disease became still more alarming, the older seats enlarging and coalescing, and many new points of attack becoming known in the departments of Herault and Var. It now attracted universal attention, and investigation of it was stimulated by a large government reward for a remedy. It continued to spread, though with diminished virulence, and at the close of 1874 it occupied more or less the whole area of the lower Rhone from Valence to the mouth, and from Montpellier to Toulouse; around Bordeaux, on the right bank of the Gironde; around Cognac in the north, and Lyons in the east.
The government offers a standing premium of 300,000 francs for an efficient remedy, and the national academy of science puts forth untiring efforts to study the disease in all its features. It has already been found in restricted localities in Spain, Portugal, Switzerland, Austria, and Prussia, either on American vines or in neighborhoods where such vines have been planted. The authorities in most of these countries, as well as in Australia, have prohibited the importation of American vines into unaffected districts. One of the most marked features of the disease is the rotting and wasting of the roots. In 1868 Prof. J. E. Planchon of Montpellier discovered the real cause in a minute plant louse working upon the root. This insect, though it had previously been described in its apterous form under three different generic names, was finally referred to its proper genus and named phylloxera vastatrix by Planchon. Since then the term phylloxera has acquired a somewhat broader meaning than it at first conveyed; it now designates not only the genus of insects, but the disease in question.
In 1869 M. J. Lichtenstein of Montpellier first suggested that the phylloxera which was devastating the vineyards of France might be the same as a species described as pemphigus mtifolim by Dr. Fitch, and known to make galls on the leaf of the grape vine in America. Following up this suggestion, Prof. O. V. Riley of St. Louis established the specific identity of the two insects in 1870, not only by careful comparisons, but by showing that the gall-inhabiting insects hibernate on the roots, and there acquire all the characteristics of the root-inhabiting individuals. This last fact was also independently proved by European observers during the same year, and the specific identity of the types inhabiting leaves and roots has since been thoroughly established by careful anatomical study as well as by experiments. In 1871 Prof. Riley discovered that the roots of vines in America are attacked by the insect in the same manner as are those of Europe. In the autumn of that year he announced this discovery, and, in the fourth entomological report of the state of Missouri, gave every reason to believe that the failure of the European vine (vitis vinifera), when planted in America east of the Rocky mountains, the partial failure of many hybrids with the European vinifera, and the deterioration and death of many of the more tenderrooted native varieties, are mainly owing to this insect.
He also showed that some of our native varieties enjoy relative immunity from its attacks. In 1873 Prof. J. E. Planchon was commissioned by the French government to visit America to study the phylloxera. His investigations corroborated Prof. Riley's conclusions as to the identity of the American and European insects, and the relative immunity of some of the American vines. His official reports of this visit have done much to dispel some of the prejudice existing among his countrymen in regard to American vines, and still more to create a large demand for such American vines as resist the insect, to be used as stocks on which to graft the French vines. - The grape phylloxera is ina, b. Wingless mother lice, back and side views, c. Granulations of skin. d. Tubercle, e. Transverse folds at border of joints.
Natural size indicated at side digenous to the North American continent east of the Rocky mountains, and is found from Canada to Florida on the wild vines of the woods, and on the cultivated vines in most and probably all of the states. It presents itself in two different types. That which makes galls on the leaves is called gallicola; it is smooth and very prolific, and exists only as an agamous wingless female. It is quite transient, abundant one year and unseen the next, and seems to be unessential to the perpetuation of the species; an abnormal deviation from the root-inhabiting type, rendered possible under certain conditions. The root insect, distinguished as radicicola, though precisely like the gall-making type when first hatched, subsequently acquires tubercles. The grape phylloxera hibernates mostly as a young larva torpidly attached to the roots, and so deepened in color as generally to be of a dull, brassy brown, and therefore with difficulty perceived, as the roots are often of the same color. With the renewal of vine growth in the spring this larva moults, rapidly increases in size, and soon commences laying eggs. These eggs in due time give birth to young, which soon become virginal, egg-laying mothers, like the first, and like them always remain wingless.
Five or six generations of these par-thenogenetic, egg-bearing, apterous mothers follow each other, and then, about the middle of July in the latitude of St. Louis, some of the individuals begin to acquire wings. These are all females, and like the wingless mothers they are parthenogenetic. Having issued from the ground while in the pupa state, they rise in the air, and spread to new vineyards, where they deliver themselves of their issue in the form of eggs or egg-like bodies, usually two or three in number, and not exceeding eight, and then perish. It is not yet positively known where these winged females prefer to lay their eggs; --but experiment indicates that while the eggs may be pushed into the tomentose buds, they are most probably laid as a rule in the minute crevices on the surface of the ground, near the base of the vine. These eggs are of two sizes, the larger about 0.02 of an inch long and the smaller about three fifths of that length. In the course of a fortnight they produce the sexual individuals, the larger ones giving birth to females, the smaller to males. These sexual individuals are born for no other purpose than the reproduction of their kind, and are without means of flight or of taking food or excreting. They are quite active, and couple readily.
The abdomen of the female, after impregnation, enlarges somewhat, and she is soon delivered of a solitary egg, which differs from the ordinary eggs of the parthenogenetic mothers only in becoming somewhat darker. This impregnated egg gives birth to a young louse, which becomes a virginal, egg-bearing, wingless mother, and thus recommences the cycle of the species' evolution. But a very important discovery made by Balbiani is that during the latter part of the season many of the wingless, hypogean mothers perform the very same function as the winged ones; i. e., they lay a few eggs, which are of two sizes, and which produce males and females, organized and constructed precisely as those born of the winged females, and like them producing the solitary impregnated egg. We have therefore the spectacle of an underground insect possessing the power of continued existence, even when confined to its subterranean retreats. It spreads in the wingless state from vine to vine, and from vineyard to vineyard, when these are adjacent, either through passages in the ground itself or over the surface. At the same time it is able, in the winged condition, to emigrate to much more distant points. The winged females begin to appear in July, and continue to issue from the ground until vine growth ceases.
They are much more abundant in August than during any other month, and on certain days literally swarm. Every piece of root a few inches long and having rootlets, if taken from an infested vine at this season, will present a number of pupaa; and an ordinary quart preserve jar, filled with such roots and tightly closed, will furnish daily for two or three weeks a dozen or more of the winged females, which gather on the side of the jar toward the light. Occasionally individuals under certain conditions abandon their normal underground habit, and form galls upon the leaves a, b. Mother gall louse, dorsal and ventral views. Natural size indicated between them. oi certain varieties of grape vine. No species of vine is entirely exempt from the attacks of the insect in one form or another; yet many indigenous American vines resist its attacks so far that they are never seriously affected. The gall lice are found on all species, but least on the European vine (vitis vinifera) and most on the river hank grape (best known as cordifolia), and especially on the Clinton and Taylor. The root lice are most injurious to the European vine, and least so to our summer grape ( V. aestivalis) and the scup-pernong (V. vulpina), on the roots of which last it has not yet been discovered.
The most susceptible native varieties, such as Catawba, Iona, Delaware, and Goethe, belong to the northern fox ( V. Idbrusca). - Just as the puncture of the gall louse causes an abnormal swelling of the leaf, so that of the root louse causes knots and swellings on the roots. These swellings, which generally begin at the tips of the rootlets, where there is excess of plasmatic and albuminous matter, eventually rot, and the lice betake themselves to fresh ones; the living tissue being necessary to the existence of this as of all plant lice. During the first year of attack there are scarcely any outward manifestations of disease, though the fibrous roots, if examined, will be found covered with nodosities, particularly in the latter part of the growing season. The disease is then in its incipient stage. The second year all these fibrous roots vanish, and the lice not only prevent the formation of new ones, but settle on the larger roots, which also eventually become disorganized and rot. At this stage the outward symptoms of the disease first become manifest, in a sickly, yellowish appearance of the leaf, and a reduced growth of cane; and about the third year the vine dies.
When the vine is about dying it is generally impossible to discover the cause of the death, the lice, which had been so numerous the first and second years of invasion, having left for fresh pasturage. The phylloxera is attacked by several enemies, few ' of which, however, reach it below ground. A host of remedies have been tried, but, with the exception of submersion and the use of sand and fertilizers, especially those rich in alkali, few are available in practical experience. - See Prof. Eiley's sixth annual "Keport on the Insects of Missouri" (1874).
Fig. 1. - Phylloxera, Type Radicicola. a. Healthy root. b. Root on which the lice are working, showing1 the knots and swellings caused by their punctures. c.Root deserted by them, on which the rootlets have begun to decay, d d d. Lice on the larger roots, natural size. e. Female pupa, dorsal view. f. Winged female, dorsal view, greatly enlarged.
Fig. 2. - Upper and Under Wings of Phylloxera.
Fig. 3. - Type Kadicicola.
Fig. 4. - Male Phylloxera, ventral view. Natural size indicated by dot in circle.
Fig. 5. - Type Gallicola. a. Egg. b. Section of gall c. Swelling of tendril.
Fig. 6. - Type Gallicola. a, b. Newly hatched larva, ventral and dorsal view. Natural sizes in circles at sides.
Fig. 7. - Type Gallicola.
Fig. 8. - Under Side of Leaf covered with Galls.