Phylloxera

Life cycle

The life cycle is strongly dependent on the vine species attacked, namely European vine or American vine. It takes place either in the form of a complete cycle or a continuous cycle between the vine (above ground) and the root (underground) or only on leaves (above ground only) or only on roots (underground only) and thus a shortened cycle. There are parthenogenetic (virgin production from unfertilised eggs) and sexual generations. According to the place of infestation, a distinction is therefore made between the yellow-green 1.5 mm long leaf phylloxera (Gallicola = leaf gall aphid) and the yellow-brown 1.35 mm long root phylloxera (Radicicola = root louse). The latter is much more dangerous as it damages the leading tissue, which leads to a lack of water and nutrients. Infestation of the leaves, on the other hand, is usually not life-threatening. Among the vine species there are those which form both leaf and root galls, the root galls but no leaf galls, and the leaf galls but no root galls. The group of completely resistant vine species forms neither leaf nor root galls.

In Europe, reproduction is usually only carried out by the root lice, while the full cycle only occurs in America. Only in the above-ground cycle do offspring with new genetic material develop, as there are males and females only here. Among the root lice, there are only females that reproduce parthenogenetically and lay 600 eggs. Young hatchlings do not immediately attack the roots, but spend the winter deep in the ground. In spring, the roots are punctured with the proboscis (half the length of the body) and saliva is introduced into the tissue. As an almost panicky defensive reaction of the vine, knotty, thickened growths are formed. The aphids then feed on these soft formations and suck them up. The pest can therefore only live by producing bile, because the hard roots themselves cannot be gnawed on directly.

In Central Europe there are four to six generations of phylloxera per year. The young lice of the last generation (Hiemalen) are the wintering form. Towards the end of high summer, nymphs develop, which are larvae with wing attachments. These leave the ground and after their last moult develop into winged grapevine lice (Sexuparae). Due to their ability to fly, they can quickly spread to other vine plants, even over long distances. They lay small male and large female eggs on the perennial bark of the vine, from which the trunkless sexual animals (Sexuales) hatch. These cannot take up any food and have the sole task of copulation during their life of only about eight days.

The mated females lay a single fertilized olive-green winter egg in a bark crack. In spring, the mayfly hatches from this, which only in American grapevine species (Vitis vinifera is resistant to the leaves) forms leaf gall and lays up to 1,200 eggs. After eight to ten days, two larvae hatch from them. One of them forms new leaf galls, especially on younger leaves. They reproduce parthenogenetically with six to eight generations per year. The others are leaf-born root lice and seek out the vine roots in the soil. There they supplement the underground development cycle or start it anew. A wintered phylloxera with 1,000 eggs produces around 25 trillion offspring by autumn. The enormously complex cycle or life cycle of phylloxera and root phylloxera is shown in the diagram:

Nodosities and tuberosities

A distinction is made between two root species and thus different effects of the infestation. In the case of lower infestation, the young, unwooded root tips are pricked first. The root galls formed by this are called nodosities. They occur not only in the European, but also in most American vine species, but are relatively harmless and do not lead to destruction. However, in the case of more extensive infestation, the older, lignified roots are also punctured and tuberosities are formed as a result. These are much more dangerous because they can penetrate much deeper into the vascular system of the roots. Certain American vine species are immune to both, the most resistant being Vitis cinerea.

Resistance of certain grape variety species

The rootstocks of some American vines are resistant to phylloxera because they have adapted over millions of years. Resistance results from three circumstances. When infested, the vines react passively at the roots, producing little or no bile, thus depriving the pests of the basis for propagation. Secondly, the medullary rays in the roots are much more closely arranged than in European vines, so that the knots can only penetrate superficially. And thirdly, a protective cork tissue forms at the puncture site. This prevents the penetration of moisture, bacteria and fungi, which in the case of non-resistant vines leads to root rot and thus complete destruction. However, American vines can also be attacked above ground, but this is far less devastating and only causes greater damage if the attack is severe. Only under particularly favourable climatic conditions are European vines attacked by the aphids, which is why they are of little importance in Central Europe. However, most American vines and hybrids are susceptible to the aphid.

Origin and discovery of phylloxera

Phylloxera originates from North America, where it is found in large areas on the east coast. It was discovered here in 1854 by the entomologist Asa Fitch (1809-1879) and was first described a year later as an "insignificant insect" with the name "Pemphigus vitifolius". This seemingly harmless description was correct, as phylloxera is actually a pest that occurs on occasion. Only through larger vineyards a wide spread up to an epidemic is possible. However, this situation was by no means given on the east coast of North America. Here the insect could not cause any great damage, since the number of wild vines in one place was always limited, the soil conditions did not favour reproduction and, in addition, many of the American vines are more or less resistant at the roots. In contrast to other natural phenomena, which also occur without human intervention, the spread of phylloxera was only possible through massive human intervention in the ecosystem with large-scale monocultures. But even this would not have been enough for a worldwide spread, but was only achieved through the trade in contaminated vines.

Occurrence in Europe

Shortly before the phylloxera, powdery mildew came to Europe via England around 1845 - the first of the four terrible Danaer gifts from North America. Phylloxera followed about five to ten years later. Of course, an exact date can no longer be determined because the damage did not become visible until a few years later. From the year 1850 onwards, American vines were imported in large numbers to England and France as ornamental vines and for crossing purposes, and with them, unnoticed, phylloxera was introduced to Europe. But this had happened earlier and phylloxera had been present in America since time immemorial. So why had it not appeared much earlier in Europe? There is a very simple explanation for this. During the sailing times, the pest had not survived the voyage, which lasted about ten weeks or more, while it crossed the sea unharmed in the short time of 10 to 14 days with the fast steamboats.

Around the year 1858 (according to other sources only 1863) an inexplicable vine death was detected near Arles in Provence and initially a fungal disease or frost damage was suspected. In the end, even God's wrath and punishment for the sins of the time had to be taken as the cause. When the dead vines were dug up, it was discovered that the entire root system had practically disappeared. Because of the insect's tiny size, it remained unrecognized as the cause at first. In 1868, a commission was set up with the vineyard owner Gaston Bazille (1819-1894), the horticulturist Félix Sahut and the physicist and botanist Jules Émile Planchon (1823-1888), who within a short time succeeded in identifying the cause of the mysterious death of the vines. However, the origin of the pest from North America remained completely unclear for some time.

In the meantime, phylloxera spread slowly but steadily in almost all European countries, almost exclusively via vine material contaminated with it. It reached Austria-Hungary in 1867 (according to another source 1872), when the director of the Klosterneuburg Viticulture Institute, August-Wilhelm Freiherr von Babo (1827-1894) from Germany was given American vines as a gift. In Germany it was first discovered in 1874 near Bonn in the Annaberg garden. But it was not until 1902 that the pest reached Würzburg, in 1907 the Moselle and finally Baden in 1913. Further stations were Portugal in 1871, Turkey in 1871, Switzerland in 1874, Italy in 1875 (South Tyrol only in 1901), Spain in 1878 and Greece in 1898. According to rough estimates, around 75% of all vineyards in Europe were destroyed by the beginning of the 20th century.

A catastrophe of unimaginable proportions, because viticulture was of great economic importance in Europe, in Italy, for example, 80% of the population lived from it. The material damage was similar to that caused by the First World War. But the New World was also badly affected, because vines imported from France and infected with phylloxera reached California in 1873, paralysing the flourishing viticulture there a few years later. Finally, the pest was also introduced to Australia in 1877 and in 1885 to Algeria, New Zealand and South Africa, and was now present on all continents. The common danger forced the countries to cooperate, which was started in 1877 with an "International Phylloxera Conference". In 1881, a phylloxera convention was concluded between the German Empire, France, Switzerland, Austria-Hungary and Portugal, with rules for the import and export of vines and border controls. At that time, the life cycle of phylloxera was already researched and well known:

Measures against the pest

As early as 1870, the French government formed a commission, whose most famous chairmen from 1885 onwards were Louis Pasteur (1822-1895) and after him Jules Lavalle (1820-1880). A prize of 20.000 Francs was offered and later even increased to an incredible 300.000. In the course of seven years, a total of 700 proposals were submitted, of which approximately half were actually tried out. However, the prize never had to be paid out. Treatments with silkworm droppings, manure and crab extract, scraping off the bark or planting various defensive plants such as hemp or valerian were carried out. Modest partial successes were achieved by flooding the vineyards with water and the so-called cultural procedure, i.e. soil injection with carbon disulphide.

The problem was that even recognized scientists made false and sometimes adventurous assumptions and passionately advocated them. The entomologist Victor Antoine Signoret (1816-1889) believed that phylloxera was not the cause but the effect. And the well-known viticulture specialist Dr. Jules Guyot (1807-1872) suspected the cause to be too sharp pruning. Even such abstruse and completely ineffective methods as the burial of a dead toad under each vine borrowed from the Roman viticulture author Pliny the Elder (23-79), the tapping of the vineyard soil to drive the insect into the sea, up to the introduction of electricity into the soil and watering the vines with white wine were tried without success.

Phylloxera fighter

As early as 1869, Léopold Laliman (1817-1897) from Bordeaux recognised that some American vines were immune to phylloxera (but this is also attributed to others). At a congress in Beaune, the above-mentioned Gaston Bazille then proposed the method of grafting the tops (scions) of European vines onto the bottoms (rootstocks) of phylloxera-resistant American vines. This was supported by Gustave Foëx (1844-1906), who suspected as early as 1868 that the phylloxera had come from outside Europe. This was confirmed by Jules Émile Planchon (1823-1888) during a study trip to America in 1873, where he met the entomologist Charles V. Riley (1843-1895), who proved that the French insect was identical to the American one. Riley was one of the first to advocate grafting on American rootstocks. But this is also attributed to the botanist Georg Engelmann (1809-1884). Who was really "the first" can of course no longer be determined, and all the people mentioned can be considered the saviours of European viticulture from phylloxera.

Solution to the problem

From 1873 to 1876, millions of documents were shipped mainly to France and other countries, most of them from Missouri. Many of them were creations of the breeder Hermann Jaeger (1844-1895). In practice, however, many of the American rootstocks did not tolerate European soil, especially the calcareous soil, which is rare in American vineyards. At first, Vitis riparia was used as a rootstock vine, but it was unsuitable for calcareous soil. It was therefore crossed with the Vitis berlandieri. Finally, in 1887, the French Ministry of Agriculture sent a delegation headed by Dr. Pierre Viala (1859-1936) to America to find suitable rootstock vines. The development lasted for decades and for a long time two competing camps faced each other, the "Sulphurists" who swore to fight with chemicals and the "Americans" who preferred refinement.

At the end of this dispute about the direction of the company, the refiners finally prevailed. In the past, numerous documents were developed for the different requirements. An important criterion is a high resistance against phylloxera. The method known as grafting was and still is the only solution. But it was very expensive, because at that time there were over ten billion vines in France alone. For this reason, attempts were also made, with moderate success, to solve the problem by crossing American vines with European vines or even American vines with each other and to use them as an alternative for wine production. The American or French hybrids were not sufficiently resistant to phylloxera and, in addition, wines of certain species possessed the foxtone, which was unpleasant for European tastes.

Countries/areas without phylloxera

It was precisely during the first successes using grafted vines that the third catastrophe struck European viticulture. Paradoxically, in 1878, with the documents introduced for the rescue from the second catastrophe, downy mildew was introduced from North America. And as a sad end to a truly dark century for viticulture, black rot was imported from America in the early 1880s. With phylloxera, it took the longest time for the effective measures to become established in all countries. Some countries were at least partially spared in certain areas. These include some Greek islands in the Aegean Sea (Crete, Paros, Rhodes, Santorini, Cyprus), as well as Afghanistan, Argentina, Armenia, Australia, Chile, China, India, the Canary Islands and Pakistan.

Especially vineyards with sandy soil are not attacked, because the pest cannot exist there. Likewise, the insect cannot survive at high altitudes. There are individual vineyards or areas with vines with true roots in many countries, including Germany and Austria. But today grafting is common everywhere, it is estimated that this accounts for 85% of all vines worldwide. Phylloxera has still not been completely defeated, however, because a new variant (biotype B) appeared in America in the 1990s, which has already destroyed many vineyards in California and New Zealand. Major problems were caused in California in the early 1960s by the recommendation of the University of California (Davis) for the AxR 1 rootstock, which was too weakly resistant to phylloxera. All the vineyards planted with it had to be cleared again.

further information

Further extensive information in connection with phylloxera is contained in addition to the above-mentioned references (hyperinks), especially with the keywords American vines, European vines, hybrids, nodosities, pre-phylloxera, tuberosities, rootstock & rootstock vine and grafting.

Phylloxera: By Joachim Schmid, Geisenheim, Photographed by himself, CC BY 3.0 de, Link and Link
Root phylloxera: By Joachim Schmid, Geisenheim, - Photographed by himself, CC BY 3.0 de, Link and Link
Phylloxera and phylloxera fly: LWG Bayern
Life cycle: Geisenheim Research Institute, B. Loskill
Entw. cycle: From unknown, Humboldt University Berlin, GFDL 1.2, Link