Grape phylloxera is an insect pest of grapevines worldwide, originally native to eastern North America. Grape phylloxera (Daktulosphaira vitifoliae Fitch 1855) belongs to the family Phylloxeridae, within the order Hemiptera, bugs); originally described in France as Phylloxera vastatrix; it is equated to the previously described Daktulosphaera vitifoliae and Phylloxera vitifoliae. The insect is commonly just called phylloxera (; from Ancient Greek: φύλλον, leaf, and ξηρός, dry). These almost microscopic, pale yellow, sap-sucking insects, related to aphids, feed on the roots and leaves of grapevines (depending on the phylloxera genetic strain). On Vitis vinifera, the resulting deformations on roots ("nodosities" and "tuberosities") and secondary fungal infections can girdle roots, gradually cutting off the flow of nutrients and water to the vine. Nymphs also form protective galls on the undersides of grapevine leaves of some Vitis species and overwinter under the bark or on the vine roots; these leaf galls are typically only found on the leaves of American vines. American vine species (such as Vitis labrusca) have evolved to have several natural defenses against phylloxera. The roots of the American vines exude a sticky sap that repels the nymph form by clogging its mouth when it tries to feed from the vine. If the nymph is successful in creating a feeding wound on the root, American vines respond by forming a protective layer of tissue to cover the wound and protect it from secondary bacterial or fungal infections. Currently, no cure for phylloxera is known, and unlike other grape diseases such as powdery or downy mildew, no chemical control or response is available. The only successful means of controlling phylloxera has been the grafting of phylloxera-resistant American rootstock (usually hybrid varieties created from the Vitis berlandieri, V. riparia, and V. ruprestris species) to more susceptible European V. vinifera vines.
Biology
Phylloxera has a complex lifecycle of up to 18 stages that can be divided into these four principal forms:
The sexual form begins with male and female eggs laid on the underside of young grape leaves. The male and female at this stage lack a digestive system, and once hatched, they mate and then die. Before the female dies, she lays one winter egg in the bark of the vine's trunk. This egg develops into the leaf form. This nymph, the fundatrix (stem mother), climbs onto a leaf and lays eggs parthenogenetically in a leaf gall that she creates by injecting saliva into the leaf. The nymphs that hatch from these eggs may move to other leaves, or move to the roots where they begin new infections in the root form. In this root form, they perforate the root to find nourishment, infecting the root with a poisonous secretion that stops it from healing. This poison eventually kills the vine. This nymph reproduces by laying eggs for up to seven more generations (which also can reproduce parthenogenetically) each summer. These offspring spread to other roots of the vine, or to the roots of other vines through cracks in the soil. The generation of nymphs that hatch in the autumn hibernate in the roots and emerge next spring when the sap begins to rise. In humid areas, the nymphs develop into the winged form or perform the same role without wings. These nymphs start the cycle again by either staying on the vine to lay male and female eggs on the bottom side of young grape leaves, or flying to an uninfected vine to do the same.
Many attempts have been made to interrupt this lifecycle to eradicate phylloxera, but it has proven to be extremely adaptable, as no one stage of the lifecycle is solely dependent upon another for the propagation of the species.
Fighting the "phylloxera plague"
In the late 19th century, a phylloxera epidemic destroyed most of the vineyards for wine grapes in Europe, most notably in France. Phylloxera was introduced to Europe when avid botanists in Victorian England collected specimens of American vines in the 1850s. Because phylloxera is native to North America, the native grape species are at least partially resistant. By contrast, the European wine grape V. vinifera is very susceptible to the insect. The epidemic devastated vineyards in Britain and then moved to the European mainland, destroying most of the European grape-growing industry. In 1863, the first vines began to deteriorate inexplicably in the southern Rhône region of France. The problem spread rapidly across the continent. In France alone, total wine production fell from 84.5 million hectolitres in 1875 to only 23.4 million hectolitres in 1889. Some estimates hold that between two-thirds and nine-tenths of all European vineyards were destroyed. In France, one of the desperate measures of grape growers was to bury a live toad under each vine to draw out the "poison". Areas with soils composed principally of sand or schist were spared, and the spread was slowed in dry climates, but phylloxera gradually spread across the continent. A significant amount of research was devoted to finding a solution to the phylloxera problem, and two major solutions gradually emerged - grafting cuttings onto resistant rootstocks and hybridization.
Response
By the end of the 19th century, hybridization became a popular avenue of research for stopping phylloxera. Hybridization is the breeding of V. vinifera with resistant species. Most native American grapes are naturally phylloxera resistant (V. aestivalis, V. rupestris, and V. riparia are particularly so, while V. labrusca has a somewhat weak resistance to it), but have aromas that are off-putting to palates accustomed to European grapes. The intent of the cross was to generate a hybrid vine that was resistant to phylloxera, but produced wine that did not taste like the American grape. The hybrids tend not to be especially resistant to phylloxera, although they are much hardier with respect to climate and other vine diseases. The new hybrid varieties have never gained the popularity of the traditional ones. In the European Union, they are generally banned or at least strongly discouraged from use in quality wine, although they are still in widespread use in much of North America, such as Missouri, Ontario, and upstate New York.
Grafting with resistant rootstock
… excerpt ends here. Continue reading the full article.
