Grape phylloxera
Grape phylloxera is an insect pest of grapevines worldwide, originally native to eastern North America. Grape phylloxera (Daktulosphaira vitifoliae (Fitch 1855) belong to the family Phylloxeridae, within the order Hemiptera, bugs); originally described in France as Phylloxera vastatrix; equated to the previously described Daktulosphaera vitifoliae, 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 there is no cure for phylloxera and unlike other grape diseases such as powdery or downy mildew, there is no chemical control or response. The only successful means of controlling phylloxera has been the grafting of phylloxera-resistant American rootstock (usually hybrid varieties created from the Vitis berlandieri, Vitis riparia and Vitis rupestris species) to more susceptible European vinifera vines.
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Phylloxera has a complex life-cycle of up to 18 stages, that can be divided into four principal forms: sexual form, leaf form, root form, and winged form.
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 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, else they 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 life cycle to eradicate phylloxera, but it has proven to be extremely adaptable, as no one stage of the life cycle is solely dependent upon another for the propagation of the species.
