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.[2] 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. source;Wikipedia
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