n. (Zool.) A small hemipterous insect (Phylloxera vastatrix) allied to the aphids. It attacks the roots and leaves of the grapevine, doing great damage, especially in Europe. It exists in several forms, some of which are winged, other wingless. One form produces galls on the leaves and twigs, another affects the roots, causing galls or swellings, and often killing the vine. The diseased condition of a vine caused by the insect just described.