Phylloxera The name of a root louse which attacks and devastates grapevines. It spread from America to Europe in the 1860's and destroyed the vineyards of France, then spread elsewhere. Most of the world's vineyards are now planted on American rootstock (which is more resistant to Phylloxera). However, in the last 20 years it has become rampant in the Napa Valley and caused major replanting.