INSECTS INJURIOUS TO THE GRAPE 



493 



it is injurious only in California, where it was imported on French 

 vines about 1S74. rt was first noticed in Sonoma County and 

 since then has spread to all the principal grape-growing regions 

 north of Tehachapi and has probably destroyed 50,000 acres. 



This aphid exists in several forms, which injure both foliage 

 and roots. On the leaves irregular spherical galls are produced, 

 and the root-inhabiting form produces galls on the roots. The 

 lea-galls are very common on American grapes, but are no 

 indication of the presence of the root form, as the roots are rarely 

 injured where the foliage is covered with leaf-galls. On the other 

 hand the European varieties rarely exhibit any leaf-galls, but are 



FIG. 354. Under side of grape leaf showing galls caused by Pyylloxera. 



(After Riley.) 



very susceptible to the root phylloxera, which multiplies without 

 any external indication of its presence until the vine is seriously 

 injured. The injury to the vine is not due so much to the sap 

 taken from the vine by the myriads of aphides which may inhabit 

 the roots, as to their poisonous effect on the root tissue and its 

 subsequent decay. Wherever the phylloxera attack the roots, 

 small swellings are produced, composed of soft tissue, which soon 

 decays. When such a gall is formed at the end of a young root, 

 its growth is stopped, and on larger roots a decay sets in which 

 finally girdles the root and all below the injured point dies. As 



