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UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



from several sources and at several points. It was first noticed in the 

 southern part of Sonoma County, in the valley surrounding the old 

 town of Sonoma, about 1874. By 1880 vines killed by the insect had 

 been found in Napa, Solano, and Placer counties, and hundreds of 

 acres had been pulled up in Sonoma Valley. Since then the insect has 

 spread to all the important grape-growing regions of California north 

 of Tehachapi*, and probably not less than fifty thousand acres have 

 been destroyed. 



The Insect. The phylloxera occurs normally in four forms, which 

 have been called by Victor Mayet: 



1. The gall insect, or form of multiplication; 



2. The root insect, or form of devastation; 



3. The winged insect, or form of colonization ; 



4. The sexual insect, or form of regeneration. 



The gall insect lives upon the leaves, and is the commonest form on 

 the wild vines in the native habitat of the insect. It rarely or never 



occurs in California. In Europe 

 it is found often upon American 

 and rarely upon European varie- 

 ties. It causes little swellings or 

 galls upon the leaves and 

 younger parts of the vine, which, 

 though sometimes very numer- 

 ous, do little permanent injury. 

 The chief danger from the gall 

 form is that it multiplies with 

 astonishing rapidity and mi- 

 grates from the leaves to the soil. 

 Here it attacks the roots and 

 gives rise to the root form, which 

 is the "form of devastation," 

 the one which finally destroys 

 all the vines it attacks which are 

 ' ' non-resistant. ' ' Every insect of the root form which reaches maturity 

 lays about twenty-five or thirty eggs, each of which is capable of 

 developing into a new egg-layer needing no fertilization. As there are 

 from five to seven such generations during the year the increase in 

 numbers is extremely rapid. 



Sometimes during the summer, usually in July or August, some of 

 the eggs laid by the root insects may develop into insects of slightly 

 different form, called nymphs. They are somewhat larger than the 



* The phylloxera is said to have been found once in Southern 'California, but as 

 the vineyard was uprooted and destroyed the insect was probably extirpated. 



FIG. 1. Under side of grape leaf showing galls 

 caused by Phylloxera. This form seldom, if 

 ever, occurs in California. 



