UNITED STATES DEPARTMENT OF AGRICULTURE 
BULLETIN No. 903 
Contribution from the Bureau of Entomology 
L. O. HOWARD, Chief 
i ,r "\ ' 
Washington, D. C. 
PROFESSIONAL PAPER- 
April 22, 1921 
THI£ 
GRAPE PHYLLOXERA IN CALIFORNIA 
By .- 
W. M. DAVIDSON, Scientific Assistant, and 
R. L. NOUGARET, Entomological Assistant, 
Deciduous Fruit Insect Investigations 
CONTENTS 
California Hisiory 1 
Accidental and Natural Spread .... 7 
Distribution of Phylloxera in California . 11 
Vineyard Destruction 15 
Nomenclature and Synonymy of the 
Grape Phylloxera 26 
Biology of the Grape Phylloxera in Cali- 
fornia . . % 27 
The Radicicole 44 
age 
The Nymph and Winged Form .... 73 
Nymphicals or Intermediate Forms . . 82 
The Sexual Forms ....:... *0 
The Gallicole and its Relation to Cali- 
fornia Conditions l 5 
Effects of Water and Heat on Phylloxera 8 
Diffusion of Phylloxera 11a 
Summary 122 
Literature Cited 127 
WASHINGTON 
GOVERNMENT PRINTING OFFICE 
1921 
