THE GREEN-BUG OR SPRING 
GRAIN-APHIS: 
HOW TO PREVENT ITS PERIODICAL OUTBREAKS 
W. R. WALTON 
Entomologist in Charge, Cereal and Forage Insect Investigations 
FARMERS’ BULLETIN 1217 
; UNITED STATES DEPARTMENT OF AGRICULTURE 
WASHINGTON : GOVERNMENT PRINTING OFFICE : 1921 
