406 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 15 



III. Average Tons Per Acre in Sacramento and San 

 Joaquin Valleys 

 During the past four outbreaks of the beet leafhopper the average 

 tons per acre harvested in the Sacramento Valley and northern part of 

 the San Joaquin Valley was as follows: 



Sacramento Valley San Joaquin Valley 



1918 8.49 5.58 



1919 6.02 3.46 



1920 6.92 5.12 



1921 6.72 4.86 



7.02 Average ■ 4.96 

 The average tons per acre would be lower if the acres abandoned on 

 account of curly leaf were to be taken into consideration. 



It is evident that the lowest average tonnage per acre was obtained 

 during 1919 when the beet leafhoppers reached their maximum in 

 numbers. Again in 1921, the average tons per acre was lower than in 

 1918 and 1920. In California general outbreaks of curly leaf occurred 

 during the following years: 1899-1900; 1905; 1913-1914; 1918-1919- 

 1920-1921. It is evident that with the exception of 1905, and 1918- 

 1921, the outbreaks of ctirly leaf occurred in two successive years, with 

 the drop in tonnage due to the disease greater in the second year. 

 During the four successive years of curly leaf, the drop in tonnage due 

 to the disease was greater in the second and fourth years and it appears, 

 seemingly, that a double two year outbreak of the blight has occurred. 

 During the three year interval between the 1913-1914 and 1918- 

 1921 outbreaks of curly leaf, the average tons per acre in the Sacramento 

 Valley and northern part of the San Joaquin Valley was as follows: 



Sacramento Valley San Joaquin Valley 



1915 9.17 7.75 



1916 10.65 8.49 



1917 9.76 6.73 



9.94 Average 7.29 



IV. Spring Migration 

 We (3) have published the results of our investigations concerning a 

 spring migration of the beet leafhopper into the Sacramento Valley. 

 The evidence for a spring migration during 1918-1920, is associated with 

 the fact that the first brood adults did not invade the cultivated area 

 after the pasture vegetation became dry on the foothills and again, 

 no specimens were found wintering over on the foothills during 1920- 

 1921. 



