642 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 17 
though it is commonly supposed by agriculturists and fieldmen that a 
good crop can be obtained when the foliage of sugar beets covers the 
rows or shades the ground by the time that the adults of the spring 
brood fly into the beet fields, the writer is fully convinced after the out¬ 
break of curly leaf in 1919 that such is not always the case. 
The primary cause for the enormous increase in numbers of the beet 
leafhoppers during 1919 hinges on two factors: (1) there were no 
summer migrations of the pest during 1918, so that a large number of 
eggs were deposited during the autumn; (2) the nymphs which hatched 
from these eggs found an abundance of green food not only in the culti¬ 
vated areas but also on the plains and foothills after the heavy Septem¬ 
ber rains germinated the seeds of the vegetation. 
Factors Concerned with the Reduction in Numbers of 
Beet Leafhoppers 
Early Drying of Pasture Vegetation.- —It was frequently ob¬ 
served in the San Joaquin Valley that heavy north winds dry the 
pasture vegetation rapidly on the plains and foothills during April 
and May. In all probability, when the pasture vegetation becomes 
wilted and begins to dry, large numbers of eggs of the beet leafhoppers 
fail to hatch, as is the case when Red Stem Filaree, weeds and sugar 
beet leaves wilt and become dry in the greenhouse. 
An examination of the climatological data of the Weather Bureau 
Office during 1923 shows that February was the driest in 11 years and 
the driest March in 27 years in California. Drought conditions con¬ 
tinued for a period of six consecutive weeks, from the middle of Febru¬ 
ary to the close of March. Desiccating northerly winds prevailed 
during March. 
The primary cause for the enormous reduction in numbers of the 
spring brood leafhoppers on the plains and foothills during 1923 was due 
to the early drying of the pasture vegetation during March instead of 
April and May as in previous years from 1918 to 1922. Mr. E. A. 
Schwing, Entomologist for the Spreckels Sugar Company Agricultural 
Experiment Station, reports that the plains and foothills of the southern 
and middle sections of the San Joaquin Valley were almost entirely free 
from hoppers except on the floor of Little Panoche Valley, where such 
nymphs as did hatch were forced to congregate on green pasture vege¬ 
tation growing in the drainage furrows. Records taken in previous 
years in Little Panoche Valley showed that the nymphs and adults 
assemble on green pasture vegetation in the drainage furrows during 
April and May. 
