308 
JOURNAL OF ECONOMIC ENTOMOLOGY 
(Vol. 11 
S. B. Freeborn: We have not as yet conducted any evaporation 
experiments on films of water but we know from experience and from 
the results of our evaporation trials with different grades of oils that 
both temperature and air circulation have a marked effect upon the 
rapidity with which the oil disappears. In the case of our evaporation 
experiments we determined that a fan which kept the air in circula¬ 
tion in the incubator was responsible for 83 per cent of the evapora¬ 
tion for whenever the fan was shut off the evaporation decreased that 
percentage for the time the fan was out of commission. I should 
imagine from these results that air circulation would be a very potent- 
limiting factor in nature. 
G. P. Gray: I am very glad to see articles on the use of petroleum 
oils appearing in the publications for it seems to me that work with 
this group will produce very satisfactory results for insecticide devel¬ 
opment. Much of the work yet to be done must be along chemical 
lines for although the physical characteristics act as indices and may 
augment or detract from the final toxic effects, it is after all the chem¬ 
ical constituents that actually do the work. 
President G. P. Weldon: I will next call for a paper entitled 
“ Notes on the Beet Leafhopper,” by H. H. P. Severin and W. W. 
Thomas. 
NOTES ON THE BEET LEAFHOPPER, EUTETTIX TENELLA 
BAKER 
By Henry H. P. Severin, Ph. D., California Agricultural Experiment Station 
and William W. Thomas, M. S., Spreckels Agricultural Experiment Station 
Ball 1 accounts for swarms of Eutettix tenella in the sugar beet fields 
of Utah in the spring of 1915, “by flights from the serious California 
outbreaks of 1914. This would involve the crossing of chain after 
chain of mountains and traveling from 600 to 800 miles in an air 
line.” 
In California, Ball found the l£afhoppers breeding in abundance on 
the native Atriplex in the Lake Tulare region. He writes, “This dis¬ 
trict extends down as far as Bakersfield and the same conditions are 
probably repeated in suitable areas in the Mojave Desert and Death 
Valley sections. The leaf hoppers were found commonly in the Im¬ 
perial Valley, and it is probable that this whole region is within the 
permanent breeding grounds and is the source of the California, 
troubles.” 
1 Ball, E. D., 1917. Utah Agr. Exp. Sta. Bull. 155. 
