BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 
9 
bination appeared to be a soluble oil plus cube resins. The soluble 
oil seemed more effective than an oil emulsion prepared with glue 
as an ernjulsifier, both when the oils were used alone and when they 
were combined with cube resins. The use of soluble oils as carriers 
for these resins also has the advantage that the solution of resins 
can be added to the oil just before the spray tank is filled. 
When cube resins were added to light medium oils they caused 
a larger increase in effectiveness than when they were combined with 
heavy oils. In practical field experiments, in which the sprays were 
applied by commercial operators, mortalities of 36 percent of tho 
adult scales on heavily infested gray wood were increased to 76 per- 
cent by the addition of cube resins. The mortality on the fruit wad 
increased from 82 to 96 percent. 
Experiments were begun at Whittier with sprays and dusts con- 
taining tartar emetic and with dusts containing potassium antimony 
citrate, in comparison with sulfur dust as used in the standard pro- 
gram for the control of the citrus thrips on lemons. Although in 
previous years serious injury resulted from the use of sulfur on lemon 
trees during the summer months, comparatively little has developed 
in the experimental blocks for the last 2 years. 
Counts of the black scale in an orchard near Redlands, Calif., in 
which one section has been dusted with sulfur each year since 1936, 
showed 0.14 scale per unit area in the dusted part of the orchard as 
compared with 4.25 per unit in the undusted part. This is in line 
with information obtained in earlier years. 
Experiments in control of the citrus rust mite were begun in 
September 1939 by the St. Lucie, Fla., laboratory under east coast 
conditions. Wettable sulfur (4,000-mesh) containing either cotton- 
seed oil or fish oil kept mite infestations at lower levels than any 
other treatments. Lime sulfur alone and lime-sulfur plus alkylated 
sulfonated diphenyl were the two least effective sprays. The 2,000- 
mesh sulfur dust (without an adhesive) gave poorer control than the 
325-mesh material. Similarly, the 4,000-mesh wettable sulfur added 
to lime-sulfur required one more application than the 325-mesh wet- 
table sulfur in the same combination. These results were less favor- 
able to the more finely divided sulfurs than those of a year ago. 
The severe freezes that occurred in January 1940 offered an oppor- 
tunity to obtain data on the effect of low temperatures on the Florida 
red scale. From counts of 500 adult female scales in 2 locations it 
was found that 32 percent survived a minimum temperature of 27.5° 
F. and 16 percent a minimum temperature of 23°. Owing to the 
number killed by the freeze, the dropping of old leaves thai were 
infested, and the picking of the fruit, the numbers of scales were 
greatly reduced, although enough survived on most trees at St. Lucie 
to reinfest the leaves and the young fruit as it developed. 
THE JAPANESE BEETLE 
Investigations of the Japanese beetle were continued at Moore-town, 
N. J., and Spencer, N. C. By the close of 1939 the area of general 
distribution of the Japanese beetle was estimated at approximately 
16.300 square miles, an increase of 1,183 over the previous year. 
An outstanding feature of the year was a further increase in the 
importance of the milky disease of Japanese beetle grubs. The dis- 
