5 CIRCULAR 920, U. S. DEPT. OF AGRICULTURE 
Ficure 1.—Treatment of trees infested with the Hall scale in the Plant Introduction Garden, 
Chico, Calif., in 1935. 
for 1 hour under double untreated canvas or rubberized covers. Some 
scales survived this procedure, and treatment or removal of them was con- 
tinued until the infestation was thought to be eradicated. 
However, in an insect survey of the Chico atea in 1940, the scale was 
found again—in an almond orchard adjoining the Plant Garden, and later 
in the garden. As a result, a joint Federal-State project was organized in 
1941 to determine the area infested and investigate the possibility of eradi- 
cation. This circular summarizes information on the biology and habits 
of the Hall scale and the progress made in determining the area of infesta- 
tion and eradicating the scale. 
DISTRIBUTION 
The Hall scale was described from Egypt by Green (8). Mackie C0) 
learned through correspondence that it was found in Turkey and Tripoli 
and that it was common over all lower Egypt. It is also recorded from 
Afghanistan (Archangelskaya 1), U. S.S. R. (Turkmenia, Uzbekistan, and 
Tadzhikistan) (Borchsenius 4), Greece (Koroneos 9), Iraq (Bodenheimer 
2, 3), and Baluchistan.* Specimens from Syria, Iran, and Israel have also 
been identified by the U. S. Bureau of Entomology and Plant Quarantine. 
The place of origin and the time of its introduction into the United States 
are unknown. 
After the infestation was discovered near Chico, in Butte County, in- 
festations were found in Oroville and Davis, Calif. All the evidence indi- 
cates that the infestation in the Plant Introduction Garden at Chico was the 
source of the other infestations. Although there had been considerable 
movement of host plants out of the Plant Garden to other parts of California 
3 Personal communication from A. M. Boyce, University of California Citrus Experiment 
Station, Riverside, Calif. Specimens identified by H. L. McKenzie, California Department of 
Agriculture, Bureau of Entomology. 
