BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 61 
aphids and one planthopper that may be possible vectors. Two 
hundred and fifty transmission experiments with the three aphids 
Aphis gossypii, Toxoptera aurantiae, and Aphis spiraecola have been 
set up. Some of the test plants already show symptoms similar to 
tristeza but such transmission has not yet been confirmed by bottle- 
graft transfers. Vector surveys showed that spiraecola is more abun- 
dant in central Florida than the other two species. On the east coast 
aurantiae and gossypii are more plentiful than spiraecola. All species 
of aphids were scarce during the first half of 1953. 
The planthopper under suspicion as a vector is Cyarda melichari. 
This is the first time this species has been reported on citrus. The 
specimens collected during the surveys will be used in further labora- 
tory transmission tests. 
First-Instar European Chafer Larvae Most Susceptible to DDT 
Complete mortality of first-instar larvae of the European chafer 
was obtained within 1 week when 10 pounds of DDT per acre was 
applied to Dunkirk sandy loam. Two weeks were required in Ontario 
gravelly loam. Second-instar larvae were killed within 6 weeks with 
15 pounds of DDT per acre. Third-instar larvae survived for more 
than 8 weeks in 21 pounds of DDT per acre. It is apparent that, if 
these grubs are to be eradicated in nursery soils, the DDT should be 
applied before the eggs hatch. Tests on which these findings were 
made were performed at Newark, N. Y., in cooperation with the New 
York Agricultural Experiment Station at Geneva. 
Hall Scale Eradication 
Surveys of almond and peach acreages in the vicinity of Cliico, 
Calif., where Hall scale has persisted since 1934, disclosed infestations 
of this minute scale insect on three additional properties in the Chico 
area. Additional infestations were found on six properties in three 
city blocks in Oroville, Calif. These properties represent an extension 
of known infested localities. A total of nearly 82,000 host plants be- 
yond the limits of known infestation were inspected during the fiscal 
year. 
An inspection of more than 6,250 deciduous fruit trees on 159 prop- 
erties that had previously received a final hydrocyanic gas fumiga- 
tion failed to reveal any living Hall scale. The control work was in 
cooperation with the California Department of Agriculture. 
At the Bidwell Park infestation in Chico, host trees on properties 
within a 2,500-foot radius of the infestation were treated. Because 
of the lightness of the Davis, Calif., infestation, treatment there was 
limited to an area within a 1000-foot radius. 
The control program consists of either the removal and destruction 
of infested trees or the application of oil sprays to host plants on in- 
fested properties coupled with three consecutive annual hydrocyanic 
acid fumigations during the period of host dormancy. 
During the 1952-53 fumigation program, 3,716 trees were treated. 
These included all known infested plantings which had not previously 
been fumigated, as well as nearby plantings in the new treatment 
areas in Chico and Davis. 
