BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 27 
Xo scales have been found in the orchard of the California Agricul- 
tural Experiment Station at Davis since the removal of infested trees 
and intensive treatment of remaining hosts nearby/ This orchard 
was first found infested in October 19 L7. 
No additional infestations of Hall scale were found in surveys, con- 
ducted in cooperation with State and local quarantine officials, of com- 
munities in California and elsewhere that had received shipments of 
host plants from infested areas at Chico or Davis. 
This program is conducted in cooperation with the California De- 
partment of Agriculture. 
Studies on Vectors of Stone-Fruit Viruses Begun 
Studies to determine the insects responsible for the natural spread 
of the plant viruses that cause western X of peach and little cherry 
diseases in western United States were started in 1948. Field plots 
were established, and other facilities for the work, including a green- 
house, an electronic microscope, and an ultracentrifuge, were erected 
or installed by this Bureau or by cooperating agencies. Leafhopper 
suspects were given the most attention in the 511 transmission tests 
that were initiated. 
This new Research and Marketing Act project is being undertaken 
in cooperation with the Bureau of Plant Industry, Soils, and Agri- 
cultural Engineering and the agricultural experiment stations of Utah, 
Washington, and Oregon. Headquarters are maintained'at Riverside, 
Calif., and work is now under way at Logan, Utah, Wenatchee, Wash., 
and The Dalles, Oreg. 
Comstock Mealybug at Low Ebb 
During the middle and late 1930's the Comstock mealybug became a 
serious pest in many apple orchards in at least 10 eastern States extend- 
ing from Connecticut to Georgia and west to include Ohio. Infesta- 
tions were most numerous and injurious in Virginia. Since no insecti- 
cide was then known to be effective against this insect, work was under- 
taken at Charlottesville, Va., in 1940 to bring the infestations under 
control by the colonization of native and imported parasites. The 
apparent effectiveness of two parasites, Allotropa burrelli Mues. and 
Pseudaphycus malinus Gahan, imported from Japan and established 
throughout the infested area, and also of a widely distributed native 
parasite, Clausenia purpurea Ishii, was such as to reduce this mealybug 
to a pest of minor importance by 1945. 
Soon after DDT became available, it was found to be highly toxic, 
not only to the young mealybugs, but also to the mealybug parasites. 
Despite the loss of effective parasites due to the use of DDT, the Com- 
stock mealybug has been reduced almost to the vanishing point in 
orchards in which DDT has been used for codling moth control. In 
1948 for the first time there were no calls for parasites for colonization, 
and surveys yielded only 3.2 mealybugs per man-hour in observation 
orchards, as compared with 27.5 in 1947. Xo mealybugs were found 
in any orchard in which DDT had been used more than one season. 
860448—49 5 
