BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 65 
Parasite of Japanese Beetle Well Distributed 
Surveys show that the spring Tiphia, Tiphia v emails Rohw., an 
introduced parasite of grubs of the Japanese beetle, is generally dis- 
tributed in and near the sections of the East where this species was 
released. The parasite was introduced from Japan and first liberated 
here in 1926. Since then it has been released at more than 2,000 points 
in the area infested by the Japanese beetle. The spring Tiphia was 
known to have become established at many of the colonization points 
and to have attained parasitization ranging up to 60 percent or more 
at these points. Comparatively little was known, however, about its 
dispersion. To determine the extent of spread, surveys were con- 
ducted in 1950 during the flight of the adult Tiphias, in the general 
area in which colonies had been released in early years. This area 
included approximately 1,400 square miles in Delaware and south- 
eastern Pennsylvania. Predetermined routes were followed and 10- 
minute stops made at half-mile intervals without regard to the loca- 
tion of the original colonization points. Even with these brief obser- 
vation periods adult parasites were <een at 86 percent of the stopping 
points. Several recoveries were made from 7 to 10 miles beyond the 
limits of the area where colonies had been released. It is evident that 
the parasite has spread through and beyond the entire area that has 
been generally colonized, thereby demonstrating a capacity for 
unaided dispersion. 
Biological Assay Method for DDT and Chlordane Residues in Soil 
Developed 
A tentative procedure for determining, by biological tests, the 
amount of residues of DDT and chlordane in the soil has been devel- 
oped at the Moorestown, X. J., laboratory. These insecticides are 
used in the soil to kill Japanese beetle grubs. When soil is treated 
with them as a means of authorizing the movement of nursery stock 
from infested to uninfested areas, it is necessary to determine annu- 
ally how much of the chemical remains in the soil from earlier treat- 
ments. The test insect used in this assay is Macrocentrus ancylivorus 
Rohw., a wasplike parasite of the oriental fruit moth. The method 
is based on the reactions of the parasite to small amounts of chlorin- 
ated hydrocarbon insecticide in extracts of the treated soil. Small 
variations in the amounts of these materials present cause significant 
differences in the time required to kill the test insects. Indications 
are that DDT and chlordane residues in soil can be assayed whether 
they occur separately or in combination. It may also be possible to 
use this method to determine amounts of other chlorinated hydro- 
carbon insecticides, such as aldrin and dieldrin, in the soil. 
WHITE-FRINGED BEETLES 
White-Fringed Beetle Numbers Reduced in All Areas 
Twenty-two counties known to have been infested by the white- 
fringed beetle were found free of the beetle in this year's scouting. In 
a few of the counties this was the second year of negative findings. 
