BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 33 
studies, started in 1951, were concluded this year. The analyses indi- 
cated that the tobacco, after curing and sweating, might contain from 
110 to 337 p. p. m. of DDT on a dry weight basis. Residues from para- 
thion or Metacide treatments ranged from 0.01 to 1.2 p. p. m. Organic 
chloride residues from TDE dust treatments ranged from 76.4 to 93.4 
p. p. m. DDT residues were not appreciably affected by either barn 
curing or sweating. Parathion residues were reduced as much as 99 
percent in both barn curing and sweating. Organic chloride residues 
from TDE dusts showed measurable loss in the sweating process. 
A greater variety of crops was included in this years study of 
residues resulting from malathion treatments of various fruits and 
vegetables. This was a continuation of the previous year's work 
in cooperation with the manufacturer of this insecticide. Fewer sam- 
ples were analyzed this year than last. Frozen strawberries, picked 12 
days after the last of two malathion dust treatments, contained 0.18 
p. p. m. of malathion. Fresh, frozen, and canned peas, potatoes, 
fresh snap beans, and canned wax beans were free of malathion. 
Bartlett pears showed only 0.02 p. p. m. at harvest. Residues on 
alfalfa ranged from to 6.5 p. p. m., but there was no correlation 
between the amounts applied and the residues found. Jonathan ap- 
ples showed 0.1 p. p. m. at harvest. Broccoli showed a deposit of 
9.2 p. p. m. immediately after dusting but had no malathion 6 days 
after treatment. From initial deposits of 15 to 82 p. p. m. on spinach, 
residues dropped to less than 1 p. p. m. 5 days after treatment. 
About 2,400 samples of cherries from orchards of 27 growers in the 
State of Washington were analyzed at fehe Bureau's Yakima labora- 
tory. This work was performed under a memorandum of under- 
standing with the Washington Agricultural Experiment Station and 
the Washington Department of Agriculture, Comparisons were also 
made of different methods of application of insecticides for control 
of the cherry fruitfly. It was found that airplane applications 
resulted in very low deposits as compared with hand guns or air 
carrier type sprayers. The variation between deposits applied with 
the same type of equipment by different operators was enormous. 
At Beltsville, Ma., a study of residues of chlorinated insecticides 
such as DDT and TDE on tobacco was made in cooperation with 
several State agriculture experiment stations and tobacco companies. 
Analyses of untreated samples from different sources disclosed that 
the natural organic chlorine content of tobacco varies considerably and 
is sometimes quite appreciable. 
Analyses were made at Beltsville of wheat and wheat products 
from storage bins that had been treated with DDT and of corn from 
a bin treated with methoxychlor. The presence of the insecticides was 
detected in these commodities. The amount of methoxychlor found 
m the shelled corn ranged from to about 1 p. p. m. In the wheat, 
more DDT was found in samples taken near the bin wall than in 
the center of the bin, as was expected. The highest amount of DDT 
found in the wheat was about 4 p. p. m. Up to 7.5 p. p. m. was 
found in the bran and shorts. The highest DDT content in samples 
of flour made from the wheat was 0.8 p. p. m. 
Samples of a great variety of crops experimentally treated with 
the newer insecticides were also analyzed for residues by Bureau 
chemists at Beltsville. These samples included wheat, barley, oats, 
hay, beans, peas, tomatoes, lettuce, tobacco, mushrooms, sugarcane, 
