BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 31 
Dieldrin-Treated Fly Strips Safe for Dairy Barn Use 
Dieldrin- treated screen strips in dairy barns as a means of fly con- 
trol will not cause detectable dieldrin contamination of milk of cows 
subsequently milked in the barns. This was learned during studies 
made in cooperation with the manufacturer of this product. 
CHEMICAL STUDIES OF INSECTICIDES 
Structural Change in Molecule Detoxifies Affinin 
A number of compounds closely related to affinin, the insecticidal 
constituent of Heliopsis longipes, were synthesized to obtain informa- 
tion on the relationship of double bonds, geometric isomerism, and 
other structural details of the molecule with insecticidal activity. 
The importance of geometric isomerism in the toxicity of com- 
pounds of this type was demonstrated in an experiment in which 
affinin, which contains at least one double bond of the cis configuration, 
was converted by exposure to ultraviolet light to "trans-aftmrn" in 
which all double bonds had the trans configuration. Although affinin 
is as toxic as pyrethrins to house flies, "£ra^-affinin" showed no tox- 
icity to this insect. 
Synthetic Organic Compounds Tested as Insecticides 
Three hundred and thirty-eight synthetic organic compounds were 
prepared and submitted under code for screening tests as insecticides, 
synergists for allethrins and the pyrethrins, or insect repellents. 
These include a number of amides, esters of chloroacetic, chlo- 
ropropionic, bromoacetic and ethoxybenzoic acids, and esters of phen- 
ethyl and pheylpropyl alcohols. 
Sixty-two compounds that had previously been prepared and tested 
as insecticides and pyrethrum synergists were prepared in further 
amounts for testing as synergists for allethrin. 
Lindane Formulations and Analysis Improved 
Experiments to improve the residual properties of lindane showed 
that the effectiveness of deposits of this insecticide can be markedly 
prolonged by the addition of chlorinated terphenyls in the formula- 
tions. At the same time the appearance of residual deposits of lin- 
dane was improved by this means through the elimination of surface 
crystallization. 
An improved method of analyzing lindane in air was developed dur- 
ing the year. The lindane from a known volume of air is adsorbed by 
drawing the air through a column af activated alumina. This means 
of sampling is rapid and efficient. The adsorbed lindane is then 
washed off the alumina with glacial acetic acid and determined color- 
imetrically by a method developed by Bureau chemists. This method 
of analysis was employed in cooperative studies on the use, for dis- 
insectization purposes, of lindane- treated filter screens in the air- 
conditioning system of a Constellation airplane. It is also being 
followed to study the lindane-in-air concentration resulting from 
the use of lindane thermal generators. 
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