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Insecticides were applied on various surfaces and exposed to different 
environmental conditions in several experiments to determine their residual 
toxicities to the house fly. DDT and gamma-EEC were initially the most 
toxic compounds. The other three materials were, in order of their dimin- 
ishing toxicity, chlordane, Rothane D-3, and toxaphene. BHC gave the most 
rapid knockdown, followed by DDT, Rho thane D-3, chlorcane, and toxaphene. 
Vapors from gamma-BHC were about three times as toxic to flies as those 
from chlordane; both were extremely toxic as fumigants. The order of per- 
sistence of the residual treatments was, from the most to the least, DDT, 
Rhothane D-3, toxaphene, chlordane, and BHC. — Bruce (5^)« 
Cristol (88) in 19^9 examined the hypothesis that the insecticide! 
activity of various polychloro insecticides is due in large measure to the 
ability of the compound to liberate hydrogen chloride at the site of action 
of the insecticide. The relative toxicities to the house fly of the 
various constituents of technical chlordane were as follows: 
Relative effective dosares 
(Technical chlordane = 0.01 ) 
Heptachlor .00*4-3 
Octachlor, active isomer .0056 
Octachlor, inactive isomer .017 
Nonachlor .020 
In reactions with 0.04 M ethanolic sodium hydroxide at k6° C. the 
insecticidally active octachloro isomer and the nonachloro compound reacted 
much more rapidly than the heptachloro compound which is the most effective 
insecticidally, showing that dehydrochlorination with alkali and insecti- 
cidal activity have no systematic relationship. 
Gersdorff e_t al « ( 173 ) determined the relative toxicities of certain 
chlorinated hydrocarbons to the house fly when applied as space sprays 
using the Campbell turntable method. Crystalline chlordane was about two- 
thirds as toxic as technical chlordane which proved to be one-fourth as 
toxic as aldrin and heptachlor. None of the sprays made with the chlorinated 
compounds caused appreciable knockdown. 
Organic insecticides in various concentrations and formulations were 
used to treat 15^ dairy barns in Hew York in 19^+9. Chlordane emulsion, 6, 
12, and 2k pounds of toxicant per 100 gallons of water, provided k weeks ox 
more control of house flies in these barns which were heavily infested 
before treatment. A mixture of chlordane (6 lbs.) and DDT (3 lbs.) was more 
effective than either chlordane or DDT alone. — Pimental et a^. ( 367 ) . 
Same as for Siphona i rritana . — Bruce and Decker ( 56) . 
Same as for Anopheles quadr imaculatus . — Jay e_t a^ ( 136 ) . 
Resistant house flies 
House flies that had developed a resistance to DDT were tested against 
other insecticides. The special stock was distinctly more resistant to all 
