BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 35 
Prospective Insecticide Diluents Examined 
Inert mineral materials from several sources were examined for 
their suitability as carriers or conditioners in the preparation of insec- 
ticide dusts and wettable powders. 
A pulverized hydrous aluminum silicate from Pennsylvania that 
has been proposed for use as an insecticide carrier was examined and 
found promising. 
Three new special grades of attapulgite were investigated as pos- 
sible cheaper substitutes for Santocel as a conditioner for high con- 
centration DDT wettable powders but they did not appear suitable 
for this purpose. 
Several mineral materials from foreign countries were examined 
to determine their usefulness as carriers. Among these was a sample 
of diatomite from Guatemala examined at the request of the Foreign 
Agricultural Service. Kesults showed that it would be useful as an 
insecticide carrier. A clay from Honduras, and a pyrophyllite, two 
talcs and three clays from Paraguay — all tested at the request of the 
Institute of Inter- American Affairs — in general showed promise for 
use in insecticides. Of two samples of supposed talcs from Mexico, 
one was found to be true talc of standard grade but the other was a 
siltlike material containing little if any talc and unsuitable as an 
insecticide diluent. 
INSECT RESISTANCE TO INSECTICIDES 
Extensive Search for Insecticides Capable of Controlling Resistant 
House Flies 
Studies are being continued in methods of controlling insecticide- 
resistant house flies. Hundreds of chemicals and combinations of 
chemicals have been studied in the laboratory and in small field tests, 
but none of them appears promising. Poison baits appear to offer 
some promise in controlling highly resistant house flies. 
Insect Metabolism of DDT Apparently Not Primary Factor in 
Resistance 
When 60 micrograms of DDT were injected into a resistant house 
fly, metabolism of the compound seemed to be blocked. After 48 hours 
most of the DDT was recovered unchanged. The presence of this 
quantity of DDT in the fly without causing visible signs of distress 
would appear to be definite proof that the ability to metabolize DDT 
is not the basis of resistance. 
Analytical methods and techniques that have been developed for 
the determination of very small amounts of insecticides have proved 
useful in this study of penetration, distribution, metabolism, and 
excretion of such materials. Through the injection of measured 
dosages of DDT into nonresistant female house flies and subsequent 
analyses, it has been determined that 0.3 microgram per fly is a 50-per- 
cent lethal dosage. To a considerable degree this DDT is metabolized 
to DDE, a relatively innocuous compound. Some DDT is apparently 
metabolized to other products as yet unidentified. Some DDE and 
unmetabolized DDT are excreted. This work is being continued. 
