INSECT CONTROL INVESTIGATIONS—KNIPLING 
in connection with the louse control 
investigations were the development 
of the MYL louse powder and the 
subsequent research on DDT which 
lead to the adoption and widespread 
use of this now well-known insecticide 
by the armed services and by civilians 
for the control of lice. 
MYL powder.—The research on vari- 
ous insecticides as louse killers actually 
started late in April 1942. During 
the first 6 months several hundred 
materials were tested against lice and 
their eggs. Some of the many syn- 
thetic organic compounds tested were 
found to be highly effective against 
lice, but a day or two after treatment 
the subject would get lousy again. 
This lack of lasting effect was the major 
objection to fumigants such as methyl 
bromide which had been developed 
as a louse fumigant earlier by Randall 
Latta of the Bureau of Entomology 
and Plant Quarantine. Others were 
not suitable because they were too 
toxic to man, because they had an 
unpleasant odor, or because they 
stained clothing. 
Pyrethrum and rotenone, two widely 
used insect killers, had previously been 
employed for louse control and were 
considered relatively nontoxic to man. 
Extensive tests indicated that these 
materials were fairly good louse killers 
provided they were properly formu- 
lated. However, rotenone was even- 
tually discarded because of skin irrita- 
tion and its extremely slow action. 
Pyrethrum was the most promising 
but supplies were very limited. In 
efforts to extend its use various ma- 
terials known as synergists, which were 
employed in pyrethrum fly sprays, 
were tested. One of these, N-isobu- 
tylundecylenamide, was shown to be 
outstanding. When used in combina- 
tion with pyrethrum it increased the 
action of the insecticide many times 
even though alone it would not kill 
lice. While research on louse-killing 
agents was underway, various tests 
were also in progress on materials that 
would kill louse eggs. As a result of 
these various studies a louse powder 
335 
was formulated which contained 0.2 
percent pyrethrins (principal toxicant); 
2 percent N-isobutylundecylenamide 
(synergist); 2 percent 2,4-dinitroani- 
sole (ovicide and added louse toxicant) ; 
0.25 percent phenol S (a mixture of 
isopropyl cresols which stabilize the 
pyrethrins); and pyrophyllite (diluent). 
This preparation, designated the 
MYL formula, was recommended to 
the armed services in August 1942. 
The powder was the most effective 
material known for use on man for 
control of body lice, head lice, crab 
lice, and fleas. It served a useful pur- 
pose and was the standard insecticide 
powder until DDT was developed and 
became generally available. 
DDT louse powder.—Available pyre- 
thrum was urgently needed for mos- 
quito control, and research on new 
materials continued in the effort to 
find a synthetic compound for louse 
control which would be equal to, or 
more effective than, the MYL powder. 
Within a few months almost a thou- 
sand chemicals were tested, and several 
samples of other materials were being 
received from various sources each day. 
Tests were underway with several 
chemicals which showed considerable 
promise, but they were not the answer 
to our problem. 
In November 1942 a prepared in- 
secticide called ‘“‘Gesarol Dust Insecti- 
cide” was received from the J. R. 
Geigy Co. of New York, a subsidiary 
of the Geigy firm in Switzerland, 
where it was developed through the 
important research of Paul Mueller 
and his associates. A sample of the 
insecticide was obtained through the 
Division of Insecticide Investigations 
of the Bureau of Entomology and 
Plant Quarantine. This prepared in- 
secticide contained as the active 
principle the material now known as 
DDT, although when we first received 
it we knew little about its chemical 
composition. Tests soondemonstrated 
that this material had insecticidal 
properties possessed by no other syn- 
thetic organic compound known at 
that time. The material showed a 
