INSECT CONTROL INVESTIGATIONS—KNIPLING 
LARVICIDE INVESTIGATIONS 
The project on mosquito larvicides, 
started in October 1942, was under 
the direction of C. C. Deonier, and 
during the 3-year program he was 
assisted for various periods of time by 
R. W. Burrell, C. B. Wisecup, J. D. 
Maple *, and others. —These men and 
their assistants tested many new chemi- 
cals (pl. 2, fig. 2) and tried to improve 
the efficiency of known mosquito larvi- 
cides such as paris green. Not much 
progress was indicated until early in 
February 1943, when DDT was tried 
for the first time. 
Before DDT was tested, the best 
mosquito larvicide known was _ the 
chemical phenothiazine, which killed 
larvae of the common Culex mosquitoes 
at concentrations as low as 1 part per 
million parts of water. When DDT 
was given preliminary laboratory tests 
at various concentrations, it was found 
that complete or near complete kill of 
Anopheles larvae resulted at the ex- 
tremely low concentration of 1 part 
of DDT to 100 million parts of water. 
A kill of approximately 50 percent was 
obtained at the then unheard of dilut- 
tion of 1 part to 400 million. There 
was reason for real optimism; here 
was a material exactly 100 times as 
toxic to mosquito larvae as was pheno- 
thiazine, the most effective synthetic 
organic larvicide previously known. 
The next problem was to compare 
the efficiency of DDT when employed 
as a dust in direct comparison with 
paris green, the standard anopheline 
larvicide. In the laboratory it was 
found that complete kill of Anopheles 
larvae was obtained at the very low 
rate of application of 1 pound of 
DDT to 100 acres of water surface. 
This was at least 25 times as good as 
“paris green. 
2 J. D. Maple entered the U. S. Navy as 
lieutenant (jg) early in 1944 and was at- 
tached to Naval Medical Research Unit No. 
2, which was detailed to the Pacific to con- 
duct further research with materials devel- 
oped at Orlando. He lost his life while on 
active duty in connection with this assign- 
ment. 
337 
With this basic information the 
research on DDT was intensified. It 
was tested in every form in which it 
might be used—as dusts, oil solutions, 
emulsions, and aerosols. Studies were 
made at different dosages, and against 
the larvae of several kinds of mosqui- 
toes. Because DDT cannot be applied 
in its natural form, DDT formulations 
employing various solvents, emulsi- 
fiers, and dust diluents, prepared by 
Howard A. Jones, our chemist, were 
investigated. 
Tests were run in the laboratory, 
and small-scale field tests were made 
(pl. 3, fig. 1). The field tests con- 
firmed the potential value of DDT as 
a mosquito larvicide: as little as 1 
pound of DDT to 20 or even to 40 
acres gave a good kill of Anopheles 
larvae. But to provide an ample 
margin of safety we recommend that 
in actual control operations (using 
ground equipment) it be applied at 
the rate of 1 pound to 10 acres. It 
was recommended to the armed serv- 
ices as a dust, in petroleum oil solution, 
and in special emulsion concentrates 
which could be diluted with water 
before application as a spray. 
When used as an oil solution, it was 
found that 5 quarts of oil containing 
1 percent of DDT, properly applied, 
would do as good a job of killing mos- 
quito larvae as 20 to 25 gallons of 
oil when used without DDT. This was 
real progress, especially from a military 
viewpoint, because of the tremendous 
saving in transportation. 
For military purposes, however, the 
emulsion was one of the most practical 
forms of DDT to use, chiefly because 
of further savings in transportation 
costs. One-half pint of a 20-percent 
DDT emulsion concentrate could be 
diluted with water from the mosquito 
breeding area and applied with results 
equal to those formerly obtained with 
the 20 to 25 gallons of oil previously 
mentioned. 
The use of DDT as a mosquito lar- 
vicide is by no means restricted to 
ground equipment, and special re- 
search was undertaken to develop it 
