340 
ings were still being killed. Special 
tests were made which demonstrated 
that the mosquitoes readily entered 
the treated buildings, and by the time 
they were affected by resting on treated 
surfaces and began leaving, they had 
accumulated a fatal dose of DDT. 
This was a vital point and practically 
assured the success of the method as 
a means of breaking the link in the 
chain of malaria transmission even 
though malaria control had not yet 
been demonstrated. On the basis of 
these observations together with those 
from residual tests against house flies, 
bed bugs, and other insects, which 
indicated that the insecticide remained 
effective for several months, the DDT 
residual treatment for malarial control 
was recommended to the armed 
services. 
More extensive tests were under- 
taken in 1944 and 1945 in the vicinity 
of Stuttgart, Ark., and in Mexico. 
These tests yielded highly important 
information and fully confirmed our 
earlier tests. The tests in Arkansas in 
1944 were undertaken in cooperation 
with the Arkansas State Board of 
Health. The treated buildings were 
almost completely free of Anopheles 
adults for 5 months, or the entire mos- 
quito season. Tests in Mexico in 1945 
in cooperation with the Rockefeller 
Foundation gave similar results. 
The Army, Navy, Public Health 
Service, and other agencies carried 
out further investigations in 1944 and 
1945 with this method of mosquito 
control in various parts of the world 
against several species of Anopheles 
mosquitoes. Results everywhere were 
phenomenal. 
At present, DDT residual treatments 
are widely employed, and this method 
alone has potentialities of freeing man- 
kind almost everywhere from malaria 
and other mosquito-borne diseases— 
diseases which according to medical 
authorities afflict more than 100 mil- 
lion people throughout the world and 
cause several million deaths each year. 
Area control of mosquitoes.—Larvicides, 
ANNUAL REPORT SMITHSONIAN INSTITUTION, 1948 
aerosols, and residual sprays will not 
take care of the adult mosquitoes that 
have dispersed from breeding places 
and which are living in extensive areas 
outdoors. In order to provide meth- 
ods of attack against mosquitoes under 
every type of situation, research on 
the destruction of mosquitoes under 
these conditions was undertaken as a 
part of our broad attack on the entire 
mosquito problem. Studies were ini- 
tiated using hand sprayers, dusters, 
small smoke machines, and aerosol 
bombs. It was shown that DDT ap- 
plied outdoors would eliminate mos- 
quitoes present even in heavy jungles. 
Hand equipment had its place in pro- 
tecting troops from mosquito attack, 
but the method was not feasible for 
large areas because of the labor in- 
volved. 
In efforts to control mosquitoes over 
extensive areas two methods of ap- 
proach were investigated. ‘These were 
aerial dispersion and the utilization of 
ground machines that would generate 
aerosols in sufficient volume to be 
carried by air currents over large areas. 
The airplane equipment developed for 
larval control has already been dis- 
cussed and the same equipment was 
also developed for utilization against 
adult mosquitoes. The early work on 
devices to generate aerosols by use of 
heat was largely undertaken by Divi- 
sion 10 of the National Defense Re- 
search Committee in cooperation with 
the Beltsville Research Center. 
Small-scale field trials in the fall of 
1943 with experimental models of 
airplane insecticide dispersal equip- 
ment demonstrated that salt-marsh 
mosquitoes could be controlled at 
dosages as low as 0.2 pound of DDT 
per acre. Results of these tests to- 
gether with the results of larval con- 
trol research were recognized as highly 
important by the Army Air Forces and 
by the Office of the Surgeon General, 
U. S. Army. The former sponsored 
tests with DDT utilizing the Chemical 
Warfare Service M-10 tanks on fast 
combat planes, and it was shown 
