342 
INSECT REPELLENTS 
The major objective in insect con- 
trol should be to destroy the insects 
themselves, but from practical consid- 
erations this is not always feasible. 
This is especially true in time of war 
when persons subject to attack are 
frequently on the move or are living 
without adequate means of protection 
from insects. When the research pro- 
grams were initiated we did not have 
the several improved methods cur- 
rently available for controlling mos- 
quitoes and other related insects. The 
need for a good insect repellent was 
therefore considered urgent when 
work began, and intensive research 
was conducted on this project from 
1942 to 1945. Even today with our 
improved materials and weapons for 
destroying mosquitoes and similar 
parasites of man, it may not be eco- 
nomically feasible to undertake con- 
trol measures in some locations, espe- 
cially in sparsely populated areas. __ 
In carrying out the repellent pro- 
gram, several thousand chemicals 
were tested to determine their value 
as mosquito repellents when applied 
to the skin or to clothing. This 
project was under the supervision of 
Dr. B. V. Travis until April 1944, when 
he joined the Navy to conduct re- 
search on all aspects of insect control 
probems in the Pacific. F. A. Morton 
assumed charge of the project during 
Dr. Travis’ absence. These men were 
assisted by several able workers for 
varying periods of time, including 
J. P. Linduska, A. L. Smith, J. H. 
Cochran, and J. H. Robinson. Work- 
ing with the scientists were from 8 to 
20 research subjects, who day after 
day permitted their arms or other 
parts of the body to be exposed to 
thousands of hungry mosquitoes. This 
was not an unpleasant job when the 
materials under test were good and 
repelled the mosquitoes for several 
hours, but a high percentage of the 
compounds were either worthless or 
were of a low order of effectiveness. 
For several years before the war, 
ANNUAL REPORT SMITHSONIAN INSTITUTION, 1948 
Phillip Granett of Rutgers University, 
working on a fellowship sponsored by 
the Carbide and Carbon Chemical 
Co., had been searching for repellents 
for mosquitoes, flies, and other insects. 
Using mosquitoes reared in the labora- 
tory, over a period of several years, 
he had treated his arms with hundreds 
of chemicals and exposed them to 
mosquitoes in cages. Similar proce- 
dures were followed in conducting the 
tests at Orlando, but the research was 
on a more elaborate scale. 
In the search for repellents, arms of 
the subject treated with the test 
material were inserted into cages 
containing from 2,000 to 3,000 hun- 
gry mosquitoes (pl. 5, fig. 2). If the 
mosquitoes soon ignored the treatment 
and proceeded to bite, the chemical was 
discarded. If, however, no bites were 
received during a period of 3 hours the 
material was considered worthy of 
further study in the laboratory and 
in the field. For field tests, as shown 
in plate 6, figure 1, the repellent crew 
usually visited the salt marshes along 
the east coast of Florida. Tests were 
not conducted unless as many as 
20 mosquitoes landed on the exposed 
portion of a leg, from ankle to knee, 
in 1 minute. On some occasions as 
many as 100 mosquitoes landed on an 
untreated leg in 1 minute. 
The first objective of the repellent 
program was to evaluate thoroughly 
all materials known or reported to 
possess repellent properties so that the 
best ones that were safe to use could 
be employed by the armed services. 
Within 6 months after the research 
was started three materials, found by 
industry to be good insect repellents, 
were tested under various conditions 
and then recommended to the military 
forces as repellents. These were di- 
methyl phthalate, Rutgers 612 (2- 
ethyl-1,3-hexanediol) and Indalone. 
All these chemicals are good in- 
sect repellents. They could be ex- 
pected to give an average of about 
2 hours of protection against the 
yellow fever and salt-marsh mosqui- 
toes. The length of protection varied, 
