INSECT CONTROL INVESTIGATIONS—KNIPLING 
however, depending on the"individual, 
the condition of the skin—whether 
dry or wet from perspiration—the 
number and species of mosquitoes, 
and other factors. 
To overcome some of the variations, 
it was decided to mix all three of the 
repellents that had been recommend- 
ed to the armed services. Tests 
against several kinds of mosquitoes 
under various conditions indicated 
that a mixture of the repellents was 
more uniformly effective against a 
variety of insects than any one of the 
three alone. In some cases the mix- 
ture was actually better than each of 
the three individual repellents. On 
the basis of these studies a 6-2-2 
combination (60 parts of dimethyl 
phthalate and 20 parts each of the 
other two repellents) was adopted by 
the services as the standard repellent. 
The repellents were primarily for ap- 
plication to the skin but they also 
served a useful purpose when applied 
to clothing so as to keep mosquitoes 
from biting through. 
During 1944 and 1945 work on 
repellents was intensified by the Or- 
lando laboratory as well as by other 
agencies in efforts to find more effec- 
tive and more desirable materials. 
The goal was a preparation, cos- 
metically acceptable, that could be 
applied with assurance that the user 
would be protected from attack for 
about 10 hours, or at least overnight. 
The Office of Scientific Research and 
Development arranged research con- 
tracts with several universities to syn- 
thesize or furnish new materials, 
especially chemicals related to known 
repellents. 
As a result of the intensified pro- 
gram several thousand new materials 
were tested and hundreds of creams 
and lotions were prepared and eval- 
uated. I cannot review here all the 
work done during this period at the 
Orlando laboratory and by research 
groups with the armed services, uni- 
versities, and in industry. Much 
worth-while information was obtained, 
the value of which may not be fully 
817369—49——27 
343 
apparent for years to come. A num- 
ber of very promising repellents were 
found. Some of them are now in use, 
and others are still being studied. 
However, in brief it may be said that 
we did not gain our objective. None 
of the new chemicals which were 
considered entirely safe to use were 
sufficiently effective to warrant their 
recommendation as replacements for, 
or to supplement, the three repellents 
and the 6-2-2 combination men- 
tioned earlier. When the war ended, 
the repellents recommended in 1942 
and 1943 were still in use by the 
services. Although far from perfect, 
they are distinctly superior to any 
repellents known prior to the war, 
when citronella and certain other 
essential oils were the only materials 
widely employed. 
Flies 
Flies of various kinds have always 
constituted a serious insect problem, 
not only because they are a source of 
annoyance, but because they spread 
filth and diseases. Some medical of- 
ficers in the services considered flies 
as important as mosquitoes. Research 
on improved methods of controlling 
flies paralleled that of mosquitoes to a 
considerable extent. 
After extensive laboratory studies, 
the first practical tests, utilizing DDT 
as a residual treatment, were con- 
ducted by treating dairies in the vicin- 
ity of Orlando. House flies have al- 
ways been numerous in this type of 
environment even though the owner 
might have employed rigid sanitation 
and other control measures. In May 
1943 fly counts were made around 
two dairies. One was treated with 5- 
percent DDT in kerosene; the other 
served as a control. Before treatment 
approximately 1,500 flies were col- 
lected around each dairy by making 
15 sweeps with an insect net in places 
where flies concentrated. Within 24 
hours after treatment the fly popula- 
tion around the treated dairy dropped 
by at least 95 percent. A week later 
the population was still less than 5 
