INSECTS AFFECTING MAN 
Developments during and subsequent to the war years in the control of vectors of 
human diseases have been outstanding. The residual spray approach to malaria control, 
first investigated for the military by the Orlando, Fla., laboratory of the Entomology 
Research Division, has been fully developed and utilized by many agencies. This method 
now forms the basis for acoordinated world-wide malaria eradication program sponsored 
by the World Health Organization, International Cooperation Administration, Pan American 
Sanitary Bureau, and local health agencies in many parts of the world. Typhus, one of the 
most devastating diseases of man, especially during periods of strife, is currently no 
longer a threat to mankind because of the basicdevelopments by the Orlando laboratory 
on louse control insecticides. These and many other similar developments in insecticides, 
attractants, and repellents have been of inestimable value in raising standards of health 
and welfare of man throughout the world. 
However, the extensive use of chemicals for insects affecting man has led to many 
problems during the past two decades. Hazards are of special significance when we are 
dealing with chemicals for direct application to man or for use in his home. Here we 
are providing maximum opportunity for acute or chronic toxic effects through exposure 
to an insecticide. Careful study and appraisal of the hazard of a chemical is absolutely 
necessary before a material can be employed. Atthe same time, however, such appraisal 
must be objective with due regard for the need. 
It is perhaps fortunate that DDT was under development during the war. Responsible 
officials concerned with vector-borne diseases were placed in a position where it was 
necessary to weigh the known hazard of the disease against the potential hazard of the 
chemical. I venture to express an opinion that if the same conservatism in appraising 
potential hazards and the same legal restrictions in the use of insecticides had existed 
during World War II which now prevail, DDT would not have been approved for direct ap- 
plication to man or for application as residual sprays in homes. Yet, this insecticide has 
been applied as a 10-percent dust inside of the clothing of hundreds of millions of men, 
women, andchildren by military and public health officials and has been applied as residual 
sprays in as many homes, without one known case of toxic effects to individuals exposed 
to such intimate insect control practices. Asaresult, literally millions of lives have been 
spared and hundreds of millions of people have escaped diseases. 
In the light of the extensive safe use experience with DDT, backed by the classical 
experiments by Hayes (4), it would seem reasonable to regard DDT as one of the safest 
insecticides ever developed. However, this chemical has been under constant fire by 
critics of the use of insecticides. 
The problem of insect resistance to insecticides has had a major impact in the field 
of medical entomology. Widespread resistance to DDT and other insecticides has oc- 
curred among houseflies, mosquitoes, body lice, bedbugs, and a number of other insects. 
More recently, resistance to organic phosphorus compounds has appeared among several 
insects affecting man. The impact of the resistance problem among so many medically 
important insects against all types of insecticides should be carefully noted in our 
appraisal of the potential significance of the insecticide resistance problem among agri- 
cultural pests in the years ahead. 
LIVESTOCK INSECTS 
Many of the same types of insects affecting man also attack livestock. In adapting 
the insecticides which proved so useful on man for the control of livestock pests, we 
encountered the first serious residue problem involving milk. Howell, et al. (5) of 
Oklahoma demonstrated that the application of DDT to dairy cows for insect control 
resulted in several parts per million of the insecticide in milk. Subsequent research 
by a number of investigators confirmed these findings. Moreover, the phenomenon of 
insecticide storage in meat and milk has been found to occur with most of the insecticides 
when the compounds are applied externally or ingested by the animal. 
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