demons trate d res is tance to DDT, a mos t serious development. Countries reporti ng res is tance
among a large number of othe r s pecies repres ent every continent and mos t of the is land
groups.
Probably the firs t medical us e of mode rn ins ecticides occurred in Italy in 1943 when the Allied
Military Government launc hed a s ucces s ful attack on typhus by dus ting enormous numbe rs of
people with DDT. This was followed two years later by extensive application of residual sprays
for the control of malaria mosquitoes. Only a year later the first signs of trouble appeare d. Both
hous eflies and mos quitoes of the genus Culex began to s how res is tance to the sprays. In 1948 a
new chemical, chlordane, was tried as a s upplement to DDT. This time good control was
obtained for two years , but by Augus t of 1950 chlordane-res is tant flies appeared, and by the
end of that year all of the hous eflies as well as the Culex mosquitoes seemed to be resistant to
chlordane. As rapidly as new chemicals were brought into us e, res is tance developed.
By the end of 1951, DDT, methoxychlor, chlordane, heptachlor, and benzene hexachloride had
joined the lis t of chemicals no longer effective. The flies, meanwhile, had become ‘fantastically
abundant’. The s ame cycle of events was being repeated in Sardinia during the late 1940s. In
Denmark, produc ts containing DDT were first used in 1944; by 1947 fly control had failed in
many places. In some areas of Egypt, flies had already become resistant to DDT by 1948; BHC
was substituted but was effective for less than a year. One Egyptian village in particular
s ymbolizes the problem. Ins ecticides gave good control of flies in 1950 and during this s a me
year the infant mortality rate was reduced by nearly 50 per cent. The next yea r, nevertheless,
flies were resistant to DDT and chlordane. The fly population re turned to its forme r level; s o did
infant mortality.
In the United States , DDT res is tance among flies had become wides pread in the Tenness ee
Valley by 1948. Other areas followed. Attempts to restore control with dieldrin met with little
s ucces s , for in s ome places the flies developed strong resistance to this chemical within only
two mon ths. After running through all the available chlorinated hydrocarbons , control agencies
turned to the organic phos phates , but here again the s tory of res is tance was repeated. The
pres ent conclus ion of experts is that ‘hous efly control has escaped ins ecticidal techniques and
once more mus t be bas ed on general sanitation.’ The control of body lice in Naples was one of
the earlies t and mos t publicized achievements of DDT. During the next few years its success in
Italy was matched by the successful control of lice affecting some two million people in Japan
and Korea in the winte r of 1945-46. Some pre moniti on of trouble ahead might have been
gained by the failure to control a typhus epidemic in Spain in 1948. Despite this failure in actual
practice, encouraging laboratory experiments led entomologists to believe lice were unlikely to
develop res is tance. Events in Korea in the winter of 1950-51 were theref ore startling. When
DDT powde r was applied to a group of Korean s oldiers the extra ordinary res ult was an actual
increase in the infes tation of lice. When lice were collected and tes ted, it was found that 5 per
cent DDT powde r caus ed no increas e in their natural mortality rate. Similar results among lice
collected from vagrants in Tokyo, from an asylum in Itabashi, and from refugee camps in Syria,
Jordan, and eas tern Egypt, confirmed the ineffectivenes s of DDT for the control of lice and
typhus. When by 1957 the lis t of countries in which lice had become res is tant to DDT was
extended to include Iran, Turkey, Ethiopia, West Africa, South Africa, Peru, Chile, France,
Yugoslavia, Afghanistan, Uganda, Mexico, and Tanganyika, the initial triumph in Italy seemed
dim indeed. The first malaria mosquito to develop resistance to DDT was Anopheles sacharovi
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