in Greece. Extensive spraying was begun in 1946 with early s uccess ; by 1949, however,
obs ervers noticed that adult mos quitoes were res ting in large numbe rs under road bri dges ,
although they we re abs ent from hous es and s tables that had been treate d. Soon this habit of
outs ide res ting was extended to caves , outbuildings , and culverts and to the foliage and trunks
of orange trees. Apparently the adult mos quitoes had become s ufficiently tolerant of DDT to
es cape from s prayed buildings and res t and recover in the open. A few months later they were
able to remain in hous es , where they were found res ting on treate d walls. This was a portent of
the extremely s erious s ituation that has now develope d. Res is tance to ins ecticides by
mos quitoes of the anophelene group has s urged upward at an as tounding rate, being created
by the thoroughnes s of the very hous es praying programs designed to eliminate malaria. In
1956, only 5 s pecies of thes e mos quitoes dis played res is tance; by early 1960 the numbe r had
ris en from 5 to 28! The numbe r includes very dangerous malaria vectors in West Africa, the
Middle Eas t, Central America, Indones ia, and the eas tern European region.
Among othe r mos quitoes , including carriers of other dis eases , the pattern is being repeated. A
tropical mosquito that carries parasites responsible for s uch dis eas es as elephantias is has
become s trongly res is tant in many pa rts of the world. In s ome areas of the United States the
mosquito vector of western equine encephalitis has developed resistance. An even more
s erious proble m concerns the vector of yellow fever, for centuries one of the great plagues of
the world. Ins ecticide resistant s trains of this mos quito have occurred in Southeas t As ia and are
now common in the Caribbean region. The cons equences of res is tance in terms of malaria and
othe r dis eas es are indicated by reports from many parts of the world. An outbreak of yellow
fever in Trinidad in 1954 followed failure to control the vector mos quito becaus e of resistance.
There has been a flare-up of malaria in Indones ia and Iran. In Greece, Nigeria, and Liberia the
mos quitoes continue to harbor and transmit the malaria parasite. A reduction of diarrheal
dis eas e achieved in Georgia through fly control was wiped out within about a year. The
reduction in acute conjunctivitis in Egypt, also attained through te mporary fly control, did not
last beyond 1950.
Less s erious in terms of human health, but vexatious as man meas ures economic values , is the
fact that s alt-ma rs h mos quitoes in Florida als o are s howing res is tance. Although thes e are not
vectors of disease, their presence in bloodthirsty swarms had rendered large areas of coastal
Florida uninhabitable until control—of an uneas y and temporary natu re—was es tablis hed. But
this was quickly lost. The ordinary hous e mos quito is here and there developing resistance, a
fact that s hould give paus e to many communities that now regularly arrange for wholesale
spraying. This species is now resistant to several insecticides, among which is the almos t
universally used DDT, in Italy, Israel, Japan, France, and parts of the United States , including
California, Ohio, New Jersey, and Massachusetts.
Ticks are another proble m. The woodtick, vector of s potted fever, has recently developed
res is tance; in the brown dog tick the ability to escape a chemical death has long been
thoroughly and widely es tablis hed. This pos es problems for human beings as well as for dogs.
The brown dog tick is a semitropical species and when it occurs as far north as New Je rs ey it
mus t live over winter in heated buildings rather than out of doors. Joh n C. Pallis ter of the
Ame ri ca n Mus eu m of Natural His tory re ported in the s ummer of 1959 that his department had
been getting a numbe r of calls from neighboring apartme nts on Central Park Wes t. ‘Every now
and then,’ Mr. Pallister said, ‘a whole apartment hous e gets infes ted with young ticks , and
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