British student of animal populations, Dr. Charles Elton, has said, ‘We are hearing the early
rumblings of what may become an avalanche in s trength.’
Sometimes resistance develops so rapidly that the ink is scarcely dry on a report hailing
s ucces s ful control of a s pecies with s ome s pecified chemical when an amende d report has to be
iss ued. In South Africa, for example, cattlemen had long been plagued by the blue tick, from
which, on one ra nch alone, 600 head of cattle had died in one year. T he tick had for some years
been res is tant to ars enical dips. Then benzene hexachloride was tried, and for a ve ry s hort time
all seemed to be well. Reports is s ued early in the year 1949 declared that the ars enic-resistant
ticks could be controlled readily with the new chemical; later in the same year, a bleak notice of
developing res is tance had to be publis hed. The s ituation prompted a wri ter in the Leather
Trades Review to comme nt in 1950: ‘News s uch as this quietly trickling through scientific circles
and appearing in s mall s ections of the overs eas pres s is enough to make headlines as big as
thos e concerning the new atomic bomb if only the significance of the matter were properly
unde rs tood.’ Although ins ect resistance is a matter of concern in agriculture and forestry, it is in
the field of public health that the mos t s erious apprehens ions have been felt. The relation
between various insects and many diseases of man is an ancient one. Mos quitoes of the genus
Anopheles may inject into the human bloods tream the s ingle-celled organism of malaria.
Other mosquitoes transmit yellow fever. Still others carry encephalitis. The housefly, which
does not bite, nevertheles s by contact may contaminate human food with the bacillus of
dys entery, and in many parts of the world may play an important part in the trans mis s ion of
eye dis eas es. The lis t of dis eas es and their ins ect carriers , or vectors , includes typhus and body
lice, plague and rat fleas, African sleeping sickness and ts ets e flies , various fevers and ticks , and
innumerable ot hers.
Thes e are important problems and mus t be met. No res pons ible pers on conte nds that ins ect-
borne dis eas e s hould be ignore d. The ques tion that has now urgently pres ente d its elf is
whether it is either wise or responsible to attack the problem by methods that are rapidly
making it wors e. The world has heard much of the triumpha nt war agains t dis eas e through the
control of ins ect vectors of infection, but it has heard little of the othe r s ide of the s tory—the
defeats , the s hort-lived triumphs that now s trongly s upport the alarming view that the ins ect
enemy has been made actually s tronger by our efforts. Even worse, we may have destroyed our
very means of fighting. A dis tinguis hed Canadian entomologist, Dr. A. W. A. B rown, was
engaged by the World Health Organization to make a comprehe ns ive s urvey of the res is tance
problem. In the res ulting monogra ph, publis hed in 1958, Dr. Brown has this to say: ‘Barely a
decade after the introduction of the pote nt s ynthetic ins ecticides in public health programmes ,
the main technical problem is the developme nt of res is tance to the m by the ins ects they
formerly controlled.’ In publis hing his monograph, the World Health Organization warne d that
‘the vigorous offens ive now being purs ued agains t arthropodborne diseases such as malaria,
typhus fever, and plague ris ks a s erious s etback unles s this new proble m can be rapidly
mastered.’
What is the meas ure of this s etback? The lis t of resis tant s pecies now includes practically all of
the ins ect groups of medical importance. Apparently the blackflies, sand flies, and tsetse flies
have not yet become resistant to chemicals. On the other hand, res is tance among hous eflies
and body lice has now developed on a global scale. Malaria programs are threatened by
resistance among mosquitoes. The oriental rat flea, the principal vector of plague, has recently
backadmin
(backadmin)
#1