they’ re hard to get rid of. A dog will pick up ticks in Central Park, and then the ticks lay eggs and
they hatch in the apartment. They s eem immune to DDT or chlordane or mos t of our mode rn
sprays. It used to be very unus ual to have ticks in New York City, but now they’ re all over here
and on Long Is land, in Wes tches ter and on up into Connecticut. We’ve noticed this particularly
in the past five or six years.’
The German cockroach throughout muc h of North America has become res is tant to chlordane,
once the favorite weapon of exterminators who have now turned to the organic phos phates.
However, the recent development of resistance to thes e ins ecticides confronts the
exterminators with the problem of where to go next. Agencies concerned with vector-borne
dis eas e are at pres ent coping with their problems by s witching from one ins ecticide to another
as res is tance develops. But this cannot go on indefinitely, des pite the ingenuity of the che mis ts
in s upplying new materials. Dr. Brown has pointed out that we are traveling ‘a one-way s treet’.
No one knows how long the s tree t is. If the dead end is reached bef ore control of dis eas e-
carrying ins ects is achieved, our s ituation will indeed be critical.
With ins ects that infes t crops the s tory is the same. To the list of about a dozen agricultural
insects showing resistance to the inorganic chemicals of an earlier era there is now added a
hos t of others res is tant to DDT, BHC, lindane, toxaphene, dieldrin, aldrin, and even to the
phos phates from which s o much was hoped. The total numbe r of res is tant s pecies among crop-
des troying ins ects had reached 65 in 1960. The first cases of DDT resistance among agricultural
ins ects appeared in the United States in 1951, about s ix years after its firs t us e. Perhaps the
mos t troubles ome s ituation concerns the codling moth, which is now res is tant to DDT in
practically all of the world’s apple-growing regions. Resistance in cabbage insects is creating
anothe r s erious proble m. Potato ins ects are es caping chemical control in many s ections of the
United States. Six s pecies of cotton ins ects , along with an assortment of thrips, fruit moths, leaf
hoppers, caterpillars, mites, aphids, wireworms, and many others now are able to ignore the
farmer’s assault with chemical sprays.
The chemical indus try is perhaps unders tandably loath to face up to the unpleas ant fact of
resistance. Even in 1959, with more than 100 major ins ect s pecies s howing definite res is tance
to chemicals, one of the leading journals in the field of agricultural chemistry spoke of ‘real or
imagined’ ins ect res is tance. Yet hopefully as the indus try may turn its face the other way, the
problem s imply does not go away, and it pres ents s ome unpleas ant economic facts. One is that
the cos t of insect control by chemicals is increasing steadily. It is no longer possible to stockpile
materials well in advance; what today may be the most promising of insecticidal chemicals may
be the dismal failure of tomorrow. The very substantial financial investment inv olved in backing
and launching an ins ecticide may be s wept away as the ins ects prove once more that the
effective approach to nature is not through brute force. A nd howeve r ra pidly technology may
invent ne w us es for ins ecticides and new ways of applying them, it is likely to find the insects
keeping a lap ahead....
Darwin himself could scarcely have found a better example of the operation of natural selection
than is provided by the way the mechanism of resistance operates. Out of an original
population, the members of which vary greatly in qualities of s tructure, behavior, or phys iology,
it is the ‘tough’ insects that survive chemical attack. Spraying kills off the weaklings. The only
survivors are insects that have some inherent quality that allows them to escape harm. These
are the parents of the new generation, which, by s imple inheritance, pos s es s es all the qualities
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