16. The Rumblings of an Avalanche
IF DARWIN were alive today the ins ect world would delight and as tound hi m with its
impressive verification of his theories of the survival of the fittest. Under the stress of intensive
chemical spraying the weaker members of the insect populations are being weeded out. Now,
in many areas and among many s pecies only the s trong and fit remain to defy our efforts to
control the m. Nearly half a century ago, a professor of entomology at Washington State
College, A. L. Melander, asked the now purely rhe torical ques tion, ‘Can ins ects become
resistant to sprays?’ If the answer seemed to Melander unclear, or slow in coming, that was
only becaus e he as ked his ques tion too s oon—in 1914 instead of 40 years later. In the pre-DDT
era, inorganic chemicals, applied on a scale that today would seem extraordinarily modest,
produced he re and there s trains of insects that could s urvive chemical s praying or dus ting.
Melander hims elf had run into difficulty with the San Jose scale, for some years satisfactorily
controlled by s praying with lime s ulfur. Then in the Clarks ton area of Was hington the i ns e c ts
became refract ory—they we re harder to kill than in the orchards of the Wenatchee and Yakima
valleys and elsewhere.
Suddenly the s cale ins ects in other parts of the c ountry s eemed to have got the s ame idea: it
was not neces sary for the m to die under the sprayings of lime sulfur, diligently and liberally
applied by orchardis ts. Throughout muc h of the Midwes t thous ands of acres of fine orchards
were des troye d by ins ects now impervious to s praying. Then in California the time-honored
method of placing canvas tents over trees and fumigating them with hydrocyanic acid began to
yield disappointing results in certain areas, a problem that led to research at the California
Citrus Experiment Station, beginning about 1915 and continuing for a quarter of a century.
Another ins ect to learn the profitable way of resistance was the codling moth, or appleworm, in
the 1920s , although lead ars enate had been us ed s uccess fully against it for some 40 years.
But it was the advent of DDT and all its many relatives that us hered in the true Age of
Res is tance. It need have s urpris ed no one with eve n the s imples t knowledge of ins ects or of the
dynamics of animal populations that within a matte r of a ve ry few years an ugly and dangerous
problem had clearly defined itself. Yet awareness of the fact that insects pos s ess a n effec ti ve
counterweapon to aggressive chemical attack seems to have dawned slowly. Only thos e
concerne d with disease-carrying ins ects s eem by now to have been thoroughly arous ed to the
alarming nature of the situation; the agriculturists still for the most part blithely put their faith
in the devel opment of ne w and eve r more toxic chemicals, although the pres ent difficulties
have been born of jus t s uch s pecious reas oning.
If unde rs tanding of the phenome non of ins ect res is tance developed s lowly, it was far otherwis e
with resistance itself. Before 1945 only about a dozen s pecies were known to have devel oped
res is tance to any of the pre-DDT insecticides. With the new organic chemicals and new
methods for their intensive application, resistance began a meteoric rise that reache d the
alarming level of 137 species in 1960. No one believes the end is in sight. More than 1000
technical papers have now bee n publis hed on the s ubject. The World Health Organization has
enlisted the aid of some 300 scientists in all parts of the world, declaring that ‘resistance is at
pres ent the mos t important s ingle problem facing vector-control prog rammes .’ A dis tinguis hed