s chedules , to minimize their contact with ins ecticides. And regardles s of what the citrus
growe rs do, they are more or less at the mercy of the owners of adjacent acreages, for severe
damage has been done by insecticidal drift....
All these examples concern insects that attack agricultural crops. What of those that carry
disease? There have already been warnings. On Nissan Island in the South Pacific, for example,
s praying had been carried on intens ively during the Second World War, but was s topped when
hostilities came to an end. Soon swarms of a malaria-carrying mos quito reinvaded the is land.
All of its predators had been killed off and the re had not bee n time f or ne w populations to
become es tablis hed. The way was therefore clear for a tremendous population explos ion.
Marshall Laird, who has described this incident, compares chemical control to a treadmill; once
we have s et foot on it we are unable to s top for fear of the cons equences.
In s ome parts of the world dis eas e can be linked with s praying in quite a different way. For
some reason, snail-like mollusks seem to be almost immune to the effects of ins ecticides. This
has been obs erved many times. In the general holocaust that followed the spraying of salt
marshes in eastern Florida (pages 115-116), aquatic snails alone survived. The scene as
des cribed was a macabre picture—s omething that might have been created by a surrealist
brus h. The s nails moved among the bodies of the dead fis hes and the moribund crabs ,
devouring the victims of the death rain of pois on. But why is this importa nt? It is important
becaus e many aquatic s nails s erve as hos ts of dangerous parasitic worms that s pend part of
their life cycle in a mollusk, part in a human being. Examples are the blood flukes, or
schistosoma, that caus e s erious dis eas e in man when they enter the body by way of drinking
water or through the s kin when people are bathing in infes ted waters. The flukes are releas ed
into the wate r by the hos t s nails. Such dis eas es are es pecially prevalent in parts of Asia and
Africa. Where they occur, insect control measures that favor a vast increase of snails are likely
to be followed by grave cons equences.
And of cours e man is not alone in being s ubject to s nail-borne disease. Liver disease in cattle,
sheep, goats, deer, elk, rabbits , and various other warm-blooded ani mals may be caus ed by
liver flukes that s pend part of their life cycles in fres h-water s nails. Livers infes ted with thes e
worms are unfit for us e as human food and are routi nely conde mned. Suc h rejections cos t
American cattlemen about 3½ million dollars annually. Anything that acts to increase the
numbe r of s nails can obvious ly make this problem an even more s erious one....
Over the pas t decade thes e proble ms have cas t long s hadows , but we have been s low to
recognize the m. Mos t of thos e bes t fitted to develop natural controls and ass is t in putting them
into effect have been too bus y laboring in the more exciting vineyards of chemical control. It
was reported in 1960 that only 2 per cent of all the economic entomologists in the country
were then working in the field of biological controls. A s ubs tantial numbe r of the remaining 98
per cent we re engaged in research on chemical insecticides.
Why s hould this be? The major chemical companies are pouring money into the univers ities to
s upport res earch on insecticides. This creates attractive fellowships for graduate students and
attractive staff positions. Biological-control s tudies , on the othe r hand, are never s o endowe d—
for the s imple reas on that they do not promis e anyone the fortunes that are to be made in the
chemical industry. These are left to state and federal agencies, where the salaries paid are far
less. This situation also explains the otherwise mystifying fact that certain outstanding
entomologists are among the leading advocates of chemical control. Inquiry into the
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