Impact of - IDL-BNC @ IDRC - International Development Research ...

Finding a molecule with specific pesticidal properties and low toxicity for
nontarget species is still the first step in a long and complicated process. Today,
however, modern pesticides must satisfy so many requirements that it seems
easier to find a needle in a haystack than to discover a new molecule that meets
the full specifications and still yields a profit. The essential requirements of a
new pesticide are:
Specific pesticidal activity;
Safe for the crops on which it is applied and not seriously affecting
nontarget species;
Not inducing resistance in the target pests;
Safe to health;
Safe to the environment;
Good market opportunities;
Able to be produced in sufficient quantities in an acceptable manner
(with respect to health, environment, and economics);
Good formulation possibilities; and
. Stable when stored.
Failure to meet one of these requirements will jeopardize successful development
of a project. Each of these core requirements can be split up into many
individual subrequirements; even one unfulfilled subrequirement can be decisive
in not pursuing product development.
Finding a pesticide
The usual process of selecting new chemicals for pesticide use is by elimination.
The first step must be testing for pesticidal activity, thereby eliminating
inactive candidates. Screening a range of molecules that are structurally
similar to a known pesticide is often the approach adopted, although sometimes
fundamental studies of the physiological properties or the biochemistry
of the target pest provide clues for identifying the class of chemicals that
would interfere with its essential biological processes.
Agrochemicals are also identified through a method of widespread screening
- the testing of any new chemical against species representing target
pests. Discovering a new pesticide often requires luck and scientific curiosity,
combined with perseverance (Fig. 1).
Early testing of pesticidal activity is carried out in the laboratory; testing for
plant toxicity and for the induction of resistance in pests follows shortly.
Promising results in laboratory tests lead to small-scale field studies and
limited toxicity data; initially, only ranges of oral and dermal acute toxicity are
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