and Integrated Pest Management - part - usaid

298 P-s'T1CIDE MANAGF~.NT AND IPM IN SOUlEAST ASIA
The development of resistance is an ever present risk in agriculture. It is the
responsibility of all those involved in agriculture - farmers, officials,
governmcnt, and industry - to ensure that development of resistance does not
prevent the continued maximum benefits from the use of existing agricultural
practices.
Resistance to pesticides can be explained by current concepts of genetics.
The heritable characteristics of organisms are controlled by many genetic
elements, the assemblage of which is similar, but not identcal in the various
individuals that comprise the population. When a pest population in an area is
treated with a pesticide, some may survive. These may have genetic properties
that protect them against the pesticide. With competitihn from the susceptible
individunals eliniinated, the survivors (susceptible as well as resistant) multiply
to fill tile ecological niche formally occupied by the total population.
Repetition of this process will select a pest population containing a high
proportion of resistant individuals. Since the selection process involves a
change in tie genetic character of a population in successive generations, the rate
at which resistance develops is greater with pests having short life cycles, e.g.,
devclopment of a resistant population may take many years with weeds, but as
little as two days with intestinal bacteria.
In oilier words, true resistance occurs when an organism from a population
which was initially controlled by a pesticide has lost its susceptibility to the
point that it now resists control with that pesticide. Resistance in a pest
population progresses through a process of natural selection. This principle of
the "survival of the fittest" means that resistance is genetically based and not the
result of some adaptation that might occur within the lifetime of given
organisms. Contrary to popular belief, resistance to pesticides does not require
action on the genetic material by the pesticide.
STRATEGIES TO COMBAT RESISTANCE
Pesticide resistance is of concern to everyone: the farmer, the public,
governments and the pesticide manufacturer. It follows that strategies to address
tie issue must involve all interested parties.
This presents a challenge to the pesticide industry. The industry must
supply products to existing agriculturl systems over which it has no direct
control. At the same time, it must anticipate future problems with resistance
and the develop:nent of new systems when developing new products. It must
also develop methods and strategies to prevent resistance to currently available
prodLucts.
Two obviOus counter-measures can be used:
* A continuing series of pesticides with new modes of action and subject to
new pathways of detoxification could be developed, so that new ones are
available should the ol ones lose their effectiveness.
* A rmange of pesticides with different modes of action can be used, so that
pests are unlikely to develop all of the genetic characters required to acquire
resistance simultaneously.