Environmentally Sound Pest Management
By: Rakesh Tuli
Application of chemical pesticides has been one of the cornerstones
of the Green Revolution. In spite of their widespread use (present world
market being more than $20 billion), global crop loss from pest damage
(insects, weeds, and diseases) has not declined significantly and is estimated
to be presently about the same (30-35 percent of total crop production),
as during the pre chemical era! Extremely small percentages of the insecticide
applied in the field (less than 0.1% in some cases), actually reaches the
target organism. The rest becomes an environmental load - endangering ground-water,
aquatic systems, pollinators, several soil-dwelling insects and microbes,
birds and finally, animals in the food chain. Increasing documentation
of the merits and demerits of chemical pesticide usage has lead to the search
for approaches in integrated pest management (IPM), wherein the major
effort is to limit pest outbreak and use chemicals only as the last resort
or as a minor component.
The center stage of IPM is reducing crop damage to an economically
feasible level with least possible disturbance to ecological dynamics.
Crop rotation, time of planting, field sanitation, use of natural predators
and parasites are some of the well known approaches in IPM. A crucial component
of IMP is the development of monitoring systems to ascertain the mode of
remedial intervention.
The most successful IPM program in the world since 1986 is the Indonesian
effort. Indonesia was transformed from the world's largest rice importing
country in 1960 to self sufficiency in 1984. It used 20 percent of the global
rice pesticides at that time. Simultaneous with increased rice productivity,
unanticipated appearance of a variety of secondary pests and breakdown
of varietal resistance were noticed. In November 1986, a government decree
banned 57 of the 66 pesticides used on rice. Over the next 2 years, a large
scale IPM programme was conducted. Presently, rice harvest is higher than
15%, national pesticides use is lower by 60% and the treasury saves in
excess of $120 million per year.
The new biotechnological approaches to IPM include the use of a variety
of bacteria, viruses, and fungi targeted against specific pests. Among
these, the bacterium Bacillus thuringiensis is the best known insecticide
that has been used in the USA since sixties. The Environmental Protection
Agency of USA has already registered 175 pesticide products based primarily
on the larvicidal crystal proteins, produced naturally by B. thuringiensis.
Over the last about seven years, the bacterial genes that code for the
larvicidal proteins have been expressed in transgenic plants of tobacco,
tomato, cotton, maize, potato, and rice.
A variety of proteins that encode insect specific metabolic and developmental
inhibitors have been identified. The related genes are being introduced
into agronomically established varieties of crop plants to provide farmers
with an array of insect resistant transgenic lines. The resistant plant
varieties produced by breeders by conventional methods (after protracted
breeding efforts of 10 or more years), fail to withstand the onslaught
of pathogens, within a few years after release. It leads to an immense
waste of time and effort. Varieties developed by genetic engineering methods
may take lesser time in designing but would be equally amenable to breakdown
of resistance. Population genetic theory predicts that breakdown of resistance
will happen more slowly in varietal mixtures, carrying an array of resistant
genes. Genetic engineering has made it possible to introduce several specific
genes together or individually in an otherwise agronomically selected variety.
it would be highly unlikely for insects and pathogens to co-evolve multiple
resistance by natural phenomena and cope with such engineered varieties
or a mixture of strategically planned lines. Thus genetic engineering has
a potential to provide environmentally and ecologically sound approach
to the management of insects and diseases in crop plants.
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