Contents - Faperta

4
Host Plant Resistance to Insects: Potential
and Limitations
Introduction
There is a large gap between potential yields and actual yields harvested by farmers.
Average yields for most crops, particularly in the developing countries, are only one-third
or less of the potential yield, and insect pests are one of the major constraints in crop production.
Insect pests have high reproductive rates, a fast generation turnover, wide genetic
diversity, and an ability to withstand, metabolize, and avoid toxic chemicals. As a result,
it is diffi cult to control several insect species through currently available insecticides. To
harvest the potential yields of high-yielding cultivars, the farmers resort to heavy use of
insecticides. However, even if 90% of the insects are killed as a result of insecticide application,
the remaining population multiplies at a much faster rate in the absence of natural
enemies (which are killed by the insecticides) (Knipling, 1979), and the farmers have to
apply insecticides more frequently and at higher doses, which fi nally results in failure
of control operations and environmental pollution. Failure to control insects has forced
farmers to give up cultivation of some crops in different countries. Indiscriminate use of
insecticides has resulted in adverse effects on nontarget organisms, insecticide residues in
food and food products, pest resurgence, development of resistance, and environmental
pollution. The current sensitivities about environmental pollution, human health hazards,
and pest resurgence as a consequence of improper use of synthetic insecticides has led to
greater emphasis on alternative methods of insect control.
Host plant resistance (HPR), natural plant products, biopesticides, natural enemies, and
agronomic practices offer a potentially viable option to control insect pests, as they are
relatively safe to the nontarget benefi cial organisms and human beings. Heavy insecticide
use has also led to an exponential increase in the number of insect species resistant to
insecticides (Georghiou, 1986). The most effective strategy for pest management is to use
selective insecticides at a low dosage in combination with plant resistance to slow the rate
of evolution of insecticide-resistant insect populations. Improving plant resistance to insect