and Integrated Pest Management - part - usaid

52 PESCIDE MANAGEMENT AND 1PM IN SOUI1 LEAST ASIA
into an integrated control system is more effective and economically profitable
than complete reliance on insecicide control on susceptible varieties.
Integration of -lost Plant Resistance for Insects and Control of Other Pests
There are many interactions among the various pests attacking the rice
plant. The different pests (insects, diseases, nematodes, rodents, and weeds),
abiotic environmental factors and the rice plant are interdependent and linked
together. Because of the linkages, control measures directed against a target pest
may cause population decreases, increases, or not affect another pest (Reissig et
al. 1985).
Insect resistance has an adverse effect on weeds and plant diseases in rice
fields. Insects attacking the seedling and vegetative growth stages slow plant
growth and reduce foliage area of susceptible varieties. As a result, the canopy
closes late and the reduced competition for light and nutrients allows greater weed
growth. Feeding by insects predisposes l)ants to attack of fungal and bacterial
diseases which invade the plant tissue. Some insects are virus vectors. Decrease
of insect feeding through resistant varieties thus may also decrease attack by
fungal, bacterial, and viral diseases.
CONCLUDING REMARKS
In a relatively short period of a few decades, remarkable progress has been
made in the development of insect resistant rice varieties and the development of
integrated control systems in which these varieties are a key tactic. Rice is
without equal in the extent to which insect resistance has been incorporated into
high yielding varieties and in the ex!cnt to which these varieties are being
commercially grown by farmers over millions of hectares in Southeast Asia.
However, much remains to be done and the potential for improvements in the
IPM system for rice is great.
There is a great need to develop rice varieties having not only resistance to
several insect pests but also mnultipest resistance - resistance to several insect
and pathogen species. Breeding programs must increase the stability of
resistance. Biotype selection is a constant threat to resistant varieties and
integrated control systems that minimize selection pressure are needed. The
genetic diversity concept to slow biotype selection is being evaluated in Vietnam
and in Indonesia, and we anxiously await the results of these novel approaches.
Future studies must consider the effect of the various biotic and abiotic stresses
on the level of host plant resistance to specific insects.
In crops other than rice, it has been shown that plants respond to the feeding
damage caused by one insect by becoming more resistant to the following
insects which attack the plant. Inter-plant pheromonal communication between
a damaged and undamaged plant has been suggested "orender t- undamaged plant
more resistant to insect attack (Baldwin and Schultz 1983). These mechanical
stresses plus plant mediated effects of adverse soils, light, temperature, moisture,
other insects, plant pathogens, and weeds on the levels of insect resistance must
be included in the development of more accurate insect economic injury levels.