and Integrated Pest Management - part - usaid

ROLE OF INSECr-RESISTANT VARIEIES INRICE IPM SYSTEMS
available. FAO, in concert with national programs, has been instrumental in
extending monitoring technology to the farmer.
Economic Injury Levels (EJLs)
Rice research programs in Southeast Asia have identified the population
levels at which economic loss occurs. For some species, the levels are still
crude and in need of further refinement but can be utilized in IPM systems. The
ElLs have mostly been developed on susceptible rice varieties. More data is
needed for the developraent of EILs for moderately resistant varieties. Also,
EILs are based on a single insect species and should be developed to include a
combination of different insect species and multipest complexes (insects and
plant pathogens).
Cultural Control
The use of agronomic practices to control insect pests is considered cultural
control. As previously mentioned in this paper, changes in agronomic practices
over the last three decades have contributed to greater insect problems through an
increase in the carrying capacity of the rice ecosystem. However, agronomic
practices such as synchronous planting, crop rotation, early maturity varieties,
avoiding excess N fertilizer, flooding fields, and stubble dcstruction are some
examples which are effective in rice IPM systems. In general, cultural control is
a farmer-bascd technology with little dependence on outside resources.
Biological Control
All rice insect species are attacked by biological agents - parasites,
predators, and pathogens - which limit their populations. There is an abundance
of natural enemies (in species and in tot;d numbers) in rice ecosystems in
Southeast Asia. It is generally believed that pest outbreaks occur when some
environmental stress decimates the biocontrol organisms and release- the
reproductive capacity of pests. Thus, conservation of biocontrol agents is a
cornerstone of any ffective rice IPM system.
Chemical Control
Because of the economic benefits, some rice production programs have
subsidized the sale of pesticides. As a result, insecticide applications have often
been more numerous than required. Insecticide evaluation programs have been
productive (Heinrichs et al. 1981) and every country has a wide assortment of
different insecticides upon which to draw. Certain insecticides, unfortunately,
have been iesponsible for BPH outbreaks (Heinrichs and Mochida 1984).
Destruction of natural enemies by insecticides appears to be a major component
in resurgence. Commercial insecticides differ greatly in their safety to natural
enemies (Fabellar and Heinrichs 1984), and insecticides which are less toxic to
natural enemies should be used in IPM systems. New insecticides which have a
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