and Integrated Pest Management - part - usaid

46 PESTCIDE MANAGEMENT AND IPM INSOUTHEAST ASIA
novel mode of action, e.g., buprofezin (Applaud), a BPH isecticide which is a
growth regulator and is extremely safe to natural enemies vnd the environment
(Heinrichs et al. 1984a), will likely play an increasing rolb in the management
of rice insects.
Host Plant Resistance
Resistant varieties are sought as the major tactic in de integrated control of
rice insect pests because they (1) are free to the farmer, (2) require no special
skills to use, (3) are safe to the environment, and (4) are compatible with the
other control tactics - cultural, biological, and chemical (Heinrichs 1986).
Screening methods have been developed for 32 rice insects throughout the
world and resistance sources of varying levels to most have been found
(l-leinrichs et al. 1985). These sources have been used as donors in national
hybridization programs throughout Southeast Asia and numerous resistant
varieties have been released including 29 from IRRI (Table 1). Varieties such as
IR36 are resistant to a complex of insects and pathogens, have tolerance to
adverse soils, and have other desirable qualities (Table 2). Insect resistant
varieties occtpy large areas in Southeast Asia. Hybrid rices in China occupy
more than 6 million hectares, and more than half of the area grows BPH resistant
rices.
Ilost plant resistance is highly compatible with other control tactics and is a
key tactic in the integrated control of rice insects. The following discussion
describes some of the ways in which host plant resistance can be integrated with
other control tactics in rice IPM systems in Southeast Asia.
HOST PLANT RESISTANCE IN INTEIGRATED CONTROL
S Y STE NI S
Host Plant Resistance and Cultural Conuail
There are examples of rice varieties that have high levels of resistance to
certain pests and in these cases the plant resistance can provide complete control.
However, such varieties exert extreme biotype selection pressure on the pest.
Such high levels of resistance are not necessary when resistance is integrated
with other control tactics.
Moderately resistant varieties, which can be manipulated to evade insect
attack, are useful in cultural control systems designed to maintain insects at
subcconoinic levels (Adkinsson and Dyck 1980). Agronomic practices used in
rice to evade insect populations include synchronous planting and early crop
maturity. Sytichronous planting of rice within an area, when related to the
effective dispersal period of the BPH, decreases pest load on the crop
(Loevinsohn 1984). Where farmers planted synchronously in Indonesia, BPH
populations were 25% of that where staggered planting was practiced (Oka
1979).
Early maturing rice lines evade BPH damage by maturing and becoming
unsuitable before the insect reaches the damaging third generation (Heinrichs et