| Yellow stem borer, Scirpophaga incertulas (Walker) is one of the major pests in Lixiahe rice area, which broke out from time to time in the past. Recently, the population density of this pest tends to increase from the light damage level in 1980s and become an important rice pest again. The dynamics of yellow stem borer population resulted from changes of the rice cropping system.. climate~ chemical control efficiency and varieties planted inthisarea. The rice cropping system is the most important factor. Relevant analysis shown that if the ratio of the early rice cropping square is reduced to less than 20% the total rice field, or the single-later-crop rice square to less than 15%, the population density would be depressed. Climate influences the population mainly by depressing the over-winter survival rate of yellow stem borer. Of which rainfall in May, when pupation and emergence of the over-winter larvae occurs, is the major factor. If the raining days in May is over 15, and the total rain water is over 150 mm, the over-wintered larvae reaches the highest mortality and this pest will not surge this year. In Lixiahe area, rice loss caused by yellow stem borer resulted mainly from the damage caused by the larvae of the 3~ generation. Multi-factor path analysis shown that the survival larvae of the 1St generation made the most contribution to the population of the 3rd generation. So, control of yellow stem borer in the l~ generation is the key in practice. Chemical control experiments shown that organophosphate and nereistoxin insecticides is more suitable for control of this pest. For high efficiency, the nereistoxin insecticides, monosultap et al, should be used 2-3 days earlier than the suitable control time for organophosphate insecticides. Finally, it is suggested that control of yellow stem borer should be concentrated on the 1St generation to depress the population density in the following generations and the 3rd generation for directly reducing the damage and the rice loss.
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