STUDIES ON THE EFFICACY OF SEVERAL INSECTICIDES IN COTROLLING RICE BROWN PLANTHOPPER, NILAPARVATA WGENS POPULATION

In this paper,the life tables and indices of population control(IPC)were applied at the methods to evaluate the effect of several insecticides on the population dynamics of the rice-brown planthopper,Nilaparvata lugens Stao1.At the same time,the population dynamics of natural enemies in rice fields were also studied,and the response of two major natural enemies to several insecticides was examined by toxicity tests.The experimental results showed that the IPC of area spraying Quinaphos(14.36)was much lower than that of the control(28.43)(the population trend of next generation was upward),while control effect was unsatisfactory,because of having killed a proportion of natural enemies in the paddy field.The IPC of MIPC was only a little higher than that of the control(29.40).The IPC of Applaud was highest(65.96)and its index of pepulation trend was lowest(.7523),this insecticide being an insect regulator with high activity on Homop-tera,killed mainly rice plant hoppers and favoured most of natural enemies in rice fields.Therefore,it not only decreased the abundance of the rice planthoppers,but also increased omparatively the effect of natural enemies.As a result,the population of the brown planthopper was controlled effectively.The life table and the index of population control(IPC)are helpful in evaluating the efficacy of insecticides harmonic to natural enemies.