二代褐飞虱对粳稻危害损失及防治指标研究

不同水稻生育期．褐飞虱的不同虫口密度的增长倍数不同；同一生育期．以低密度的增殖倍数大于高密度．但总虫量仍以高密度处理极显地高于低密度处理。水稻产量损失与二代褐飞虱百丛虫量间呈显正相关(r=0．9557^ )，两关系式为：Y=-16．3732 9．437tg(x)；防治指标为150-200头／百丛。当二代楫飞虱早发、中等以上发生程度时．必须施药防治。

ECONOMIC DAMAGE TO JAPONICA BY THE SECOND GENERATION POPULATION OF THE BROWN PLANTHOPPER

A field trial was performed to estimate the damage to Japonica (Wuyugens 3)by the second- generation population of the brown planthopper. Nilaparavata lugen (Stal). and the economic threshold for the pest.Infestation was established in caged ricefield plots (10 hills per plot) at the densities of 1 00. 250. 500. and 1000 nymphs (lst or 2ndinstar) per 100 hills with 3 replications. Three plots without infestation were sprayed with theinsecticide buprofezin and used as control treatment.The results showed that the increase ofthe population d iffered among the treatments with varying levels of initial infestation. Higher reproductive potential was observed in the treatments with lower levels of infestationthough the density was eventually greater in the plots infested at higher densities. The yieldloss was significantly correlated with the population density:(Y=- 16.3732+9.43lg(x),r=0.9557*).The economic threshold was thus estimated to be 150- 200 planthoppers per100 hills. This suggests that spray is needed when the second- generation population infeststhe crop earlier at a medium level.