Grading for Spodoptera frugiperda (Smith) occurrence degree with the indices of ratio of plants with larva and larval density at corn seedling stage.
The data of rate of plant with larva and larva density of Spodoptera frugiperda (Smith) at corn seedling stage were investigated and obtained. The exponential function model of those two parameters was established as Y=1.1518 X1.1694. The standard for occurrence degree of S. frugiperda at corn seedling stage was put forward, which was based on the rate of plant with larva and larva density. The results can provide a reference for field investigation and classification of S. frugiperda.