In this paper, the theor of gre s stem was applied to set up a grey equation for the population size of the hibernating larvae of Dendrolimus tabulaeformis Tsai et Liu, in which the average number of the caterpillar climbing up or down trees in the previous year was used to project that in the next year.The aveiage number of the caterpiller climbing down trees in the previous year alone can also be used to predict the average number of the caterpillar that may climb up trees in the next year. The model Set ...