Abstract: To reveal the influence of atmospheric water vapor conditions on the outbreak of Cnaphalocrocis medinalis in 2003, the geographic distributions of the pest per 667 m² of China on June 16th, July 21st, and September 1st,2003were analyzed under the support of ArcGIS, and the air relative humidity and water vapor flux fields on 850, 925 and 1 000 hPa that had the greatest influence on the pest immigration were selected to do simulation and objective analysis. The results showed that the transferring status of water vapor and the distribution ofrelative humidity on the upper air had significant indicative meanings for the immigration. In the regions of C. medinalis outbreak, the air relative humidity on each layer from the ground to 850 hPa was higher than 50%. The shorter the distance to the landing region of C. medinalis, the higher the humidity was, while the shorter the distance to the takingoff region, the lower this humidity was. 850 hPa was the main layer of water vapor transferring during C. medinalis migration, and the key pathway of the migration. On this height, the direction of water vapor transferring was basically concurrent with that of C. medinalis migration.

Key words: Tropical rain forest, Endangered species, Photoinhibition, Photosynthetic acclimation, Antioxygenic enzymes, Flexibility