Abstract: The relationship between emigration activities of brown planthopper (Nilaparvata lugens Stal) and rice leaf roller (Cnaphalocrocis medinalis Guenée) and solar height angles is analysed Models of occured areas of emigration and their distribution are developed. Solar height angles at occured areas of emigration of two species can be evaluated by solar height angle formula at noon: h_θ=90°-φ+σ_θ……. Regression analyses are made on T's and solar height angles, and the predictive models are developed.

Key words: Solar height angle, Emigration, Mathematical model, Nilaparvata lugens, Cnaphalocrocis medinalis