During most years,there are only very small immigration of rice planthoppers (Nilaparvata lugens and Sogatella fercifera ) into the rice planting areas in northern China.with and no direct causality between the outbreaks of rice planthoppers in southern and northern China.But in 1991,huge populations of rice planthopper arrived at the coast of Bohai Sea,which is 1500 km from the planthopper source area.What carries such large populations outside their normal areas? Where and how did the outbreak popu...