Effective radius of the tow net used for the collection of migrating insects on the East China Sea was measured at various wind speeds generated by a wind tunnel. A linear equation Y=69.4+1.22X was obtained in which Y indicates the collecting efficiency (%) transformed from the effective radius and X the wind speed (m/s) in a range of wind speeds of 4.9m/s to 13.1m/s. Aerial densities per 10³m³ of the whitebacked planthopper, Sogatella furcifera HORVÁTH, the brown planthopper, Nilaparvata lugens STÅL and the small brown planthopper, Laodelphax striatellus FALLÉN, were estimated based on surveys conducted in 1977, 1979 and 1980 on the East China Sea.