Abstract: Understanding flight behavior is basic to the study of insect migration. We investigated the flight activity and capacity of the cotton aphid, Aphis gossypii, in Nanjing, Jiangsu Province. Insects were captured using yellowbasin traps placed on the top of a 20 m high building. Ovaries of trapped females were dissected and aphids collected from Hibiscus syriacus trees for tethered flight tests In spring, summer and autumn. The results show that the daily emergence peaks of alates occurred between 19:00 and 20:00.There were two migration peaks, occurring on 8 May and 25 October in 2001. 95.7% of female aphids trapped in basin traps in May had < 7 ovarioles. However, 35.2% of alate aphids captured on H. Syriacus had > 7 ovarioles. The average number of ovarioles in alate aphidstrapped in basin traps (3.94±1.65) and on H. syriacus trees (5.88±1.92) were significantly different. In cotton fields, alate aphids flying low in the sky were observed from middle to late August, 2001 These had < 6 ovarioles. Flight behaviour was not observed in aphids with > 6 ovarioles. The flight capacity of cotton aphids was measured using tethered flight tests. The results show that the flying rate and the average flight distance were greater in spring and autumn than in summer. Maximum flight distances in spring, summer and autumn were 3.89 km, 1.44 km and 6.15 km, respectively.

Key words: Aphis gossypii, emergence rhythm, flight activity, ovarioles, flight distance