Abstract: The flight capacity of female adult in relation to oviposition in Oriental armyworm, Mythirnna separata (Walker), one of the most detrimental migratory insect pests in China, was determined by the tethered-flight technique under laboratory condition. The females were more capable of flight as their age increased in daysand reached a peak on the days immediately after ovipositon began, with an average of 10.1 hours in duration and 58.6 kilometers in distance during the 12-hour test,indicating that there is perhaps no oogenesis-flight syndrome in this species. The flight capacity of the female, however was significantly declined 2 days after oviposition (DAO) and almost ceased on 6 DAO. The flight capacity of female was also highly related to the number of egg they laid. About 55% of the moths flow, over 36 kilometers when they laid less than 300 eggs while none of them could fly such distance when they laid more than 1200 eggs. It is therefore deduced that the incidence of migration is just at the post-teneral stage of the adult in M. seperatcr since the female's flight capacity was sharply declined as the ovipositional period extended and egg number increased. The flight capacity remained in the ovipositing female is of great significances in food and ovipositional site finding for its weeklyovipositional period both in the laboratory and in the field.

Key words: Mythirnna separata, flight capacity, oviposition, migration.