Abstract: The relationship between utilization of protein and lipid and sustainedflight in the moths of Oriental armyworm. Mythimna separata (Walker) was determined in the laboratory conditions. Under six testing regimes of tethered flight (0, 6, 12, 24, 36 and 48 hours), the body weight and lipid content in the moths declined significantly as the duration of flight extended while the content of protein was insignificantly affected. The tendency of body weight loss was consis- tent with the reduction of lipid content, and lipid consisted of 60% of the body weight reduction. It seemed that the rate of lipid reduction was more steady as the flight period extended. The amount of lipid utilized during flight in females was 8.9-23.6 mg/h (actual flight) and 1.7-4.0 mg/km, while that in males was 7.2-11.8 mg/h and 1.4-2.2 mg/km according to our calculation. Based on the results obtained, it was concluded that the lipid is the major energy source for sustained flight in the moth of M. separata.

Key words: Mythimna separata, flight, lipid utilization