Abstract: The electron microscope examination of ultrastructure of flight muscle of female adults in both gregarious and solitary phases of the oriental migratory locust, Locusta migratoria manilensis (Meyen) was performed. The results show that 7 days after emergence, the adults of both phases have the similar structures of indirect flight muscle, where the thick and thin filaments form a hexagonal lattice with myosin and actin in the ratio of 1∶3. The development of flight muscle and formation of mitochondrion are gradually changeable process with differences between the different day-old adults. The sarcomere length (2.1-3.4 μm) of 7 or 10 day-old adults in the gregarious phase is shorter than that in the homologous solitary phase. The myofibril diameter of 7 day-old adults in the gregarious phase is thicker than that in the solitary phase. The mitochondrion displays some shapes in the early adult period and grows daily. The mitochondrion content in myofibril is 20%-43%, which are different between the phases: 42.96% in 7 day-old adults of the gregarious phase and 22.45% in those of the solitary phase;  41.32% in 10 day-old adults of the gregarious phase and 29.98% in those of the solitary phase. It is inferred that the above differences in sarcomere length, myofibril diameter and mitochondrion content in flight muscle may contribute to different flight abilities in the two phases of L. migratoria manilensis adults, of which those in the gregarious phase can migrate for longer distance.

Key words: Locusta migratoria manilensis, gregarious phase, solitary phase, flight muscle, ultrastructure