Abstract: Embryonic development of the oriental armyworm, Mythimna separata(Walker) requires 93 h for eclosion at (25-3-1)℃. The zygote nucleus is slightly posterior to the center of the egg at 0.5 h. The cleavage nuclei continue to divide, and migrate toward the periplasm through 8 h when blastoderm begins to form at the periphery. The germ band is formed in the posterior region of the egg at 10 h. Gastrulation begins at 20 h. The stomodeum invaginates at 28 h, followed by the proctodeum at 32 h. The midgut rudiment arises at 42 h by fusion of anterior and posterior mesenteron rudiments. The midgut closes at 54 h and Malpighian tubules are well developed, nearly simultaneous with blastokinesisby 42 h. Neuroblasts appear at 20 h, brain formation begins at 32 h, and ventral nerve cord is defined by 40 h. Formation of the tracheal system begins at 40 h and is completed by 68 h. Procuticle is first secreted on the mandibles at 68 h and progresses steadily backward until the entire body enclosed in cuticle by 87 h. Dorsal closure begins at 42 h with dorsal growth of the lateral walls of ectoderm. Fusion of the two lateral walls occurs at 54 h and completes before hatching.

Key words: Mythirnna separata, embryogenesis, histogenesis, blastokinesis