Abstract: Diflubenzuron inhibits reproduction of the armyworm Mythirnna separata (Walker)when the female moths were fed continuously with sucrose solution containing 50 ppm diflubenzuron. The activity of corpora allata of adults was adversely affected,but the vitellogenin synthesis of fat body, ovarian development and oogenesis couldstill proceed normally. The levels of DNA, RNA and protein in the cell nuclei of the ovaries were found to increase. However, no larvae would hatch from the eggs. It was observed that treatment of the adults or eggs with diflubenzuron did not influence the general course of embryonic development, but it had detrimental effects on the formation of integument and tracheal system of the developing embryos.The epidermal cells in the integument became flattened, smaller in size, and without nuclei. The procuticle became very thin or vanished. The tracheal trunks could not form and the respiratory function of the embryo could not perform normally. Asa result, the embryos would die within the chorion. The DNA level in the nuclei and mitochondria of the embryos was found to decrease. It seems that sterilization in the armyworm may result in part from inhibition of DNA synthesis besides the inhibition of chitin synthesis.

Key words: Mythimna separata (Walker)——diflubenzuron——ovarian deve- lopment, embryonic development