The dose of radiation applied to the Oriental leafworm (also known as the common cutworm), Spodoptera litura (F.) (Lepidoptera: Noctuidae) for use in inherited sterility (IS) sterility programs must not materially reduce the quality and competitiveness of the released males. To assess the quality of sub-sterilized male moths and their F₁ progeny, their flight and mating behaviors were investigated. Thus, parental (P) generation S. litura males that had been irradiated with either 100 or 130 Gy and their F₁ male descendants were subjected to flight assay tests to assess flight ability, orientation towards a pheromone source and mating behavior, i.e., mating performance using various sex ratios, sequential matings, and effect of female age. The orientation behavior of either P or F₁ males towards pheromone-baited traps was not different from that of non-irradiated males. Mating abilities of irradiated P generation males and their F₁ male progeny with non-irradiated females were studied using several sex ratios, but large differences were not found even when the sex ratio was increased from 1:1 to 5:1. A study on sperm use patterns revealed the precedence of sperm of the last male to mate, for example, when a non-irradiated female was sequentially mated with a non-irradiated P male, followed by an irradiated P male and finally by an F₁ male, as well as in all other possible sequences of such males. Mating success, remating propensity and fertility were significantly influenced by mating sequences that included irradiated males. Further, the age of the female at the first mating influenced fertility in matings with F₁ males, and mating success and remating propensity were reduced in several of sequences of matings involving non-irradiated and irradiated males and F1 males, with reductions being more apparent when females were aged 5–6 d. The present study indicates that gamma doses of either 100 or 130 Gy are suitable for the suppression of S. litura using an IS approach.