The fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), a severe pest on agricultural crops occurring throughout the tropical Americas, has been reported to occur in China since 2019. To develop novel pest management practices, we studied the effect of delayed mating on the reproductive performance and longevity of S. frugiperda. Delayed mating, progressing from 0 to 7 days, was respectively imposed on both sexes simultaneously, female only, and male only. We demonstrated that delayed mating reduced mating success, number of eggs laid, egg hatch rate, and female oviposition period, while increased copulation duration and longevity. The correlations between the number of delayed days and mating success, number of eggs laid, hatch rate, and oviposition period were all significantly negative irrespective of the sex that was delayed. Meanwhile, there was a positive correlation between delayed days and copulation duration when both sexes were delayed simultaneously or males delayed only. Overall our results indicated that delayed mating in both males and females drastically reduced female reproductive output.