We studied the effects of age at mating on reproductive parameters for once-mated beet armyworm, Spodoptera exigua (Hubner), moths in the laboratory. The age of moths at mating significantly influenced the transfer of spermatophores by virgin males and the receipt of spermatophores by virgin females. Female age at mating significantly affected fecundity, fertility, and longevity. Two days after emergence was the optimum mating age for females to achieve their maximum reproductive potential. However, females laying the greatest number of eggs lived the fewest number of days. Male age at mating significantly influenced the fecundity and fertility of their mate and their own longevity. Females mating with 2-d-old males laid the most eggs and had the highest fertility. Males mating on day 2 after emergence lived significantly fewer days than males that mated on day 1 or on days 10 or 11. To document the effects of an adult mortality factor on S. exigua reproductive potential, the age at which moths mate must be standardized.