Abstract: The effects of copulation duration on reproductive parameters were studied in twoimportant biological control agents, Neoseiulus womersleyi (Schicha) and Neoseiuluslongispinosus (Evans), to better understand their population growth potential. Fecundityincreased as copulation period increased in both species. Females which mated for only 10minutes did not oviposit, whereas 15 minutes of copulation sufficed to produce some eggs inboth species. Fecundity remarkably increased in both species when the copulation periodexceeded 90 minutes. Both pre- and post-oviposition periods of N. womersleyi and N.longispinosus decreased with the increase of copulation duration, but differently between thetwo species. Copulation duration had no effect on the adult longevity of N. womersleyi and N.longispinosus, but adult N. womersleyi lived longer than adult N. longispinosus. The size of thespermatophore inside the spermathecae increased in proportion to the copulation duration inboth species. Fecundity was consistent with the sizes of the spermathecae and spermatophores.When copulation period increased, males first filled one spermatheca and then filled the other.Egg production depended on the quantity of sperm transferred during copulation. The resultsobtained in this study suggest that copulation duration had similar effects on egg production inN. womersleyi and N. longispinosus, thereby have similar reproductive potential and matingproperties under laboratory conditions.