Feeding and ovipositional behavior of mated female Aedes aegypti differs significantly from that of unmated females. The feeding pattern of virgins is weakly cyclic and oviposition is inhibited even though a full complement of eggs is formed. In mated females in contrast, feeding shows a pronounced cyclic character geared to the gonotrophic cycle, with oviposition occurring readily on completion of oogenesis. The accessory gland component of semen, but not sperm, determines this "mated-type" behavior in both feeding and oviposition. Accessory gland substance is effective in inducing these effects on either injection or implantation into the thorax of virgin females: Thus neither the usual site nor method of insemination is critical. In the presence of this material, feeding by females, either naturally mated or receiving an implant, is suppressed during the terminal stages of each gonotrophic cycle. On completion of oogenesis, oviposition occurs, with restoration of high feeding activity and initiation of the subsequent gonotrophic cycle. In females lacking functional ovaries neither mating nor implantation of male accessory gland substance has this effect on feeding activity, and the feeding pattern remains of the "virgin" type.