The West Indian sweetpotato weevil Euscepes postfasciatus (Coleoptera: Curculionidae) is one of the major pests of sweetpotato, Ipomoea batatas (L.) Lam. (Convolvulaceae). A sterile insect technique (SIT) program for eradicating this weevil is underway in Okinawa Prefecture. Although mated females of E. postfasciatus temporarily become unreceptive to subsequent mating, the physiological mechanism underlying this has not been clarified, despite its practical importance. To elucidate this mechanism, we investigated the effects of male-derived substances on the inhibition of mating receptivity of virgin females by injecting the substances into their abdomens. The length of time from injection to mating in virgin females was significantly longer in females injected with accessory gland B solution than in those injected with control solution. For those injected with the contents of seminal vesicles, or accessory glands A and C, there were no significant differences compared to the control. In this study, we showed that mated females have a long refractory period (about 14 d) because males of E. postfasciatus inhibit female remating by using seminal fluid substances. We discuss the optimal timing of the release of sterilized insects in SIT eradication programs, to exploit the mating system of E. postfasciatus.