Technical Abstract: Males of the plant bug Lygus hesperus, a major crop pest, prefer to court virgins over recently mated females. Because males deliver a large spermatophore mass to the females during copulation that contains more than just sperm, we investigated whether they transferred an odorant molecule rendering females less attractive. We found that topical application of homogenates of the spermatophore or the male accessory glands (AG) from which this mass is derived, both made virgin females less acceptable as potential mates. Additionally, we found that the fatty molecule myristyl acetate occurs in male accessory glands, is absent in virgin females, but is present in the seminal receptacles of mated females. The same distribution of myristyl acetate was also found in L. elisus and L. lineolaris. We hypothesized that myristyl acetate has a repellent effect on L. hesperus males seeking an appropriate mate. Using topically applied synthetic myristyl acetate at biological concentrations, we found that it was as effective as the AG homogenate at reducing the attractiveness of virgin females. Collectively these results indicate that males use myristyl acetate as a seminally transferred antiaphrodisiac for passive mate guarding, and usage of the compound may be widespread among Lygus bug species.