For most species that have been studied, considerable variation exists in male postcopulatory reproductive success, including female sperm use, reproductive investment and remating patterns. We investigated postcopulatory sexual selection in the beetle Diaprepes abbreviatus (L.) (Coleoptera: Curculionidae) by examining the correlation of two measures of a male's success (proportion of eggs fertilized (P2) and number of eggs that a female laid after mating with him) with male body size, copulatory behaviour and copula duration. We allowed each female to mate with an irradiated sterile male and a normal male. Relative duration of intromission (i.e. the difference in the intromission durations of the two males) and relative stroking rate, but not the absolute duration and stroking rate, were positively correlated with P2. The number of eggs that a female laid was negatively related to the thrusting rate of her mate. Irradiated males mated for a shorter duration and thrusted at a lower rate than normal males. Irradiated males also fertilized a lower proportion of eggs than normal males, and females were more likely to remate after mating with an irradiated male than after mating with a normal male. These findings suggest that behavioural traits may influence male postcopulatory reproductive success. Furthermore, since variation in male stroking rate and intromission duration are associated with variation in male fertilization success, these traits may have evolved through postcopulatory sexual selection.