We investigated interbreeding and admixture in Tetrix subulata grasshoppers from two maternal-origin populations that differed in life-history and dispersal traits. We compared reproductive output of females that had been experimentally mated with males from the same or from a different population. Interbreeding affected clutch size and number of clutches: in one population, females in the admixed treatment produced smaller clutches; in the other population, females in the admixed treatment produced more clutches. Behavioral observations indicated that individuals can discriminate scents emitted by individuals from different populations, so that females might adjust reproductive allocation depending on male origin. However, hatchability of eggs and survival of nymphs were not affected by the mating treatment. Admixture affected the production of viable offspring in the F2 generation, but the effect was opposite in the two populations of maternal origin. Results suggested that responses to interbreeding and admixture can differ between populations within a species.