Sexual selection sometimes favors male traits that benefit their bearers, but harm their mates. The harmful effects of male traits may also extend to females of other species via heterospecific mating interactions. This could affect the coexistence of closely related species during secondary contact. We examined the evolution of the interspecific interfering capability of a beetle (Callosobruchus chinensis) with a congener (C. maculatus) using C. chinensis males reared under conditions of monogamy and polygamy for 17 generations. After experimental evolution, C. chinensis males reared under polygamous conditions imposed greater impacts on offspring production by C. maculatus females than did C. chinensis males reared under monogamous conditions. However, the mechanism by which differential mating regimes altered the effect of C. chinensis males on C. maculatus females was unclear, because we did not find evidence for the expected genital evolution in C. chinensis, despite their body size divergence. Our findings suggest that traits that originally evolved through sexual selection in two allopatric species could influence the coexistence of these species or the likelihood of reinforcement during secondary contact.