Mate competition provides the opportunity for sexual selection which often acts strongly on males, but also the opportunity for sexual conflict that can alter natural selection on females. Recent attention has focused on the potential of sexual conflict to weaken selection on females if male sexual attention, and hence harm, is disproportionately directed toward high over low quality females, thereby reducing the fitness difference between these females. However, sexual conflict could instead strengthen selection on females if low quality females are more sensitive to male harm than high quality females, thereby magnifying fitness differences between them. We quantify the effects of male exposure on low vs. high quality females in Drosophila melanogaster in each of two environments (“simple” and “complex”) that are known to alter behavioural interactions. We show that the effects of male harm are greater for low compared to high quality females in the complex but not the simple environment, consistent with mate competition strengthening selection on females in the former but not in the latter environment.