Reproductive interference, reproductive interactions between heterospecific individuals including mating, is commonly reported across taxa but its drivers are still unclear. Studying interspecific matings in the context of their conspecific mating system— by relating an individual’s conspecific mating behavior to its heterospecific interactions— offers a powerful approach to address this uncertainty. Here we compare inter- and intraspecific mating dynamics in the squash bug Anasa tristis and its close relative Anasa andresii under semi-natural conditions. Using replicated enclosures, we surveyed the mating behavior of individually marked A. tristis and A. andresii (5 males and 5 females of each species per trial) at hourly intervals using a robotic camera system over a 14-day period. We uncovered high levels of reproductive interference (19% of individuals engaged in interspecific matings) but the majority of mating activity took place between conspecifics. A. tristis females which engaged in interspecific matings had comparable hatching success with those which did not. Therefore, in this system, relatively high levels of reproductive interference may emerge under semi-natural conditions as a byproduct of limited intraspecific pre-copulatory choice paired with limited fitness penalties for at least one of the species involved.