In sexually reproducing species males often experience strong pre- and postcopulatory sexual selection leading to a wide variety of male adaptations. One example is mate guarding, where males prevent females from mating with other males either before or after they (will) have mated themselves. In case social conditions vary short-term and in an unpredictable manner and if there is genetic variation in plasticity of mate guarding (i.e. genotype-by-environment interaction, G x E), adaptive behavioral plasticity in mate guarding may evolve. Here, we test for genetic variation in the plasticity of precopulatory mate guarding behavior in the lek-mating lesser wax moth Achroia grisella. When offered two females in rapid succession, virgin males of this species usually copulate around 10-20 min with the first female. With the second female, however, they engage in copulation posture for many hours until they have produced another spermatophore, an unusual behavior among insects possibly functioning as precopulatory mate guarding. Previous studies showed the mating latency with the second female to be shorter under higher perceived sperm competition risk. We accordingly measured the mate guarding behavior of males from six inbred lines under either elevated perceived male-male competition risk or under control conditions allowing us to test for G x E interactions. We found significant inbred line-by-competitor treatment interactions on mating latency and copulation duration with the second female suggesting genetic variation in the degree of behavioral plasticity. However, we found no significant G x E interaction on the sum of mating latency and copulation duration. Our results suggest a potential for adaptive evolution of mate guarding plasticity in natural populations of lek-mating species. Future studies using selection experiments and experimental evolution approaches in laboratory populations, or comparisons of multiple natural populations will be helpful to study under which conditions plasticity in male mate guarding behavior evolves.