In many social insects, workers are capable of producing males. Workers are more highly related to their own sons than to the sons of the queens, and so it is surprising that queens often monopolize male production even though they are outnumbered by the workers. A possible explanation is that workers prevent each other from reproducing when their relatedness to the sons of the queens is higher than their relatedness to the sons of other workers. Using microsatellite loci to assess genetic relatedness, we determined that workers of the wasp species Parachartergus colobopterus should prevent each other from reproducing. Analyses of the male genotypes showed that queens were producing the males in accord with our prediction. We did not find evidence for policing behavior however, so these results are also consistent with the hypothesis that worker reproduction has colony-level costs which have led to a conventional settlement.