The extreme male dimorphisms exhibited by some non-pollinating fig wasps have often been thought to be a consequence of a genetic polymorphism, and have been cited as an example of how frequency-dependent selection can maintain alternative alleles in a population. If true, then the proportions of each morph in one generation should reflect their mating success in previous generations. Here, we test the genetic polymorphism assumption in the male dimorphic species Otitesella pseudoserrata, and demonstrate that it is impossible for such a mechanism to generate alternative morphs in the highly variable proportions observed. These results suggest that male dimorphism is not a classic case of alternative strategies attributable to alternative alleles at a single locus. Rather, it would seem that although the fitnesses of the alternative morphologies are frequency dependent, their actual proportions in a generation are determined through a facultative decision.