Sex determination in the haplodiploid order Hymenoptera has been studied extensively but is still not well understood. While cytoplasmic and environmental factors have been shown to occasionally influence sex determination in the Hymenoptera, the genetic mechanism, Complementary Sex Determination (CSD), is the only well known form of sex determination in this order. However, CSD does not explain sex determination in members of the superfamily, Chalcidoidea. In the Chalcidoids, temperature and the cytoplasmic reproductive parasite, Wolbachia, have often been demonstrated to have a significant effect on sex determination. This study has employed heat-treatment of Wolbachia-infected Trichogramma during their development to induce the production of diploid males. This is the first documented case of diploid males occurring in the Chalcidoids in the absence of mutation. Such a finding may provide valuable insight into the mechanisms used by Wolbachia in order to manipulate host reproduction and may have important implications for evaluating sex determination in Trichogramma and other Chalcidoids as well as for understanding the evolution of sex determining factors in the Hymenoptera.