ABSTRACT: In Hymenoptera, sex is determined by a single-locus complementary sex determining system (sl-CSD). Males are normally haploid (hemizygous at the sl-CSD locus) but if the genotype of the sl-CSD locus is homozygous, they develop into diploid males. Here, we study the effects of ploidy and the sl-CSD-locus genotype by comparing gene expression differences between haploid males, diploid males and virgin queens at three developmental stages, pupae, 1 day and 11 days after eclosion. Keywords: diploid males, sl-CSD, ploidy-spcific gene, sex-specific gene, doublesex, sex-biased gene Six-condition experiment: haploid male pupae, diploid male pupae, queen pupae, 1-day-old haploid male adults, 1-day-old diploid male adults, 1-day-old queen adults (accession number GSM1031732 - GSM1031734, GSM1031737 - GSM1031738, GSM1031740 - GSM1031742, GSM1031745 - GSM1031746; reprocessed for this study), 11-day-old haploid male adults, 11-day-old diploid male adults, 11-day-old queen adults (accession number GSM1031748 - GSM1031750, GSM1031753 - GSM1031754, GSM1031756 - GSM1031758, GSM1031761 - GSM1031762; reprocessed for this study). Biological replicates: 5 colonies (x 2 genotypes for each colony). Samples were labeled with Cy3 and were compared to the same common reference RNA labeled with Cy5.