Mechanisms
Several models have been proposed for the genetic mechanisms of haplodiploid sex-determination. The model most commonly referred to is the complementary allele model. According to this model, if an individual is heterozygous for a certain locus, it develops into a female, whereas hemizygous and homozygous individuals develop into males. In other words, diploid offspring develop from fertilized eggs, and are normally female, while haploid offspring develop into males from unfertilized eggs. Diploid males would be infertile, as their cells would not undergo meiosis to form sperm. Therefore the sperm would be diploid, which means that their offspring would be triploid. Since hymenopteran mother and sons share the same genes, they may be especially sensitive to inbreeding: Inbreeding reduces the number of different sex alleles present in a population, hence increasing the occurrence of diploid males.
After mating, fertile Hymenopteran females store the sperm in an internal sac called the spermatheca. The mated female controls the release of stored sperm from within the organ: If she releases sperm as an egg passes down the oviduct, the egg is fertilized. Social bees, wasps, and ants can modify sex ratios within colonies to maximize relatedness among members, and to generate a workforce appropriate to surrounding conditions.
Read more about this topic: Haplodiploid Sex-determination System