In the ichneumonid wasp Diadromus pulchellus (Wesmael), diploid males may regularly be produced in laboratory populations by inbreeding. They are viable, produce diploid sperm and are equally capable of multiple inseminations as are haploid males. Their spermatozoa are also able to penetrate the oocyte. Progeny sired by diploid males are essentially haploid sons with only a few daughters. The sons are normal haploid individuals, produced in a frequency significantly higher than in crosses between females and haploid males. The daughters are normal diploid females probably resulting from the fertilization of an oocyte by an exceptional haploid sperm rarely produced by diploid males. Triploid individuals were not observed and their absence was correlated with the high mortality observed during the first developmental stages. The death of these individuals is discussed in the light of the phenomenon of superparasitism to explain the increase in the frequency of sons produced in crosses with diploid males. Despite their viability, their ability to produce sperm and their normal potential insemination, diploid males of Diadromus pulchellus are therefore almost sterile.
Males of the hymenopteran Diadromus puichellus are normally haploid, but diploid males can be obtained by inbreeding. Inbred crosses within strains that are polymorphic at the enzymatic loci Pgm-2 and Ao-4 or that differ by a body colour mutation produce heterozygous diploid males in offspring. The genotypic distributions observed in such progeny were compared with expected results under the one-locus sex determination model or the two independent loci model. The results show that only the one-locus multi-allele model fits the data and allow a provisional estimate of 15 sex alleles. These conclusions generalize the case of existence of a single locus to determine sex in Hymenoptera and are discussed at the evolutionary level.
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