Populations of many parasitoid species used in biological control often exhibit male-biased sex ratios. Male-biased sex ratios may hinder the establishment of introduced species or may result in prohibitively expensive production costs for commercial insectaries in terms of the number of females produced. One explanation for male-biased sex ratios is complementary sex determination (CSD). Under CSD, females develop from fertilized eggs and are heterozygous at the sex locus (loci); males develop from either unfertilized (haploid) eggs or fertilized (diploid) eggs that are homozygous at the sex locus (loci). Diploid males are either nonviable or sterile and their production results in male-biased sex ratios and reduced population growth. Among the parasitic Hymenoptera, the superfamily Ichneumonoidea is the only one with species known to possess CSD. Our studies of Aphidius colemani (Braconidae) suggest that CSD is operating in this species. Outcrossed matings between different populations result in significantly more male-biased sex ratios across repeated generations (~55% male); after 10 generations of inbreeding, females outcrossed to males from a different population produced female-biased sex ratios. These findings indicate that rearing methods at commercial insectaries need to take this into account.
Species 1: Hymenoptera Braconidae Aphidius colemani
Keywords: diploid males, sex ratios
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