Sex Determination in the Sawfly, Athalia rosae ruficornis (Hymenoptera): Occurrence of Triploid Males

Abstract

Single-pair matings of Athalia rosae ruficornis between individuals originating from different localities resulted in F1 progenies consisting of only diploid females and haploid males. Brother-sister single-pair matings of these F1 populations, however, revealed two types of females: one-half of them produced only diploid females and haploid males, while the other half produced diploid females, haploid males, and diploid males. Using the F2 progenies from crosses in which diploid males appeared, brother-sister single-pair matings were made between diploid females and haploid males and between diploid females and diploid males. In the former, the F3 progenies consisted of diploid females, diploid males, and haploid males. In the latter, triploid females, triploid males, and haploid males were produced. Clearly, diploid males produce unreduced diploid sperm. These results indicate that sex is determined by the single-locus, multiple-allele system: hemizygous and homozygous individuals develop into males and heterozygous ones develop into females. Triploid males, found for the first time in the hymenopteran species, look quite normal in morphology except for a larger size. They produce unreduced triploid sperm and copulate with females, but are apparently sterile.