On Sex Determination in the Diaspine Scale Pseudaulacaspis Pentagona (Targ.) (COCCOÏDEA)

SUMMARY In the diaspine scale, Pseudaulacaspis pentagona, the males are haploid, with eight chromosomes, and the females are diploid, with 16. Meiosis is normal in the female and replaced by a simple mitosis in the male. Mating is required for the production of any offspring, either male or female. Egg production affords an example of combined sexual dimorphism and dichronism; the mothers first produce a series of eggs containing coral-colored female embryos and then, without interruption, lay a series containing pinkish-white male embryos. Cytological study of early embryogeny shows that a chromosome set is eliminated to produce the haploid condition of the male embryos. Chromosomes broken by X-rays were used as genetic markers to demonstrate that the eliminated set is of paternal origin. Symbionts, yeast-like in appearance, are present at the distal end of both male and female embryos. The polyploid sector of the embryo stems from the fusion of a cleavage nucleus with both polar bodies and is pentaploid with 40 chromosomes. As would be expected on a simple genetic basis, irradiation of fathers preferentially reduces the number of daughters.