In the males of most mealy bug species one set of chromosomes is heterochromatic and the other euchromatic. Recent work showed that the heterochromatic set is of paternal origin and almost completely inert genetically. In interspecific hybrids one would expect the sons to survive to adulthood and to resemble the males of the maternal species. Crosses between six species from three genera failed to produce offspring beyond the first instar stage. The production of hybrid male embryos indicated that a chromosome set can be heterochromatized in a foreign egg. The failure of the male embryos to survive is probably caused by the activity of the paternal set of chromosomes. Several explanations for the death of the male embryos are suggested. Gynogenetic females are known to develop after heavy doses of paternal irradiation in Planococcus citri. Attempts to obtain gynogenetic females in two other species failed. However, gynogenetic Pl. citri daughters were obtained after Pl. citri females were mated to Pseudoc...