Cytological Evidence of Pseudo-arrhenotoky in Two Phytoseiid Mites, Phytoseiulus persimilis Athias-Henriot and Amblyseius womersleyi Schicha.

Abstract

Pseudo-arrhenotoky was investigated by chromosome observation in Phytoseiulus persimilis and Amblyseius womersleyi, both of which have the basic number of chromosomes. To confirm male diploidy at the early stage of embryogenesis, eggs were supplied for chromosome observation immediately after they were deposited. In addition, eggs were collected under two prey conditions, “ ample” and “ poor” and their chromosomes were observed in order to examine the relationship between ploidy and sex. Eggs deposited by the two species showed haploid-diploid sequences corresponding to those of male and female offspring under both “ ample” and “ poor” prey conditions. However, male diploidy and heterochromatinized chromosomes were not observed in the deposited eggs. Therefore, the first eggs expected to be males were extracted from the body cavities of female P. persimilis for chromosome observation. The observation confirmed male diploidy at an earlier stage of embryogenesis which takes place in the female body cavity. The coexistence of haploid and diploid cells in the same egg was also observed at the next stage. However, no heterochromatinized chromosomes were observed at any embryonic stages in the female body cavity, under the present experimental conditions. The present study suggests that pseudo-arrhenotoky occurs at least in P. persimilis with the common number of chromosomes, and that the timing of genome elimination is different from that of the species with an aberrant number of chromosomes.