CYTOGENETIC MECHANISMS IN APHIDS

Egg maturation, spermatogenesis, sex determination, and chromosomal or ganization are reviewed in aphids with emphasis on the complex life cy cles which makes the cytogenetical mechanisms of this group very pecul iar. Maturation of the parthenogenetically developing egg is still a m atter of controversy in that two opinions exist: that of those who con sider it a modified meiosis, and that of those who consider it an ordi nary mitosis. For male production, an oocyte needs to lose half of its sex chromatin during the single egg maturation division. This process is environmentally controlled by a change in length of the daily phot operiod. In male meiosis, both pre-reductional and post-reductional di visions have been reported. At anaphase I, the single X-chromosome get s stretched on the spindle, and passes into one of the secondary sperm atocytes which receives more cytoplasm 2nd undergoes the second divisi on, while the other degenerates. At present, over 4000 species of aphi ds have been reported the world over and chromosomes of about 20% of t hese species have been investigated, but only for a small minority hav e the homologous chromosomes been clearly identified.