The cytology of several species of iceryine coccids, with special reference to parthenogenesis and haploidy

Four species of iceryine coccids have been studied cytologically in connection with certain breeding experiments. These are Icerya littoralis, Icerya montserratensis, Echinicerya anomola, and Crypticerya rosae. For the three first‐named species the complete chromosomal history has been established, and the evidence on the fourth, Crypticerya rosae, is sufficient to indicate that it differs in no essential respect from the others. The following résumé may, therefore, be considered to apply to all four species. The females are diploid, with a chromosome number of four, and the males are haploid, with a chromosome number of two. Oogenesis proceeds quite normally; two tetrads are formed and two maturation divisions occur in which the chromosomes are reduced to two in each female pronucleus. All eggs undergo this reduction: if the eggs are then fertilized, the diploid number is thus restored and development into females ensues; if the eggs remain unfertilized, whether in the body of a virgin or of a fertilized female, they develop parthenogenetically, with no restoration of diploidy, into haploid males. The spermatogenesis of the haploid males involves a single meiotic division, demonstrably equational in character; the accompanying cytoplasmic division is suppressed, and from each of the binucleate spermatids thus produced two spermatozoa are formed. These conditions are contrasted with the functional hermaphroditism and haploid parthenogenesis of Icerya purchasi.