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No abstract

Amounts of DNA-Feulgen staining in individual somatic nuclei and mature sperm of the parthenogenetic wasps, Habrobracon juglandis, H. serinopae, and Mormoniella vitripennis, were determined with a scanning microdensitometer. The haploid genome for both species of Habrobracon was estimated to be 0.15-0.16 X 10-(12) gDNA, corresponding to a molecular weight of roughly 10 X10(10) daltons. The haploid genome of M. vitripennis is approximately twice this value, 0.33-0.34 X 10-(12) g, or about 20X10(10) daltons. Measurements made on dividing nuclei from syncytial preblastoderm embryos of H. juglandis and M. viripennis showed that the chromosomes of impaternate males were present in the haploid number and contained the C amount of DNA; whereas nuclei from female preblastoderm embryos contained the diploid number of chromosomes and the 2C amount of DNA. However, hemocyte and brain cell nuclei from either male or female adult wasps contained 2C and 4C amounts of DNA. Both sexes also showed equivalent levels of polyploidy (8C, 16C, or 32C) in Malpighian tubule nuclei. Therefore, in these parthenogenetic species,, a mechanism must exist the compensates during later development for the initial two-fold difference in the chromatin content of somatic nuclei in haploid male and diploid female embryos. Hemocytes from impaternate Mormoniella diploid males and triploid females contain the 2C and 3C amounts of DNA, respectively Therefore dosage compensation involves an additional cycle of DNA replication only in hapoid cells, and it insures that a certain minimum quantity of DNA is received by each somatic cell.

Normal oogenesis in the adult wasp, Habrobracon juglandis, is described. Accounts are given of: (1) the mitotic behavior of oogonia and cystocytes: (2) the production of synaptonemal complexes by pro-oocytes in the germarium; (3) the formation of an egg chamber and its movement through the vitellarium; (4) the ultrastructural details of the transfer of cytoplasmic organelles to the oocyte by the nurse cells; and (5) the production of accessory muclei and protein yolk spheres in the ooplasm. Comparisons are drawn between Habrobracon and other insects with respect to: (1) the cystocyte divisions, the origin of ring canals, and the control of pro-oocyte differentiation; (2) the possible symbiotic relationships of bacteria which reside in ovarian tissue; (3) the proposed functions performed by accessory nuclei and protein yolk spheres; and (4) the synthesis of rRNA by the nurse cells.

The chromosomes of the ovarian nurse cells of Drosophila melanogaster fall apart during their cycles of endoreduplication. However, chromosomal synapsis occurs in the pseudonurse cells produced in certain mutant females. The resulting polytene chromosomes undergo developmental changes that are strikingly different from those recorded for the giant chromosomes of the larval salivary gland cells.