Cytogenetic mechanism of cytoplasmic incompatibility in the uzifly, Exorista sorbillans (Diptera: Tachinidae)

Cytogenetic mechanism of Wolbachia-induced cytoplasmic incompatibility is investigated in the uzifly, Exorista sorbillans, a parasitoid of silkworm, Bombyx mori. The results revealed the condensation of chromatin to form the paternal pronucleus upon the sperm entering in to the egg, and subsequently condensed paternal and maternal pronuclei fused to form the diploid zygote in compatible crosses. In fertilized eggs from incompatible crosses, only the maternal pronucleus had individual chromosomes. The uncondensed paternal pronucleus scattered near maternal pronucleus, and in some eggs reappear as a diffused tangled chromatin mass and tend to get fragmented during the first mitotic division. Moreover, the abnormalities in the first mitotic division extend with the fragmentation and nonorientation of chromosomes on equatorial plane of first metaphase plate. The initiation of chromosome separation in late metaphase was an indication of beginning of anaphase in compatible crosses. In case of incompatible crosses, the chromosome separation had not occurred even at late metaphase/early anaphase leading the failure of development of viable embryo. However, abnormal behavior of paternal chromatin does not interfere with mitotic division of maternal chromosomes. The mechanism is discussed with applied strategy for the management of uzifly, Exorista sorbillans. © 2006 The Japan Mendel Society