Homozygous males produce motile sperm capable of fertilizing eggs, but defective in pronuclear function. Development of fertilized eggs initiated; arrested after several nuclear divisions in three-fourths of the embryos, the remainder developing beyond blastoderm and proving to be haploid upon cytological examination. Nuclear division cycle protracted compared to wild type, and the syncytial blastoderm nuclei undergo an extra division to produce twice the normal density prior to cellularization (Edgar, Kiehle, and Schuberger, 1986, Cell 44: 365-72). A small fraction of the eggs diploidize and yield viable daughters, mostly by fusion of products of the first meiotic division (85%); fusion of products of second meiotic divison rare or nonexistent. Incidence of gynogenetic diploids becomes appreciable in crosses to a stock designated G9 by Fuyama (1986, Genetics 114: 495-509).