MORPHOLOGY AND ULTRASTRUCTURE OF THE SEROSAL CELLS (TERATOCYTES) IN CARDIOCHILES-NIGRICEPS VIERECK (HYMENOPTERA, BRACONIDAE) EMBRYOS

The morphogenetic changes of the serosal membrane during embryonic dev elopment of Cardiochiles nigriceps Viereck (Hymenoptera : Braconidae) were investigated. Eggs observed soon after oviposition into the natur al host Heliothis virescens (F.) (Lepidoptera, Noctuidae) showed a tra nsparent chorion and a uniform texture. After 5 hr, the embryo exhibit ed a distinct granular appearance and by 12 hr attained the germ band stage. A serosal membrane originated from the anterior pole of the emb ryo between 14 and 15 hr after the egg was laid, eventually forming wi th the cells both in the anterior and posterior pole a continuous enve lope around the developing embryo. Ultrastructural observations reveal ed that the serosal cells in contact with the abdominal region of the embryo, beginning 24-25 hr after oviposition, formed a syncytium. Howe ver, the syncytial tissue did not extend to the cells around the head and thorax. The serosal cells at both embryo poles increased in size w ithout losing their structural organization, and developed into terato cytes when the larva hatched. In contrast, the serosal cells surroundi ng the body of the embryo persisted longer on the head and thorax regi on of the newly hatched larva, while the syncytial tissue degraded mor e rapidly after hatching. In vitro rearing experiments showed that C. nigriceps embryos removed from parasitized host larvae just before and just after serosa formation, hatched only when the medium used was fo rmulated with the addition of fetal bovine serum. Embryos did not deve lop or hatch when placed in a serum-free medium. Once the syncytium de riving from the serosal membrane became evident, embryos readily devel oped and hatched in serum-free media. The results of this study seem t o suggest that the serosal embryonic membrane could have a nutritional role for the developing parasitoid embryo.