Oogenesis in supplementary reproductives of Reticulitermes lucifugus Rossi (Isoptera Rhinotermitidae): an ultrastructural study

Summary

The Reticulitermes lucifugus ovary consists of about 40 panoistic ovarioles. A transverse septum between the terminal filament and germarium is absent, where two successive developmental stages of oogonia are recognizable. Early meiotic oocytes with synaptonemal complexes and nuclear vacuoles characterize the prophase region. Previtellogenic oocytes first show microvilli and later, in the cortical ooplasm, endocytotic vesicles about 70nm in diameter. Small yolk spheres and 120nm coated vesicles characterize early vitellogenic oocytes, while 180nm vesicles prevail in mid- and late vitellogenesis. The observations support heterosynthetic yolk production and endocytosis of yolk precursors. Prefollicular cells surrounding oogonia and early meiotic oocytes have a scarcely differentiated cytoplasm. Around early previtellogenic oocytes, follicular cells build a monolayered epithelium, first flat then cuboidal and release a granular material on the oocyte side. They closely adhere to each other and extend microvilli interdigitating with those of the oocyte. During vitellogenesis they are first columnar then globose and show large intercellular spaces which disappear in the final stage of vitellogenesis when they again become flat. Follicular cells apparently regulate transfer of materials for oocyte growth and after vitellogenesis synthesize egg envelope precursors. During choriogenesis they show an extended proteosynthetic apparatus whose products are exocytosed on the egg-facing surface and, after choriogenesis, produce a finely granular matrix covering the egg, easing oviduct transit and binding together newly laid eggs. The postovulatory follicle becomes the “corpus luteum” composed of degenerating, non-steroidogenic cells.

Key words:

• Reticulitermes lucifugus
• Isoptera
• oocyte growth
• follicular cells
• choriogenesis
• ultrastructure