Histo-physiology of the salivary glands of the red cotton bug, Dysdercus koenigii (Pyrrhocoridae-Heteroptera)--histological, histochemical, autoradiographic and electron-microscopic studies.

1. Gross morphology, histology, histochemistry and ultrastructure of the salivary glands of Dysdercus koenigii have been studied. The mode of origin of saliva was investigated by tracer techniques. 2. Differences in histological structure of the glandular lobules, consistency and staining properties of the lumen contents, as also in their capability to incorporate materials from haemolymph have been observed, pointing to a possible division of labour among the different parts of the gland. 3. 3H-thymidine experiments showed that some of the nuclei of the gland cells incorporate the label asynchronously, indicating their polyploid growth or repair DNA synthesis or even specific gene amplification. 4. 3H-uridine incorporation patterns showed that the gland cell nuclei are the principal centres of RNA synthesis. The synthetic products move into the cytoplasm and then into the glandular lumen. The RNA exported into the lumen conjugates with the protein to form RNP which provides the material for the formation of the protective sheath around the mandibular, and maxillary stylets at the time of piercing and sucking. 5. Autoradiographic experiments with 3H-L-histidine showed that the site of heavy labelling shifts from outside inwards with progressive incubation times, indicating that the glandular epithelium is capable of transporting haemolymph materials (proteins?) into the lumen. Some of the haemolymph protein fractions could possibly be used as the precursors of salivary components, in addition to the endogenously synthesised materials. 6. Salivary histochemical studies revealed the presence of glycogen both in the lumen and in the granular epithelium. 3H-glucose labelling patterns are in agreement with the histochemical localization of glycogen and suggest that the blood sugar (trehalose) might be appropriated by the gland cell epithelium for the formation of glycoproteins. 7. Ultrastructural observations of the gland cells showed that the basal borders of the cells are highly folded to form pits. Pinocytotic uptake of the haemolymph materials may be facilitated by these pit formations. The apical borders of the cells facing the lumen develop numerous microvilli and the secretion granules escape into the lumen by pinocytosis, as revealed also by the autoradiographic studies with tritiated histidine. The distribution of golgi vesicles, mitochondria, microtubules is not uniform. They tend to show a higher density towards the apical border than towards the basal border of the cells. This difference may be related to the well-known functions of these organelles in packing the secretion products and to provide energy and channels for their transport. The rER exists in the form of numerous vesicles scattered evenly throughout the cytoplasmic space. But they also exist as stacks of membranes. Their proximity with golgi vesicles seems to be significant for the packing process of the secretion products.