Abstract
The structural precursor of the stylet sheath is a proteinaceous substance secreted from the A-follicle of the principal salivary gland of Nilaparvata lugens STÅL and Laodelphax striatellus FALLÉN, and from the IV-cells of the principal salivary gland of Nephotettix cincticeps UHLER and Inazuma dorsalis MOTSCHULSKY. This substance was also found to be impregnated with a lipoid substance, which is secreted from the G- and H-follicles and the V-cells to prevent the proteinaceous substance adhering onto the stylets during coagulation. It is considered that a quinone-tanning reaction is involved in the stylet sheath formation: In N. lugens and L. striatellus, the proteinaceous substance from the A-follicle is solidified by quinones elaborated in the E-follicle where a polyphenol oxidase occurres; while in N. cincticeps and I. dorsalis, the polyphenol compounds secreted with the proteinaceous substance from the IV-cells become oxidized to quinones by the action of polyphenol oxidase discharged from the V-cells, and the resultant quinones react with the proteinaceous substance. These structural precursor and quinone-tanning reagents are thought to be secreted separately so as to avoid the gelling of the proteinaceous substance within the ducts and the salivary cannal. It is doubtful that disulphide bonds are concerned in the coagulation of the sheath material, because no histochemical evidence indicated the occurrence of SH-rich proteins in the salivary glands of the rice plant leafhoppers. It is likely that the stylet sheath serves to bundle the stylets protruded beyond the rostrum, and anchors the mandibular stylets to facilitate the penetration of the maxillary stylets into the plant tissues.
