Composition and variability of the saliva of coreids in relation to phytoxicoses and other aspects of the salivary physiology of phytophagous Heteroptera

Abstract

AbstractIn the saciform, principal salivary glands of Mictis profana (Fabr.) (Coreidae: Heteroptera, Pentatomorpha), the contents of all lobes other than the posterior form gels consistent with their contributing to the solidifying saliva (stylet sheath); the posterior lobe secretes most if not all of a sucrose‐hydrolysing enzyme that occurs in the nongelling (watery) saliva. Evidence for the occurrence of such an enzyme in the saliva of other coreids is presented. That in M. profana has a pH optimum near neutral and a substrate specificity consistent with sucrase (sucrose α ‐D‐glucohydrolase, EC 3.2.1.48) as distinct from plant invertase (β ‐D‐fruccofuranosidase, EC 3.2.1.26). Apart from some maltose‐hydrolysing activity in the salivary glands, also consistent with sucrase, no other carbohydrases and neither proteinase nor lipase were detected. Phosphatases were found in gland extracts but not in secreted saliva. The saliva contains catechol oxidase (EC 1.10.3.1) from the accessory gland and ducts. Topical application of pilocarpine caused individual M. profana to secrete up to 58 μl watery saliva which showed continuous and independent variation of sucrase activity (up to ca 0.012 Units/μl) and pH (6–8), although high sucrase content tended to coincide with high pH. Total protein varied up to 10 μg/μl, and free amino acids up to 1.8 μg/μl leucine eq. Of the many proteins and/or protein subunits separable by electrophoresis of gland contents and saliva, four had sucrase activity, the most mobile with MW ca 66000. TLC indicated inter alia phenyl alanine and tyrosine, but no DOPA nor other diphenolic substrates of the catechol oxidase in the watery saliva. The soluble components of the saliva, which also has marked surfactant properties, are discussed in relation to the feeding process of coreids and the characteristic lesions they produce in their food plants.