The Action and Composition of the Saliva of An Assassin Bug Platymeris Rhadamanthus Gaerst. (Hemiptera, Reduviidae)

ABSTRACT The responses of whole insects, selected organs, and tissues to treatment with the saliva of an assassin bug Platymeris rhadamanthus are described. The excitability of muscle and nerve is rapidly abolished. In the general lysis that follows immobilization only cuticular and collagenous structures are spared. The disruption of lipid layers in the walls of nervous tissue is histologically demonstrable at an early stage. The saliva contains at least six proteins, and lacks mucoprotein or other mucoid substance. Three proteolytic fractions were recognized after starch-gel electrophoresis at pH 8·6, one of them forming the major component of the saliva. Attempts to locate a toxic fraction were unsuccessful. The alkaline endopeptidase activity of whole saliva characterized with an azocasein substrate closely resembles gut proteases of other insects examined with the same substrate. Hyaluronidase is present in the saliva and with protease acts as a spreading factor by breaking down the intercellular matrix. Lipase and esterase activity were not detected in the saliva, but gut-wall extracts were lipolytic. The saliva shows weak phospholipase activity. ATP-ase, and serotonin were not detected. The mode of action of assassin bug saliva as a venom and in external digestion is discussed. It is suggested that its toxicity is due to the disruption of phospholipid layers of the cell wall and is the first manifestation of general lysis during external digestion.