Detection of pectinesterase and polygalacturonase from salivary secretions of living greenbugs, Schizaphis graminum (Homoptera: Aphididae)

Pectinesterase (EC 3.1.1.11) and polygalacturonase (EC 3.1.1.15) were successfully detected in induced salivary secretions of living greenbugs, Schizaphis graminum (Rondani). The method involved the construction of agarose-pectin gel plates on which the aphids were allowed to feed through Parafilm, followed by staining of the gels with ruthenium red. The specific activities of pectinesterase and polygalacturonase were detected by formation of dark red circular and clear halos, respectively, around the site of stylet sheaths left by the aphids. The assay indicates the saliva of biotypes E and C contains both enzymes. The method combines a living, feeding organism with an enzyme assay system in a unique and simple way and provides conclusive evidence for the nature of secreted materials. It also provides an opportunity to investigate the formation of stylet sheaths by this and other aphid species. The toxicity of the enzymes to host plants and the importance of the enzymes to greenbug feeding are discussed.