THE SIGNIFICANCE OF PECTINASE IN PLANT PENETRATION BY APHIDS

Abstract

The feeding punctures of 36 examples of forms of 19 species of aphids on their host plants were examined histologically. The types of plant penetration by the aphids' stylets were compared with the occurrence of pectinase in the saliva of these insects. In 17 cases the aphids penetrated only between cells, and all these insects possessed pectinase; in 9 cases the aphids penetrated directly through cells, and all these aphids lacked pectinase. In five instances aphids possessing pectinase penetrated directly through cells; and there were five examples, all possessing pectinase, that penetrated both between and through cells in the same probe. No aphid lacking pectinase penetrated between cells in the pectic middle lamella. It is suggested that pectinase aids intercellular penetration by its hydrolytic action, but that the enzyme is not necessary when the aphid penetrates directly through cells.