Xylem feeding by spittlebug nymphs: some observations by optical and cryo-scanning electron microscopy

• Published in: American journal of botany 1998-04, Vol.85 (4), p.449-460
• Main Authors: Crews, L.J, McCully, M.E, Canny, M.J, Huang, C.X, Ling, L.E.C
• Format: Article
• Language: English
• Subjects: Anatomy and Morphology; Botany; Canals; CELL STRUCTURE; Cercopidae; CHEMISTRY; CHIMIE; CIRSIUM ARVENSE; COLOR; COLOUR; COULEUR; ESTRUCTURA CELULAR; Flowers & plants; Fluorescence; GEUM ALEPICUM; GLYCINE MAX; Hemiptera; HISTOCHEMISTRY; Homoptera; HOST PARASITE RELATIONS; Insect stylets; Insects; Liquids; Nymphs; PHILAENUS SPUMARIUS; PIGMENT; PIGMENTOS; PIGMENTS; Plant tissues; PLANT VASCULAR SYSTEM; Plants; plant–insect interactions; PROTEINAS; PROTEINE; PROTEINS; QUIMICA; RELACIONES HUESPED PARASITO; RELATION HOTE PARASITE; ROSACEAE; SALIVA; salivary sheath; SALIVE; SAP; SAVIA; Scientific imaging; SEVE; SISTEMA VASCULAR DE LA PLANTA; spittlebug; STRUCTURE CELLULAIRE; stylet track; SYSTEME VASCULAIRE DES PLANTES; TISSUE ULTRASTRUCTURE; ULTRAESTRUCTURA; ULTRASTRUCTURE; XILEMA; XYLEM; xylem embolisms; xylem tension; Xylem vessels; XYLEME; xylem‐feeding insects
• ISSN: 0002-9122; 1537-2197
• DOI: 10.2307/2446427

The feeding of spittlebug nymphs (Philaenus spumarius) from mature xylem vessels was studied by optical and cryoanalytical scanning electron microscopy. Feeding did not produce xylem embolisms and vessels remained liquid-filled during the day. Saliva secreted by the insect forms a hardened lining (salivary sheath) between the stylet bundle and the plant tissues. This sheath is continuous through the hole made by the stylets as they enter a vessel, and it extends into the vessel and along its periphery beyond the breach. The sheath is heterogeneous, with a thin outer layer adjoining the plant tissues and a thicker layer that contacts the stylet bundle. Both layers give positive histochemical reactions for proteins and, in fresh tissues. contain a red, strongly autofluorescent pigment, possibly condensed tannin derived from the plant (which is lost during tissue preparation), and other phenyl propanoid compounds, which are retained and which may produce the intense reaction of the periodic-acid-Schiff's-positive inner layer. It is concluded that the salivary sheath allows the insects to feed from functioning vessels without embolizing them or losing xylem fluid to the surrounding tissues. These findings and others in the entomological literature indicate low daytime tensions in the xylem conduits of the host plants