Submitted to: Arthropod Structure and Development
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2003
Publication Date: 9/22/2003
Citation: LEOPOLD, R.A., FREEMAN, T.P., BUCKNER, J.S., NELSON, D.R. MOUTHPART MORPHOLOGY AND STYLET PENETRATION OF HOST PLANTS BY THE GLASSY-WINGED SHARPSHOOTER, HOMALODISCA COAGULATA, (HOMOPTERA: CICADELLIDAE). Arthropod Structure and Development. 2003. v. 32. p. 189-199. Interpretive Summary: The fine structure of the mouthparts of the glassy-winged sharpshooter, a vector of Pierce's Disease in grape, leaf scorch in oleander and almond and variegated chlorosis in citrus, was studied to gain insight on the feeding mechanisms of this insect. This insect feeds on the xylem fluid of a wide range of plants and during feeding transfers the bacteria which cause blockage of the xylem vessels. The mouthparts are of the piercing-sucking type and are typical for this group of insects. Several unique features associated with the segmented mouthpart structures that physically support the piercing stylets were identified. These features include an array of different types of surface sensory receptors that have not been previously described. These sensilla are hypothesized to have a function in the orientation of the insect to the plant and also in the correct positioning of the mouthparts into feeding sites within the host plants. Examination of proteinacious salivary sheaths, which surround the piercing stylets during feeding and remain evident after feeding, revealed that the insect successfully found xylem vessels on about 65% of its probes into plant tissues. The shorter length of mouthpart stylets of the very young sharpshooter nymphs apparently limit feeding to sites on the host plant where the xylem vessels are close to the surface, such as the leaf veins and margins.
Technical Abstract: The ultrastructural morphology of the mouthparts the glassy-winged sharpshooter, Homalodisca coagulata, and method of plant penetration was examined using light microscopy, SEM, and TEM methods. The gross morphology of the labrum, labium, and stylet fascicle was consistent with what has been described for other plant-sucking homopterans. The ultrastructural examination of the mouthparts revealed unique details that have previously gone unreported. Several types of sensilla-like structures having the form of pegs and multi-lobed objects were identified on the outer surfaces of the labrum and within the labial groove. Dendritic canals terminated in an extensive network of smaller canals at the distal tip of the maxillary stylets below a series of surface denticles suggesting that this area may have a sensory function associated with locating xylem elements of host plants. Examination of salivary sheath pathways established that 65% of the plant penetrations by this insect terminated in the xylem vessels of the host plant. Probing by the insect was largely intracellular and terminal branching of a single probe site was common. Plant surface feeding sites varied with the stage of development which correlates with the depth of the xylem vessels and the length of the maxillary stylets of the various instars.