Mouthpart morphology and stylet penetration of host plants by the glassy-winged sharpshooter, Homalodisca coagulata, (Homoptera: Cicadellidae)

The ultrastructural morphology of the mouthparts of the glassy-winged sharpshooter, Homalodisca coagulata, and method of plant penetration was examined using light microscopy, scanning electron microscopy, and transmission electron microscopy 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.