External morphology of the mouthparts of the whitebacked planthopper Sogatella furcifera (Hemiptera: Delphacidae), with special reference to the sensilla.

The whitebacked planthopper, Sogatella furcifera (Horváth), is a major pest of rice in Asia, with the adults and larvae sucking the phloem sap and affecting plant growth. The ultrastructural morphology of the mouthparts, with distribution of sensilla located on the maxillae and labium in adult S. furcifera was observed using scanning electron microscopy and illustrated, with a brief discussion of their taxonomic and putative functional significance. The gross mouthparts comprising an uppermost small cone-shaped labrum, a three-segmented labium with a deep longitudinal groove on the anterior side, and a stylet fascicle consisting of two mandibular and two maxillary stylets, are consistent with the conventional piercing-sucking type of mouth parts found in Hemiptera. The mandibles bear 5 teeth on the external convex region on the distal extremity. Smooth maxillary stylets, interlocked to form a larger food canal and a smaller salivary canal, are asymmetrical only in the internal position of longitudinal carinae and grooves. Two dendritic canals are also found in each maxilla and one in each mandible. The cross-section of the stylet fascicle is oval. The labial tip is a rosette shape. Two types of sensilla trichoides, two types of uniporous peg sensilla, two pairs of sensilla basiconica and a pair of subapical labial sensory organs have been detected at different locations on the labium, specifically the labial tip is divided into dorsal paired sensory fields with 9 pairs of uniporous peg sensilla and 1 pairs of dome-shaped sensilla, and ventral paired sensory fields with 2 pairs of sensilla basiconica.