Comparative Morphology Of The Mouthparts In Cicadellidae

Mouthparts are the feeding apparatus of insects, which have been modified in various feeding structures to perform the ingestion of vast diversity of food by different feeding strategies. Research on mouthpart morphology could provide insight on the feeding mechanism of insects. Leafhoppers are one of the largest families of plant-feeding insects over20000species worldwide, and feed by sucking the sap of vascular plants. Whereas studies on the mouthpart morphology and the fine structures of the mouthparts in Cicadellidae are relatively few. Therefore, a comparative study on modality and fine structure of leafhopper mouthpart and accompanying sensilla is documented among eight cicadellid species, Kollapaulula (Walker)(Cicadellinae), Atkinsoniella thalia (Distant)(Cicadellinae), Bothrogonia qiongana Yang et Li (Cicadellinae), Evacanthus heimianus (Kuoh)(Evacanthinae), Nephotettix apicalis (Motschulsky)(Deltocephalinae), Japananus hyaliims (Osborn)(Deltocephalinae), Xestocephalus bicolor Matsumura (Xestocephalinae) and Idioscopus spatulatus (Idiocerinae) by means of light and scanning electron microscopy. The aims of this study are to elucidate and compare mouthpart morphology to determine whether they show mouthpart diversity that can be applied in the systematics of the Auchenorrhyncha suborder and in the discussion about the mouthpart diversity phenomenon.The mouthparts of leafhoppers resemble those of other piercing-sucking insect pests, consisting of a tube-like structure including the labrum, labium and a stylet fascicle comprising two mandibular and two maxillary stylets. The three-segmented labium has a deep longitudinal groove on the ventral surface, within which lies the stylet fascicle, consisting of two inner maxillary stylets partially surrounded by two somewhat shorter and serrate-edged mandibular stylets, and above which is a small cone-shaped labrum. The labium is covered with sensilla, symmetrically positioned on either side of the labial groove or arranged on the distal end. The maxillary stylets are interlocked to form2separate compartments, a larger food canal and a smaller salivary canal. Also, there are dendritic canals in each maxilla and mandible.The labrum is short and generally conical, and is attached to the anterior margin of the anteclypeus and overlays the labial groove of the1st and2nd labial segments. The surface of the labrum is rugose, with some visible small triangular cuticular processes arranged singly or pairwise in K. paulula, A. thalia, B. qiongana, J. hyalinus, X. bicolor and I.spatulatus, while no protrusion arise from the surface in E. heimianus and N. apicalis. Rows of tufts of bristlelike prominences are present at the edge of the labrum in B. qiongana. The modified labium is cylindrical, composed of three segments and its anterior surface is bisected by a deep labial groove extended its entire length, which encases the stylet fascicle. The lengh of three segments of labium is varing among different species. Distal segment are longer than other two segments in N. apicalis and X. bicolor, but the length of three segments in other species almost equal to each other.All segments of the labium are covered with different types of sensilla mainly distributed on each side of the labial groove and distally, with fewer sensilla on the lateral and dorsal surface. Six types of sensilla were found on the labium, including s. trichodea Ⅰ, s. trichodea Ⅱ, s. basiconica Ⅰ, s. basiconica Ⅱ, grooved pegs and coeloconic sensilla. Among them, S. trichodea Ⅱ are most numerous and multiform in8species. Grooved pegs are seen in E. heimianus and I.spatulatus, whereas coeloconic sensilla are found in K. paulula, A. thalia, B. qiongana and E. heimianus.The stylet fascicle is needle-like, composed of two mandibular and two maxillary stylets. The mandibular stylets are abutted on each lateral side of the maxillary stylets and slightly shorter than the maxillary stylets. The most noticeable feature of the mandibular stylet is the sculpturing on its tip. There are two rows of numerous teeth-like projections on the inner edges of each mandibular stylet, and serrate flanges on the convex external surface of each stylet. The flanges are more prominent in K. paulula, A. thalia, B. qiongana, as well as the lateral projections are more sharper. The maxillary stylets are smooth and sharply pointed, but some pointed spines at evenly spaced intervals present at the joint between the two stylets in K. paulula, A. thalia, B. qiongana.Eight species of leafhopper in5subfamilies were morphologically studied for their mouthpart morphology. They are different in the pattern and number of the s. trichodea Ⅱ, the number of s. basiconica Ⅰ, teeth-like projections and serrate flanges on mandibular stylet, the shape and number of cuticular processes on labrum. The mouthpart morphology in Cicadellinae and Deltocephalinae can be easily distinguished. The diversity of the mouthpart morphology in Cicadellidae can be used in the systematics.