Comparative Morphology Of The Mouthparts In Auchenorrhyncha (Insecta: Hemiptera)

Mouthparts are the feeding apparatus of insects, which have been modified in variousfeeding structures to perform the ingestion of vast diversity of food by different feedingstrategies. Research on mouthpart morphology could provide insight on the feedingmechanism and taxonomy of insects. Auchenorrhynchan of Hemipteran feed exclusively onplant sap which they extract with their sucking mouthparts, and many of them are vectors ofphytoplasma or plant virus. The ultrastructural morphology of the mouthparts, withdistribution of sensilla located on maxillae and labium in seventeen species of seven familiesincluding Atkinsoniella grahami, Cicadella viridis, Mileewa bramchiuma, Exitianus indicus,Taurotettix elegans, Handianus limbicosta, Laburrus impictifrons, Aguriahana triangularis,Tricentrus brunneus, Euricania clara, Parvala quadruple, Sogatella furcifera, Philagraalbinotata, Lepyronia colepterata, Philaenus spunarius, Aphrophora costalis and Meimunamongoli, were observed using scanning electron microscopy and illustrated, with a briefdiscussion of their taxonomic and putative functional significance.The mouthparts of Auchenorrhynchan resemble those of other piercing-sucking insectpests, consisting of an uppermost small cone-shaped labrum, a three-segmented labium with adeep groove in the anterior side, and a stylet fascicle consisting of two mandibular and twomaxillary stylets. The labium is covered with different sensilla, symmetrically positioned oneach side of the labial groove or arranged on the distal end. The two maxillary stylets areinterlocked to forming a larger food canal and a smaller salivary canal, and being surroundedby two shorter and serrate-edgesd mandibular stylets. One or two dendritic canals are found ineach maxilla and mandible.The labrum is short and generally conical, and is attached to the anterior margin of theanteclypeus and overlays the labial groove of the1st and2nd labial segments. The surface ofthe labrum is rugose, with or without small irregular cuticular processes which are subject tomany variations of form and arrangemeng in different insects. Among them, the surface of thelabrum is covered with some triangular cuticular processes in Cicadellidae and clusters ofpegs arranged in a row in Aphrophoridae, whereas no protrusion arises from the surface inCicadidae. Moreover, the sensilla on the labrum are first found in Hemiptera mouthparts researching, including coeloconic sensillum in Cicadellidae and trichoid sensillum inDelphacidae, Aphrophoridae and Cicadidae. Thus, the structural characteristics of the labrumcan be used as identified characters and their potential utilities for phylogenetic analysisconcerned.All segments of the labium are covered with different types of sensilla, and mainlydistributed on each side of the labial groove and distally, with fewer sensilla on the lateral anddorsal surface. Nine types of sensilla are found on the labium, including basiconic sensilla,trichoid sensilla, campaniform sensilla, digitiform sensilla, auricillica sensilla, coeloconicsensilla, chaetica sensilla, leaf shape and l lotus shape sensillum. Among them, basiconi sensilla,trichoid sensilla and coeloconic sensilla are the most abundant with many subtypes. Thesesensilla on the tip of the third labial segment are involved in host recognition and feeding sitelocation.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 slightlyshorter than the maxillary stylets. The most noticeable feature of the mandibular stylet is thenumber and formation of the serrate ridge on its tip which are variable in different families.There are more than ten in cicadellidae whereas only three to five serrate ridges are found inRicaniidae and Issidae. Slab construction and longitudinal ribs only found in Aphrophoridaeare unique characteristics of spittlebug insects.The gross mouthparts of Auchenorrhynch are consistent with conventionalpiercing-sucking type, based on the studies for mouthpart morphology of seventeen species inseven families of Auchenorrhyncha. In the Auchenorrhycha, the mouthpart morphologyexhibit a very wide range in form and structure. The morphological variations wereconsidered important from the taxonomic point of view, including different cuticularprocesses on labrum, different sensilla on labrum, different sensilla on labium, differentteeth-like projections and serrate flanges on mandibular stylet, absence or presence of thornalong with the joins of the two maxillary stylets, variable number of the dendritic canal.