ORIGINAL PAPER Morphology and distribution of the external labial sensilla in Fulgoromorpha (Insecta: Hemiptera)

Abstract The present paper describes the sensory struc-tures on the apical segment of the labium in fifteen ful-goromorphan families (Hemiptera: Fulgoromorpha), using the scanning electron microscope. Thirteen morphologi-cally distinct types of sensilla are identified: five types of multiporous sensilla, four types of uniporous sensilla and four types of nonporous sensilla. Three subapical sensory organ types are also recognized, formed from one to sev-eral sensilla, each characteristic of a family group. Sensilla chaetica (mechanoreceptive sensilla) fall into three cate-gories dependent on length and are numerous and evenly distributed on the surface of the labium except where they occur on specialized sensory fields. The planthopper mor-phological ground plan is represented by two apical pair of sensory fields (dorsal and ventral) on which 11 dorsal pairs of sensilla (10 peg-like pairs? 1 specialized pair dome or cupola-like) and 2 ventral pairs of sensilla basiconica occur. Two main patterns (cixiid and issid) together with more specialized ones (derbid, lophopid, flatid and fulgo-rid) are reported. Disparity and diversity of the sensory structures are analyzed from a taxonomic and functional perspective. A gustatory function is provided for several chemoreceptive labial sensilla, as in the antennal flagellum sensilla in some other Hemiptera. This represents a more recently evolved function for the planthopper labium. Finally, further lines of study are suggested for future work on the phylogeny of the group based on the studied characters