SEM study of the mouthparts of Nacolus tuberculatus (Walker) (Hemiptera: Cicadellidae) with comparative notes on other Hemiptera

The fine structure of the mouthparts of adult Nacolus tuberculatus (Walker), a widely distributed species of the morphologically aberrant leafhopper subfamily Hylicinae, was observed under the scanning electron microscope. The results showed that the mouthparts of this species are similar to those of previously studied leafhopper species in most aspects, consisting of a cone-shaped labrum, a three-segmented labium and a stylet fascicle with two interlocked maxillary stylets incompletely enclosed by two mandibular stylets. Small barbs on the inner edge of the right maxillary stylets similar to those found in Heteroptera, were observed for the first time in the leafhoppers. Three kinds of sensilla were found on the labium, including four types of sensilla trichodea (I, II, III and IV), two types of sensilla basiconica (I and II), and one type of sensilla coeloconica. The morphology of the mouthparts of N. tuberculatus and the possible functions of the sensilla located on the labium are discussed. Further comparative studies of the mouthparts of other leafhoppers are needed to reveal the degree to which the observed structures vary among major lineages and determine their significance for systematic and evolutionary studies.