Comparative Analysis and Systematic Mapping of the Labial Sensilla in the Nepomorpha (Heteroptera: Insecta)

The present study provides new data concerning the morphology and distribution of the labial sensilla of 55 species of 12 nepomorphan families (Heteroptera: Nepomorpha) using the scanning electron microscope. On the labial tip, three morphologically distinct types of chemosensilla have been identified: two types of papillae sensilla and one type of peg-in-pit sensilla. Twenty-one morphologically distinct types of the mechanosensilla as well as two types of the trichoid sensilla (contact-chemoreceptive sensillum) have been identified on all labial segments in representatives of subfamilies. In Nepomorpha, morphological ground plan of the labial sensory structures is represented by an apical sensory field with 10–13 pairs of papillae sensilla and the peg-in-pit ones placed more laterally; numerous trichoid sensilla are placed on the IV segment; the chaetica sensilla are present and placed in groups or rows distributed along the labium near the labial groove on the dorsal side, and also several chaetica sensilla are unevenly scattered on the surface of that segment; the cupola and peg sensilla are numerous and evenly scattered on the fourth labial segment; the prioprerecptive sensilla, one pair is positioned on the dorsal side and on the fourth segment of the labium. The new apomorphical characters have been established for the labial sensilla in the Nepomorpha.