Occurrence of the Latero-subapical Labial Sensillum in Borysthenes maculata and Andes marmorata (Hemiptera: Fulgoromorpha: Cixiidae)

Abstract

A peg-like structure, found on each lateral side of the distal segment of the labium, close to the labial apex, in two cixiid planthopper species Borysthenes maculata (Matsumura) and Andes marmorata (Uhler) (Hemiptera: Fulgoromorpha: Cixiidae), is reported for the first time with scanning electron micrograph. It is an elongate, peg-like structure hidden in an elongate, narrow, shallow cavity parallel to the longitudinal axis of the labium. In B. maculata, the peg, being about 82 μm proximal to the labial tip, is about 27.6–29.4 μm long and 6.8–7.6 μm wide with a blunt apex. The peg in A. marmorata, being about 60 μm proximal to the labial tip, is distinctly short and narrow and is about 10.2–12.0 μm long, tapering gradually from a basal width of about 2.7 μm to a blunt apex of 0.88 μm wide. The structure, being two in number (one at each lateral side of the labium), is present in both male and female adults. Light microscopic survey shows that this structure is common in cixiid species. It also is present in species of the relatively primitive fulgoromorphan families, e.g., Achilixiidae, Delphacidae and Achilidae, but it is absent in other relatively advanced fulgoromorphan families, e.g., Fulgoridae, Dictyopharidae, Lophopidae and Eurybrachidae. It is regarded as a homologous structure with the previously described ‘multi-lobed sensillum’ in Delphacidae and is herein named ‘latero-subapical labial sensillum’. The function of the structure is not clear but it seems likely that it is a sensory structure. The phylogenetic significance of this structure is briefly discussed.