Scanning Electron Microscopy of Antennae and Mouthparts of Mezira yunnana Hsiao (Hemiptera: Aradidae): Specialized Microstructures Reflecting Adaptation to Mycetophagy.

Simple Summary: Antennae and mouthparts are key organs for food searching and feeding in insects. In the present study, the microstructures of the antennae and mouthparts of the flat bugs Mezira yunnana Hsiao were demonstrated. Five types of antennal sensilla and three types of labial sensilla were documented. Labial tip gustatory sensilla form a small group of only three pairs, which is essentially different in this species from other true bugs. The labial tip is constricted distally, which is rarely observed in other pentatomomorphans. Teeth on the external surface of the mandibular apex are ridge-like and uniform. These characteristics may be associated with the species' unique fungi-feeding habit. Many species of the family Aradidae (also known as flat bugs) feed on fungal mycelia and fruiting bodies. In order to better understand the morphological adaptation to this unique feeding habit, we examined the microstructure of antennae and mouthparts of an aradid species, Mezira yunnana Hsiao, using scanning electron microscope, and documented the fungal feeding process under laboratory conditions. The antennal sensilla include three subtypes of sensilla trichodea, three subtypes of sensilla basiconica, two subtypes of sensilla chaetica, sensilla campaniformia, and sensilla styloconica. The apex of the second segment of flagellum has a large number of various sensilla forming a sensilla cluster. The labial tip is distally constricted, which is rarely observed in other Pentatomomorpha species. The labial sensilla include three subtypes of sensilla trichodea, three subtypes of sensilla basiconica, and a sensilla campaniformia. The tip of the labium has only three pairs of sensilla basiconica III and small comb-shaped cuticular processes. The external surface of the mandibular apex has 8–10 ridge-like central teeth. A series of key morphological structures associated with mycetophagous feeding habit were identified, which will facilitate future studies on adaptive evolution of species in Pentatomomorpha as well as in other heteropteran lineages. [ABSTRACT FROM AUTHOR]