Antennal sensory structures in water bugs of Nepoidea (Insecta: Hemiptera: Nepomorpha), their morphology and function

The Nepoidea superfamily belongs to the water bugs' infraorder (Nepomorpha) and consists of two families-Belostomatidae and Nepidae. Species from those families are the largest of all nepomorphans and are considered to be top predators in aquatic ecosystems. A characteristic feature of the group is the existence of short antennae concealed in grooves behind the eyes, which is an adaptation to the water habitat. The antennae bear many types of sensillar structures, which receive signals from the environment. Among such structures, mechanosensilla were of the greatest diversity. The antennal sensilla of species from both families were examined under the scanning electron microscope. 11 essential morphological types of sensilla were distinguished, including 5 new mechanosensilla types (sensilla paddle-like, cone-like, squamiformia, brush-like and club-like). Basal types of mechanosensilla such as trichodea, chaetica, basiconica (subtype 1) and campaniformia occur in Nepoidea and other Heteroptera. In some representatives of both families, sensilla paddle-like and sensilla basiconica type 1 were observed. Moreover, sensilla chaetica and cone-like were found in some species of Belostomatidae, whereas in Nepidae sensilla squamiformia, brush-like and club-like were observed. Apart from mechanosensilla, one type of thermo-hygrosensilla (ampullacea) and two different shaped olfactory sensilla basiconica (subtypes 2, 3) and coeloconica (subtypes 1, 2, 3) were found. It could indicate sensilla use in the identification of the water reservoirs and locating prey.