The metathoracic scent gland system in Hydrocorisae (Heteroptera: Nepomorpha)

Abstract. The metathoracic scent gland system is a basic feature of the order Heteroptera. It occurs widely not only in the terrestrial forms (Geocorisae) and water-surface bugs (Amphibicorisae) but also in the totally aquatic bugs (Hydrocorisae) and their littoral relatives (Ochteridae, Gelastocoridae). In Hydrocorisae the metathoracic scent gland conforms to Carayon's (1971) omphalian type (orifice median and undivided or, if divided, orifices close together towards the mid-ventral line) but shows marked differences in structure and physiological function between species from different families. There is taxonomic interest in the distribution of the three distinctly different types of metathoracic occlusion apparatus. Naucoridae and Belostomatidae have a median lip-valve, Notonectidae and Gelastocoridae a pair of stop-valves, Corixidae a median flap-valve. The valve opener muscles are usually dorso-ventral but are ventral in Corixidae; the cuticular microsculpture in the metathoracic efferent system specifically in Hydrocorisae with stop-valves (Notonectidae, Gelastocoridae) is similar to that widely present in Geocorisae. Groupings of Hydrocorisae from variations in the metathoracic occlusion apparatus differ from others based upon variations in the chemical constitution of the secretions. It is considered that the facts now known on metathoracic scent gland structure and function accord well with the hypothesis that Hydrocorisae constitute a polyphyletic assemblage.