Bioacoustics of Anisops sardeus

Morphology – As the genus Anisops is not included in the keys used frequently for identification of aquatic Heteroptera in Hungary and Central Europe, we give a short morphological description of the genus and the species. Prima facie, Anisops adult looks like a Notonecta larva, but Anisops specimens are much more slender in every developmental stage than those of Notonecta . Body length of European Anisops species is 4.8–8.4 mm , body width is 1.3–2.0 mm, body shape is elongated, laterally slightly flattened. The most conspicuous descriptive marks, which separate Anisops species from all genera in the family Notonectidae are (1) the hemielytral pit which can be seen behind the posterior edge of the scutellum, in the suture of the hemielytra; (2) extension of the ventral abdominal keel onto the last abdominal segment; and (3) one-segmented front tarsi of the males. Genital capsulae of Anisops species are asymmetrical, but symmetrical in the case of Notonecta . The species of the genus could be identified by the following features: (1) length and width of the body, (2) distances between the eyes measured at anterior and posterior edges of the eyes, and proportion of these distances, (3) shape of the 3rd and 4th rostral segments of the males, and (4) characteristics of the stridulatory combs on the femur of the front legs of the males. Genital parts do not play crucial role in the identification procedure on the species level ( BROOKS 1951 ). Anisops sardeus is the largest among the European species (body length of males 7.5–8.4 mm , females 7.2–7.5 mm , maximum width of males 1.8–1.9 mm , females 1.9–2.0 mm). Head is yellow coloured with brown eyes. Hemielytra are transparent, but their colour are defined by the colour of the underlying body parts, so it appears to be yellow, just like the whole dorsal side of the body. Ventral surface is brown or black. Legs are yellow. In males of A. sardeus , the front edge of the head is conically protruded; it is clearly visible in dorsal or lateral view. The initial form of this protrusion can be seen also in the older larval stages. The head of the females is rounded ( BROOKS 1951 ).