Bioacoustics of Oecanthus castaneus

Description. Male holotype . Like other species within the genus Oecanthus , it is slender-bodied and fragile (Figs 162 , 163 ). Head : weakly prognathous (Fig. 164 A ); head and pronotum with a light mid-line bordered by two thin dark lines (Fig. 164 B ); no black postocular marking; scape and pedicel with a small black spot on their ventral face (Fig. 164 A ); black dot on the scape sometimes very weak; spot on the pedicel somewhat thickened or callous. Pronotum : as wide as long, sometimes slightly wider than long (Table 8 ); saddle-shaped with ventral caudal corners of the paranotal lobes strongly curved inwards; hind margin slightly undulated, with bristles (Fig. 164 B ). Metanotal gland : metascutum and metascutellum both well-modified and of more or less equal length (Fig. 166 ); main scutal relief inverted U-shaped with slightly swollen anterior and lateral margins (Fig. 166 a ); posteriorly, with two posterad projecting flat processes, both with a tuft of long setal brushes on both sides of their apex; a deep transverse depression situated beneath the two processes; scuto-scutellar suture obtusely trapezoid (Fig. 166 b ); main scutellal relief V-shaped, smaller than the scutum (Fig. 166 c ), with a U-shaped depression in its anterior face; anterior margin of the scutellum, along the scuto-scutellar suture, with a pair of posterad, hook-like processes, bearing some setae; posterior margin of the scutellum with an obtuse angle; a median scutal tubercle is absent. Right tegmen : veins light; tegmina marked more or less extensively blackish-brown; base of the tegmina dark brown due to the infumation of the cells and margins of the veins; cells bordering the file and the plectrum intensively marked dark brown; chordal area with a large brown spot; cells in the dorsal field thinly margined brown along the veins and variably and locally marked with smooth infumation (Fig. 167 A, C ). Stridulatory file : stridulum with 54 teeth, situated on a proximally sharply raised ridge, which gradually descends to the same level as the anal vein towards the plectrum (Fig. 167 C ). Hind wings : light-coloured, apex brown, surpassing the tegmina with 2.2 mm . Legs : TI with an oval inner and outer tympanum; TI with an outer, apical, ventral spur; TII with an inner, apical, ventral spur (Fig. 164 E ). Fore- and mid-legs with scattered small black spots (Figs 162 , 163 ); FIII with thinly distributed small black spots on the lateral and dorsal outer surface and with black markings on the ventrolateral carinae (Fig. 164 C ); TIII with two outer and three inner, dorsal, subapical spurs (Fig. 164 F ), serrulated over the entire length, with small, but thick spines on the tibiae’s dorsal margins; serrulation denser in the basal than in the apical part; inner serrulation: no spine before the first subapical spur, 0 spines between the first and second spur, 1–2 spines between the second and third spur and 12–13 above the third spur; outer serrulation: 2–3 spines before the first subapical spur, 3–4 spines between the first and second spurs and 13–14 spines above the second spur; inner, apical three times shorter than inner, apical, dorsal spur; inner, apical, dorsal spur two times longer than outer, apical, dorsal spur; spurs and spines dark; ventral lobe of the hind knee dorsally lined black (Fig. 165 A ). Abdomen : cerci slightly sinuous in both the basal and apical fifth and densely covered with long hairs (Fig. 164 D ); subgenital plate with a rounded apex (Fig. 164 C ). Genitalia : Pseudepiphallic sclerite is a narrow transverse bridge that is widely U-shaped; the anterior margin is slightly curved in dorsal view. Main lobes ( MLPs .) placed on the posterior margin, more or less diamond-shaped in dorsal view, with rounded inner sides and angled outer sides; in lateral view, MLPs angled obliquely up- and backwards, resembling two triangular blades or scoops; inner space between the two main lobes slightly smaller than the width of one lobe at its base. Two widely-rounded, triangular pseudepiphallic apodemes ( Ps . Ap.) directing anteriorly. Pseudepiphallic parameres ( Ps . P.) much shorter than MLPs ., rounded apically and directed inwards. Rami long and slender; arc projecting anteriorly, with two long distal prolongations and two short ectophallic apodemes (Ec. Ap.) (Fig. 168 ). Colouration : sides of the head yellowish to orange, dorsally orange-brown to brown; eye colour orange-light reddish-brown ( in vivo ); scape and pedicel orange to orange-brown, the remaining antennomeres blackish brown; tarsi, tibiae and femora light yellow to orange-brown, gradually darkening towards the joints (Figs 162 , 163 ); abdominal tergites largely coloured dark brown with light margins (Figs 162 , 163 ); sternites light; cerci light; subgenital plate mottled brown at its base, rest light yellow. Morphometrics holotype . Body length (anterior margin labrum – apex subgenital plate): 11.7 mm ; pronotal length: 1.9 mm ; pronotal width: 2.0 mm; right tegmen length: 10.3 mm ; width dorsal field right tegmen: 3.6 mm ; total width right tegmen: 5.4 mm ; cercus length: 4.2 mm ; FIII length: 7.1 mm ; TIII length: 8.0 mm; stridulatory file length 1.4 mm ; stridulatory teeth number 54. Female. Same as male, except for the following characteristics: tegmina dark brown on the dorsal and lateral fields, translucent along the transition between the dorsal and lateral fields; due to light underwings, tegmina appear to be striped (Fig. 172 ); ovipositor short, apex denticulated; cerci slightly surpassing the apex of the ovipositor (Fig. 165 C ); subgenital plate triangular with a rounded apex. Biometrics of holo- and paratypes are shown in Table 8 .

Diagnostic notes. Oecanthus castaneus Felix & Bouwman , sp. nov. can be separated from O. chopardi by its distinctive warm appearance due to its orange-brown colours and extensive brown markings on the wings (Figs 162 , 163 ). Oecanthus chopardi is never brownish, but always uniformly whitish to pale straw, often with bright greenish tones (Fig. 173 ). Where the sides of the head, pronotum and legs are orange-brown in O. castaneus sp. nov. , they are whitish to pale straw in O. chopardi . Dorsally, the head and pronotum of O. castaneus sp. nov. are darker brown, whereas O. chopardi has greenish tones in those parts (Fig. 173 ). O. castaneus sp. nov. has almost entirely blackish-brown antennae, except for the lighter scape and pedicle, while in O. chopardi , the antennae are light and of the same colour as the body (Figs 173 , 177 ). The tegmina of O. castaneus sp. nov. are extensively marked blackish-brown, but there is variation in the extent (Fig. 167 A ). The base of the tegmina is variably dark brown and the file and the plectrum are flanked with intensive blackish markings (Fig. 167 A, C ). There is a large brown spot in the chordal area, halfway to the inner edge of the tegmina. The veins in the distal part of the dorsal field are all bordered brown, the cells are marked with infumated spots and the wing’s apex is heavily infumated (Fig. 167 A ). In O. chopardi , the tegmina are translucent white to greenish, with only two small dark markings, one on the distal part of the file bordering the plectrum and a smaller one in the chordal area (Fig. 167 B ). The tegmina in male O. castaneus sp. nov. are slightly narrower and shorter than O. chopardi (Table 8 ; Fig. 167 ); in females, they are at least shorter (width not measured). The female cerci and ovipositor of O. castaneus sp. nov. are shorter (<4.0 mm and < 4.5 mm , respectively) than in O. chopardi (> 4.5 mm and> 5.0 mm, respectively) (Table 8 ; Fig. 165 ). In O. castaneus sp. nov. , both inner and outer ventral lobes of the hind knee are lined black dorsally (Fig. 165 A ), whereas, in O. chopardi , they are only tipped black (Fig. 165 B ). The female subgenital plate of O. castaneus sp. nov. is triangular with an obtuse apex; in O. chopardi , it is more trapezoid with a broadly rounded to truncated apex. The metanotum of both species does not differ markedly, which is a common phenomenon in closely-related species ( Walker and Gurney 1967 ). Character Sex O. castaneus sp. nov. O. chopardi Body length Male 11.2 (9.6–11.7; n = 8) 11.3 (11.2–11.4; n = 2) Female 10.9 (9.5–11.8; n = 3) 11.8 (11.2–12.4; n = 2) Pronotal length Male 1.8 (1.6–1.9; n = 12) 1.9 (1.8–2.0; n = 3) Female 1.8 (1.6–1.9; n = 8) 1.9 (1.8–2.0; n = 5) Pronotal width Male 1.9 (1.7–2.1; n = 12) 1.9 (1.8–2.0; n = 3) Female 1.8 (1.6–1.9; n = 8) 1.9 (1.9–2.1; n = 5) Cercus length Male 3.7 (3.3–4.2; n = 8) 4.3 (3.4–4.9; n = 3) Female 3.8 * (3.5–4.0; n = 3) 5.1 * (4.4–5.6; n = 5) Tegmen length (right) Male 9.7 * (8.9–10.5; n = 14) 10.9 * (10.6–11.2; n = 5) Female 10.0 * (9.4–10.7; n = 8) 11.6 * (11.3–12.0; n = 5) Tegmen width dorsal field (right) Male 3.3 * (2.9–3.7; n = 14) 4.0 * (3.9–4.0; n = 5) Tegmen total wdth (right) Male 5.1 * (4.8–5.2; n = 7) 6.0 * (5.7–6.3; n = 4) Stridulatory file length (right) Male 1.4 (1.3–1.4; n = 8) 1.7 (n = 3) Stridulatory teeth number (right) Male 50 (45–54; n = 7) 59 (n = 1) FIII length Male 6.8 (5.9–7.3; n = 13) 7.1 (6.9–7.4; n = 4) Female 6.7 (6.3–7.1; n = 8) 7.7 (7.4–8.0; n = 5) Ovipositor length Female 4.1 * (3.9–4.3; n = 8) 5.4 * (5.1–5.7; n = 5) The stridulatory file in O. castaneus sp. nov. is straight with 45–54 teeth (Fig. 167 C ). The only studied specimen of O. chopardi has 59 teeth (Table 8 ) and a slightly more sinuous file (Fig. 167 D ). The pseudepiphallic sclerite in O. castaneus sp. nov. forms a transverse, narrow bridge with a slightly curved anterior margin in the dorsal view (Fig. 168 A ). In O. chopardi , the transverse bridge is broader and the anterior margin is almost straight in dorsal view (Fig. 168 B ). The main lobes of the pseudepiphallus differ slightly between both species. In O. castaneus sp. nov. , the two lobes point more directly caudal and are somewhat slender, while in O. chopardi , the lobes curve more inwards and are somewhat coarser with a broader base (Fig. 168 ). O. castaneus sp. nov. is distinguished from the following three species of Oecanthus known from the Arabian Peninsula: O. pellucens (Scopoli, 1763) , O. dulcisonans Gorochov, 1993 and O. turanicus Uvarov, 1912 . These three species have a median scutal tubercle, a TIII with 5–6 pairs of subapical spurs and no ventral apical spurs on TI or TII . These species lack the dark markings on the tegmina and the diagnostic colouration of O. castaneus sp. nov. ; they all are pale, plain straw-coloured or greenish. O. dulcisonans and O. turanicus are significantly larger ( 14–17 mm in males).