Bioacoustics of Yoyetta australicta

Description of adult male ( Plates 1A, 1B, 1E, 1F, 1I ; Figs 2–6 ). Head almost as wide as lateral margins of pronotum; mostly black with a yellow triangular marking between lateral ocelli, with flat edge on posterior margin; two similar, smaller markings between lateral ocelli and adjacent compound eyes, these sometimes reaching posterior margin; supra-antennal plates black, occasionally edged dull orange; ocelli pale brown; postclypeus black, inner dorsal surface with a dull yellow longitudinal marking, ventral surface with orange lateral margins; anteclypeus shiny black; rostrum reaching bases of hind coxae, mostly brown basally becoming black apically; antennae black. Thorax mostly black (rarely dark brown). Pronotum with a narrow yellow fascia along midline surrounded extensively by black; interior of pronotum brown to dark brown, with irregular black areas, especially along paramedian and lateral fissures; pronotal collar black on anterior margin, dark brown over remainder. Mesonotum black sometimes with subtle areas of dark brown coloration along parapsidal sutures; cruciform elevation pale brown to pale orange-brown apart from a broad black midline and black anterior arms; scutal depressions black, surrounded posteriorly by orange colouration in some specimens; wing grooves mainly dark orange-brown suffused with black. Metanotum dull orange suffused with black. Thorax below mainly black with leg cavities bordered dull orangebrown. Legs mainly black with dull orange markings. Fore and mid coxae black, edges dull orange; hind coxae black with orange apex; fore femora with inner surface shiny black, outer surface dull orange with a black longitudinal marking, femoral spines and surrounds black; mid and hind femora black with dull orange along outer edges; fore tibiae black; mid tibiae dark orange brown to black; hind tibiae orange-brown with weak dark-brown to black markings; tarsi orange-brown to dark orange-brown; meracantha black on basal half, pale brown apically, overlapping anterior margin of opercula. Wings with fore wing costal margin a mixture of orange-brown and dark orange-brown to black; CuP+1A pale brown adjacent to basal cell; all other venation dark brown to black; basal membrane light orange-brown to pink. Hindwing venation dark brown; plagas and adjacent area surrounding vein 3a light brown to orange-brown. Opercula ( Figs 2A, 2B ) broadly rounded, with each plate narrowing slightly towards apex, sometimes with flat posterior edge; black basally, plates grey; each 2.0– 2.8 mm wide. Timbals ( Figs 3A, 3B ) with five long ribs all attached to basal spur, separated from the anterior cuticle and separated ventrally; long ribs 1–4 spanning the timbal membrane, long rib 5 shorter, occupying dorsal half of timbal only, about equal in width (thickness) to adjacent long rib 4; timbal plate with well developed, elongate dome bearing a distinct point of apodeme attachment near centre. Abdomen with tergite 1 black; tergite 2 predominantly black, sometimes with diffuse dark orange areas sublaterally on posterior margin, curved to follow outer margin of exposed timbals, tergites 3–7 predominantly orange each with a black mark on dorsal midline, this mark being broadest on tergite 3 and narrowing on each subsequent tergite towards the posterior, sometimes also with diffuse black mixed with orange-brown along posterior margins; tergite 8 black except for orange on anterior lateral margins. Sternite I mainly dull orange; sternite II orange suffused with black medially and laterally; sternites III–VI orange, sometimes each with a faded, black spot on the midline; sternite VII orange with a small, diffuse black spot at centre of posterior margin; sternite VIII dark brown becoming brown or orange-brown apically. Genitalia ( Figs 4A, 4B , 5 , 6 ) with pygofer upper lobe of moderate size, gradually tapering to a broadly rounded apex; basal pygofer lobe small and weakly developed, broadly rounded; median lobe of uncus short, not as long as the distance between the apices of the upper pygofer lobe and dorsal beak, ‘duck-bill’ shaped; claspers robust, clawlike, partially meeting, in ventral view their inner margins diverging and their outer margins gently turned outwards; aedeagus with theca recurved distally through 180 degrees, the vesica widening with serrated ventrolateral flanges subapically, these narrow and become folded with teeth directed dorsally towards apex, apex terminating in a sharp spine, weakly upturned, lacking a pair of upright basal lobes; pseudoparameres long, almost reaching most distal part of theca, slender, hair-like and slightly bulbous apically. Description of adult female ( Plates 1C, 1D, 1J ). Similar to male but differing as follows. Abdomen appears orange suffused with black. Tergite 1 mainly black with dark orange areas sublaterally; tergite 2 black suffused with orange laterally, black medially with two orange markings either side of submedially; tergites 3–8 orange suffused with black, with a continuous, broad, and black dorsal midline, the black protruding laterally along posterior margins, each tergite with a sublateral black spot. Sternite II predominantly black; sternites III–VIII orange; sternite VIII with black wedge-shaped markings adjacent to midline. Abdominal segment 9 pale orangebrown on midline, orange-brown on anterior half of lateral sides, black over remainder. Ovipositor sheath black, extending less than 0.5 mm beyond apex of abdominal segment 9. Measurements (in mm; range with mean in parentheses for 30 males and 16 females , including smallest and largest specimens). Length of body including head : male 18.0–22.2 (20.49); female 17.9–22.3 (20.40). Length of fore wing : male 19.7–25.8 (23.86); female 22.5–29.6 (26.04). Width of fore wing : male 7.1–9.0 (8.29); female 7.4– 9.5 (8.61). Width of head (including eyes) : male 5.0–6.0 (5.41); female 5.4–6.5 (5.86). Width of pronotum (across lateral angles) : male 4.9–6.6 (5.63); female 5.3–7.3 (6.41). Width of abdomen : male 5.3–6.7 (5.77); female 5.0–7.1 (56.03). Length of ovipositor : female 4.5–7.2 (5.90). Morphological variation within and between populations . This species occurs in two geographically disjunct populations (one in South Australia and one in New South Wales / Australian Capital Territory ). Separate sets of morphological diagrams were prepared for each of the populations during this study. Both sets have been included to provide an indication of consistency between the populations (e.g. in structure of aedeagus). Some differences can be seen in the size and shape of the opercula ( Fig. 2A , cf. 2B). The differences were found to be within the bounds of normal variation in opercula size and shape among individuals within and between populations and no consistent differences were found between the disjunct populations. Some differences are also evident in the ventral pygofer ( Fig. 5B , cf. Fig. 6B ). However, in this case, the differences are an artefact of differences in the position of the pygofer when it was drawn (the pygofer in Fig. 6B directed was positioned slightly more ventrally than the same structure in Fig. 5B , which appears more upright). Morphological distinguishing features . Males of Y. australicta n. sp. can be distinguished from other species in the Y. tristrigata species group by the following combination of characters: (1) median lobe of uncus short, not as long as the distance between the apices of the upper pygofer lobe and dorsal beak; (2) head width ≥ 5 mm ; (3) timbal with five long ribs, all separate from anterior cuticle and surrounded by pale timbal membrane; (4) timbal long rib 5 about equal in width (thickness) to adjacent long rib 4 (though shorter in length); (5) thorax mainly black; (6) tergite 2 mainly black; (7) opercula each ≥2.0mm wide; (8) apex of theca produced as a long spine with ornamentation and without a pair of upright basal lobes; (9) theca recurved distally through 180 degrees; and (10) apex of theca weakly upturned. Females can be distinguished from most other species in the Y. tristrigata species group by having the following combination of characters: (1) thorax mainly black; (2) tergites predominantly orange; (3) fore wing length> 22 mm ; (3) head width> 5.2 mm . They may be impossible to distinguish from specimens of Y. delicata n. sp. and Y. repetens , although none of these species have been found co-occurring. Larger female specimens of Y. australicta n. sp. from South Australia (with fore wing length> 27 mm ) may also be indistinguishable from larger examples of Y. ignita n. sp. ; however, Y. ignita n. sp. does not occur in South Australia . Calling song ( Figs 7 , 8 ). The male calling song of Y. australicta n. sp. is produced mainly in flight. However, like many other flying and calling species in the genus Yoyetta , males may also call whilst sitting on a branch or trunk (usually on a Eucalyptus sp. tree). Irrespective of whether an individual is flying or stationary, the calling song is composed of simple, repetitive ticking. Detailed examination of the song structure reveals that each ‘tick’ has a single, dominant pulse, with weaker subsequent peaks possibly an artefact of reflections of the dominant pulse on surrounding structures in the environment ( Figs 7 , 8 ). Gaps between pulses range from 0.27– 0.67 s . The ticking rate ranges from slow in cool conditions to moderate in warm to hot conditions (1.5–3.8 pulses/s). It may vary between individual insects under the same conditions depending on the extent to which they have ‘warmed up’ (LWP, pers. obs. ). When stationary, within a single tree, groups of males tend to call in unison or almost in unison. Simulated attraction of males by finger snapping indicates that females respond to the male call using carefully timed wingflicks immediately following each pulse. Most observations of calling behaviour in this species have been made in the Australian Capital Territory (ACT) and in South Australia . In the ACT, the stationary males have been observed producing a quiet macrosyllable at the end of a short bout of ticking; however, this has never been recorded. This attribute has not been observed in the South Australian population. As with most single pulse calls with high energy, the frequency band is broad, extending from approximately 8–12 kHz ( Figs 7 , 8 ). A pronounced highest amplitude dominant frequency is apparent between 10 and 11 kHz ( Figs 7 , 8 ). This is the first species in the genus Yoyetta to be described with a repeated, single pulse call. Notably, Y. landsboroughi and Y. nigrimontana produce calls with a similar, clearly defined pulse structure, though in these two species, the pulses are grouped.