Bioacoustics of Pteronemobius

Diagnosis Highly variable in size, from small to relatively large ground crickets, with a body length between 4 mm and 9 mm depending on species; coloration variegated light to dark brown. Forewings fully developed in both sexes and exceeding the combined length of head and pronotum. Twenty-five to forty percent of females have short forewings ( Fig. 28B, F ); 20% to 25% have long forewings ( Fig. 28C, E ). Hindwings are present in up to 40% of individuals in both sexes ( Fig. 28C, F ). Stridulatory apparatus complete. Tympana present on posterior side of Tibia I. Tibia III with three or four outer and four inner subapical spurs in both sexes, alternate. The fourth inner subapical spur in males is small, glandular ( Figs 23C , 25C ). Length of Tibia III outer ventral apical spur approx. 80% that of ventral inner apical spur. Length of Tarsomere III-1 outer apical spur approx. 50% to 60% that of inner apical spur.

Out of 368 crickets examined, 99 fit the diagnosis for the genus Pteronemobius ( Otte & Alexander 1983 ; Rentz & Su 2019 ). The genus is easily recognizable because of the presence of a short, thickened, conical sub-apical spur (tsai4) on the dorsal inner edge of tibia III in males ( Figs 1A , 23C , 25C ). Out of 99 crickets in the genus Pteronemobius , 49 fit the description of P. truncatus / tarrios based on morphology, as previously identified by Messenger (1991) . It should be noted that the two species P. truncatus and P. tarrios can only be separated from one another based on their song, not by their morphology ( Otte & Alexander 1983 ). Even their songs are deceptively similar, and are distinguished mainly by the pulse rate, which is faster in P. truncatus (40 to 65 Hz), slower in P. tarrios (30 to 40 Hz) in temperature ranges typical for Australia ( Otte & Alexander 1983 ) ( Fig. 5 ). Based on analysis of the song, the New Zealand specimens are assigned to the species P. truncatus (see Table 5 , Fig. 5 ). The remaining 50 specimens of Pteronemobius fit the description of P. arima Otte & Alexander, 1983 based on morphology ( Figs 6 , 8 ). This species had never been detected in New Zealand before. The original species description by Otte & Alexander (1983) does not include a drawing of the genitalia, or a spectrogram of the song. Rentz & Su (2019) identified P. arima and a closely related taxon they treated as “ Pteronemobius sp. near arima ” and presented a spectrogram of the song for both. According to Rentz & Su (2019) , P. arima sings at a frequency of 7 kHz and produces short chirps ( 0.1 s to 0.2 s ) separated by intervals of 0.5 s or longer, whereas “ Pteronemobius sp. near arima ” sings at a frequency of 5.5 kHz and produces longer chirps ( 0.5 s ) separated by shorter intervals ( 0.15 s ). No temperature data are given for either of the above recordings. My recordings (T = 18°C) show chirps with duration and interval in between the two above taxa, and a frequency that matches that of P. arima ( Table 6 ; Fig. 26 ). To complicate things further, two adult male specimens of P. arima I collected at Oxley Creek Commons in Brisbane, Queensland, in November 2023 are identical to the New Zealand specimens in their measurements, but different in four morphological traits. The two Australian specimens are (1) darker in colour, almost entirely black; (2) have shiny forewings, not textured or wrinkled; (3) have a different wing geometry, with PCSD / PCLD values of 0.586 and 0.610, compared to a range between 0.665 and 0.796 in New Zealand specimens; and (4) have a stridulatory file that stops short of the harp vein. While Brisbane falls within the geographic distribution range for P. arima indicated by Otte & Alexander (1983) , it is a long way away from the type locality in the Northern Territory. Based on the information available, I suggest that Pteronemobius arima Otte & Alexander, 1983 might be a species complex rather than a single species. I am not comfortable assigning the New Zealand specimens to P. arima without the examination of additional reference material from the species type locality. I therefore refer to the New Zealand taxon as Pteronemobius cf. arima Otte & Alexander, 1983 , where the abbreviation ‘cf.’ is used as suggested by Sigovini et al. (2016) . The two New Zealand species of Pteronemobius are easily separated by size, P. truncatus being nearly double the size of P. cf. arima in all dimensions ( Table 6 ; Fig. 7 ). The wing structure ( Fig. 8 ) and texture are also different; the forewings of P. truncatus are shiny and reflect light like a mirror, whereas the forewings of P. cf. arima are wrinkled and textured and matt in their look. The songs differ mainly in the length of the chirp ( Figs 24 , 26 ) and in the sound volume, the call of P. cf. arima being a mere whisper that is easily overheard and very hard to record in the field.