Pteronemobius Jacobson, 1904

Hegg, Danilo, 2024, Small crickets of New Zealand (Orthoptera: Grylloidea: Trigonidiidae and Mogoplistidae), with the description of two new genera and species, European Journal of Taxonomy 955 (1), pp. 1-87 : 17-19

Identification of species in the genus Pteronemobius Jacobson, 1904

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.

Figures

Fig. 1. Nomenclature and abbreviations in cricket body parts. A. Hind leg, inner view of tibia and tarsus in Trigonidiidae. Labelling of spurs after Desutter-Grandcolas et al. (2016: fig. 8d). ‘i’ is for ‘inner’ in all abbreviations and is replaced by ‘o’ for outer in the opposite view, not shown. B. Dorsal view of right forewing in ground cricket (subfamily Nemobiinae). Labelling of wing veins after Josse et al. (2023). C. Dorsal view of head. D. Lateral view of ovipositor. E. Tympanum on right Tibia I (rear facing).

Fig. 23. Pteronemobius truncatus (Saussure, 1877). A–B. Lateral and frontal view of head, adult ♀. Herangi Range (MPN OR0219). C. Glandular sub-apical spur (tsai4) on dorsal inner edge of tibia III in adult ♂. Cambridge, Waikato (MPN OR0214). D. Left hindwing in female, dorsal view. Cambridge, Waikato (MPN OR0346). E. Egg. Coromandel (MPN OR0397). F–G. Apex of ovipositor. Herangi Range (MPN OR0219). F. Dorsal view. G. Lateral view. H. Ovipositor, lateral view. Cambridge, Waikato (MPN OR0204). Scale bars = 500 μm.

Fig. 25. Pteronemobius cf.arima Otte &Alexander, 1983. A–B. Lateral and frontal view of head, adult♀. A. Spirits Bay, Northland (MPN OR0248). B. Kerikeri, Northland (MPN OR0223). C. Glandular subapical spur (tsai4) on dorsal inner edge of tibia III in adult ♂. Kerikeri (MPN OR0234). D. Egg. Maitai Bay, Northland (MPN OR0366). E–F. Apex of ovipositor. Spirits Bay (MPN OR0248). E. Dorsal view. F. Lateral view. G. Ovipositor, lateral view. Kerikeri (MPN OR0225). Scale bars = 500 μm.

Fig. 5. Comparing the song of Pteronemobius truncatus (Saussure, 1877) and of P. tarrios Otte & Alexander, 1983. Data from Otte & Alexander (1983) and from this study. A. Pulse rate as a function of air temperature. B. Peak frequency as a function of air temperature.

Fig. 6. Morphometric measurements for the New Zealand species of Pteronemobius Jacobson, 1904. This figure replicates Otte & Alexander (1983: fig. 129). Measurements for the Australian specimens of P. truncatus (Saussure, 1877) and of P. arima Otte & Alexander, 1983 were extracted from Otte & Alexander (1983). Measurements for the New Zealand specimens of P. truncatus and of P. cf. arima are from the materials examined in this study. A. Relationship between pronotum length and hind femur length in males of Pteronemobius (Otte & Alexander 1983: fig. 129a–b). B. Relationship between ovipositor length and hind femur length in females of Pteronemobius (Otte & Alexander 1983: fig. 129c).

Fig. 8. Dorsal view of the right forewing in the New Zealand species of Pteronemobius Jacobson, 1904. A–B. Pteronemobius truncatus (Saussure, 1877). A. Drawing from Otte & Alexander (1983: fig. 132b). B. Kohuroanaki Loop Track, Te Paki (MPN OR0197). C. Pteronemobius arima Otte & Alexander, 1983. Drawing from Otte & Alexander (1983: fig. 132m). D. Pteronemobius cf. arima Otte & Alexander, 1983. Maitai Bay, Karikari Peninsula, Northland (MPN OR0246). Scale bars = 1 mm.

Fig. 26. Pteronemobius cf. arima Otte & Alexander, 1983 song, recorded in the field at 18°C. Maitai Bay, Karikari Peninsula. A. Spectrogram of a sequence of six chirps. B. Oscillogram of a sequence of six chirps. C. Oscillogram of one chirp consisting of eleven pulses. D. Power spectrum of one chirp.

Fig. 7. Morphometric measurements for the New Zealand species of Pteronemobius Jacobson, 1904. In all graphs, orange shapes indicate P. cf. arima Otte & Alexander, 1983; yellow shapes indicate P. truncatus (Saussure, 1877). Both sexes are included unless stated otherwise. A. Boxplot of the ratio of the short and long diagonals in the right male forewing’s posterior cell of the harp (see Fig. 1B). The whiskers include the minimum and maximum values. B. Stridulatory file in male cricket’s right forewing. C. Dimensions of male cricket’s right forewing (Fig. 1B). D. Body length vs ovipositor length (Fig. 1D). E. Major vs minor axis of tympanum (Fig. 1E). For each cricket, the measurements of both left and right tympana are included. F. Length of middle vs dorsal inner apical spurs on tibia III (Fig. 1A).

Fig. 24. Pteronemobius truncatus (Saussure, 1877) song, recorded in the field at 24°C. Mangonui, Northland. A. Spectrogram of a sequence of five thrills. B. Oscillogram of a sequence of five thrills. C. Oscillogram of one thrill consisting of 48 pulses. D. Power spectrum of one thrill.