Isoplectron pallidum ( Richards, 1972 ) Hegg & Morgan-Richards & Trewick, 2024

Hegg, Danilo, Morgan-Richards, Mary & Trewick, Steven A., 2024, Revision of the New Zealand cave wētā genus Isoplectron Hutton (Orthoptera: Rhaphidophoridae), with synonymy of Petrotettix Richards and Setascutum Richards, and the description of a new genus, European Journal of Taxonomy 971, pp. 1-75 : 39-41

Isoplectron pallidum ( Richards, 1972) comb. nov.

Figs 1A–B , 3 , 6 , 8 , 10H , 12I , 13D , 14J–L , 17J–L , 20A–B , 22A

Setascutum pallidum Richards, 1972: 165–166 , fig. 6.1–6.3.

Setascutum pallidum – Hegg et al. 2022: 4, fig. 1A.

Diagnosis

The smallest species in the genus Isoplectron , I. pallidum has a body length between 8 and 13 mm, the hind tibiae slightly longer than the body in males.

Throughout its distribution range, I. pallidum is sympatric with I. armatum and with Praecantrix silvatica gen. et sp. nov.; indeed, we have found all three species on the same tree trunk. Similar in its look to I. armatum , I. pallidum is most reliably differentiated from the two species listed above by the presence of dorsal linear spines on the first and second hind tarsal segments.

In the Kakanui Mountains and in the St Marys Range in North Otago, I. pallidum is also sympatric with Praecantrix saxicola gen. et sp. nov. In spite of what the name might suggest, the latter species is in fact the one that is reliably identified by its pale colour. The two species also tend to occupy different microhabitats, with I. pallidum most commonly found on rock bluffs, P. saxicola among scree. We have, however, found the two species on the same bluff.

Etymology

‘ Pallĭdus ’ (adj.) is Latin for ‘pale’. Named by Richards (1972) because of the pale coloration of the single specimen she examined. The name is somewhat misleading within this genus.

Material examined (see also Supp. file 1: Table S4 and Fig. S6 )

Holotype

NEW ZEALAND • ♀, adult; Central Otago (CO), Duffers Saddle, Old Woman Range ; 45.1689° S, 169.0757° E; 1250 m a.s.l.; 12 Sep. 1968; J.S. Dugdale leg.; in crevice on rock tor; NZAC 03015582 .

Representative male

NEW ZEALAND • ♂, adult; Dunedin (DN), Staircase Hut track, Waianakarua River; 45.28210° S, 170.69724° E; 400 m a.s.l.; 3 Sep. 2016; D. Hegg leg.; on tree trunk; night search; NMNZ AI.071891 .

Other material

NEW ZEALAND – Dunedin (DN) • 1 ♀; same data as for representative male; GenBank : PP155125; MPN CW3163 • 1 ♀; Mt Cargill, Dunedin ; 45.81242° S, 170.55488° E; 620 m a.s.l.; 22 Nov. 2016 ;

D. Hegg leg.; on rocky outcrop; night search; GenBank: PP155123; MPN CW3448 • 1 ♂; same data as for preceding; MPN CW5605 • 1 ♀; same data as for preceding; MPN CW5604 . – Central Otago (CO) • 1 ♂; same data as for holotype; 26 Nov. 2016; D. Hegg leg.; in crevice on rock tor; night search + insect net; GenBank: PP155122; MPN CW3486 • 1 ♂; same data as for holotype; MPN CW3488 • 1 ♀; same data as for preceding; MPN CW3487 • 2 nymphs; same data as for preceding; MPN CW3458 , CW3485 • 4 ♂♂; same data as for preceding; 7 May 2017; MPN CW5384 to CW5387 • 3 ♀♀; same data as for preceding; MPN CW3439 to CW3441 • 1 nymph; same data as for preceding; MPN CW3442 • 1 ♂; Nevis Road ; 45.16186° S, 169.10122° E; 1120 m a.s.l.; 26 Nov. 2016; D. Hegg leg.; in crevice on rock tor; night search + insect net; MPN CW5383 • 1 ♀; same data as for preceding; MPN CW5382 • 1 nymph; Mt Rosa Track , Queenstown; 45.045° S, 168.963° E; 30 Nov. 2006; L. Cook and P. Johns leg.; in wētā motel; MPN CW703 • 2 nymphs; Nevis Bluff ; 45.042° S, 169.012° E; 400 m a.s.l.; Nov. 2009; M. McDonald leg.; MPN CW1040 , CW1042 • 1 ♂; Alexandra ; 45.256° S, 169.404° E; 250 m a.s.l.; Dec. 2013; T. Jewell leg.; on rock tor; GenBank: PP155121; MPN CW2577 • 1 ♂; same data as for preceding; MPN CW2578 • 1 ♀; same data as for preceding; MPN CW2579 • 1 nymph; Earnscleugh Tailings Reserve , Alexandra; 45.24230° S, 169.36039° E; 130 m a.s.l.; 18 Nov. 2022; D. Hegg leg.; on willow tree next to river; night search + insect net; GenBank: PP155124; MPN CW5553 • 1 ♂; Sutton Salt Lake , Middlemarch; 45.57555° S, 170.08818° E; 250 m a.s.l.; 23 Feb. 2021; D. Hegg leg.; on rock tor; night search + insect net; MPN CW5603 • 1 ♀; same data as for preceding; MPN CW5602 • 2 nymphs; same data as for preceding; MPN CW5209 , CW5210 • 1 ♀; Danseys Pass Road ; 44.96188° S, 170.32864° E; 650 m a.s.l.; 7 May 2016; D. Hegg leg.; on rock slabs at edge of river; night search + insect net; GenBank: PP155127; MPN CW3014 • 2 nymphs; same data as for preceding; MPN CW3015 , CW3016 • 1 ♂; Mt Kyeburn , Danseys Pass; 44.95412° S, 170.31028° E; 1160 m a.s.l.; 16 Jan. 2017; D. Hegg leg.; on rock bluffs; night search + insect net; GenBank: PP155128; MPN CW3456 • 2 ♀♀; same data as for preceding; MPN CW4231 , CW4245 • 1 ♀; Mt Kyeburn , Danseys Pass; 44.95466° S, 170.31002° E; 1120 m a.s.l.; 16 Apr. 2017; D. Hegg leg.; on rock bluffs; night search + insect net; GenBank: PP155126; MPN CW3455 • 1 ♂, 1 ♀; same data as for preceding; MPN CW4246 , CW4247 • 5 ♂♂; Crown Range Road ; 44.98128° S, 168.94333° E; 980 m a.s.l.; 14 Nov. 2020; D. Hegg leg.; on rock tor; night search + insect net; MPN CW5560 to CW5563 , CW5601 • 1 ♂; Bendigo ; 44.96156° S, 169.28727° E; 330 m a.s.l.; 4 Jun. 2023; D. van der Westhuizen leg.; sparse rocks; casual find; MPN CW5637 . – Central Otago / Otago Lakes (CO / OL) • 1 ♂; Jollies Hill Pass ; 45.57260° S, 168.50332° E; 400 m a.s.l.; 28 Aug. 2020; D. Hegg leg.; on pine tree trunk in highway rest area; casual find; MPN CW5113 . – Otago Lakes (OL) • 2 nymphs; Skippers Canyon ; 44.892° S, 168.676° E; Nov. 2009; M. McDonald leg.; MPN CW1041 , CW1043 • 1 ♂; Mt Iron , Wānaka; 44.69332° S, 169.16855° E; 320 m a.s.l.; 12 Oct. 2018; D. Hegg leg.; on tree trunk; night search + insect net; MPN CW4975 • 1 ♀; same data as for preceding; MPN CW4974 .

Description

MEASUREMENTS. See Table 1. No sexual dimorphism in body length.

HEAD. As per generic description. Vertex mottled dark brown with pale patches. Black streaks run from the posterior margin of each eye to the pronotum, resembling the temples in a pair of sun-glasses. Frons pale, with broad, irregular, dark vertical stripes below the scapes of the antennae. Scapes and pedicels of antennae pale mottled cream and brown. All other segments of the antennae are reddish.

THORAX. As per generic description. The pronotum, mesonotum and metanotum are typically coloured brown to dark brown, with elaborate patterns and pale patches on the two posterior segments ( Fig. 22A ). A pale colour band running through the whole length of the body is also common ( Fig. 12I ).

LEGS. Fore and mid femora approximately half as long as body. Hind tibiae same length as body in females, on average 15% longer than body in males. Fore femora always unarmed at the apex. Mid femora armed with one retrolateral spine at the apex; prolateral apical spine absent. Hind femora armed with one to three retrolateral ventral linear spines, and up to three prolateral ventral linear spines. A conspicuous spine on the posterior lower margin of the hind femur is often present, but is never as large as in adult male I. armatum . Fore tibiae armed with two pairs of ventral linear spines, and with one pair of ventral apical spines. A retrolateral dorsal spine at the apex of the fore tibia is rarely present. Mid tibiae armed with two pairs of ventral linear spines, one pair of ventral spines and one retrolateral dorsal spine at the apex. A prolateral dorsal spine at the apex of the mid tibia is always absent. Hind tibiae armed with about 25 dorsal linear spines (min 13, max 34) on both the anterior and the posterior edge ( Fig. 13D ). Hind tibiae armed at the apex with two ventral sub-apical spines, two ventral apical spines, two dorsal apical spines and two dorsal sub-apical spines. The dorsal apical spines are always largest, whereas the ventral sub-apical spines are smallest. First hind tarsal segment armed with eight to twenty dorsal linear spines; second hind tarsal segment armed with three to eleven dorsal linear spines.

ABDOMEN. Typically mottled brown ( Fig. 22A ). Dark colour morphs with a pale longitudinal band ( Fig. 12I ) are also commonly encountered.

MALE TERMINALIA. Subgenital plate triangular, very narrow at apex, lacking a keel but with a visible median suture ( Fig. 14K ). Cerci on average 20% of body length, covered in long hairs; tapering gradually along their whole length and ending with a blunt tip at the apex. Styli slender and tapering, generally shorter than subgenital plate. Paraprocts form a horseshoe covered in dense, stout spinules; two triangular lobes rising vertically at the base of the paraprocts are also covered in spinules ( Fig. 14J, L ). Under the suranal plate there is a retractable cover which presumably protects the genitalia when not in use ( Fig. 20A–B ; compare with Fig. 14J ).

FEMALE TERMINALIA. Subgenital plate consists of two small lobes at an angle, touching at the vertex ( Figs 6 , 17J ). Ovipositor on average 80% of body length, relatively straight in the basal half, tapering and moderately recurved upwards only near the apex. Lower valve of ovipositor with 5 to 7 teeth below at the apex. Dorsal surface of upper valve more heavily serrated in distal half than in I. armatum ( Fig. 17K–L ).

Distribution and habitat

Isopletron pallidum is only known from the Otago Region in New Zealand’s South Island, between the east coast and Lakes Wānaka and Wakatipu, at elevations ranging from 250 m to 1250 m a.s.l. It occupies a range of habitats including montane forests, rock tors and bluffs. Populations may be locally dense, with several specimens hiding in cracks in the rock or under bark on tree trunks.

Figures

Fig. 1. Comparison of rhaphidophorid terminalia in nymphs and adults. A–B. Isoplectron pallidum (Richards, 1972) comb. nov., ♂. Crown Range Road, Central Otago. A. Nymph, final instar (MPN CW5561). B. Adult (MPN CW5601). C–D. Praecantrix silvatica gen. et sp. nov., ♀. Catlins Forest, Southland. C. Nymph, final instar (MPN CW4951). D. Adult (MPN CW4946). Scale bars: 500 μm.

Fig. 3. A. Phylogenetic relationships of six genera of New Zealand Rhaphidophoridae Walker, 1869 inferred from whole mitochondrial genome sequences using Maximum Likelihood approach and 1000 bootstraps. B. Map of New Zealand, showing locations of specimens of Isoplectron Hutton, 1896 and Praecantrix gen. nov. used in phylogenetic analyses (Figs 6–7). Colours correspond to different genera: red = Isoplectron; green = Praecantrix. Two letter codes indicate the New Zealand entomological regions (Crosby et al. 1998). These codes are reported in the Material examined section for each species.

Fig. 6. Isoplectron pallidum (Richards, 1972) comb. nov. Adult ♀, subgenital plate. Duffers Saddle, Old Woman Range. A. MPN CW5387. B–C. Holotype (NZAC 03015582). B. Photograph of museum specimen. C. Original drawing by Richards (1972). Scale bar: 1 mm.

Fig. 8. Gene tree for the eight morphologically identified species of Isoplectron Hutton, 1896 using Maximum Likelihood analysis of ~850 bp of mtDNA (COI) from 86 specimens. Node support labels are the result of 1000 ML bootstrap replicates.

Fig. 10. Known distribution of cave wētā in the genera Isoplectron Hutton, 1896 and Praecantrix gen. nov. A–C. All of New Zealand. A. Isoplectron armatum Hutton, 1896. Solid shapes indicate material collected as part of this study; empty circles indicate additional locations of material examined by Hutton (1896). Shapes represent different subspecies: circle = Isoplectron armatum armatum Hutton, 1896; diamond = Isoplectron armatum aciculatum Karny, 1937. B. Praecantrix silvatica gen. et sp. nov. Shapes represent different subspecies: dark green square = Praecantrix silvatica silvatica gen., sp. et subsp. nov.; light green diamond = Praecantrix silvatica lutea gen., sp. et subsp. nov. D. Map of North Island. E–J. Map of South Island. F. Isoplectron serratum (Richards, 1972) comb. nov. Solid shapes indicate material collected as part of this study; empty diamonds indicate additional locations of material examined by Richards (1972). Scale bars: 200 km.

Fig. 12. Dorsal view of cave wētā in the genera Isoplectron Hutton, 1896 and Praecantrix gen. nov. A–I. Isoplectron. A. I. armatum armatum Hutton, 1896, adult ♂. Parsons Bush, Lake Ōhau (MPN CW5123). B. I. armatum aciculatum Karny, 1937, adult ♀. Ohakune (MPN CW5644). C. I. bicolor sp. nov., adult ♂. Mt Arthur Tablelands (MPN CW3760). D. I. serratum (Richards, 1972) comb. nov., adult ♂. The Gap, Torlesse Range (MPN CW3182). E. I. maculatum sp. nov., holotype, adult ♂. Middle Mt Peel, South Canterbury (NMNZ AI.071892). F. I. ferratum sp. nov., holotype, adult ♂. Cave Brook, Gouland Downs (NMNZ AI.071896). G. I. virgatum sp. nov., adult ♀. Cave Brook, Gouland Downs (MPN CW3794). H. I parallelum sp. nov., adult ♀. Ahumairangi Town Belt, Wellington (MPN CW5598). I. I. pallidum (Richards, 1972) comb. nov., adult ♂. Mt Kyeburn, Danseys Pass (MPN CW3456). J–L. Praecantrix. J. P. silvatica silvatica gen., sp. et subsp. nov., adult ♂. Mt Arthur Hut (MPN CW5390). K. P. silvatica lutea gen., sp. et subsp. nov., adult ♂. Peel Forest (MPN CW4968). L. P. saxicola gen et sp. nov., holotype, adult ♂. Mt Wakefield (NMNZ AI.071904). Scale bar: 10 mm.

Fig. 13. Left hind tibia of cave wētā in the genera Isoplectron Hutton, 1896 and Praecantrix gen. nov., adult ♂, dorsal view. A–I. Isoplectron. A. I. armatum armatum Hutton, 1896. Parsons Bush, Lake Ōhau (MPN CW5123). B. I. armatum aciculatum Karny, 1937. Ohakune (MPN CW 5646). C. I. bicolor sp. nov., holotype. Cave Brook, Gouland Downs (NMNZ AI.071889). D. I. pallidum (Richards, 1972) comb. nov. Duffers Saddle, Old Woman Range (MPN CW5385). E. I. serratum (Richards, 1972) comb. nov. The Gap,Torlesse Range (MPN CW3182).F. I. maculatumsp. nov., holotype. Middle Mt Peel, South Canterbury (NMNZ AI.071892). G. I. virgatum sp. nov. Cave Brook, Gouland Downs (MPN CW3776). H. I. ferratum sp. nov., holotype. Cave Brook, Gouland Downs (NMNZ AI.071896). I. I. parallelum sp. nov. Ahumairangi Town Belt, Wellington (MPN CW5569). J–K. Praecantrix J. P. silvatica lutea gen., sp. et subsp. nov. McLean Falls, Catlins Forest (MPN CW3901). K. P. saxicola gen et sp. nov., holotype. Mt Wakefield (NMNZ AI.071904). Scale bar: 5 mm.

Fig. 14. Adult male terminalia of cave wētā in the genus Isoplectron Hutton, 1896. Left column: dorsal view; central column: ventral view (subgenital plate); right column: lateral view. A–C. I. armatum armatum Hutton, 1896. A–B. Kaiterau Trail, Kaikōura (MPN CW4938). C. Pioneer Park, Ōpihi River (MPN CW5554). D–F. I. armatum aciculatum Karny, 1937. Ohakune. D. MPN CW5647. E–F. MPN CW5646. G–I. I. bicolor sp. nov., Cave Brook, Gouland Downs. G–H. Holotype (NMNZ AI.071889). I. MPN CW3758. J–L. I. pallidum (Richards, 1972) comb. nov. J, L. Staircase Hut track, Waianakarua River (NMNZ AI.071891). K. Mt Kyeburn, Danseys Pass (MPN CW3455). Scale bars: 1 mm.

Fig. 17. Adult female terminalia of cave wētā in the genus Isoplectron Hutton, 1896. Left column: subgenital plate; central and right columns: ovipositor. A–C. Isoplectron armatum armatum Hutton, 1896. South Mavora Lake (MPN CW4927). D–F. I. armatum aciculatum Karny, 1937. Ohakune. D. MPN CW5648. E–F. MPN CW5650. G– I. I. bicolor sp. nov., paratype (NMNZ AI.071890). Chaffey Hut, Cobb River. J–L. I. pallidum (Richards, 1972) comb. nov. Duffers Saddle, Old Woman Range (MPN CW5387). Scale bars: 1 mm.

Fig. 20. Retractable cover in adult male terminalia of cave wētā in the genus Isoplectron Hutton, 1896. A–B. I. pallidum (Richards, 1972) comb. nov. Crown Range Road (MPN CW5560). A. Dorsal view of retractable cover. B. Ventral view of subgenital plate and apex of retractable cover. C. I. serratum (Richards, 1972) comb. nov., dorsal view. Mt Altimarloch, Black Birch Range (MPN CW5588). D. I. maculatum sp. nov., holotype, dorsal view. Middle Mt Peel, South Canterbury (NMNZ AI.071892). Scale bars: 1 mm.

Fig. 22. Live Isoplectron Hutton, 1896 in their natural habitats. A. I. pallidum (Richards, 1972) comb. nov., adult ♀. Staircase Hut Track, Waianakarua. B. I. maculatum sp. nov., adult ♂. Middle Mt Peel, South Canterbury. C–F. I. serratum (Richards, 1972) comb. nov. C. Adult ♀. The Gap, Torlesse Range. D. Adult ♂. Mt Richmond, Richmond Range. E. Mating pair. Mt Altimarloch, Black Birch Range. F. Female nymph. Mt Altimarloch, Black Birch Range.