Trigonidiinae Saussure, 1874

Subfamily Trigonidiinae Saussure, 1874 View in CoL

Out of 368 crickets examined, forty-three are trigs (subfamily Trigonidiinae ). Thirty of these fit the original description and the type material for Trigonidium ( Metioche) maoricum , with a black, shining body, arcuate ovipositor, hind tibiae with three pairs of dorsal spurs, no auditory tympana on the anterior tibiae, and no hindwings. Trigonidium ( Metioche) maoricum has no abdominal gland and has a stridulum with 30–40 teeth on the male forewing.

While Chopard (1968) placed the species in Metioche , the description of Metioche clearly states that insects have forewings without a stridulum in both males and females ( Stål 1877; Otte & Alexander 1983; Rentz & Su 2019). Trigonidium , on the other hand, has a stridulum on the right forewing in males ( Rambur 1838; Otte & Alexander 1983; Rentz & Su 2019). As a result, the species Trigonidium ( Metioche) maoricum is reassigned here to Trigonidium ( Trigonidium) Rambur, 1838 . This is in agreement with Otte & Alexander (1983), who moved most Australian species placed by Chopard (1968) in Metioche back to Trigonidium .

The remaining thirteen trigs examined in this study don’t fit the original description of Trigonidium ( Trigonidium) maoricum , in that they have auditory tympana on both the anterior and posterior sides of the fore tibiae, a stridulum with 30 to 40 teeth in males, and a set of hindwings. These characters fit the genus Trigonidomorpha ( Chopard 1925; Otte & Alexander 1983; Rentz & Su 2019) and appear to be most closely related to Trigonidomorpha sjostedti . One male trig from Whitianga, Coromandel ( NZAC 03037192) had hindwings when it was collected, but had shed its hindwings five days later.

All male New Zealand trigs I examined have the same genitalia and the same stridulum with 30 to 40 teeth, regardless of the presence or absence of hindwings and / or auditory tympana. Mitochondrial DNA analysis at the COI locum supports the hypothesis that the two morphs belong to the same species ( Fig. 31 View Fig ) and validates the observations made by Ingrisch (1977). I am therefore giving an amended description and diagnosis for the genus Trigonidium and for the species Trigonidium ( Trigonidium) maoricum . I am also synonymising the Australian species Trigonidomorpha sjostedti with Trigonidium australianum ( Chopard, 1925) . Since Trigonidomorpha sjostedti is the type species for the genus Trigonidomorpha , the latter genus is synonymised with Trigonidium . The species Trigonidomorpha obscuripennis Chopard, 1957 from Réunion Island, used by Chintauan-Marquier et al. (2016) to reinstate the genus Trigonidomorpha , should be reassigned to a new genus based on molecular data and on its macroscopically different tegmina.

Mitochondrial DNA analysis at the COI locum fails to separate the Australian species Trigonidum ( Trigonidium) australianum from Trigonidium ( Trigonidium) maoricum ( Fig. 31 View Fig ). The two taxa seem to only differ in a few measurements ( Table 7 View Table 7 ), including the number of teeth in the stridulatory file, which is less than 20 in T. australianum ( Otte & Alexander 1983; Table 7 View Table 7 in this paper). Since I have been unable to examine the male genitalia of T. australianum , I am not committing to a synonymy of these two taxa just yet. I do suggest, however, that they are likely to be the same species, and at the most two different subspecies.