Trigonidiinae Saussure, 1874

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 : 19

Subfamily Trigonidiinae Saussure, 1874

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 ) 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 ). The two taxa seem to only differ in a few measurements ( Table 7 ), including the number of teeth in the stridulatory file, which is less than 20 in T. australianum ( Otte & Alexander 1983; 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.

Figures

Fig. 31. Gene tree for Trigonidium Rambur, 1838 using Maximum Likelihood analysis of ~700 bp of mtDNA (COI) from 23 specimens and 1000 bootstrap replications. The tree with the highest log likelihood (-3571.04) is shown. Numbers next to the branches indicate the percentage of trees in which the associated taxa are clustered together. The tree is drawn to scale, with branch lengths measured in the number of substitutions per site. Specimens in blue were collected as part of this study; the remaining 15 sequences were obtained from the GenBank (Benson et al. 2013) and BOLD (Ratnasingham & Hebert 2007) databases. Detailed information for each specimen included in this analysis can be found in Supp. file 1: Table S11.