Tragosoma nigripenne Bates, 1892

Laplante, Serge, 2017, Description of a new Nearctic species of Tragosoma Audinet-Serville (Coleoptera: Cerambycidae: Prioninae), with species validations, new synonymies and a lectotype designation, Insecta Mundi 2017 (578), pp. 1-17 : 9

Tragosoma nigripenne Bates, 1892

This taxon, described from Durango, Mexico, is currently valid and has always been regarded as a distinct species. Galileo (1987: 177) questioned its validity because of the variability of character states previously used to distinguish it from “ T. depsarium ” (including T. harrisii ), notably the form of the median lateral prothoracic process. However, Galileo decided to keep it as a valid species because her hypothesis was based on insufficient material. I studied specimens of T. nigripenne from the state of Durango, 17 males and 12 females from CNC, NHM, MNHNP and IRSNB. Early in my study, I observed that the T. nigripenne morphological characters studied fell within the range of the variation observed in T. harrisii , and found no reliable diagnostic characters that could separate the two species with confidence. I considered then, like Galileo, the possibility that the two taxa be synonyms. I noted though that the specimens from Durango had the median lateral prothoracic process less developed on average than in most T. harrisii studied. The ratios LA-3/LA-4 obtained for the two species, both in males and females ( Table 1), and the scatter graphs ( Fig. 9 and 10 ) show that they largely overlap although they slightly differ. Therefore, LA-3/LA-4 is not a good diagnostic character but indicates however that these species are possibly distinct. A full barcode (658 base pairs) was obtained from a specimen (CNC) collected near the type locality in Durango and compared with barcodes from the same dataset of nine T. harrisii mentioned in the Tragosoma harrisii section above. The analysis showed that the difference between the T. nigripenne specimen and the nine T. harrisii ranged from 3.77–4.77% (mean = 4.28%) ( Fig. 11 ). Barcodes of additional T. nigripenne specimens are needed to confirm this difference but this value supports the validity of T. nigripenne and I consider it as a distinct species.

Three of the presumed syntypes of T. nigripenne were studied, two males and a female, out of five currently present in NHM. All of them have the same first four labels: [1, small, round, white disc with pale blue margin]: “SYN- / TYPE” [p] // [2, rectangular, white label]: “Ciudad, / Durango. / Höge.” [p] // [3, rectangular, white label]: “Tr. E. Soc. 1892. / 92-90” [p] // [4, rectangular, white label]: “ Tragosoma [p] / nigripenne, [hw] / Bates [hw]”. One of the males (no. 1), the one re-pinned through the left elytron and with a gelatin capsule under it containing the right mesothoracic leg and the apical three antennomeres of an antenna, bears a fifth label, a larger, rectangular, white one, entirely handwritten: “ Tragosoma / nigripenne / Bates ♂ ”. I have also studied four more specimens that could potentially be syntypes, each showing a collecting label similar to those in NHM, two females in MNHNP (via collection Oberthür) and two, a male and possibly a female (antennae and abdomen missing), in IRSNB. The fact that I saw more than one male among the presumed type series despite Bates’s (1892: 146) statement to the effect that “All the examples are females, except one” casts doubt on the authenticity of the supposed syntypes. The fact that each of all those specimens bears the same data label may indicate that they are from the same collecting series, and therefore genuine syntypes, and that Bates wrongly identified the sex of some specimens. Further research is needed to find all the original syntypes and to show their authenticity.

Figures

Figure 11. Neighbor joining tree for the 16 barcodes of Tragosoma included in the dataset; each record with province or state of origin, GenBank accession number, and sample ID. Full length sequences (658 base pairs) analyzed, unless otherwise indicated in parentheses.

Figures 9–10. Scatter plots with medians of LA-3 (on horizontal axis) in relation with LA-4 (on vertical axis) measured (in mm) for samples of T. depsarium, T. harrisii, T. nigripenne, T. soror, and T. spiculum. 9) For males. 10) For females.