Calosoma (Ctenosta) roeschkei Breuning, 1927

Length: 18-25 mm. C. roeschkei is closely related to C. scabrosum but can be distinguished by its more transverse pronotum, which is less narrowed towards the rear and has sides that are more regularly curved. Additionally, its elytra are slightly wider and less constricted at the apex, and the upper body has a lighter bronze coloration.
In 1927, Breuning described specimens from the Usumbara Mountains in southern Tanzania, near the Kenyan border, as a new population of C. scabrosum, which he named C. scabrosum ssp. roeschkei. His description noted the pronotum as being straighter at the rear with less pronounced posterior angles, the elytra as slightly flatter and wider at the shoulders, and the upper body as having a vivid bronze color with coppery foveae on the primary intervals.
Later, in 1940, Jeannel described a new species, Ctenosta aethiops, emphasizing certain chaetotaxic characteristics but also reiterating the morphological features previously identified by Breuning in C. scabrosum ssp. roeschkei. However, Jeannel suggested that the specimens attributed to C. roeschkei belonged to C. orientale, which we now know to be an Asian species not found in Africa..
Upon review, it is clear that the characteristics noted by Jeannel are present in all specimens Breuning attributed to C. scabrosum roeschkei. Breuning was the first to identify this taxon, and thus the name roeschkei takes precedence over aethiops, which was described 13 years later.
Even more recently, a research by Hackel and colleagues (2016) examined Jeannel’s C. aethiops type specimen. By comparing the shape of the aedeagus apex, they identified it as a slightly larger-than-average male of C. imbricatum hotentottum. In the same study, the authors examined the geographic distribution of C. roeschkei and C. scabrosum, concluding that the distribution is allopatric and that C. roeschkei is therefore a geographical subspecies of C. scabrosum, occupying the southern part of its range. The morphological differences between the two taxa are considered minor and inconsistent.
Actually Breuning (1927 and 1928) initially proposed that C. scabrosum roeschkei was the vicariant form of C. scabrosum in East Africa, extending as far as Ethiopia (Addis Ababa), where a contact zone between the two populations was suggested. However, the geographic range of C. roeschkei is much larger than originally assumed and partially overlaps with that of C. scabrosum in the northern region.
Jeannel reported C. aethiops (now considered C. roeschkei) from Chad, and more recent findings include specimens from Niger, Ethiopia, Sudan, and Somalia, where C. scabrosum also occurs. However, no instances of the two taxa being captured together have been documented, except for some reports from the area between Agadez and Arlit (https://www.insecte.org/forum/viewtopic.php?t=193243).
In conclusion, the likely sympatry, along with the absence of specimens showing intermediate morphological characteristics in the contact zones, suggests that C. roeschkei should not be considered a geographical subspecies of C. scabrosum.
Finally, it is worth noting that in the past C. aethiops (= C. roeschkei) has sometimes been mistaken for Calosoma (Campalita) chlorostictum due to its similar elytral sculpture and bronze upper body coloration. However, the two species can be easily distinguished by carefully examining the body shape (C. roeschkei has elytra that are visibly convex posteriorly) and other key features of the subgenus Ctenosta, such as chaetotaxy (lack of bristles near the basal angles of the pronotum) and the shape of the pronotum, which has nearly absent basal angles.
C. roeschkei is found in tropical Africa, southeast of the Sahara. Known locations include Niger, Burkina Faso, Chad, Sudan, Eritrea, Ethiopia, Somalia, Kenya, and Tanzania.

Examined specimens and literature’s data:
Burkina Faso. Essakane (SB)
Chad. Ennedi Ouest: Mortcha (sub aethiops Jeannel, 1940: 128); Wadi Fira, Iriba (www.inaturalist.org)
Eritrea. Asmara (RS), Tessenei (Rougemont, 1976: 247)
Ethiopia. Gamu Gofa: Woito (SB); Hararge: Dire Daua (sub C. aethiops Jeannel, 1940: 127); Shewa: Addis Ababa (Breuning, 1928b: 96), Buffet d'Aouache (Rougemont, 1976: 247); Sidamo: 40 km W Konso 600m (SB)
Kenya. Coast prov: NW of Garsen (SB), N. of Bura (SB), Kasigau Teita Hills (SB), Turkana Mts Murueris (sub orientale Jeannel, 1940: 129), Taveta (Breuning, 1927: 186), Kilifi (www.inaturalist.org); North Eastern prov: El Wak (Häckel et al, 2016: 15, TL), Garissa (www.ebay.it); Northern prov: Tsavo East Voi (SB); Amboseli nat. park (EM, SB); Eastern prov: prov: Mwingi (SB), Marsabit (SB), Sosoma (Häckel et al, 2016: 15); Rift Valley prov: Archers Post (SB, TL), Ngurunit (Ebay.com), Samburu East (www.inaturalist.org)
Niger. Agadés reg: Azbin (20 km from Agades?, sub aethiops Jeannel, 1940: 127), Arlit (DP), W. Border of Aïr Massif (SB).
Somalia. Jowhar (Vil. Duca Abruzzi) (sub C. rugosum, MFi); Abarey, Shabelle Swamps (AVT, SB); Afgoi (AC, AVT, EM); Genale (AC); Balad (AVT); Berbera (Breuning, 1928b: 96)
Sudan. White Nile (Jeannel, 1940: 127); Gazira, Vad Medani (Häckel et al, 2016: 15); Red Sea prov. 190 km E of Atbara. Khor Adarot (SB)
Tanzania. Arusha reg., Mto Wa Mbu (SB); Natron Lake (ex coll. Battoni, Vigna Taglianti & Bruschi, 1988: 243); Tanga reg. Usumbara mts. (holotype of Calosoma scabrosum roeschkei) (NBC)

Notes: C. roeschkei is diurnal as well as nocturnal, and it is mainly a soil dweller. Active individuals, that are winged and attracted to light at night, were captured during or immediately after the different raining periods that characterize the monsoon climates: in Somalia from March to May and in November December; in Niger and in Ethiopia (Rougemont, 1976: 247) from August to September; in Tanzania and Kenya from October up to January.
The species was named after Hans Friedrich Wilhelm Roeschke (1867-1934), a German entomologist primarily interested in beetles.

Calosoma (Ctenosta) roeschkei ♂ Breuning, 1927 Usumbara (holotype of C. scabrosum roeschkei) (coll. Naturalis Biodiversity Centre, Leiden) photo by the courtesy of Ben Brugge

Calosoma (Ctenosta) roeschkei ♂ Breuning, 1927 Somalia: Lower Shebeli, Abarei, Lake Joware, 13-14.V.1988, Bruschi & Vigna

Calosoma (Ctenosta) roeschkei ♀ Breuning, 1927 Somalia: Lower Shebelli, Afgoi, Lafoole (Fac. Agric.), at light, 7.V.1988, Bruschi