Isognathotermes zenkeri (Desneux, 1904)

Josens, Guy, Deligne, Jean, Harry, Myriam, Roy, Virginie, Akama, Pierre D., Coulibaly, Tenon, Dosso, Kanvaly, Goergen, Georg, Hasson, Michel, Kasangij, Patrick Kasangij A, Kifukieto, Carmel, Ru, Bruno Le, Loko, Laura Estelle Yêyinou, Ndiaye, Abdoulaye Baila, Roisin, Yves, Sion, Noémie, Šobotnik, Jan, Stiblik, Petr, Kuenda, Soki Kue Di, Traoré, Saran, Viage, Manuela, Wango, Solange Patricia, Kaymak, Esra, Bourguignon, Thomas & Hellemans, Simon, 2025, An integrative revision of the genus Isognathotermes (Termitidae: Cubitermitinae) with description of seven new species and four new subspecies, European Journal of Taxonomy 1024, pp. 1-197 : 161-167

Isognathotermes zenkeri (Desneux, 1904)

Figs 26–31, 70, distribution map: Fig. 49; Table 18

Termes Zenkeri Desneux, 1904a: 148–149 .

Termes ( Eutermes) Zenkeri – Desneux 1904b: 46 , pl. 2 fig. 12.

Cubitermes ( Termes) Zenkeri – Wasmann 1911: 158 .

Mirotermes ( Cubitermes) Zenkeri – Sjöstedt 1913: 369 , pl IX.

Cubitermes Zenkeri – Sjöstedt 1926: 236 .

Cubitermes zenkeri – Snyder 1949: 166. — Bouillon & Vincke 1971: 269. — Ruelle 1975: 8. — Krishna et al. 2013: 1945. — Josens & Deligne 2019: 60–61 .

Isognathotermes zenkeri – Hellemans et al. 2021: 233.

Diagnosis

The workers and soldiers of I. zenkeri are larger than those of the other species with a fungifaber EVA , but the imagines are almost indistinguishable from those of I. severus and I. ugandensis .

The worker has a fungifaber EVA ; it is among the large-sized workers of the genus Isognathotermes ( Fig. 30) with the largest apico-marginal distances in the genus (WMlAmD = 0.23–0.25 mm).

The soldier is among the large-sized soldiers of the genus Isognathotermes ( Fig. 28); the mandibles are shorter than the head but longer than in other species of the genus (SMlL = 2.75–2.99 mm; SMlL/SHdL = 0.86–0.92), some soldiers of I. bulbifrons can have equally long mandibles but they have another EVA. Gulamentum with almost straight, parallel lateral edges, only slightly curved.

The imago is among the middle- to large-sized imagines of the genus Isognathotermes ( Fig. 26) with the largest left and right apico-marginal distances; IMlAmD = 0.26–0.28 mm ( Fig. 27); ocellus large, protruding and removed from eye by a distance shorter than 0.6 ocellus small diameter.

Etymology

This species was named in honour of G.A. Zenker who discovered this species and collected the type material.

Material examined

Five samples from one (?) location, all labelled as Termes , or Eutermes , or Cubitermes zenkeri .

Syntypess of Termes zenkeri Desneux, 1904

CAMEROON • soldier, worker, ♀ (alate); Bipindi ? ( 3°5′ N, 10°24.5′ E); before 1904; G. Zenker leg.; study code: DJ 0283; initially Termes zenkeri ; NHMM • soldier, worker, ♀ (alate); Cameroon , from Hill collection; [no date, no location]; G. Zenker (?) leg.; study code: DJ 0730; initially Termes zenkeri ; AMNH • soldier, worker, ♀ (alate); Kamerun , from Holmgren collection; [no date, no location]; G. Zenker (?) leg.; study code: DJ 0731; initially Termes zenkeri ; AMNH • soldier, worker, ♂ (alate); Bipindi ( 3°5′ N, 10°24.5′ E); 1903; G. Zenker leg.; study code: DJ 0962; initially Eutermes zenkeri ; RBINS .

Krishna et al. (2013: 1945) mention that other type (sub)samples are deposited in NHRM, and in the Zoologisches Museum der Natur, Hamburg, Germany, not examined.

Other material examined

CAMEROON • soldier, worker, ♀ (alate), ♀ (queen); Bipindi? ( 3°5′ N, 10°24.5′ E); [no date]; G. Zenker leg.; study code: DJ 0321; initially C. zenkeri ; AMNH. Five samples from one (?) location, all labelled as Termes , or Eutermes , or Cubitermes zenkeri .

Historical review

Desneux (1904a: 148–149) described this species under the name Termes Zenkeri (species name incorrectly published with a capital letter and only corrected in 1949). He provided a short description of alate imago, soldier, and worker along with a few measurements, mentioning some differences with C. fungifaber .

The species was later referred to under the name of Termes ( Eutermes) Zenkeri by Desneux 1904b, Cubitermes ( Termes) Zenkeri by Wasmann (1911: 158), Mirotermes ( Cubitermes) Zenkeri by Holmgren (1912), and Cubitermes Zenkeri by Sjöstedt (1926: 236).

Sjöstedt (1926: 218–226) included the species in imagines’ and soldiers’ keys of Cubitermes species and inserted it in a “ Zenkeri -Gruppe” of large Cubitermes species.

Snyder (1949: 166) catalogued Cubitermes zenkeri in the subfamily Termitinae while Krishna et al. (2013: 1945) housed it in the subfamily Cubitermitinae . Espousing the view of Ruelle (1975: 8) they considered Cubitermes kemneri as a junior synonym of C. zenkeri .

Bouillon & Vincke (1971: 269) described the enteric valve of C. zenkeri as belonging to the first of three types, the “simple type ” without any spatula.

Josens & Deligne (2019: 39–42) placed this species within the fungifaber valve pattern group. Therefore, C. zenkeri cannot be the senior synonym of C. kemneri as the types of both species belong to different valve pattern groups, i.e., fungifaber - and finitimus -group respectively.

Hellemans et al. (2021: 233) placed this species in the restored genus Isognathotermes . This species is confusing: all the known samples seem to come from the same site (Bipindi, Cameroon) and the same collector (G. Zenker), and it has not been collected since, despite the numerous collecting campaigns that have been organised in Cameroon.

Redescription

Imago

COLOUR. Head capsule: well sclerotised, and very dark, C6–C7; fontanelle concolorous or almost so with head capsule. Postclypeus C5–C6, slightly paler than head capsule. Antennae C5, slightly paler than head capsule without any difference between proximal and distal articles. Thorax: pronotum C5–C6, as postclypeus, slightly paler than head capsule; meso- and metanotum C5–C6, concolorous with pronotum. Legs C4–C5; tibia concolorous with femur. Wings hyaline with brown to grey tinge (Cf3–Cf4), anterior veins darker. Abdomen: tergites C6. Sternites appreciably paler in middle (C3–C4) with both sides darker (C4–C6); posterior sternites darker (C4–C6) than anterior.

SETATION. Head capsule, with some prominent setae set amongst a high density of short, fine setae forming a dense mat. Labrum and postclypeus with some prominent setae mixed with shorter ones. Antennae with some prominent setae, some more numerous smaller setae and, mainly distally on most articles, a bunch of very fine, bent setae (visible only at high magnification, 50 × or more). Thorax: pronotum with prominent setae mainly on margins and shorter ones in middle; meso- and metanotum with some fine, pale setae, arranged in a medio-longitudinal strip, generally visible at 40–80×; some large setae sometimes present on metanotum. Legs very pilose, furnished (among numerous fine setae) with some stronger setae: 4–10 on the carina of fore coxa and 1–4 on the ventral side of fore coxa; tibia pilose fore, mid, and hind tibia furnished with 15–30 spines and bearing 3, 2, 2 apical spurs and 0, 2, 0 subapical spurs respectively. Abdomen: tergites with many large and small setae. Sternites with long setae, erect or directed slightly forward, and many long and smaller setae directed backwards.

STRUCTURE (measurements in Table 18, Figs 26, 70). Size: the imagines of I. zenkeri are among the medium- to large-sized species of the genus Isognathotermes ( Fig. 26) with the largest left and right apico-marginal distances ( Fig. 27). Head capsule: compound eyes large and shortly oval; ocelli large, protruding and shortly to moderately oval, removed from eyes by a shorter distance than 0.6 ocellus small diameter; fontanelle generally a tiny round or elongate marking. Antennae: 16 articles on alate individuals, shortened by amputation by three articles in the queen. Labrum: cupola shaped, wider than long. Left mandible with apical tooth large sized in the genus and always more prominent than first marginal; marginal teeth three in number; second marginal appearing as an undulated edge, third marginal tooth with a blunt tip; only the apical tooth is acute in unworn specimens; premolar tooth partly hidden; molar tooth bearing a rounded molar prominence dorsally and ending posteriorly in a tiny acute apophysis. Right mandible with apical tooth large sized in the genus and always more prominent than first marginal; marginal teeth two in number; first marginal tooth well developed with a sharp tip when fresh; second marginal tooth smaller and with a blunt tip even when fresh; molar tooth bearing a ventral rounded flange and ending posteriorly in a kind of heel. Thorax: pronotum appreciably wider than long and narrower than head width (including the eyes), straight to very weakly sellate with anterior lobe short and very slightly elevated. Fore coxa flanged ventrally resulting in a carina. Wings: R1 fused entirely with costal margin, sclerotised; Rs simple, sclerotised; M and Cu not or weakly sclerotised with 3–4 and 10–13 branches, respectively. Gut not studied.

Soldier COLOUR. Head capsule C4–C6, darkened by age, with a smooth gradient from a darker frons to a paler back. Antennae and labrum approximately concolorous with head capsule. Mandibles dark (C7–C8) generally with an abrupt clearing on their bases (one palette level) which is generally the same colour as frons. Thorax and legs paler than head capsule (C3–C5), darkened by age. Abdomen grey to red-brown owing to digestive bolus.

SETATION. Head capsule with few scattered setae; on frons a dense bunch of setae surrounds and overhangs fontanelle. Antennae with some prominent setae, more numerous smaller setae and at distal extremity of distal articles, a bunch of very fine, bent setae (visible only at high magnification, 50 × or more). Labrum always with 7–10 large setae on each lobe. Thorax: pro- and mesonotum with a small number of setae mainly located on margins. Legs: fore coxa bears at least one fine seta and 2–3 spines on carina and 0–1 spine on ventral side; trochanter with some strong lined-up setae, or with 5–6 spines; fore, mid, and hind tibia bearing 3, 2, 2 apical spurs and 0, 2, 0 subapical spurs respectively (the latter sometimes weakly developed) and a row of 9–14 spines along their shaft. Abdomen: tergites with some large setae, mainly on their posterior margins. Sternites with long setae, erect or slightly directed forward, often coloured, and smaller setae directed backwards.

STRUCTURE (measurements in Table 18; Figs 28, 70). Size: the soldiers of I. zenkeri are among the large-sized soldiers in the genus Isognathotermes ( Fig. 29). Head capsule: always clearly sclerotised; appreciably longer than wide. Dorsal view: lateral sides mostly subparallel with a slight narrowing near posterior third or fourth, from antennal sockets sides converge towards bases of mandibles; posterior side regularly convex or with a short straight part. Upper profile slightly concave; angle between extended mandibles and frons obtuse; frons with a slight anterior hump ( Fig. 70). Gulamentum in ventral view with almost parallel sides, very weakly constricted in its posterior half; with sides of anterior part generally forming an acute widening or even a kind of ear on each side. Antennae: of 15 articles. Labrum: always deeply bifurcate and wider than long, with lyre-shaped sides; lobes angular, generally with fine, whitish, or translucent tips; anterior margin concave. Mandibles: sabre-like; inner edges smooth with one distinct but very small marginal tooth, near molar tooth on each mandible; mandibles shorter than head but the longest in relative value in the genus (85–90% of head length); entire surface of both mandibles smooth and glossy. Right mandible equally or slightly more curved than left. Thorax: pronotum sellate, as wide as about 60% of head width, with straight or indented anterior margin and posterior straight margin. Fore coxa flanged ventrally resulting in a sharp carina. Gut: enteric valve seating on left side, best seen in ventral view, situated in second half of abdomen. Caecum always rather small, best seen in ventral view, near centre of abdomen, three-lobed. Arrangement of enteric valve cushions showing trilateral symmetry, the odd cushions being about 20% longer than the even cushions, generally without any crest.

Worker COLOUR. Head capsule pale but darkened by age. Antennae: proximal articles pale (C2–C3), distal articles always one to two levels darker (C4–C5). Thorax, nota, and legs pale but darkened by age.

Abdomen grey to red-brown owing to digestive bolus.

SETATION. Head capsule and postclypeus with few, erect, scattered setae. Labrum with few, robust scattered setae. Antennae with some prominent setae, some more numerous smaller setae and at distal extremity of distal articles, a bunch of fine, bent setae (visible only at high magnification, 50 × or more). Thorax: nota with some scattered setae. Legs: fore coxa always carinated, bearing one fine seta and furnished with 3–4 spines on carina and one on ventral side; fore trochanter with 6–7 spines, all except one lined up; fore, mid, and hind tibia bearing 3, 2, 2 apical spurs and 0, 2, 0 subapical spurs respectively and a row of 8–15 spines. Abdomen: tergites with scattered setae. Sternites with long setae, erect or slightly directed forward, often coloured, and smaller setae directed backwards.

STRUCTURE (measurements in Table 18, Figs 30, 70). Size: the workers of I. zenkeri are part of the large-sized workers in the genus Isognathotermes (but with large overlapping on several other species: Fig. 30). Head capsule: weakly sclerotised (except mandibles). Antennae of 14 or 14.5 articles. Labrum: cupola shaped. Left mandible: apical tooth well developed, the largest in the genus, with a sharp tip when fresh; marginal teeth three in number, first marginal tooth well developed but with a blunt tip even when fresh, second marginal appearing as an undulated edge, third marginal tooth with a blunt tip; premolar tooth partly hidden underneath molar tooth; this latter bearing a rounded molar prominence dorsally and ending posteriorly in a tiny acute apophysis. Right mandible: apical tooth well developed, the largest in the genus, with a sharp tip when fresh and sometimes with a wavy inner edge near the base; marginal teeth two in number; first marginal tooth well developed with a sharp tip when fresh; second marginal tooth smaller and with a blunt tip even when fresh; molar tooth bearing a ventral rounded flange and ending posteriorly in a kind of heel. Thorax: pronotum sellate, as wide as 70–75% of head width. Fore coxa flanged ventrally resulting in a sharp carina. Gut: enteric valve seating on left side, best seen in ventral view, situated in second half of abdomen. Arrangement of enteric valve cushions of the fungifaber pattern with triradial symmetry: the odd PCs, in their downstream part, are rather narrow and bear crests that are as high as or higher than they are wide, with long and strong bristles; 19–27 supporting bristles on each side of the odd PCs; secondary cushions are wide at the upstream end, narrowing noticeably downstream with a homogeneous spine scattering. Caecum with three lobes, either small or with one lobe somewhat extended forwards, visible in ventral view, near centre of abdomen,

Chorology-ecology

Only one collecting site is suspected in the Atlantic Equatorial coastal forest ecoregion of Cameroon ( Fig. 49). Its precise origin is uncertain: in the original description, Desneux (1904a) only mentions that it came from “ Kamerun ” and that it was discovered by G. Zenker in a large nest ( 1 m high) at the base of a tall tree. Georg August Zenker was working at Jaunde [= Yaoundé] from 1889 to 1895 and was later domiciled at Bipindi from 1896 to 1922 ( Wikipedia 2024a, German version), it is therefore believed that Termes zenkeri was found at Bipindi. However, this large and very characteristic species has never been found again despite numerous collections that were made in Cameroon, especially around Mbalmayo and in the region from Yaoundé to Kribi (including Bipindi). As Zenker collected in a vast region of Cameroon, it is quite possible that I. zenkeri , a species with a supposedly limited area, did not originate from Bipindi.

Molecular data

No genetic sequence is currently available.

Incertae sedis – species inquirenda

This chapter contains a species already described ( I. congoensis ( Emerson, 1928)) , but of uncertain matches; one potential species already named ( I. bredoi ) but not described (nomen nudum) and two potential species with unclear identity (a possible cryptic species of I. planifrons and an unknown species from Malawi). All these samples are classified “ Incertae sedis ” and “Species inquirenda”.