Isognathotermes bulbifrons (Sjöstedt, 1924)

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 : 43-56

Isognathotermes bulbifrons (Sjöstedt, 1924)

Figs 26–31, 33, 35 –37, distribution map: Fig. 38; Table 3

Cubitermes bulbifrons Sjöstedt, 1924b: 256 (soldier only).

Cubitermes heghi Sjöstedt, 1924b: 255 .

Cubitermes gibbifrons Sjöstedt, 1924b: 255 . Syn. nov.

Mirotermes ( Cubitermes) kemneri Emerson, 1928: 509 , fig. 54. Syn. nov.

Cubitermes bulbifrons – Sjöstedt 1926: 247–248 (all castes). — Snyder 1949: 157. — Ruelle 1975: 7. — Krishna et al. 2013: 1916–1917. — Josens & Deligne 2019: 60–61 .

Cubitermes heghi – Sjöstedt 1926: 249, pl 9 fig. k. — Ruelle 1992: 500.

Mirotermes ( Cubitermes) heghi – Emerson 1928: 511–513, fig. 56.

Mirotermes ( Cubitermes) congoensis – Emerson 1928: 519–520, fig. 61, as possible synonym? Cubitermes sp. affinis subarquatus “spC” – Roy et al. 2006: 4–5. Syn. nov.

Isognathotermes bulbifrons – Hellemans et al. 2021: 233.

Diagnosis

The individuals of this species come in two forms, one medium sized (previously called I. gibbifrons ) and a large one (previously called I. bulbifrons ) ( Fig. 72); these two species are here synonymised on the basis of chorological-ecological data and the sequencing of their mitogenomes.

The worker has a finitimus EVA ( Fig. 5) and is among the medium sized to the largest workers of the genus Isognathotermes ( Fig. 30; WHdW = 1.11–1.43 mm) it can hardly be distinguished from the workers of other species which have the same kind of EVA.

The soldier has generally a recognizable finitimus EVA ; it is among the medium to the largest sized soldiers of the Isognathotermes species with a finitimus EVA (SHdL = 2.65–3.76 mm; Figs 28–29), with less curved mandibles (SMlc = 0.14–0.31 mm) than I. magniplanifrons sp. nov. As it is suggested by its name, its head is bulbous: the upper profile is moderately to strongly concave (SHdC = 0.01– 0.12 mm), on average, clearly more than that of I. magniplanifrons (but this is shared with I. severus , I. minitabundus , and I. ugandensis which have fungifaber EVAs).

The imago is among the medium to the largest sized imagines in the genus Isognathotermes with a finitimus EVA , (IHdW = 1.44–1.73 mm); the larger ones can be confused with the imago of I. magniplanifrons sp. nov. Its mandibular apico-marginal distance is clearly larger (IMlAmD = 0.20– 0.30 mm) than in any other Isognathotermes species with a finitimus EVA ( Fig. 27). Some samples could be confused with I. finitimus (same size, mandibles of I. bulbifrons less curved than in I. finitimus ) or with I. phallicaecalis sp. nov. that has a different caecum.

This species is also defined by its ecology: all known samples come from forested regions up to about 300 km from the Atlantic coast ( Fig. 38).

Etymology

The name bulbifrons from the Latin bulbus (onion) and frons (forehead) refers to the fact that the frons of the soldier viewed from the side is distinctly bulbous, as Sjöstedt pointed out in the original description.

Material examined

Sixty-five samples from 23 locations (and four incipient or young colonies from one location). Of the 55 old museum samples examined, three were initially labelled as Cubitermes bulbifrons , five as C. gibbifrons , 14 as C. heghi , one as C. kemneri , two as C. subarquatus , one as C fungifaber , 17 as Cubitermes sp. , and five as Cubitermes 2, and seven were not identified. Of the four incipient or young colonies, two were labelled as C. gaigei and two as C. heghi . This species also includes six samples of C. aff. subarquatus “spC” (in Roy et al. 2006).

Paratypes of Cubitermes bulbifrons Sjöstedt, 1924

DEMOCRATIC REPUBLIC OF THE CONGO • soldier, worker; Mukimbungu ; 5°8.5′ S, 14°2.3′ E; ca 1904; K.E. Laman leg.; study code: DJ 0298; initially C. bulbifrons ; AMNH .

Syntypes of Cubitermes gibbifrons Sjöstedt, 1924

DEMOCRATIC REPUBLIC OF THE CONGO • soldier, worker; Mukimbungu ; 5°8.5′ S, 14°2.3′ E; ca 1904; K.E. Laman leg.; study code: DJ 0280; initially C. gibbifrons ; NHMM .

Paratypes from type colony of Cubitermes heghi Sjöstedt, 1924

DEMOCRATIC REPUBLIC OF THE CONGO • soldier, worker; Mukimbungu; 5°8.5′ S, 14°2.3′ E; ca 1904; K.E. Laman leg.; study code: DJ 0290; initially C. heghi → C. bulbifrons ; AMNH.

Paratypes from type colony of Mirotermes ( Cubitermes) kemneri Emerson, 1928

CAMEROON • soldier, worker; Bipindi ; 3°5′ N, 10°24.5′ E; 1920; G. Zenker leg.; study code: DJ 0297; initially C. kemneri ; AMNH .

Other material examined

ANGOLA • soldier, worker; Quimucanda ; 8°5.14′ S, 15°7.43′ E; 27 Nov. 2024; J. Šobotnik leg.; study code: DJ 0970; BE RMCA INS. Iso. 059892 .

CAMEROON • soldier, worker, ♀ (queen); Edea ; 3°29′ N, 9°50′ E; [no date, around 1912]; from J. Bequaert collection; study code: DJ 0610; initially C. bulbifrons ; AMNH • soldier, worker; Bipindi ; 3°5′ N, 10°24.5′ E; 1920; G. Zenker leg.; study code: DJ 0109; initially C. heghi in RMCA; BE RMCA INS. Iso. 059152 • soldier, worker, ♀ (alate); Mbalmayo ; 3°31′ N, 11°30′ E; 17 Oct. 1962; G. Becker leg.; study code: DJ 0723; initially C. heghi ; NHMUK • soldier; Edea ; 3°29′ N, 9°50′ E; Jul.–Sep. 1973; N.M. Collins leg.; study code: DJ U120; initially C. heghi ; NHMUK 13671911 • soldier; Edea ; 3°29′ N, 9°50′ E; Jul.–Sep. 1973; N.M. Collins leg.; study code: DJ U122; initially C. heghi ; NHMUK 13671907 • soldier, worker, ♀ (alate); Edea ; 3°29′ N, 9°50′ E; Jul.–Sep. 1973; N.M. Collins leg.; study code: DJ 0727; initially C. heghi ; NHMUK • soldier, worker, ♀ (queen); Edea ; 3°29′ N, 9°50′ E; Jul.–Sep. 1973; N.M. Collins leg.; study code: DJ 0725; initially C. heghi ; NHMUK • soldier, worker, ♂ (king), ♀ (queen); Edea ; 3°29′ N, 9°50′ E; Jul.–Sep. 1973; N.M. Collins leg.; study code: DJ 0726; initially C. heghi ; NHMUK • soldier, ♀ (queen); Edea ; 3°29′ N, 9°50′ E; Jul.–Sep. 1973; N.M. Collins leg.; study code: DJ U104; initially C. gaigei ; NHMUK 13671901 • soldier, ♀ (queen); Edea ; 3°48′ N, 10°8′ E; Jul.–Sep. 1973; N.M. Collins leg.; study code: DJ U109; initially C. gaigei ; NHMUK 13671899 • soldier, worker; Kala ; 3°51′ N, 11°22′ E; 27 Apr. 1992; A. Dejean leg.; study code: DJ 0063; initially C. subarquatus in RMCA; BE RMCA INS. Iso. 059154 • soldier, worker; Nkolbisson ( Yaoundé); 3°52.25′ N, 11°27.25′ E; 20 Jun. 1992; A. Dejean leg.; study code: DJ 0062; GenBank no PQ679245 (mitogenome); initially C. subarquatus in RMCA; BE RMCA INS. Iso. 059153 • soldier, worker; Akok ; 2°47′ N, 10°17′ E; ca 1995; P. Eggleton et al. leg.; study code: DJ 0714; initially C. bulbifrons ; NHMUK 13671835 • soldier, worker; Bilik ; 3°31′ N, 11°17′ E; ca 1995; P. Eggleton et al. leg.; study code: DJ 0706; initially C. heghi ; NHMUK 13671839 • soldier; Ebogo ; 3°31′ N, 11°30′ E; ca 1995; P. Eggleton et al. leg.; study code: DJ U094; initially C. heghi ; NHMUK 13671838 • soldier; Ebogo ; 3°31′ N, 11°30′ E; ca 1995; P. Eggleton et al. leg.; study code: DJ U095; initially C. heghi ; NHMUK 13671842 • soldier; Eboufek ; 3°31′ N, 11°30′ E; ca 1995; P. Eggleton et al. leg.; study code: DJ U098; initially C. heghi ; NHMUK 13671843 • soldier, worker, ♀ (queen); Eboufek ; 3°30′ N, 11°53′ E; ca 1995; P. Eggleton et al. leg.; study code: DJ 0715; GenBank no PQ679207 (mitogenome); initially C. heghi ; NHMUK 13671836 • soldier, worker; Mbalmayo ; 3°31′ N, 11°30′ E; ca 1995; P. Eggleton et al. leg.; study code: DJ 0713; initially C. heghi ; NHMUK 13671837 • soldier, worker; Mbalmayo ; 3°31′ N, 11°30′ E; Apr. 1996; P. Eggleton et al. leg.; study code: DJ 0712; initially C. heghi ; NHMUK 13671840 • soldier, worker; Mbalmayo ; 3°25.1′ N, 11°27.1′ E; 17 Apr. 2015; J. Šobotnik leg.; study code: DJ 0253; BE RMCA INS. Iso. 059151 • soldier; Ejokou ; 3°20′ N, 11°27′ E; 12 Mar. 2018; J. Šobotnik leg.; study code: DJ 0968; BE_ RMCA _INS. Iso. 059947 .

DEMOCRATIC REPUBLIC OF THE CONGO • soldier, worker; Luali ; 5°6′ S, 12°29′ E; 26 Aug. 1912; J. Bequaert leg.; study code: DJ 0058; initially C. fungifaber in RMCA; BE RMCA INS. Iso. 059234 • soldier, worker; Luali ; 5°6′ S, 12°29′ E; 26 Aug. 1913; J. Bequaert leg.; study code: DJ 0614; initially C. gibbifrons ; AMNH • soldier; Sona Pangu ; 5°30′ S, 13°55′ E; 9 Apr. 1948; A. Emerson leg.; study code: DJ U117; initially C. gibbifrons ; NHMUK 13671905 • soldier, worker, ♂ (king), ♀ (queen); Sona Pangu ; 5°30′ S, 13°55′ E; 9 Apr. 1948; A. Emerson leg.; study code: DJ 0615; initially C. gibbifrons ; AMNH • soldier, worker; Luki ; 5°39′ S, 13°4′ E; 19 Apr. 1965; A. Bouillon leg.; study code: DJ 0890; initially Cubitermes sp. in RMCA; BE RMCA INS. Iso. 059229 • soldier; Luki ; 5°39′ S, 13°4′ E; 20 Sep. 1965; G. Mathot leg.; study code: DJ B280; initially Cubitermes sp. in RMCA; BE RMCA INS. Iso. 059218 • soldier; Luki ; 5°39′ S, 13°4′ E; 20 Sep. 1965; G. Mathot leg.; study code: DJ B281; initially Cubitermes sp. in RMCA; BE RMCA INS. Iso. 059219 • soldier; Luki ; 5°39′ S, 13°4′ E; 20 Sep. 1965; G. Mathot leg.; study code: DJ B284; initially Cubitermes 2 in RMCA; BE RMCA INS. Iso. 059222 • soldier; Luki ; 5°39′ S, 13°4′ E; 20 Sep. 1965; G. Mathot leg.; study code: DJ B288; initially Cubitermes sp. in RMCA; BE RMCA INS. Iso. 059224 • soldier; Luki ; 5°39′ S, 13°4′ E; 20 Sep. 1965; G. Mathot leg.; study code: DJ B289; initially Cubitermes sp. in RMCA; BE RMCA INS. Iso. 059216 • soldier, worker; Luki ; 5°39′ S, 13°4′ E; 20 Sep. 1965; A. Bouillon (?) leg.; study code: DJ 0176; BE RMCA INS. Iso. 059225 • soldier, worker; Luki ; 5°39′ S, 13°4′ E; 20 Sep. 1965; G. Mathot leg.; study code: DJ 0888; initially Cubitermes sp. in RMCA; BE RMCA INS. Iso. 059226 • soldier, worker; Luki ; 5°39′ S, 13°4′ E; 20 Sep. 1965; G. Mathot leg.; study code: DJ 0889; initially Cubitermes sp. in RMCA; BE RMCA INS. Iso. 059227 • soldier, worker, ♀ (queen); Luki ; 5°39′ S, 13°4′ E; 20 Sep. 1965; G. Mathot leg.; study code: DJ 0915; initially Cubitermes sp. in RMCA; BE RMCA INS. Iso. 059231 • soldier, worker, ♀ (queen); Luki ; 5°39′ S, 13°4′ E; 20 Sep. 1965; G. Mathot leg.; study code: DJ 0916; initially Cubitermes sp. in RMCA; BE RMCA INS. Iso. 059232 • soldier; Mbamba Kilenda ; 4°55′ S, 15°30′ E; 19 Oct. 1966; C. Nkakala leg.; study code: DJ B311; initially Cubitermes sp. in RMCA; BE RMCA INS. Iso. 059150 • soldier; Luki ; 5°39′ S, 13°4′ E; 1 Apr. 1971; A. Bouillon leg.; study code: DJ B278; initially Cubitermes sp. in RMCA; BE RMCA INS. Iso. 059214 • soldier; Luki ; 5°39′ S, 13°4′ E; 1 Apr. 1971; A. Bouillon leg.; study code: DJ B279; initially Cubitermes sp. in RMCA; BE RMCA INS. Iso. 059215 • soldier, worker, ♂ (king); Kai Tshianga ; 5°51.5′ S, 12°42′ E; 2 Apr. 1971; A. Bouillon leg.; study code: DJ 0917; initially Cubitermes 2 in RMCA; BE RMCA INS. Iso. 059233 • soldier; Kai-Tshianga ; 5°52′ S, 12°42′ E; 2 Apr. 1971; A. Bouillon leg.; study code: DJ B305; initially Cubitermes 2 in RMCA; BE RMCA INS. Iso. 059217 • soldier; Kai-Tshianga ; 5°52′ S, 12°42′ E; 2 Apr. 1971; A. Bouillon leg.; study code: DJ B306; initially Cubitermes 2 in RMCA; BE RMCA INS. Iso. 059220 • soldier; Kai-Tshianga ; 5°52′ S, 12°42′ E; 2 Apr. 1971; A. Bouillon leg.; study code: DJ B307; initially Cubitermes sp. in RMCA; BE RMCA INS. Iso. 059223 • soldier, worker; Kai-Tshianga ; 5°52′ S, 12°42′ E; 2 Apr. 1971; A. Bouillon leg.; study code: DJ 0892; initially Cubitermes sp. in RMCA; BE RMCA INS. Iso. 059228 • soldier; Kiemi ; 5°32′ S, 12°49′ E; 2 Apr. 1971; A. Bouillon leg.; study code: DJ B310; initially Cubitermes 2 in RMCA; BE RMCA INS. Iso. 059221 • soldier, worker; Kiemi ; 5°16′ S, 12°34′ E; 2 Apr. 1971; A. Bouillon leg.; study code: DJ 0893; initially Cubitermes sp. in RMCA; BE RMCA INS. Iso. 059230 .

GABON • soldier; Mekambo ; 1°0.4′ N, 13°56′ E; Jan. 1957; P.-P. Grassé and C. Noirot leg.; study code: DJ P158; GenBank no PQ679204 (mitogenome); MNHN EP9829 • soldier; Piste du Bouéni ; 0°20′ N, 13°11′ E; Jan. 1957; P.-P. Grassé and C. Noirot leg.; study code: DJ P170; MNHN EP9831 • soldier; route Makokou–Booué ; 0°35′ N, 12°45′ E; Jan. 1957; P.-P. Grassé and C. Noirot leg.; study code: DJ P161; GenBank no PQ679219 (mitogenome); MNHN EP9830 • soldier; Piste du Bouéni ; 0°44′ N, 13°12′ E; Jan. 1957; P.-P. Grassé and C. Noirot leg.; study code: DJ P160; MNHN EP9881 • soldier; Piste du Bouéni , km 53; 0°44′ N, 13°12′ E; Jan. 1957; P.-P. Grassé and C. Noirot leg.; study code: DJ P165; MNHN EP9882 • soldier, worker; Route Makokou–Mekambo ; 0°41′ N, 13°2′ E; 24 Mar. 1962; J. Pasteels leg.; study code: DJ 0722; initially C. heghi ; NHMUK • soldier, worker; Simintang ; 0°34′ N, 12°42′ E; 16 Apr. 1962; J. Deligne leg.; study code: DJ 0721; initially C. heghi ; NHMUK • soldier; Forêt des Abeilles ; 0°19′ S, 12°7′ E; 1995; C. Bordereau (?) leg.; study code: DJ P215; MNHN EP9828 • soldier; La Lopé N.P.; 0°15′ S, 11°35′ E; 7 Mar. 1998; M. Harry leg.; study code: DJ P246; GenBank no PV564650 (mitogenome); MNHN EP9883 • soldier, worker; La Lopé N.P.; 0°15′ S, 11°35′ E; 9 Mar. 1998; M. Harry leg.; study code: DJ 0621; GenBank nos DQ246543 ( COII) DQ246533 ( ITS2) PQ679175 (mitogenome); initially C. aff. subarquatus “spC” (cf. Roy et al. 2006); MNHN EP9834 • worker; La Lopé N.P.; 0°12.7′ S, 11°33.5′ E; 9 Mar. 1998; M. Harry leg.; study code: DJ 0627; GenBank nos DQ127304 ( COII), DQ246537 ( ITS2), PQ679232 (mitogenome); initially C. aff. subarquatus “spC” (cf. Roy et al. 2006); MNHN EP9835 • soldier, worker; La Lopé N.P.; 0°15′ S, 11°35′ E; 9 Mar. 1998; M. Harry leg.; study code: DJ 0628; GenBank nos DQ127303 ( COII), DQ246531 ( ITS2), PQ679186 (mitogenome); initially C. aff. subarquatus “spC” (cf. Roy et al. 2006); MNHN EP9836 • soldier, worker; La Lopé N.P.; 0°16.7′ S, 11°33′ E; 9 Mar. 1998; M. Harry leg.; study code: DJ 0922; MNHN EP9832 • soldier, worker; La Lopé N.P.; 0°16.7′ S, 11°33′ E; 11 Mar. 1998; M. Harry leg.; study code: DJ 0629; GenBank nos DQ127307 ( COII), DQ246534 ( ITS2), PQ679180 (mitogenome); initially C. aff. subarquatus “spC” (cf. Roy et al. 2006); MNHN EP9837 • soldier, worker; La Lopé N.P.; 0°12.7′ S, 11°33.5′ E; 13 Mar. 1998; M. Harry leg.; study code: DJ 0630; GenBank nos DQ246544 ( COII), DQ246535 ( ITS2), PQ679240 (mitogenome); initially C. aff. subarquatus “spC” (cf. Roy et al. 2006); MNHN EP9838 • soldier, worker; La Lopé N.P.; 0°12.7′ S, 11°33.5′ E; 13 Mar. 1998; M. Harry leg.; study code: DJ 0631; GenBank nos DQ127306 ( COII), DQ246536 ( ITS2); initially C. aff. subarquatus “spC” (cf. Roy et al. 2006); MNHN EP9839 • soldier, ♂ (king); La Lopé N.P.; 0°15′ S, 11°35′ E; 16 Mar. 1998; M. Harry leg.; study code: DJ P239; MNHN EP9833 .

Historical review

The soldier alone was first described shortly as Cubitermes bulbifrons by Sjöstedt (1924b: 256) on a sample from Mukimbungu, DRC; all castes were subsequently described in Sjöstedt (1926: 247–248) on a sample from Gabon. In the same papers, Sjöstedt (1924b: 255) described shortly the soldier of Cubitermes heghi , whose soldier and worker he described with more details (1926: 249) on a sample from Mukimbungu, DRC. He considered both species as very similar, C. bulbifrons being somewhat larger than C. heghi . Sjöstedt (1926: 221–226) included both species in a key of the Cubitermes soldiers and inserted them in a “ bulbifrons -Gruppe” of species with an upwards humped frons. He also included C. bulbifrons in a key of the imagines ( Sjöstedt 1926: 218–220).

Snyder (1949: 157) catalogued Cubitermes bulbifrons and C. heghi in the sub-family Termitinae .

Ruelle (1975: 7) established C. heghi as a junior synonym of C. bulbifrons ; however, Ruelle (1992: 500), changed his mind and established C. bulbifrons as a junior synonym of C. heghi for a reason of page priority. Krishna et al. (2013: 1916) housed Cubitermes bulbifrons in the sub-family Cubitermitinae ; espousing the view of Ruelle (1975) but contesting the reversal of precedence proposed by Ruelle (1992), they therefore considered this species as the senior synonym of C. heghi . Synonymy of the two species is compatible with their enteric valve morphology, as both species belong to the same finitimus valve group ( Josens & Deligne 2019: 42–44).

Hellemans et al. (2021: 233) placed this species in the restored genus Isognathotermes .

Cubitermes aff. subarquatus “spC”, mentioned by Roy et al. (2006) in La Lopé National Parc, Gabon was considered a cryptic species on a genetical base. Hellemans et al. (2021: 231) placed it in the restored genus Isognathotermes and maintained its cryptic status. But with the recent sequencing of several samples of I. bulbifrons (not available in 2021), it turned out that C. aff. subarquatus “spC” must become a junior synonym of I. bulbifrons .

Mirotermes ( Cubitermes) kemneri was described by Emerson (1928: 509); this species was synonymized with C. zenkeri by Ruelle (1975: 8; 1992: 501). However, the EVAs do not support this synonymy ( Josens & Deligne 2019: 42–44, 62). Cubitermes kemneri is proposed, here, as a junior synonym of I. bulbifrons .

Despite the difference in size, recent sequencing of the mitogenomes confirmed synonymy of I. gibbifrons with I. bulbifrons , a synonymy that had been suspected by the fact that several samples of I. bulbifrons and I. gibbifrons had been found in the same locations.

The NHMUK collection contains two samples from incipient colonies (DJ 0725 and DJ 0726) and two samples of very young colonies (DJ U104 and DJ U109) that were collected at Edea, Cameroon, by N.M. Collins; they are identified as I. bulbifrons based on their queens (not at all physogastric but wingless and with shortened antennae). If the soldiers had been used instead, the resulting identification would have be ‘ I. congoensis’. It is indeed well known ( Noirot 1955; Mathot 1964; and personal (G.J., J.D.) observations) that the first soldiers and workers produced by young colonies are significantly smaller than the soldiers and workers of mature colonies. In the PCA ( Fig. 22), the ellipse labelled “c+b” pools I. congoensis and the young societies of I. bulbifrons : it shows a strong difference of size (x-axis) from mature colonies (labelled ‘bulb’); moreover, it is stretched because it is made up on the one hand of the two incipient colonies plus the two I. congoensis samples (the four points furthest to the left = smallest individuals) and, on the other hand, of the two very young colonies (slightly larger individuals). Therefore, the samples identified as I. congoensis (the imagines of them being unknown), might also be incipient colonies of I. bulbifrons , hence their location in the chapter Incertae sedis .

Redescription

Imago

The description provided by Emerson (1928: 511–513) under the name Mirotermes ( Cubitermes) heghi concerned in fact Cubitermes (now Polyspathotermes ) sulcifrons . The imago of P. heghi has indeed a much smaller fontanelle and, among the species of the former Cubitermes genus of West Africa, only imagines of P. sulcifrons show a fontanelle as large as that described and figured by Emerson ( Josens & Deligne 2019: 62). Further, the imago of Cubitermes kemneri was never described, so the imago of I. bulbifrons was only described to-date by Sjöstedt (1926: 247–248) based on alates and queen from Gabon (not examined).

COLOUR. Head capsule: well sclerotised, dark, C6–C7; fontanelle concolorous or almost so with head capsule. Postclypeus C5–C6 slightly paler (one level) than head capsule. Antennae C5–C6 without any difference between proximal and distal articles. Thorax: pronotum C6–C7, as head capsule; meso- and metanotum C6–C7, as pronotum. Legs C4–C5, tibia usually slightly (one level) darker than femur. Wings hyaline with brown to grey tinge (Cf3–Cf4), anterior veins darker. Abdomen: tergites C6–C7. 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, mainly near the eyes, and a higher density of shorter, finer setae everywhere. 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 magnification 50× or more). Thorax: pronotum with prominent setae mainly on margins and many shorter ones in middle; meso- and metanotum with some fine, pale setae, arranged in a medio-longitudinal strip, generally visible at 20–40×; sometimes three to four larger setae on metanotum. Legs very pilose, furnished (among numerous fine setae) with some fine spines: 6–11 on the carina of fore coxa and 1–3 on the ventral side; tibia pilose; fore, mid, and hind tibia furnished with 30–40 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 3; Figs 26–27, 35). Size: the imagines of I. bulbifrons are, on average, rather variable ( Fig. 26); some individuals (with I. zenkeri ), have the largest apical teeth and the largest apico-marginal distances (IMlAmD = 0.20–0.30 mm ( Fig. 27). Head capsule: compound eyes nearly round; fontanelle generally a tiny elongate marking; ocelli nearly round to oval removed from eyes by a distance about equal to 0.7 to 1.3 ocellus small diameter. Antennae: 16 articles on alate individuals, always shortened by amputation by one to three articles in queens and kings. Labrum: cupola shaped. Left mandible with apical tooth, on average, longer than in most other species of the genus and always longer and more prominent than first marginal; marginal teeth three in number but second one only suggested by a slight undulation of edge between first and third marginal teeth; only the apical tooth is acute in unworn specimens; premolar tooth with proximal end obscured or partly obscured by molar prominence in dorsal view; molar tooth bearing a rounded molar prominence dorsally and ending posteriorly in a tiny acute apophysis. Right mandible with apical tooth always longer and 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 slightly 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 sharp carina. Wings: R1 fused entirely with costal margin, sclerotised; Rs simple, sclerotised; M and Cu not or weakly sclerotised with 2–3 and 10–11 branches, respectively.

Soldier

COLOUR. Head capsule generally Cd4–Cd6 becoming fader and darker (e.g., Cf5–Cf7) in long preserved samples; there is frequently a gradient from a darker frons to a paler back (e.g., C6 → C4). Gulamentum concolorous with or somewhat darker than head. Antennae and labrum somewhat paler (one to two levels) than head capsule. Mandibles dark (C7–C8) generally with an abrupt clearing on their bases (two palette levels) which is generally the same colour as frons. Thorax, nota and legs paler than head capsule (C3–C5) somewhat darker in long preserved samples. Abdomen grey to red-brown owing to digestive bolus, sometimes with a yellow tinge on tergites.

SETATION. Head capsule with few scattered setae; on frons a dense bunch of hair-like setae surrounds and overhangs fontanelle. Antennae with some prominent setae, 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). Labrum always with 5–9 large setae on each lobe. Thorax: pro- and mesonotum with some setae located mainly on margins. Legs: fore coxa furnished with 0–3 spines on carina and not any one on ventral side; trochanter generally with some long lined-up setae, sometimes with four to seven spines; fore, mid, and hind tibia bearing 3, 2, 2 apical spurs and 0, 2, 0 subapical spurs respectively; all tibiae furnished with a row of 6–15 spines. Abdomen: tergites with some large setae, mainly or only on their posterior margins. Sternites with long setae, erect or slightly directed forward, often coloured, and smaller setae directed backwards.

STRUCTURE (measurements in Table 3; Figs 28–29, 36). Size: the soldiers of I. bulbifrons are rather variable, the largest of them are (with those of I. magniplanifrons ) the largest of the genus Isognathotermes ; this is best seen in the length of the soldiers’ heads ( Fig. 28). Head capsule: always clearly sclerotised and appreciably longer than wide. Dorsal view: lateral sides mostly subparallel with a narrowing near posterior third or fourth (however, in the soldiers of incipient or very young colonies, lateral sides are slightly convex without any narrowing); from antennal sockets sides converge more or less clearly towards bases of mandibles; posterior side variable. In profile: upper profile always clearly concave, even in soldiers from incipient colonies; frons with a small frontal hump (rarely with no hump) overhanging the fontanelle, even in soldiers from incipient colonies. Gulamentum in ventral view always more or less constricted in its posterior half, with sides of anterior part softly curved or forming an acute widening or even a kind of ear on each side; generally, with a flat posterior part from side view. Antennae: of 15, sometimes 14.5, articles (only 13 articles in one soldier from an incipient colony). Labrum: always deeply bifurcate and wider than long, with sides generally lyre-shaped, rarely straight; lobes angular, with fine, whitish or translucent tips; anterior margin concave. Mandibles: sabre-like, almost hooked distally; inner edges smooth with one distinct but generally very small marginal tooth, near molar tooth on each mandible; mandibles clearly shorter than head; entire surface of both mandibles smooth and glossy. Right mandible generally slightly more curved than left. Thorax: pronotum sellate, as wide as 52–68% of head width, with generally entire anterior and posterior margins. Fore coxa flanged ventrally resulting in a carina. Gut: enteric valve seating on left side, best seen in ventral view, situated in posterior half of abdomen. Arrangement of enteric valve cushions showing trilateral symmetry: the odd cushions are on average 17% longer than the even cushions, generally without any hump or with humps weakly developed, however, the pilosity becoming abruptly very dense shows the place where a hump is expected ( Fig. 6); secondary cushions wide at the upstream end narrowing noticeably downstream with a homogeneous spine scattering. Caecum always rather small, best seen in ventral view, near centre of abdomen, lobed (two or three small lobes).

Worker

COLOUR. Head capsule pale (C1–C3) turning grey in long preserved samples. Antennae: proximal articles pale (C2–C3), distal articles always one to two levels darker (C4–C5). Thorax, nota and legs pale (C1–C3). 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 1–3 on ventral side; fore trochanter with 5–7 spines; fore, mid, and hind tibia bearing 3, 2, 2 apical spurs and 0, 2, 0 subapical spurs respectively and a row of 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 3; Figs 30–31, 37). Size: the workers of I. bulbifrons are among the medium sized to the largest of the genus Isognathotermes (with large overlapping on several other species: Fig. 30). Head capsule: weakly sclerotised (except mandibles). Antennae: generally 14.5 articles, 14 in workers from incipient colonies. Labrum: cupola shaped. Left mandible: apical tooth well developed with a sharp tip when fresh; marginal teeth three in number, first marginal well developed but Fig. 36 (continued on next page). Isognathotermes bulbifrons (Sjöstedt, 1924) and junior synonym species: soldiers. Lateral and dorsal views of a soldier’s head capsule, ventral view of its mandibles, and dorsal view of its labrum. A. From type colony of Cubitermes bulbifrons Sjöstedt, 1924 (DJ 0298). B. From type colony of Cubitermes heghi Sjöstedt, 1924 (DJ 0290). C. From type colony of Mirotermes ( Cubitermes) kemneri Emerson, 1928 (DJ 0297). D. From type colony of Cubitermes gibbifrons Sjöstedt, 1924 (DJ 0280). with a blunt tip even when fresh, second marginal faint (visible as an undulated edge but disappearing in worn mandibles), third marginal with a blunt tip; premolar tooth with its proximal end generally hidden under molar prominence; molar tooth bearing a rounded molar prominence dorsally and ending posteriorly in a tiny acute apophysis. Right mandible: apical tooth well developed with a sharp tip when fresh; marginal teeth two in number; first marginal well developed with a sharp tip when fresh; second marginal 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 64 to 78% 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 posterior half of abdomen. Arrangement of enteric valve cushions of the finitimus pattern with triradial symmetry: the odd PCs, in their downstream part, are wide and bear at that place a high density of rather short bristles on a globular bulge; supporting bristles are generally numerous: 22–38 on each side of the odd PCs; secondary cushions are wide at the upstream end, narrowing noticeably downstream with a homogeneous spine scattering. Caecum always rather small, visible in ventral view, near centre of abdomen, shortly lobed (three, rarely two or four, small lobes, sometimes only sketched).

Fig. 36 (continued). E. From “ C. aff. subarquatus spC” (DJ 0621). F. From an incipient colony of I. bulbifrons (DJ 0725). G. From type colony of Mirotermes ( Cubitermes) congoensis Emerson, 1928 (DJ 0299), probably also an incipient colony of I. bulbifrons (Sjöstedt, 1924) (labrum somewhat distorted by dessication).

Fig. 37 (continued on next page). Isognathotermes bulbifrons (Sjöstedt, 1924) and junior synonym species: soldiers and workers. PC1s of soldier’s and worker’s enteric valves, worker’s caecum and foreleg. A. From type colony of Cubitermes bulbifrons Sjöstedt, 1924 (DJ 0298). B. From type colony of Cubitermes heghi Sjöstedt, 1924 (DJ 0290), the downstream end of worker’s PC1 is twisted. C. From type colony of Mirotermes ( Cubitermes) kemneri Emerson, 1928 (DJ 0299). D. From type colony of Cubitermes gibbifrons Sjöstedt, 1924 (DJ 0280).

Chorology-ecology

This species has been collected in the northwestern Congolian lowland forest and the Atlantic equatorial coastal forest ecoregions ( Cameroon, Gabon, DRC and Angola) up to about 300 km from the Atlantic coast ( Fig. 38).

Molecular data

The species I. bulbifrons corresponds to the Cubitermes “spC” in Roy et al. 2006 and Hellemans et al. 2021, proposed on basis of the COII gene. Our present sampling includes full mitogenomes from Gabonese samples previously published under the appellation “ Cubitermes aff. subarquatus spC” by Roy et al. (2006), which we herein formally assign to I. bulbifrons .

Ten mitogenomes of I. bulbifrons collected from Gabon and Cameroon are published alongside this work (GenBank accessions: see Supp. file 3 and ‘Material examined’). Overall, mitogenomes exhibit less than Fig. 37 (continued). E. From “ Cubitermes aff. subarquatus spC” (DJ 0621). F. From an incipient colony of I. bulbifrons (Sjöstedt, 1924) (DJ 0726). G. From type colony of Mirotermes ( Cubitermes) congoensis Emerson, 1928 (DJ 0299 & 0484), which is, probably, also an incipient colony of I. bulbifrons .

2% dissimilarity with each other (Supp. file 4 with the samples DJ 0621 and DJ P158 being the most dissimilar). Of the ten samples sequenced, nine belonged to the large form of I. bulbifrons and only one (DJ P246) to the former I. gibbifrons (the medium-sized form of I. bulbifrons ).