Revision of the palm-pollinating weevil genus Elaeidobius Kuschel, 1952 (Curculionidae, Curculioninae, Derelomini) with descriptions of two new species

Abstract. The genus Elaeidobius Kuschel, 1952 (Curculionidae, Curculioniae, Derelomini) is an Afrotropical genus associated with the male inflorescences of the oil palm Elaeis guineensis Jacq. The activity of species in this genus is critical for pollen transportation and for the fruit set of this economically important palm. In this study, the genus Elaeidobius was revised using an integrative taxonomic approach, combining traditional taxonomic treatment of species and an analysis of sequences of mitochondrial genes (COI and COII). A total of eight species is now recognized: five now formally included within it [E. bilineatus Hustache, 1924) comb. nov., E. kamerunicus (Faust, 1898) comb. nov., E. plagiatus (Fåhraeus, 1844) comb. nov., E. singularis (Faust, 1898) comb. nov., E. subvittatus Faust, 1898)], one transferred here from the genus Prosoestus to the genus Elaeidobius, E. spatulifer (Marshall, 1950) comb. nov., and two newly described species (E. pilimargo Haran & Kuschel sp. nov., E. piliventris Haran & Kuschel sp. nov.). The following new synonymies are proposed: Prosoestus armatus voss, 1956 = E. bilineatus (Hustache, 1924) comb. nov. and Derelomus uelensis Hustache = E. singularis (Faust, 1898). An illustrated key to the species is provided with photographs of the adult habitus and male genitalia.

Among these genera, the genus Elaeidobius has received attention due to its association with the inflorescences of the African oil palm (Elaeis guineensis Jacq., Arecaceae) a species native to tropical Africa, where it is traditionally used by local populations for its oil (Sheil et al. 2009). The activity of species belonging to Elaeidobius is critical for pollen transportation and for the fruit set of this plant (Mariau et al. 1991;Li et al. 2019). In return, the palm provides these weevils with support for larval development, constituting an exemplary case of mutualism. In a context of widespread cultivation of this oil palm across its native range and elsewhere, there is a need to review the identity of species of Elaeidobius to gain a better understanding of their exact role in pollinating their host.
The genus Elaeidobius was first created by Kuschel (1952) for Derelomus elaeisae Bondar, 1942 in a key of New World genera of Derelomini. Apart from this key, no diagnosis was provided for this monobasic new genus (Alonso-Zarazaga & Lyal 1999), but among other genera the species of Elaeidobius were distinguished by the presence of transversal eyes, of a prosternal process forming a protruding lamina and of a lateral carina on the pronotum. Later, Kuschel (1955) recognized the synonymy between Elaedobius elaeisae (Bondar, 1942) and Derelomus subvittatus Faust, 1898, an African species associated with Elaeis guineensis that was accidentally introduced into South America with this palm. As a consequence of this synonymy, other African species closely related to E. subvittatus (Faust, 1898) fell into this genus, although no transfer has been formally made (E. bilineatus Hustache, 1924, E. kamerunicus Faust, 1898, E. plagiatus Fåhraeus, 1844and E. singularis Faust, 1898.
As a result of this, the genus Elaeidobius is lacking a formal taxonomic treatment. In this study, the genus is revised. An integrative taxonomic approach, combining traditional taxonomic treatment of species and sequencing of mitochondrial gene fragments, is used to clarify species identity. An illustrated key to the species is provided with photographs of the adult habitus and male genitalia. An update of known distribution and host plant records is also provided.

Diagnosis
Eyes flat, following contour of head. Head not or hardly depressed above forehead. Elytra with interstria 9 or 10 costate in part, with costa at apex flat, not extending to apical margin; area on declivity between interstriae 3 and 9 not impressed. Fore and middle tibiae mucronate, hind tibiae with or without mucro. Claws free, simple. Tergites well-pigmented, divided or not along midline; spiracle surrounding not darkened.
Among the Afrotropical Derelomini, the genus Elaeidobius is close to the genera Derelomus and Prosoestus Faust, 1899, which both contain species associated with inflorescences of Arecaceae Bercht. & J.Presl. The species belonging to the genus Elaeidobius can be distinguished by the key provided at the end of the results section.

Distribution
This genus is native to West and central Africa (  Lajis et al. 1985;Hussein et al. 1989).

Species-group: subvittatus Diagnosis
Characterised by a smaller size (1.4-3.0 mm) and a more compact body. Prosternum in male armed with a protruding process, variable in shape and size, occasionally absent in smaller specimens. Pronotum lacking depressions and fold on anterior half and fovea on middle of disc on either side of midline. Lateral carina of prothorax forming a constriction near collar (Fig. 5A), followed by a distinct indentation. Three species in this group. (Hustache, 1924)   Colour. reddish or yellowish brown with dark markings on pronotum and elytra, also sterna darkened.
Prothorax. Disc with a pair of dark stripes, slightly convergent; lateral carina continued to apex with a distinct indentation or interrupted, in lateral view strongly curving upwards before apical collar.
elytra. Presence of irregular dark stripes, generally with a short one in middle of interstria 2, and an elongate one along interstria 6 from basal quarter to top of declivity, often expanding on interstriae 5 and 7, a further stripe on interstria 9; punctures of striae as wide as width of interstriae or slightly smaller; interstriae with a row of very short recumbent hairs. Prosternal process in male variously developed, from a large spatulate structure to a reduced or even absent one.

Life history
Adults are found on inflorescences of Elaeis guineensis (Arecaceae), the African oil palm. (JH pers. obs.).

Remarks
Elaeidobius bilineatus has, in lateral view, the marginal carina of the prothorax strongly upcurved, a character that safely distinguishes this species from all others of the genus. As Elaeidobius is said to be a West African genus, its presence in Tanzania is unexpected and it has to be confirmed whether it is a native or an introduced element. Elaeidobius bilineatus was described by Hustache as Derelomus bilineatus based on two female specimens from Haut uelé (Democratic republic of Congo) (Hustache 1924). These two specimens were located in the MRAC collection, bearing a red "holotype" label. As the original description of this species did not designate a holotype, one of them was designated as the lectotype for this species and was labelled accordingly. The second syntype was labelled as paralectotype. The other specimens from the same collecting event (2 ♀♀) are not part of the type series. We examined the holotype of the species Prosoestus armatus voss, 1956, described from a single male specimen from Senegal (La Digue nr Rufisque). A detailed observation of the external and internal morphology of this specimen showed no difference from the lectotype of Elaeidobius bilineatus. As a result of this, Prosoestus armatus voss, 1956 should be considered as a junior synonym of E. bilineatus.

Other material
Other specimens identified and labelled by G. Kuschel at NHMUK and NZAC.
Colour. Derm dorsally reddish brown, ventrally dark brown, elytra vaguely darker on interstria 2 and laterally on interstriae 6 and 7; antennae and legs reddish or yellowish.
head. Forehead not impressed in either sex. rostrum in male about as long as prothorax, in female 1.2 × as long, moderately robust and downcurved, with a slight postmental elevation in male.
Prothorax. uniformly coloured, lacking stripes and foveae; lateral carina in dorsal view uninterrupted at apex, with conspicuous cuticular expansion in male, carina in lateral view moderately upcurved in male, gently in female towards apical collar. elytra. A low costa on interstria 9 gradually fading towards end; pubescence inconspicuous, very sparse, with a row of more conspicuous hairs on interstriae. Prosternal process of male variable in size, the apex rounded without a lateral lobe.
genitalia. Penis as long as last four ventrites; body deeply pigmented, 2.9 × as long as apodemes (ratio w/l: 0.19), widest near basal third, then tapering to less than one third of its width, widening moderately to an asymmetrical apex (Fig. 4B); internal sac without sclerite.

Remarks
The species is distinguished by a uniform dark colour, and in the male by a prominent spade-like prosternal process and lack of a postmental tubercle. No DNA-grade material of this species could be obtained in the course of this study. (Faust, 1898) Figs 1C, 2C, 4C, 5A-B, E, G, M, 7
head. Forehead slightly impressed. rostrum in male as long as prothorax, in female 1.2 to 1.3 × as long as prothorax, with small postmental tubercle in male visible in lateral view.
Prothorax. Disc lacking impressions; carina interrupted or not at collar, with small cuticular expansion, in lateral view gently curved upwards towards apex. elytra. Interstriae with a distinctive row of elongate hairs on middle, hairs as long as width of interstriae; striae with a row of very short recumbent hairs; prosternum in male large and trilobed, or rudimentary and reduced to a cuticular elevation, sometimes absent.
genitalia. Penis as long as last three ventrites plus ⅓ of ventrite 2; body 3 × as long as apodemes, about 4 × as long as wide (ratio w/l: 0.24), slightly asymmetrical, tilted to the right (Fig. 4C); internal sac without an obvious sclerite.

Remarks
Elaeidobius subvittatus is readily distinguished from all other species by its smaller size, and in males by a small tubercle on the underside at the rostrum apex. The populations of South America were introduced accidentally. This taxon was described on a single female from Landana. In the collection of J. Faust housed at MTD, we found this specimen bearing a red "type" label with the identification "subvittatus Fst.", "Landana, Congo". This specimen is the holotype of Derelomus subvittatus Faust, 1898 and was labelled accordingly. Hustache, 1924, was described from three specimens (1 ♂, 2 ♀♀) from Yambata, 10 Dec. 1912 (Democratic republic of Congo). This species was then put in synonymy with D. subvittatus (= Elaeidobius subvittatus Faust) by Marshall (1930). The three syntypes of D. maynei were located in MrAC. The male is designated here as the lectotype of this species and the two females are labelled as paralectotypes.

Species-group plagiatus Diagnosis
Characterised by larger size and slender body. Prosternum in male never armed with a protruding process. Pronotum with depressions and fold on anterior half and fovea on middle of disc on either side of midline. Lateral carina of prothorax regular, not forming a constriction or indentation near collar (Fig. 5C). Five species in this group. (Faust, 1898) Hustache, 1924: 76 [syn. by Marshall 1930. Derelomus congoanus Hustache, 1924: 77 [syn. by Marshall 1930.
head. Forehead in male with prominent carinae against eyes and depressed between them, in female with low or obsolescent carina and not depressed; rostrum in male 1.1 × as short as prothorax, in female 1.5 × as long as prothorax, cylindrical, 5-carinate in basal half, underside in male with short erect hairs and no postmental tubercle.
Prothorax. Disc in lateral view nearly flat, usually with minute fovea on either side of middle; carina fine, in male obsolete or obsolescent on basal half, ending in prominent, somewhat auriculate carina without constriction at base of collar.
elytra. In male alutaceous, dull, moderately curved from shoulders to apex; base of interstria 4 usually raised to a yellow tumour or swelling bare of erect hairs; apical ⅔ of sutural interstria raised, bearing long erect setae; interstria 9 in male swollen, somewhat inflated, bearing long curved erect setae, in female costate, with costa flat, not continued to apex.
genitalia. Penis as long as last three ventrites; body about 3 × longer than wide (ratio w/l: 0.36), symmetrical, sides sub-parallel, relatively broadly rounded at apex (Fig. 4D); with small median sclerites in the body.

Life history
On and in flowers of Elaeis guineensis (Arecaceae), the oil palm. Males and females show a peak of flight activity around the inflorescences between 3 and 6 hours after sunrise (Auffray et al. 2017).

Remarks
Elaeidobius kamerunicus is distinctive in its dark body colour and yellow spots on elytra. This species is being imported by increasing numbers of countries to facilitate pollination of oil palms in plantations (Syed 1982). In its native range, E. kamerunicus exhibits two genetically differentiated populations that are roughly distributed on each side of the cameroon volcanic line (Haran et al. 2020). This taxon was described based on a single female from Cameroon without more detailed indications. In the collection of J. Faust housed at MTD, we found this specimen with the identification "kamerunicus" and bearing a red "type" label. This specimen is the holotype of Derelomus kamerunicus Faust, 1898 and was labelled accordingly. Derelomus callosus Hustache, 1924 was described based on a series of individuals from two localities of the Democratic republic of Congo (Yambata, 10 Dec. 1912 andKindu, Nov. 1913). This species was later put in synonymy with D. kamerunicus (= Elaeidobius kamerunicus) by Marshall (1930), but no particular specimen from these series was designated as holotype. In the collections of the MRAC, three male specimens from these localities and bearing the red labels "Holotypus" and "Paratypus" were located. The specimen from Yambata and bearing the label "Holotypus" is here designated as the lectotype for D. callosus. The two specimens from Kindu and bearing the label "Paratypus" are labelled as paralectotypes. Derelomus congoanus was described based on a series of individuals from two localities of the Democratic republic of Congo (Yambata, 10 Dec. 1912 andHaut-uelé, Moto, 1920). This species was also put in synonymy with D. kamerunicus (= Elaeidobius kamerunicus) by Marshall (1930). The specimens used to describe Derelomus congoanus are in fact females of Elaeidobius kamerunicus that Hustache took to be a distinct species. As for the previous species, no particular specimen from the type series was designated as holotype. In the collection of the MRAC, one female from Haut-Uelé (1920) and bearing a red label "Holotypus" was located. It is here designated as the lectotype of Derelomus congoanus and labelled accordingly. In the same collection, 8 females from Yambata (10 Dec. 1912) and bearing a red "Paratypus" label were labelled as paralectotypes of this species.  Colour. Yellow or reddish brown metasternum, antennal club in part darker; often prothorax and elytra with dark stripes or oblique bands; in male, elytra with long erect setae on margins and on suture but not on base of interstria 4.

Elaeidobius pilimargo
head. Strongly punctate, punctuation partly confluent towards frontal fovea; forehead in male with prominent carinae against eyes and depressed between them, in female with low or obsolescent carina and not depressed; rostrum in male as long as prothorax, in female 1.2-1.4 × longer, cylindrical, 5-carinate in basal ⅔, median carina widening near antennal insertion, apical ⅓ smooth and punctate, underside in male lacking erect hairs and postmental tubercle; antennae yellowish or reddish brown, insertion on rostrum median in male, antemedian in female; scape slightly curved, gradually thickening toward apex, first segment of funicle elongate, in male as long as segments 2-4, in females longer than segments 2-4, segment 2 longer than wide, 3 isodiametric, 4-7 transverse, gradually widening to width of club.
Prothorax. Sub-trapezoidal (w/l ratio: 1.46), converging in a straight or nearly straight line, deeply bisinuous at base, concavely curved at apex; apical collar at base with a transverse row of black dots; disc in lateral view nearly flat, with four impressions anteriorly, and a pair of large, deep foveae on either side of middle; integument with double punctuation, glabrous in appearance, with a very short pubescence mainly on sides at basal half; carina in lateral view obsolete or obsolescent towards base, weakly sinuous near apex, sharply carinate on collar.
elytra. Widest near middle (w/l ratio: 0.70), in male not tectiform, base of interstriae 3-5 raised to a tumour or swelling, apical ⅔ of suture darker, slightly raised with a row of erect setae, interstria 10 in male swollen, somewhat inflated bearing long upwardly curved erect setae, interstria 9 in female costate in basal ⅔; striae as wide as width of interstriae or slightly narrower, gradually fading apicad; stria 9 absent basally, starting from near height of fore coxae; dark stripe on elytra generally present on interstria 6 in basal half and between middle of interstriae 3 or 4 to 8 before declivity.
aBdomen. Tergite 7 with about 14 plectral granules; ventrites with short suberect, scattered whitish hairs; in male ventrites 1 and 2 impressed in middle, without specific pilosity on margin on impression.

Life history
All the specimens collected recently were found on inflorescences of the oil palm, Elaeis guineensis (Arecaceae) (JH pers. obs.).

Remarks
Elaeidobius pilimargo sp. nov. is characterised by its elytral margins bearing long erect setae and presence of a swelling on base of interstria 4 without erect setae in males (Fig. 5J-K). The likely females examined are not part of the type series because their identity cannot be guaranteed based on morphology. Elaeidobius pilimargo sp. nov. is morphologically close to E. singularis. Both species show a genetic distance of 2.01% on COII (JHAR00409_0201, Senegal / JHAR00283_0101, Ghana). The sequencing of the COI gene for specimens of E. singularis failed repetitively, probably due to polymorphism in the primer sequences. Within the E. plagiatus species group, the COI sequence of E. pilimargo sp. nov. showed a genetic distance of 2.88% with E. piliventris sp. nov. (JHAR02182_0101). Colour (♂). Yellowish or reddish brown, pronotum usually with vague, dark stripe, elytra with a short dark stripe on interstria 6 in basal third, and an oblique stripe from near middle of interstriae 3 or 4 to 8; integument with very short, scattered recumbent white hairs, usually forming 1-2 series on each interstria of elytron; in male elytra lacking long erect setae on margins, suture and at base of interstria 4.

Elaeidobius piliventris
head. Strongly punctate, punctuation party confluent towards frontal fovea; forehead flat between eyes; rostrum in male as long as or 1.1 × as long as prothorax, in female 1.2-1.4 × longer, cylindrical, 5-carinate in basal ⅔, median carina widening near antennal insertion, apical ⅓ smooth and punctate, underside in male lacking erect hairs and postmental tubercle; antennal scape and segments 13 of funicle reddish brown, segments 4-7 and club usually dark brown; insertion of antennae on rostrum in apical ⅔ in male, antemedian in female; scape slightly curved, gradually thickening towards apex, first segment of funicle elongate, in male slightly shorter than segments 2-4, in females longer than segments 2-4, segment 2 longer than wide, 3-7 transverse, gradually widening to width of club.
Prothorax. Sub-trapezoidal (ratio w/l: 1.33), in male sides converging in straight or nearly straight line, in female moderately rounded, deeply bisinuous at base, concavely curved at apex; apical collar at base with a transverse row of black dots; disc in lateral view nearly flat, with a pair of large, deep foveae on either side of middle; integument with double punctuation, glabrous in appearance, with a very short pubescence mainly on sides on basal half; carina in lateral view weak towards base, sharply carinate on collar.
elytra. Widest near middle (ratio w/l: 0.70), in male not tectiform, base of interstria 4 slightly swollen, not raised to a tumour, apical ⅔ of suture darker, lacking row of erect setae; interstria 10 in male flat, not inflated and lacking long erect setae, interstria 9 in female costate in basal half; striae as wide as width of interstriae or narrower, gradually fading apicad; stria 9 absent basally, starting from near height of fore coxae; dark stripe on elytra generally present on interstria 6 in basal half and between middle of interstriae 3 or 4 to 8 before declivity.
genitalia. Penis a little longer than combined length of last three ventrites, body about 2 × as long as wide (ratio w/l: 0.48), symmetrical, with relatively long, tapering apex (Fig. 4F); internal sac with a pair of small median sclerites.

Life history
All the specimens collected recently were found on the inflorescences of the oil palm, Elaeis guineensis (Arecaceae) (JH pers. obs.).

Material examined
Lectotype BETWEEN GHANA AND CONGO RIVER • ♀; "Guinea. Westermann" "♀" "Typus" "Derelomus plagiatus Colour. Yellowish or pale reddish brown; reddish or dark brown on head, rostrum, underside, a large trapezoidal central area on pronotum, a stripe on interstria 6 in basal half and an oblique band between interstriae 3 or 4 to 8 before declivity; male with long erect setae on elytral margins and erect setae on suture and swelling at the base of interstria 4.
head. Forehead in male sharply carinate on sides near eyes, flat or impressed, in female not or obsoletely carinate on sides, not impressed; rostrum in male as long as prothorax, or a fraction longer, robust, moderately downcurved, without erect hairs or tubercle on underside, in female 1.5 × as long as prothorax.
Prothorax. Trapezoidal, with nearly straight sides; disc nearly flat in lateral view, medially with two shallow impressions and two vague impressions between middle and apex; median impressions with small fovea on either side of middle; marginal carina in male obsolescent at least on basal half, carinate at apex near collar, distinctly projecting forward. elytra. In both sexes shiny, with slightly rounded sides, widest near middle, in male tectiform, distinctly sloping to the sides; striae gradually fading towards apex; base of interstria 4 in male not or slightly tumescent, with erect setae on the swelling similar to those on suture; interstria 9 in male swollen and bearing long erect setae throughout, in female costate on basal half, here rendering stria 8.
genitalia. Penis nearly as long as combined length of last 3 ventrites, Body symmetrical, 3.3 × as long as apodemes, about 3 × as long as than wide (ratio w/l: 0.32), with rather large frena (Fig. 4G).

Remarks
Elaeidobius plagiatus is distinguished in the male by long erect setae on margin of elytra, on suture and at base of interstria 4, in female by a large dark trapezoidal central area on the pronotum and a rather wide apical half of the foretibiae. The usually long marginal erect setae of males can be very short as well, as is the case with the paralectotype of D. ciliatus from Kindu (Congo) that Hustache took to be a female. Such males are also observed in low proportions in Angola.
Elaeidobius plagiatus was described by Fåhraeus as Derelomus plagiatus from "Guinea", an area that comprised the current zone between Ghana and the Congo river. In the collection of Fåhraeus housed at NHRS, a female specimen with the locality "Guinea Westermann" and bearing a red "Typus" label was located. As no particular holotype specimen was designated in the original description, this specimen was designated as the lectotype for Derelomus plagiatus Fåhraeus, 1844 and labelled accordingly. Derelomus ciliatus Hustache, 1924 was described based on a series of individuals from two localities in the Democratic republic of Congo (Haut-uelé, Moto, 1922 andKindu, 1913). This species was later put in synonymy with D. plagiatus Fåhraeus (= Elaeidobius plagiatus Fåhraeus) by Marshall (1930) but no particular specimen from these series was designated as holotype. In the collections of the MrAC, three male specimens from these localities and bearing the red labels "Holotypus" and "Paratypus" were located. The specimen from Haut-Uelé and bearing the label "Holotypus" is here designated as the lectotype for D. ciliatus Hustache. The second specimen from Haut-Uelé and the one from Kindu, both bearing the label "Paratypus" are labelled as paralectotypes for this species.  (Faust, 1898) in dorsal view showing the flat pronotum and the lateral cuticular expansion near head. B. Pronotum of E. subvittatus (Faust, 1898) in ventral view, showing the trilobate cuticular expansion between the coxae. C. Pronotum of E. plagiatus (Fåhraeus, 1844) comb. nov. in dorsal view showing the fovea on either side of midline. D. Apex of rostrum of E. bilineatus (Hustache, 1924) comb. nov. in lateral view. E. Apex of rostrum of E. subvittatus (Faust, 1898) in lateral view showing the protruding tubercle on underside. F. Elytra of E. bilineatus (Hustache, 1924) comb. nov. in dorsal view. G. Elytra of E. subvittatus (Faust, 1898) in dorsal view. H. Elytra of E. singularis (Faust, 1898) comb. nov. in lateral view. I. Elytra of E. kamerunicus (Faust, 1898) (Faust, 1898) in dorsal view. Not to scale. (Faust, 1898) comb. nov. Figs. 1H, 3D, 4H, 5H Derelomus singularis Faust, 1898: 224. Derelomus uelensis Hustache, 1932. syn. nov.
head. Forehead in male impressed. rostrum in male a fraction shorter than prothorax, without erect hairs or tubercle on underside, in female 1.5 × longer than prothorax.
Prothorax. Disc with a pair of large, deep foveae; apical collar at base usually with a transverse row of black dots; lateral carina fine, continued to apex. elytra. Without long erect setae on margin and suture, in male often with a conspicuous swelling at base of interstria, in small males reduced or absent; prosternum without protruding process.
aBdomen. Ventrite 1-2 flattened on middle, not impressed, with fine, appressed pubescence and no semi-erect hairs. Tergites 3-6 undivided on midline, tergite 7 strongly advancing forward against tergite 6; granules of stridulatory organ evenly distributed on entire line, up to 18 in number per row.
genitalia. Penis a little longer than the last three ventrites; body 2.3 × as long as apodemes, about 2 × as long as wide (ratio w/l: 0.48), symmetrical, tapering with slight curve to apex (Fig. 4H); internal sac with a pair of small frena.

Remarks
Elaeidobius singularis is readily distinguished in the male by having a tumescent 4 th interstria at the base (though reduced or even absent at times in some small individuals), and no semi-erect hairs on the abdomen, and by the elytra without long erect setae on the margin and on the suture. This taxon was described on a male and a female from Landana in the current Democratic republic of Congo. In the collection of J. Faust housed at MTD, we found a male and a female pinned on the same pin with the identification "D singularis Faust." "Landana, Congo" and bearing a red "type" label. The description of this species does not refer to a holotype, therefore the male syntype was designated as the lectotype of Derelomus singularis Faust, 1898 and was labelled accordingly. The female syntype was labelled as the paralectotype of this species.
Hustache described D. uelensis based on five specimens collected by L. Burgeon in Moto (Democratic republic of Congo). In the collections of the MrAC, only one specimen from Moto could be located and bore a red paratypus label. This specimen is here designated as the lectotype for D. uelensis and labelled accordingly. The other four specimens of this series are from Kindu and not from Moto as reported by Hustache (1932). These specimens also bear paratypus labels and were labelled as paralectotypes of this species. observations made on the external and internal morphology of specimens of this series showed no difference from the holotype of Elaeidobius singularis. Consequently, the name Derelomus uelensis should be considered as a junior synonym of Elaeidobius singularis. confirmed the interspecific splits recognized morphologically with all species forming a distinct cluster (Fig. 6). All intraspecific genetic distances were below 1.3% apart from E. subvittatus, which showed 2.5% between the central and West African populations. The tree topology was also consistent with the species groups recognized based on morphology, with the E. subvittatus species group forming a cluster separated from all the species of the E. plagiatus group. The genebank accessions for the COI and COII sequences used are reported in Table 3.

Discussion
This study recognized eight valid species in the genus Elaeidobius, two of them described as new here. The new species E. pilimargo sp. nov. and E. piliventris sp. nov. were probably confused under E. singularis in previous studies (Desmier de Chenon 1982;Beaudoin-ollivier et al. 2010;Yalamoussa et al. 2011;Li et al. 2019). As a result, all previous work dealing with this species should be considered with care. The genus Elaeidobius exemplifies the critical importance of detailed integrative taxonomic studies to clarify species identity, especially for groups of economic importance occurring in tropical areas where the entomofauna is generally poorly known.
Apart from E. kamerunicus, the species of Elaeidobius show a remarkable homogeneous general appearance, with a dark elytral pattern on a yellowish cuticular background. This homogeneity probably originates from strong selective constraints to mimic the colour and shape of the inflorescences of Elaeis guineensis (Fig. 7). Despite this homogeneity, species can be readily distinguished from each other by the long erect setae on the elytra, the cuticular sculptures and the penis of males. Females of E. singularis, E. pilimargo sp. nov. and E. piliventris sp. nov., however, show no external morphological features enabling species to be distinguished from each other. As all the species of this group are sympatric and found together on the same inflorescence, only males can be reliably identified based on morphology. The standard Barcode (COI) and COII showed interspecific genetic distances that corroborate morphological recognition of species. Within the plagiatus species group, low genetic distances of about 2% were observed between the closely related species E. singularis and E. pilimargo sp. nov. Morphological and molecular close relations between these species suggests that somewhat recent speciation processes have occurred in this group. A formal phylogenetic analysis of the genus and related genera was beyond the scope of the present work and will be developed in a future study. of all the species, only males of E. kamerunicus, E. pilimargo sp. nov. and E. plagiatus display long hairs on the elytra that are a typical adaptation to pollen transport. The exact role of the other species in pollen transportation is unclear. Interestingly, most efforts have been focused on E. kamerunicus for the pollination of Elaeis guineensis from Africa, while this species is sometimes far less abundant on inflorescences than E. pilimargo sp. nov. and E. plagiatus in that region (JH pers. obs.). The exact role of each species in pollinating this palm remains unclear (Li et al. 2019) and should be explored, especially in the light of the new species described here.
More generally, the inflorescences of Elaeis guineensis show a remarkable assemblage of eight sympatric weevil species in a single genus. In addition to this diversity, two species of the genus Prosoestus, P. minor Marshall, 1935 andP. sculptilis Faust, 1899, have also been reported to develop on the same host (Mariau et al. 1991). The maintaining of this high diversity of species on a single host is unexpected. A recent detailed study of the assemblage of species pollinating the Neotropical palm Syagrus coronata Becc. showed a contrasting case where only one specialist species of Derelominae was associated with inflorescences (Medeiros et al. 2019). The diversity of Elaeis-associated Derelomini raises the question of the driver of speciation processes in this group, and of the stability of this assemblage over evolutionary times.