On the genus Hamma Buckton, 1905 (Hemiptera: Auchenorrhyncha) in Equatorial Africa, with descriptions of three new species

As part of the classifi cation of Membracidae from Gabon and Equatorial Guinea, a new species group of the genus Hamma Buckton, 1905 is proposed, and three new species are described: Hamma nigrum sp. nov., Hamma spinellii sp. nov. and Hamma caneparii sp. nov. An updated checklist and key to the genus Hamma are provided.


Introduction
As already stated by Bayendi , new species in the genus  will probably continue to be found for many years. The present study is the third on the family Membracidae Rafinesque, 1815, specifically dealing with the genus Hamma in Gabon.
Gabon represents one of the most well-conserved natural areas in Sub-Saharan Africa and a sanctuary for equatorial forests. Its wildlife conservation policy is encouraging and promotes research and conservation. The MSNS (Museo di Storia naturale del Salento, Italy) pursues a research strategy in agreement with the local authorities to provide the necessary tools for wildlife preservation.
In the present paper we follow Capener (1968) and Wallace & Deitz (2004) in placing the genus Hamma in the tribe Centrotini Amyot & Serville, 1843. Previous studies of Centrotinae Amyot & Serville, 1843 in Africa and the genus Hamma in particular are summarized in the works of Stål (1866), Goding (1932), Capener (1968,  and . The overall classification of the African Centrotinae is also summarized in the works of Funkhouser (1950), Metcalf & Wade (1965) and McKamey (1998), as noted by Wallace & Deitz (2004), who published the most recent genus-level revision of the subfamily.
In their recent paper on the genus Hamma , the current authors raised the number of species in the genus to 19 in Africa as a whole and 9 in Gabon alone. Thanks to new research, they discovered new material which appears to belong to three new species.
The objective of the zoological studies of the MSNS on the Membracidae includes examination of hundreds of specimens collected in Gabon from 2010 until 2019, with subsequent publication of the relevant results. Unfortunately, it will remain a long-term objective as the financial resources of the MSNS are very sparse and are mainly based on private generosity.

Material and methods
The examined material is part of the MSNS and Antonio Susini's private collections. The collections of the RMCA (Royal Museum for Central Africa, Tervuren, Belgium) and MNHN (Muséum national d'histoire naturelle, Paris, France) were also checked.
The specimens were collected in Batouala in Ogooué Ivindo Province, Gabon, close to Mount Sassamongo at about 660 m above sea level; in Inzambò (a small village on Mount Iboundji at 427 m above sea level) in Ogooué Lolo Province, Gabon, during a survey in 2012; and in Mossumu in Equatorial Guinea in 2015.
Collection was conducted at night, using a 500-watt blended light lamp suspended in front of a white cotton sheet against a wall, collecting actively from 7 pm to about midnight and irregularly until sunrise.
According to the literature (Funkhouser 1950;Capener 1962), treehoppers should usually be collected during the daytime. However, subsequent studies (Kopp & Yonke 1973) demonstrated that Centrotinae are attracted to light, albeit unreliably in terms of quantity. There are well-documented occurrences of massive collection of Membracidae that are attracted to light at night (including other genera not yet studied; see also Bayendi Loudit et al. 2014). Some specimens were killed using ethyl acetate vapours and dried for storage; they were briefly dipped in warm water (for about 30 sec at 60°-70°C) prior to study. Other specimens, after killing in ethyl acetate, were stored in 70% ethanol; they needed no wetting procedure. In both cases the specimens were pinned with micropins from the underside between the second pair of legs. Usually, it was preferred not to pierce the scutellum, avoiding possible breakage. The specimens were placed in the groove of a specially-built spreading board , and their right wings were spread. After drying (twice for ten minutes in the oven at 50°C) the micropins were better joined to the thorax by means of water-soluble glue; afterwards, the specimens were mounted on a plastozote cube. This preparation, very unusual in the Membracidae collections and described in Bayendi , allows the examiner to quickly observe the wing pattern and the lateral and dorsal abdomen morphology. The genitalia were not examined in order to preserve the limited number of collected specimens and also because the body's external characters are distinctive enough.
The investigated habitats ranged from secondary forest to deforested lands and crops around the equator. Here, both Gabon and Equatorial Guinea present in very general terms two dry seasons (December-January, and May-August) and two rainy seasons (February-April, and September-November) with many exceptions. Our surveys cover a period during the rainy seasons.
With regard to the Gabonese locations, the forests there presents transitional characteristics between the Western Congolese forest with Atlantic influences and the true Congolese forest, without a clear line of demarcation (Vande Weghe 2010).
The Guinean location (the village of Mossumu, near Nyefang) presents a mosaic of secondary forest, from quite degraded to well preserved.
In the species descriptions the following conventions are used: vertex width is the distance between the compound eyes measured along the centro-ocular line; vertex height is the distance measured from the ventral margin to the upper margin, perpendicular to the centro-ocular line (see Bayendi Loudit et al. 2014: fig. 4). The total length of the body is measured laterally from the head to the apex of the abdomen; the pronotal length is measured from the anterior profile of the pronotum to the apex of the posterior process; the tegminal length is measured from the costa base to the apex of the spread wing.   The description of three proposed new species is here reported. They were discovered in Gabon and Equatorial Guinea by the third author. The following checklist and keys include the new entries since 2014 (Durante & Susini 2017, plus present data).  (Vignon, 1930) 13. 15. Pterostigma as long as broad (Distant 1916b: fig. page 328) ........Hamma grahami (Distant, 1916) -Pterostigma about three times as long as broad (Fig. 1)  16. Caudal node of the posterior process half the width of the head in dorsal view (Fig. 2)    The following species are here considered to be part of a well-defined group, characterized by a similar exterior morphology (especially well-pronounced suprahumeral horns; pronotal posterior process with four nodes; third node of the posterior process anchor-shaped in dorsal view; welldeveloped terminal spine on the posterior process; wings with dark pattern). We include also Hamma heimi .

Diagnosis
Species belonging to the genus Hamma with the thorax entirely black and pronotum smooth; suprahumeral horns with a laterally pointing thorn; a posterior process with four nodes, V-shaped in lateral view between the second and fourth nodes; last node roundish in dorsal view, ending in a well-developed terminal spine. Pterostigma about three times as long as broad.

Differential diagnosis
The general black colour clearly distinguishes this species from the following two (i.e., spinellii sp. nov. and caneparii sp. nov.), although not from Hamma heimi. The roughly triangular shape of the supraocular callosity (Fig. 4B) is also diagnostic with respect to all other species in the group.
The anchor-like third node (Fig. 5B) of the posterior process clearly distinguishes it from all other species in the group, being rhomboidal in dorsal view, whereas it is roughly circular in heimi, and truly anchor-like in spinellii sp. nov. and in caneparii sp. nov.
Diagnostic characters with respect to heimi include: -upper margin of the head more arcuate than in heimi; -punctation on the pronotum finer than in heimi; -first (proximal) node of the posterior process roughly circular in lateral view, dome-shaped in heimi.

Etymology
The species takes its name from the Latin adjective ‛nigrusʼ, meaning ‛blackʼ, in the neuter form in accordance with the grammatical gender.
Head. Brilliant black, convex, punctate, with very small and sparse setae; vertex almost twice as wide as high; shallow concavity between the ocelli; upper margin arcuate, rounded, slightly sinuate; ventral margin W-shaped with the lower parts not very pronounced; ocelli clearly above the centro-ocular line. Frontoclypeus pear-shaped, lateral lobes completely fused to frontoclypeus with margins barely distinguishable; rostrum dark brown; antennae light brown.
PronotuM. Brilliant black, punctate, almost completely naked; metopidium smooth, almost twice as wide as high, median carina percurrent, unpunctate, straight until the base of the posterior process and subsequently sinuate, supraocular callosities barely noticeable, small and unpunctate, roughly triangular; humeral angles prominent and blunt; suprahumeral horns well developed, with a tower-shaped base (width/height ratio: 1.48), slightly tuberculate, sometimes with dorsal tip reddish-brown, with a robust brown thorn projecting outwards and curving upwards slightly in frontal view. Posterior process brilliant black, punctate, emerging posteriorly from the pronotum and continuously from the posterior margin; sinuate in lateral view, with four nodes, the first of which (proximal) almost spherical; second node small, dome-shaped in lateral view (flattened in dorsal view) with four to eight small spines dorsally; third node anchor-like in dorsal view with one to three spines at the end of the lateral arms; fourth node subspherical, almost twice as big as the first, with many spines and a robust terminal spine at the caudal end; dorsal and ventral carinae discontinuous, black, in some parts tending to brown. A few spines dorsally and ventrally along the trunk of the posterior process between the third and fourth nodes. Each spine bears a very thin light apical seta. scutelluM (Fig. 5). Entirely black, punctate, with the base longer than the height, emarginate, with scutellar apices acute with a few translucent setae; base swollen except for the corners, with one ogival tubercle on each side of the swelling, each tubercle with a tuft of small whitish setae.
Forewing. Almost three times as long as wide (l/w ratio 2.94, mean value), hyaline; basally sclerotized, punctate, dark brown-black in colour. Pterostigma sub-triangular with very rounded corners, blackish in colour; venation black to brown; a large sub-pentagonal brown patch extending from costa to inner margin in the median area; a Y-shaped brown patch extending from costa to anal angle, connected with the previous patch at the level of the second discoidal cell.
abdoMen. Urites black with punctation (in one specimen with white suffusion), and thin brown caudal border.

Diagnosis
Species belonging to the genus Hamma with thorax eminently brown, pronotum smooth and metopidium not densely tuberculate; suprahumeral horns with a laterally pointing thorn; a posterior process with four nodes, V-shaped in lateral view between the second and fourth nodes; last node roundish in dorsal view, ending in a well-developed terminal spine. Pterostigma almost three times longer than broad.

Differential diagnosis
The general light brown colour is diagnostic, heimi and nigrum sp. nov. being black, and caneparii sp. nov. having a mosaic of russet brown and black.

Etymology
The species is dedicated to Dr Matteo Spinelli, Milano. Head. Black with brown suffusion along the margins and at the centre, convex, punctate, with small white setae; vertex width one and a half times the height; shallow concavity between the ocelli; carina present; upper margin arcuate but roughly square with two evident corners, one directly above each ocellus; ventral margin W-shaped with the lower parts not very pronounced; ocelli slightly above the centro-ocular line. Frontoclypeus pear-shaped, lateral lobes completely fused to frontoclypeus with margins barely distinguishable; rostrum and antennae light brown.

Holotype
PronotuM. Light brown with one triangular black patch on the metopidium on each side of the carina, punctate, almost completely naked; metopidium tuberculate in its dorsal region, twice as wide as high, median carina percurrent, unpunctate, straight, with some swelling, supraocular callosities bean-like, slightly or not at all punctate, with a small club-shaped darker formation inside them, shallow and very finely punctate; humeral angles prominent and blunt; suprahumeral horns well developed, with a tower-shaped base, tuberculate, with a robust brown and black-tipped thorn pointing laterally? Posterior process light brown, punctate, emerging posteriorly from the pronotum and continuously from the posterior margin; sinuate in lateral view, with four nodes, the first of which (proximal) almost spherical; second node small, dome-shaped in lateral view (flattened in dorsal view) with seven-eight small spines latero-dorsally; third node anchor-like in dorsal view with one (left) or two (right) small spines at the end of the lateral arms; fourth node subspherical, almost one and a half times larger than the first, with many spines and a robust terminal spine at the caudal end; dorsal and ventral carinae continuous, of the same colour. A few spines along the dorsal carina, and dorsally and ventrally along the trunk of the posterior process between the third and fourth nodes. Each spine bears a very thin light apical seta. scutelluM (Fig. 5). Entirely brown, punctate, with the base longer than the height, emarginate with scutellar apices acute with a few translucent setae; base with a triangular swelling except at the corners; lateral corners of the swelling with a tuft of small shiny ochraceous setae.
Forewing. Length about two and a half times width (l/w ratio 2.56), hyaline; basally sclerotized, punctate, grey-brown in colour with three to four brown stripes distally. Pterostigma sub-triangular with very rounded corners, blackish in colour; venation grey-brown; large brown shaded trapezoidal patch extending from costa to inner margin in the median area; I-shaped patch extending from costa to anal angle with light grey-brown anterior half and dark grey-brown posterior half.
abdoMen. Tergites grey-brown with black punctation and lighter caudal borders; sternites brown, as are the borders, and covered in translucent setae.

Diagnosis
Species belonging to the genus Hamma with thorax a mosaic of russet brown and black, pronotum smooth and metopidium not densely tuberculate; suprahumeral horns with a laterally pointing thorn; a posterior process with four nodes, V-shaped in lateral view between the second and fourth nodes; last node roundish in dorsal view, ending in a well-developed terminal spine. Pterostigma twice as long as broad.

Differential diagnosis
The general colour (a mosaic of russet brown and black) is diagnostic, heimi and nigrum sp. nov. being black, and spinellii n. sp being light brown.
Other diagnostic characters with respect to spinellii sp. nov. are: -the narrow width relative to height of the basal element of the suprahumeral horns (frontal view) ( Other diagnostic characters with respect to heimi and nigrum sp. nov. are: -upper margin of the head (Fig. 4D) roughly square; -metopidium ( Fig. 4D) tuberculate; -suprahumeral horns (Fig. 4D) with a robust straight thorn, not curving upwards in frontal view; -anchor-like third node posteriorly prolonged; rhomboidal or roughly circular in nigrum sp. nov. and heimi.

Etymology
The species is dedicated to our friend Claudio Canepari, Milano, a specialist in Coccinellidae.
Head. Entirely black, convex, punctate; vertex almost twice as wide as high; carina not distinguishable; shallow concavity medially above the ocelli; upper margin sinuate; ventral margin W-shaped with lower parts not very pronounced; ocelli slightly above the centro-ocular line. Frontoclypeus russet and pear-  shaped, lateral lobes completely fused to frontoclypeus with margins not distinguishable; rostrum and antennae ochraceous.
PronotuM. Mosaic of russet brown patches with one triangular black area at the base of the metopidium and black areas behind the suprahumeral horns; punctate, naked; ochraceous tuberculate areas at the dorsal border of the metopidium; metopidium one and a half times wider than high, median carina percurrent and unpunctate, straight; elongated supraocular callosities, slightly arcuate, not punctate; humeral angles prominent and blunt; suprahumeral horns well developed, with a tower-shaped base (shorter than in spinellii sp. nov.), tuberculate, with a robust brown, black-tipped thorn pointing outwards. Posterior process patchy, black and russet in colour, punctate, emerging posteriorly from the pronotum and continuously from the posterior margin; sinuate in lateral view, with four nodes, the first of which (proximal) almost spherical, elongated posteriorly in dorsal view; second node small, dome-shaped in lateral view (flattened in dorsal view) with four small dorsal spines; third node anchor-like in dorsal view with two (left) or one (right) small spines at the end of the lateral arms; fourth node subspherical, slightly larger than the first, with many spines and a strong terminal spine at the caudal end; dorsal and ventral carinae continuous, of the same colour. A few spines along the dorsal carina and dorsally and ventrally along the trunk of the posterior process between the third and fourth nodes, some of which bearing a very thin light apical seta. scutelluM (Fig. 5). Same colour as the pronotum, punctate, with the base longer than the height, emarginate with scutellar apices light, acute with a few translucent setae; base with a triangular swelling except at the corners; lateral corners of the swelling with a tuft of small brilliant whitish setae.
Forewing. About two and a half times as long as wide (l/w ratio 2.57), hyaline; basally sclerotized, punctate, amber and brown in colour. Pterostigma trapezoidal with rounded corners, dark brown in colour; venation amber except for the median, cubital and anal veins in the median area, which are brown; large brown shaded trapezoidal patch extending from costa to inner margin in the median area; S-shaped patch extending from costa to anal angle with light grey-brown anterior half and brown posterior half. Presence in the right forewing of a small supplementary discoidal cell between the second apical cell and the first discoidal cell.
abdoMen. Tergites black and brown with punctation and lighter caudal borders; sternites brown with borders of the same colour covered by translucent setae.

Discussion
This third paper on the genus Hamma in Gabon raises the number of known species to 22 in Africa as a whole and to 12 in Gabon alone. Regarding the latter, it should be emphasized that 8 new species have been described since 2014, based on collections made every year from 2010 until 2019, with few specimens collected for each species. This observation coincides with many others made by the authors regarding other orders of Insects, such as Coleoptera, Lepidoptera, Orthoptera and so on, and suggests that Gabon is a very significant centre of endemism. In quite a few cases, many specimens belonging to a small number of species are collected, whereas other species are represented by few specimens or only one, collected during several field trips over ten years. This is the case, for instance, of the Afrotropical genus Tumicla Wallengren, 1863 (Lepidoptera), unrecorded in Gabon until now, and recently discovered together with eight as-yet undescribed species, all of which are represented by very few specimens (Durante & Apinda Legnouo 2020). The same trend has been observed in Membracidae genera, based on a preliminary classification into different species. This indicates that the vast majority of species from tropical and equatorial regions described in the past two centuries are in fact composed of a small number of individuals spread over such a large range that it is extremely difficult to collect them in large numbers. On the contrary, until now the most accepted conclusion has been that the small numbers are due to the inadequacy of research and collection methods. Although the latter view undoubtedly has merit, due to the objective difficulties in terms of logistics and obtaining collection permits in tropical countries, the authors stress that many species are indeed composed of very low density populations with respect to the high complexity of tropical environments and the wideness of their range (as shown by the relation between population density and trap collection of insects -see Petrovskii et al. 2012). They also argue that many species are probably composed of very few populations or only one, confined to a small area. The latter observation is supported by the fact that specimens of certain species are often found in only one specific location, even when the area around it is well explored (Durante pers. obs.).
The case of H. nigrum sp. nov. (its disjunct distribution) could be thought of as an example of a species that once had a large distribution that was subsequently fragmented and reduced, or, alternatively, as a concrete case of shallow investigation in its range. The third hypothesis is that the Guinean specimens are morphologically identical to the Gabonese ones (a case of convergence), but they belong to a separate species, and this would confirm the punctiform (single-area) distributional hypothesis. The genitalia of the H. nigrum sp. nov. specimens were not dissected due to the scarcity of the material.