Taxonomic revision of the African assassin bug genus Fusius (Heteroptera: Reduviidae: Peiratinae)

. The African assassin bug genus Fusius Stål, 1862 is revised after the examination of type specimens with redescriptions of four species. Lectotypes of Pirates ( Fusius ) H-flavum Reuter, 1881 and Pirates rubricosus Stål, 1855 are designated. The status of P. ( Fusius ) H-flavum Reuter, 1881 is revalidated with its current name as F. hflavus (Reuter, 1881) stat. rev. et comb. nov. Seven new synonyms are proposed: F. dilutus Miller, 1957 = F. gowdeyi Miller, 1957 syn. nov. = F. liberiensis Miller, 1957 syn. nov. = F. dilutus anonymus Dispons, 1969 syn. nov. = F. dilutus vicinus Dispons, 1969 syn. nov.; F. distinctus Miller, 1957 = F. sylvestris Miller, 1957 syn. nov.; F. hflavus (Reuter, 1881) = F. hargreavesi Miller, 1957 syn. nov.; F. rubricosus (Stål, 1855) = F. ugandensis Miller, 1957 syn. nov. A key is provided to separate the four species of this genus. Diagnosis and distribution of Fusius are briefly discussed.


Introduction
As the sixth largest subfamily within Reduviidae Latreille, 1807 (Hemiptera: Heteroptera), Peiratinae Amyot & Audinet-Serville, 1843 contains more than 300 species in 35 genera worldwide (Maldonado Capriles 1990;Chłond 2007;Zhang & Weirauch 2011;Melo 2012;Liu et al. 2020aLiu et al. , 2020bLiu et al. , 2021Liu et al. , 2022)).The diagnosis of Peiratinae includes the anterior lobe of pronotum obviously longer than the posterior, the elongate fore coxa, the prominent fossula spongiosa on the fore and mid tibiae and the asymmetric male genitalia which is unique among assassin bugs (Amyot & Audinet-Serville 1843; Weirauch et al. 2014).Peiratinae has the highest species diversity in the Afrotropical Region with 15 genera distributed in the African mainland and three genera distributed in Madagascar (Liu et al. 2020b).Taxonomic studies have been carried out on half of the Afrotropical genera, and most of these studies have demonstrated that there are still some peiratine taxa with distinct intraspecific morphological variations or sex dimorphism that need further revisions as they may lead to misidentifications and synonymies (Coscarón & Morrone 1995;Coscarón 1997Coscarón , 2002;;Zhang & Weirauch 2011;Chłond 2018;Liu et al. 2020aLiu et al. , 2020c)).
The genus Fusius Stål, 1862 was erected by Stål (1862) for the species, Pirates rubricosus Stål, 1855. Miller (1953) redescribed this species and recorded some biological observations, such as "preying on the abundant dipterous larvae in the mass of cow-dung" and its "extremely painful bite".Reuter (1881) described Pirates (Fusius) H-flavum Reuter, 1881, but this species was treated as a variety of F. rubricosus (Stål, 1855) by Villiers (1948) and he expressly mentioned that this variety indicates individuals with posterior lobe of pronotum and hemelytron yellow ("Lobe postérieur du pronotum et élytres rouges (f.t.) ou jaunes (var.H. flavum)").Since this variety was not adopted for a species or subspecies before 1985, it is unavailable (ICZN 1999, Arts 45.5 & 45.6.4).Thus, Villiers' act (1948) could be considered as synonymizing P. (Fusius) H-flavum with F. rubricosus despite the distinct difference in body color.Miller (1957) proposed seven new species of this genus with hand-painted illustrations of the parameres and the median pygophore process of the male genitalia and provided a key to separate them.However, in the revision of Fusius by Dispons (1969), F. gowdeyi Miller, 1957 andF. liberiensis Miller, 1957 were relegated as subspecies of F. dilutus Miller, 1957while F. sylvestris Miller, 1957 was relegated as subspecies of F. distinctus Miller, 1957. Dispons (1969) also described another two subspecies of F. dilutus, F. dilutus anonymus Dispons, 1969 andF. dilutus vicinus Dispons, 1969.Since then, there has been no more taxonomic study on this genus.

Material and methods
This study is based on specimens held in the Natural History Museum (NHMUK), London, United Kingdom and the Swedish Museum of Natural History (Naturhistoriska Riksmuseet, NHRS), Stockholm, Sweden.Male genitalia were soaked in hot 20% lactic acid solution for approximately 15 minutes to remove soft tissue, rinsed in distilled water, then dissected under a binocular dissecting microscope.Dissected genitalia were placed in vials with glycerin and pinned under the corresponding specimens after examination and imaging.Photographs were taken using a Canon 7D Mark II digital camera mounted with a Canon macro lens EF 100 mm or an Olympus E-M1 II digital camera with an Olympus M. Zuiko digital ED 60 mm lens.Helicon Focus ver.5.3 was used for image stacking.Measurements were obtained using a calibrated micrometer and given in millimeters.Body length represents the distance between the apex of the head and the tip of the abdomen in resting position.The distribution map was built using the online version of SimpleMappr (Shorthouse 2010).The distribution data are based on our examination of museum specimens, supplemented by data from Reuter (1881), Miller (1957), Villiers (1963), Dispons (1969) and Maldonado Capriles (1990).Morphological terminology mainly follows Lent & Wygodzinsky (1979) and Liu et al. (2020aLiu et al. ( , 2020bLiu et al. ( , 2021)).
Head.Roughly conical in dorsal view, anteocular part longer than postocular, postocular part elliptical; eye small, transverse width of eye shorter than half width of interocular space in dorsal view, reniform in lateral view, not reaching dorsal and ventral margins of head; ocelli tiny and not elevated, separated from each other; antenna with scape thickest and slightly curved, pedicel longest and slender, basiflagellomere and distiflagellomere gracile; first and second visible labial segments thick, second segment longest and slightly swollen, third segment tapered; neck without lateral tubercle (6)(7)(8)(10)(11)(12)(13)(14).
tHorax.Pronotum somewhat trapezoidal, collar process reduced; anterior lobe nearly twice as long as posterior lobe, slightly narrower than posterior lobe, flat with a median, longitudinal, thin sulcus on posterior portion, sculpture thin and shallow; pronotal transverse sulcus deep; dorsal surface of posterior lobe of pronotum coarse and shallowly punctate; humerus round, posterior margin of pronotum arcuate, but nearly straight in middle.Scutellum subtriangular, width greater than length, Y-shaped ridges thick with apex of scutellar process knob-shaped and horizontal, disc of scutellum with an oval depression.Stridulitrum long with total-striate type of sculpture.Surfaces of pleura and sterna finely wrinkled and granulose; metapleural sulcus arcuate, located close to supporting sclerite; meso-and metasterna with a median longitudinal ridge.Fore femur strongly thickened but compressed laterally, ventral surface of fore femora with a row of small denticles; fore and mid tibiae clavate, gradually thickened to apex, fore tibia with fossula spongiosa occupying about 2/5 of tibial length, mid tibia with fossula spongiosa occupying about 1/3 of tibial length.Hemelytron extending beyond tip of abdomen (6)(7)(8)(10)(11)(12)(13)(14).

Diversity and distribution
Four species, occurring in the Afrotropical Region (Fig. 16).

Remarks
In the original description, Miller (1957) recorded that all four paratypes of F. dilutus Miller, 1957 are males.However, after examining the type specimens, we found that one paratype from Calabar (NHMUK 013586562) and the paratype from the Cameroons (NHMUK 013586563) are female (see detailed specimen information above).
In his revision of Fusius, Dispons (1969) realized that the characters Miller (1957) used to separate these species were relatively inconspicuous and that some of them were only intraspecific differences.Therefore, F. dilutus, F. gowdeyi Miller, 1957 andF. liberiensis Miller, 1957 were included in one group with the bicolor anterior lobe of the pronotum, the presence of the asymmetrical process on the fifth abdominal sternite and the same type of the male genitalia, and the latter two species were degraded as subspecies of F. dilutus (Dispons 1969).Dispons (1969) also described another two subspecies of F. dilutus, F. dilutus vicinus Dispons, 1969 andF. dilutus anonynmus Dispons, 1969.In the key Dispons (1969) provided, the following characters were used to distinguish the five subspecies of F. dilutus: the anterior lobe of the pronotum with coppery green luster or not, the red area along the anterior margin of the anterior lobe of the pronotum narrow or wide and the pronotal transverse sulcus nearly straight or distinctly angulate medially.
After examining type specimens and other material of these taxa, we found that the coppery green luster may have faded in some dry specimens, for example, the luster is not obvious in holotypes of F. dilutus (Fig. 1A) and F. liberiensis (Fig. 4A) as Miller (1957) and Dispons (1969) recorded that could be a diagnostic character.The red area along the anterior margin of the anterior lobe of the pronotum could be a character that changes continuously, varying from thin and obscure to distinct and moderately wide.Dispons (1969) recorded that the pronotal transverse sulcus is nearly straight in F. dilutus dilutus and distinctly angulate medially in F. dilutus liberiensis and F. dilutus gowdeyi.However, we observed that the pronotal transverse sulcus of the holotype of F. dilutus (Fig. 1A) is also angulate medially, and on the contrary, the pronotal transverse sulcus of the holotype of F. gowdeyi (Fig. 3A) seems straighter.So, the shape of the pronotal transverse sulcus is not a stable character to distinguish different subspecies neither.Besides, the presence of the asymmetrical process on the fifth abdominal sternite is indeed observed in all male type specimens of these taxa, which could be a structural diagnosis of F. dilutus.
Moreover, the variations of the characters mentioned above are independent of distribution, and according to the label information and existing literature, the distribution of this species is continuous across central Africa and mainly at low altitude (see Fig. 16, circular marks).In particular, the type locality of F. dilutus anonymus is unknown (Dispons 1969), which makes it harder to assign specimens into this subspecies.

Additional material
Coloration.Body color black and red in large part (Figs 6-8); head black with labium brown; antenna blackish brown to black ; anterior lobe of pronotum black, posterior lobe of pronotum red (Figs 6A, 7A, 8A); scutellum, pleura and sterna black ; legs blackish brown to black, except tarsi brown ; base of clavus red, middle part with an oblong black spot, most apex yellowish white; corium red with a triangular black spot on area between Cu and Pcu; membrane blackish brown with a yellowish white band crossing two cells, margins of band irregular, apical part of membrane paler (Figs 6A, 7A, 8A); connexivum red with inner part sometimes reddish brown (Figs 6-8); abdominal sternites black with lateral area red (Figs.6B, 6C, 7B, 7C, 8B, 8C).

Remarks
The character Miller (1957) used to distinguish F. distinctus Miller, 1957and F. sylvestris Miller, 1957is "legs, abdomen ventrally, except narrowly ventro-laterally, black" in F. distinctus, or "legs, abdomen ventrally, except broadly ventro-laterally, piceous" in F. sylvestris. In Dispons' revision (1969) of Fusius, F. sylvestris was degraded as subspecies of F. distinctus and the character he used in the key  to distinguish the two subspecies is "lateral part of abdominal sternites with narrow red band, rest area black" in F. distinctus distinctus or "lateral part of abdominal sternites with broad red band, rest area dark brown" in F. distinctus sylvestris.
Firstly, "black", "piceous" and "dark brown" are relatively similar colors, and from our observation, the main colors of the abdominal sternites of the type specimens of these two nominal species are too similar to be well distinguished (Figs 6B, 7B, 8B).In addition, the red area on the lateral part of the abdominal sternites of the holotype of F. distinctus is relatively narrow indeed (Fig. 6C), but it is broad in the paratypes of F. distinctus (Fig. 7C), and not significantly narrower than that in the holotype of F. sylvestris (Fig. 8C).So, the color pattern of the abdominal sternites is an intraspecific variation and could not be a stable diagnostic character.The type localities of F. distinctus and F. sylvestris, DR Congo and Uganda, are two neighboring countries without obvious geographical barrier between them.Hence, as there is no distinct morphological differences and geographical isolation between the two subspecies Dispons (1969) proposed, we regard F. sylvestris Miller, 1957 as a junior subjective synonym of F. distinctus Miller, 1957.Fusius hflavus (Reuter, 1881)

Diagnosis
Body color black and yellowish brown in large part; anterior lobe of pronotum black with yellowish brown stripes that are thin and obscure, or only anterior margin of anterior lobe yellowish brown; legs dark brown, apices of coxae, bases of trochanters, and apex of fore femur with irregular yellow markings, basal half of hind femur yellow; fore and hind tibiae with basal half yellow and apical half dark brown, mid tibia dark brown except most base yellow; clavus blackish brown except most base yellowish brown; sub-apical margin of sixth abdominal sternite of male strongly sclerotized and distinctly irregular; median pygophore process somewhat fusiform with basal part narrower than middle part, apical half twisted in caudal view, inner side of apex with a small process in lateral view.

Holotype of Fusius hargreavesi
Coloration.Body color black and yellowish brown in large part ; head black with labium yellowish brown; antenna with scape brown, remaining segments blackish brown ; anterior lobe of pronotum black with yellowish brown stripes, stripes thin and obscure (Fig. 10A), or even only anterior margin of anterior lobe yellowish brown (Fig. 11A), posterior lobe of pronotum yellowish brown markings, basal half of hind femur yellow; fore and hind tibiae with basal half yellow and apical half dark brown, mid tibia dark brown except most base yellow; tarsi brown ; clavus blackish brown except most base yellowish brown; corium yellowish brown with a triangular black spot on area between Cu and Pcu; membrane blackish brown with obscure yellow marking crossing two cells, apical part of membrane paler (Figs 10A, 11A); connexivum yellowish brown (Figs 1-4); second to sixth abdominal sternites blackish brown with lateral part yellowish brown, seventh sternite yellowish brown in large part with diffused brown markings, eighth sternite and genitalic part dark brown to blackish brown (Figs 10B-C, 11-C).
StruCture.As in generic description.Sub-apical margin of sixth abdominal sternite of male strongly sclerotized and distinctly irregular (Figs 10B, 11B).male genitalia.Median pygophore process somewhat fusiform with basal part narrower than middle part, apical half twisted in caudal view (Fig. 11B), inner side of apex with a small process in lateral view (Fig. 11C); left paramere slightly longer than right paramere [according to Miller's illustration (1957: 63, fig. 19c)].

Remarks
Pirates (Fusius) H-flavum Reuter, 1881 was regarded as a variety of F. rubricosus (Stål, 1855) by Villiers (1948), and he mentioned that this variety indicates individuals with the posterior lobe of the pronotum and the hemelytron yellow.The holotype of F. hargreavesi Miller, 1957 (Fig. 11) and the lectotype of P. (Fusius) H-flavum (Fig. 10) share the same color pattern.This color pattern is peculiar in Fusius as other species are all black and red in large part, which indicates that the above two nominal species could be a synonymy.
From the observation of the holotype of F. hargreavesi (Fig. 11B) and Miller's illustrations (Miller 1957: 63, fig. 19c), we could find that the median pygophore process of this species is somewhat fusiform with the basal part narrower than the middle part, the apical half twisted in caudal view, which is quite different from that of F. rubricosus (median pygophore process robust with basal half somewhat rectangular, apical half suddenly narrowed and tapered to apex, see Fig. 15A-B).

Fusius rubricosus
Coloration.Body color black and red in large part ; dorsal surface of head black, ventral surface of head dark brown, labium yellowish brown; antenna with scape brown, remaining segments blackish brown ; anterior lobe of pronotum black with red stripes, red stripes distinct, posterior lobe of pronotum red (Figs 12A,13A,14); scutellum black , pleura and sterna dark brown (Figs 12-13); coxae and trochanters dark brown; fore femur dark brown, apically with irregular yellow markings, mid femur dark brown except base yellow, hind femur with basal half yellow and apical half dark brown; tibiae dark brown with basal part yellow in various proportion; tarsi brown ; base of clavus red, middle part with an oblong black spot, apex yellowish white (Figs 12A,13A,14); corium red with a triangular black spot on area between Cu and Pcu (Figs 12A,13A,14); membrane blackish brown with a yellowish white band around two cells, size of this band varies among individuals (Figs 12A, 13A, 14), sometimes not across membrane (Figs 13A, 14A), sometimes yellowish white area occupying large part of membrane (Fig. 14D), apical part of membrane paler (Figs 12A, 13A, 14A-C); connexivum reddish orange to red ; second to sixth abdominal sternites brown to blackish brown in middle and yellowish brown in lateral part, seventh sternite yellowish brown with brownish markings on basal portion, eighth sternite and genitalic part brown to blackish brown (Figs 12B, 13B).
StruCture.As in generic description.Sub-apical margin of sixth abdominal sternite of male strongly sclerotized and distinctly irregular (Figs 12B, 13B).male genitalia.Median pygophore process robust with basal half somewhat rectangular, apical half suddenly narrowed and tapered to apex (Fig. 15A-B); left paramere (Fig. 15D) distinctly longer than right paramere (Fig. 15E), apex of left paramere rounded (Fig. 15D), area near apex of right paramere with a round process (Fig. 15E); apical margin of dorsal phallothecal sclerite bluntly rounded (Fig. 15F); process on lower right corner of lateral phallothecal sclerite distinct and horned (Fig. 15I).Other structures as in generic description.(Stål, 1855).Scale bar = 2.00 mm.spongiosa occupying only the apex of the ventral surface in Parapirates) and the abdomen oval (vs the abdomen nearly roundly rectangular in cross section in Parapirates).The species of Fusius with the redblack body color share the similar color pattern with Peirates stridulus (Fabricius, 1787) (recorded by Signoret in Fairmaire & Signoret 1858) and Oblongiala zimbabwensis Liu & Cai, 2020.However, the species of Fusius can be easily separated from the latter two species by the more robust body shape, the reduced collar process and the interocular distance more than three times as long as the width of the eye in dorsal view (vs the interocular distance less than 2.5 times as long as the width of the eye in dorsal view in P. stridulus and O. zimbabwensis).

Distribution and habitat of Fusius Stål, 1862
Fusius is mainly distributed in rainforests or savannas in Africa with low altitude (Fig. 16).The distribution of F. dilutus extends from west to east across central Africa.Fusius distinctus has been only recorded in DR Congo, Cameroon and Uganda so far.Fusius hflavus is distributed in western Africa along the Gulf of Guinea while F. rubricosus widely occurs in southeast Africa.Peiratinae species are primarily ground dwelling and nocturnal (Weirauch et al. 2014), andMiller (1953) once recorded that he captured two females of F. rubricosus on grass stems and under a mass of cow-dung.It can be speculated that species of Fusius usually hide in some cryptic microhabitats such as in rotted wood, animal wastes and cracks of grass or rocks during the daytime to avoid the high temperature and become active at night.