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Plectoplebeia, a new Neotropical genus of stingless bees (Hymenoptera: Apidae)

Gabriel A.R. Melo About the author

ABSTRACT

A new stingless bee genus, Plectoplebeia gen. nov., is proposed to accommodate a peculiar Neotropical species currently placed in Plebeia Schwarz, 1938. The brief, but convoluted taxonomic history of its type species, Trigona nigrifacies Friese, 1900, is documented, with Trigona (Plebeia ) intermedia Wille, 1960 being placed as its junior synonym. Plectoplebeia gen. nov. resembles an enlarged species of Plebeia , differing by its larger body size, wider distance between the clypeus and the eye, presence of a shallow depression on the frons above the antennal sockets, coarser punctures on the head and mesosoma, a shorter, convex scutellum, an elongate propodeum and metapostnotum, long wings, with a higher number of hamuli, and by an elongate metasoma, with an unusually long first tergum. The single included species, Plectoplebeia nigrifacies comb. nov., is known only from the Bolivian Yungas, an ecoregion extending from west-central Bolivia to southeastern Peru.

KEY WORDS:
Bolivia; Meliponini; Peru; taxonomy; Yungas

Currently a total of 32 genera are recognized for the extant Neotropical fauna of stingless bees (Camargo & Pedro 2007Camargo JMF, Pedro SRM (2007) Meliponini Lepeletier, 1836, p. 272-578. In: Moure JS, Urban D, Melo GAR (Eds.). Catalogue of Bees (Hymenoptera, Apoidea) in the Neotropical Region. Curitiba, Sociedade Brasileira de Entomologia.). This classification system was laid down along the 20th century and mostly through the work of Moure, who departed from contemporaneous authors in raising to genus-level the many subgenera of Trigona Jurine, 1807 and for proposing additional new genera (Moure 1942Moure JS (1942) Abelhas de Salobra (Hym. Apoidea). Papéis Avulsos [São Paulo] 2(21): 291-321., 1943Moure JS (1943) Abelhas de Batatais (Hym. Apoidea). Arquivos do Museu Paranaense 3: 145-203., 1944Moure JS (1944) Abejas del Perú. Boletin del Museo de Historia Natural "Javier Prado" 8(28/29): 67-75., 1946Moure JS (1946) Contribuição para o conhecimento dos Meliponinae (Hym., Apoidea). Revista de Entomologia 17(3): 437-443., 1950Moure JS (1950) Contribuição para o conhecimento das espécies brasileiras de Hypotrigona Cockerell (Hymen., Apoidea). Dusenia 1(4): 241-260., 1951Moure JS (1951) Notas sôbre Meliponinae (Hymenopt. - Apoidea). Dusenia 2(1): 25-70., 1953Moure JS (1953) Nogueirapis , no [sic, recte novo] grupo de Trigonini da Região Neotropical. (Hymenoptera - Apoidea). Ciência e Cultura 5(4): 247-249., 1989Moure JS (1989) Camargoia , um novo gênero neotropical de Meliponinae (Hymenoptera: Apoidea). Boletim do Museu Paraense Emílio Goeldi, Série Zoologia 5(1): 71-78., Camargo & Moure 1983Camargo JMF, Moure JS (1983) Trichotrigona , novo gênero de Meliponinae (Hymenoptera, Apidae), do Rio Negro, Amazonas, Brasil. Acta Amazonica 13(2): 421-429.). In a summary presented by Moure (1961Moure JS (1961) A preliminary supra-specific classification of the Old World meliponine bees (Hym., Apoidea). Studia Entomologica 4: 181-242.), a total of 28 genus-group names, involving 11 genera, were then recognized in his classification of the New World stingless bees.

Moure's classification system, including additions from subsequent authors, has close association with biological features of the taxa at genus-level, in particular details of their nesting habits (Camargo & Moure 1988Camargo JMF, Moure JS (1988) Notas sobre os Meliponinae (Hymenoptera, Apidae) colecionados por Filippo Silvestri na bacia do Rio da Prata. Revista Brasileira de Entomologia 32(2): 293-314.), and more recently has been corroborated, to a great degree, by independent evidence from molecular data (Costa et al. 2003Costa MA, Del Lama MA, Melo GAR, Sheppard WS (2003) Molecular phylogeny of the stingless bees (Apidae, Apinae, Meliponini) inferred from mitochondrial 16S rDNA sequences. Apidologie 34: 73-84., Rasmussen & Cameron 2010Rasmussen C, Cameron SA (2010) Global stingless bee phylogeny supports ancient divergence, vicariance, and long distance dispersal. Biological Journal of the Linnean Society 99: 206-232.). In the comprehensive study by Rasmussen & Cameron (2010Rasmussen C, Cameron SA (2010) Global stingless bee phylogeny supports ancient divergence, vicariance, and long distance dispersal. Biological Journal of the Linnean Society 99: 206-232.), however, a few taxa came out as paraphyletic (Leurotrigona Moure, 1950 and Scaura Schwarz, 1938) or polyphyletic (Plebeia Schwarz, 1938), indicating that further studies are needed to improve the current classification.

The purpose of the present contribution is to propose a new genus-level taxon for a peculiar Neotropical species currently placed in the genus Plebeia . The distinct features of this taxon have been discussed by Wille (1960Wille A (1960) A new species of stingless bee (Meliponini) from Bolivia. Revista de Biologia Tropical 8(2): 219-223., 1979Wille A (1979) Phylogeny and relationships among the genera and subgenera of the stingless bees (Meliponinae) of the world. Revista de Biologia Tropical 27(2): 241-277.) and Michener (1990Michener CD (1990) Classification of the Apidae (Hymenoptera). University of Kansas Science Bulletin 54(4): 75-164.). The two most recently proposed stingless bee genera for the Neotropical fauna, Meliwillea Roubik, Lobo & Camargo, 1997 and Paratrigonoides Camargo & Roubik, 2005, are also both monotypic, each with a single species representing relictual lineages that fall outside the genera to which they are related (Roubik et al. 1997Roubik DW, Lobo-Segura JA, Camargo JMF (1997) New stingless bee genus endemic to Central American cloudforests: phylogenetic and biogeographic implications (Hymenoptera: Apidae: Meliponini). Systematic Entomology 22: 67-80., Camargo & Roubik 2005Camargo JMF, Roubik DW (2005) Neotropical Meliponini: Paratrigonoides mayri , new genus and species from western Colombia (Hymenoptera, Apidae, Apinae) and phylogeny of related genera. Zootaxa 1081: 33-45.).

MATERIAL AND METHODS

Material from the following institutions was examined: DZUP - Coleção de Entomologia Pe. Jesus Santiago Moure, Universidade Federal do Paraná, Curitiba, Brazil; ZMB - Museum für Naturkunde, Berlin, Germany. The following collection is also cited in the text: SEMK - Division of Entomology, Natural History Museum, University of Kansas, Lawrence, USA. In the list of type material, the quotation marks indicate the different labels for the same specimen, the backslashes (\) indicate different lines on the same label.

The format of the genus description follows that of Camargo & Roubik (2005Camargo JMF, Roubik DW (2005) Neotropical Meliponini: Paratrigonoides mayri , new genus and species from western Colombia (Hymenoptera, Apidae, Apinae) and phylogeny of related genera. Zootaxa 1081: 33-45.), with distinctive or autapomorphic characters highlighted in boldface. The general morphological terminology follows Urban (1967Urban D (1967) As espécies do gênero Thygater Holmberg, 1884 (Hymenoptera, Apoidea). Boletim da Universidade Federal do Paraná, Zoologia 2: 177-309.), Silveira et al. (2002Silveira FA, Melo GAR, Almeida EAB (2002). Abelhas Brasileiras: Sistemática e Identificação. Belo Horizonte, Authors' edition, 253p.) and Michener (2007Michener CD (2007) The Bees of the World. Baltimore, Johns Hopkins University Press, 2nd ed.). Antennal flagellomeres are indicated as F1, F2, etc.; metasomal terga and sterna, respectively, as T1 to T7, and S1 to S8. The density of punctation and intervals between the punctures are based on relative puncture diameter, pd (e.g. <1pd: less than 1x the puncture diameter between the punctures). The color images of the holotype of Trigona nigrifacies were obtained on a camera Nikon Coolpix 995 attached to a stereomicroscope Leica MZ7, while those of the paratype of Trigona intermedia on a Leica DFC295 in a stereomicroscope Leica M125; in both cases the images were processed by the software Zerene Stacker.

TAXONOMY

Plectoplebeia gen. nov.

urn:lsid:zoobank.org:act:BFA974A0-1CA9-4CBE-A148-C1B5EDFB8800

Type species: Trigona nigrifacies Friese, 1900.

Diagnosis and Comments. At a first glance, the type species of Plectoplebeia resembles just an enlarged Plebeia . The somewhat rounded head shape, a mostly smooth, shiny integument, a relatively short body pilosity and possession of a narrow depressed rim along the posterior margin of the inner surface of the hind tibia suggest a species of Plebeia . It differs from Plebeia by a larger body size, wider distance between the clypeus and the eye, coarser punctures on the head and mesosoma, a shorter, convex scutellum, a higher number of hamuli, and by an elongate metasoma, with an unusually long first tergum. While these features suggest Mourella and Schwarziana , Plectoplebeia lacks the long plumose body pilosity, the plumose sternal fimbria, and the modified hind tibia characteristic of these two genera. Unique features of Plectoplebeia include a shallow depression on the lower portion of the frons, the very short scutellum, the elongate propodeum and metapostnotum, the rectangular first segment of the metasoma, the elongate and sinuous hindtibia, and the long wings.

The type species of Plectoplebeia , Trigona nigrifacies , has had a brief, but convoluted taxonomic history. It was described by Friese (1900Friese H (1900) Neue Arten der Bienengattungen Melipona Ill., und Trigona Jur. Természetrajzi Füzetek 23: 381-394.) from a single worker collected in Peru ("Callanga"). Friese refers it to Schwarziana quadripunctata (Lepeletier, 1836), an indication that could have hinted on the identity of the taxon, but the brief and limited original description was not of much help in the subsequent recognition of the species. The taxon remained completely ignored for more than a century until its mention in Camargo & Pedro (2007Camargo JMF, Pedro SRM (2007) Meliponini Lepeletier, 1836, p. 272-578. In: Moure JS, Urban D, Melo GAR (Eds.). Catalogue of Bees (Hymenoptera, Apoidea) in the Neotropical Region. Curitiba, Sociedade Brasileira de Entomologia.). Based on personal communication by Claus Rasmussen, who examined the type specimen (Fig. 1), Camargo & Pedro (2007Camargo JMF, Pedro SRM (2007) Meliponini Lepeletier, 1836, p. 272-578. In: Moure JS, Urban D, Melo GAR (Eds.). Catalogue of Bees (Hymenoptera, Apoidea) in the Neotropical Region. Curitiba, Sociedade Brasileira de Entomologia.: 572) attributed it to Plebeina Moure, 1961, a stingless bee genus from the Afrotropical region, and excluded the taxon from the Neotropical fauna. Indeed, the type specimen bears a label from C. Eardley, dated from 2003, as "Plebenia [sic] denoiti (Vachal)" (Fig. 1). Despite having examined and labeled the type specimen, Eardley (2004Eardley CD (2004) Taxonomic revision of the African stingless bees (Apoidea: Apidae: Apinae: Meliponini). African Plant Protection 10: 63-96.) does not mention it in his revision of the African stingless bees. Probably trusting Eardley's identification as correct, C. Rasmussen also added a label, dated from 2007, to warn of the supposedly wrong locality data (Fig. 1).

This mistaken interpretation of Friese's species was probably triggered by where the type specimen has been placed in the ZMB collection. It has been curated under the name "Trigona beccarii v. nigrifacies ", a homonymous taxon described by Friese (1912Friese H (1912) Neue afrikanische Trigona -Arten. Archiv für Naturgeschichte, Abteilung A 78(7): 169-170.) from Africa (Fig. 2), and likely was placed under this name by a past curator when organizing Friese's collection following its incorporation to the ZMB. Indeed, under the name "nigrifacies ", referring to a stingless bee, a drawer label and catalog card have been made only for the African taxon in the ZMB collection, with the older name from South America being completely ignored. Of course, the peculiar features of this species do not suggest other better known groups of the Neotropical region and could easily mislead someone when doing a quick inspection. A new label indicating the type status was added, as well as a barcode label currently used in the ZMB for digitalization of the collection (Fig. 1). The specimen has also been moved to a new position within the drawer.

Figures 1-2
Plectoplebeia nigrifacies : (1) labels of the holotype of Trigona nigrifacies Friese, 1900; (2) place under which the holotype of T. nigrifacies was found in the ZMB collection.

As established below, Trigona (Plebeia) intermedia , a name proposed by Wille (1960Wille A (1960) A new species of stingless bee (Meliponini) from Bolivia. Revista de Biologia Tropical 8(2): 219-223.) for three workers from Bolivia, is considered a junior synonym of Friese's Trigona nigrifacies . This synonymy is based on direct comparisons between type specimens, here illustrated in Figs. 3-11.

Figures 3-7
Holotype worker of Trigona nigrifacies Friese, 1900: (3) habitus, side view; (4) head, frontal view; (5) head and mesosoma, dorsal view; (6) metasoma, dorsal view; (7) hind leg, side view.

Figures 8-11
Paratype worker of Trigona (Plebeia ) intermedia Wille, 1960: (8) habitus, side view; (9) head, frontal view; (10) head and mesosoma, dorsal view; (11) specimen labels.

Description. Worker. a) Body length about 5.5 to 6.0 mm. b) integument between punctures mostly smooth and shiny, fine rugulosity present on parts of head and mesosoma; metapostnotum with fine transverse rugulosity along basal portion and on middle of dorsal area, remainder finely areolate to reticulate. c) Body dark brown to black except for vestiture and markings described below; mesoscutum black; wing membrane light brown infumated. d) Yellow markings obscured on head, with most of mandible, broad stripe on mid of clypeus, lower parocular area and supraclypeal area dark reddish brown; on mesosoma, yellow markings as follows: a transverse stripe on pronotum, a spot on the pronotal lobe, one stripe on each side of mesoscutum, axilla, distal margin of scutellum, apex of fore femur and basis of all tibiae. e) Vestiture: erect hairs on body uniformly pale-yellow to light brown, darker on inner surface of tarsi, mostly simple, except on pronotal lobe, tegula, anterior margin of mesoscutum and along anterior portion of mesepisternum; in addition, with a fine shorter pilosity, covering the face, gena, mesoscutum, lateral mesepisternum, metepisternum and propodeum laterally, mostly erect, except for gena, mostly simple on clypeus and mesoscutum, and finely branched on remainder; metapostnotum glabrous; labial palpi with long, curled, simple setae; setae on metasomal sterna simple. f) Head ca. 1.2x wider than long, about as wide as mesosoma; maximum interorbital distance about 1.15x greater than length of eye; inner orbit of eye slightly convergent below, upper interorbital distance ca. 1.2x the lower distance; upper alveolar tangent at middle of face; vertex rounded, not forming post-ocellar carina; malar space moderate, approximately 5/8 of diameter of third flagellomere; preoccipital ridge indicated as a low carina on upper part of head, on lateral portion rounded; gena, at side view, about as wide as compound eye. g) Clypeus 2.0x wider than long, convex; epistomal suture, between subantennal sutures a widely open V; supraclypeal area lacking modifications, not forming a flange at each side; mid portion of lower frons, adjacent to antennal sockets, slightly depressed and forming a shallow scapal basin. h) Labrum normal. i) Mandible bidentate. j) Scape slightly longer than alveolo-ocellar distance and slightly narrower than diameter of third flagellomere; pedicel and third flagellomere, respectively, as wide as long. k) Pronotum short, ca. 0.6 x length of scutellum; anterior margin normal, not emarginate, bordered by a short translucent lamella. l) Scutellum short, 1.9x wider than long; posterior margin semicircular, when viewed from above leaving a narrow portion of the metanotum visible; surface weakly convex along its mid line; basal fovea lacking. m) Forewings longer than body length, ca. 3.0x length of hind tibia; pterostigma ca. 4.2 x longer than wide, 1.4x wider than diameter of third flagellomere; marginal cell ca. 3.8 x longer than wide, lanceolate, slightly open at apex; bifurcation between M and Cu coinciding with cu-anal vein; submarginal angle between Rs and Rs + M straight, ca. 90°; angle between M and Rs + M obtuse, ca. 120°; first abscissa of M ca. 0.9x length of first abscissa of Cu; submarginal cells weakly veined, first r-m almost obsolete; hind wing with jugal lobe about as long as 0.44x vanal lobe length; hamuli 6 to 7. n) Hind tibia very long, ca. 2.8x longer than wide; anterior margin, in side view, forming a gentle curve; postero-distal edge slightly pointed; corbicula occupying distal half, gently depressed, more strongly concave at apex; corbicular setae simple, except for tuft on distal edge; internal surface with very wide keirotrichiate area, with a narrow posterior rim, glabrous, depressed, approximately 1/7 the greatest width of keirotrichia te area, depressed rim gradually becoming obsolete toward basis of tibia and lacking from basal quarter of tibia; tibial comb normal, penicillum covered externally by fine curled hairs. o) Hind basitarsus ca. 0.75x as wide as tibial width and ca. 0.6x its own length, apex 1.3x basal width; posterior margin sinuous, postero-distal edge projecting slightly, rounded; internal surface without basal sericeous area, hairs irregularly distributed. p) Metapostnotum conspicuously protuberant, slanted dorsal portion about 1.5x as long as posterior vertical portion in side view. q) Metasoma moderately elongate, approximately rectangular in dorsal view; tergum 1 about 0.75x as long as its maximum width. r) Labium normal, approximately 0.75x as long as head length; galea much shorter than length of hind tibia. s) Nest unknown.

Etymology. The new genus is named as a combination of plecto , from Latin meaning "weave, twine, twist", with Plebeia , the name of the stingless bee genus which it resembles.

Plectoplebeia nigrifacies (Friese, 1900) comb. nov.

Trigona nigrifaciesFriese, 1900Friese H (1900) Neue Arten der Bienengattungen Melipona Ill., und Trigona Jur. Természetrajzi Füzetek 23: 381-394.: 387. Holotype worker, Peru: Cusco, "Callanga" (ZMB, examined).

Trigona (Plebeia) intermediaWille, 1960Wille A (1960) A new species of stingless bee (Meliponini) from Bolivia. Revista de Biologia Tropical 8(2): 219-223.: 219. Holotype worker, Bolivia: Cochabamba, Chapare, Yungas del Palmar (SEMK, not examined). Syn. nov.

Diagnosis and Comments. For species diagnosis, see above "Diagnosis and Comments" for the genus. The species is known from only five workers collected in three different localities: Callanga, Cusco, in Peru (Friese 1900Friese H (1900) Neue Arten der Bienengattungen Melipona Ill., und Trigona Jur. Természetrajzi Füzetek 23: 381-394.), Yungas del Palmar, Chapare and Mapiri, Larecaja, in Bolivia (Wille 1960Wille A (1960) A new species of stingless bee (Meliponini) from Bolivia. Revista de Biologia Tropical 8(2): 219-223., Camargo 1988Camargo JMF (1988) Meliponinae (Hymenoptera, Apidae) da coleção do "Istituto di Entomologia Agraria", Portici, Itália. Revista Brasileira de Entomologia 32(3/4): 351-374.). Based on information provided by Gade (1999Gade DW (1999) Nature and Culture in the Andes. Madison, University of Wisconsin Press.), Rasmussen & Vivallo (2014Rasmussen C, Vivallo F (2014) Lectotype designations and new synonymies in the Neotropical bee genus Centris Fabricius, 1804 (Hymenoptera: Apidae). Zootaxa 3856(4): 585-594. doi: 10.11646/zootaxa.3856.4.7
https://doi.org/10.11646/zootaxa.3856.4....
) have recently pointed out that Callanga, in Peru, refers to the zone in Cusco covering the watersheds of a river under the same name and tributary of the river Madre de Dios. All three localities are within the domain of the Bolivian Yungas, an ecoregion extending from west-central Bolivia to southeastern Peru.

Redescription. Holotype worker. Approximate body length: 5.5 mm; maximum head width: 2.33 mm; length of forewing: 6.0 mm; maximum width of T2: 2.0 mm. Color : head and mesosoma predominantly dark brown to black, with the following yellow maculae: a narrow band on each side of the pronotal collar and a small spot on anterior portion of pronotal lobe; a narrow stripe along each side of the mesoscutum; entire dorsal portion of axilla; a broad band along posterior margin of scutellum; a small spot on the apex of the fore femur; a small spot on the basis of all three tibia, more conspicuous on the fore tibia and almost entirely obscured on the hind tibia. Reddish brown are the entire mandible, except for dark brown basis and apical margin, most of the labrum, a broad band along the midline of the clypeus and on the lower parocular area, the entire supraclypeal area, most of the pronotal lobe, the fore tarsus and the last tarsomeres of the mid and hind legs, the inner surface of the hind tibia and of the hind basitarsus. Wing veins and pterostigma brown; wing membrane very lightly brown infumated. Metasoma mostly dark brown; most of T1, a broad semicircular band on the basis of the T2, a smaller band on T3 and most of the sterna reddish brown. Pubescence : predominantly pale-yellow to light brown; tarsi with brown setae; erect pilosity well developed on head and mesosoma, mostly simple, except on pronotal lobe, tegula, anterior margin of mesoscutum and along anterior portion of mesepisternum. Clypeus densely covered with short pubescence, mostly simple on upper two-thirds and plumose on lower one-third; longer erect simple setae abundant, about 2-3x longer than short hairs. Entire frons with a dense pile of short plumose pubescence and sparser intermingled simple and longer hairs, longest setae on upper frons and vertex about 0.24-0.28 mm in length; erect setae on scape short, longest ones on upper surface about as long as diameter of scape (0.12:0.12); upper two-thirds of gena with a dense pile of short decumbent plumose pilosity. Mesoscutum with a dense pile of short simple pubescence and sparser intermingled longer hairs; setae along anterior margin mostly plumose, longest ones about 0.36-0.40 mm in length, those on remainder of sclerite simple and shorter (0.18-0.22 mm); longest setae on scutellum about 0.40-0.44 mm in length. Lateral portion of mesepisternum with conspicuously long erect setae, those near wing and along omaular region mostly plumose and those on remainder of sclerite simple; also with a stratum of finely plumose hairs, which are relatively short and not very dense, leaving the integument clearly visible; metepisternum and lateral portion of propodeum with similar vestiture, shorter plumose pilosity denser compared to mesepisternum. Metapostnotum entirely glabrous. Tergum 1 mostly glabrous, with only sparse minute hairs around basal depression and on lateral portion near the spiracle; T2 with only sparse minute hairs along marginal zone, pubescence becoming denser on lateral portion of sclerite; T3-T5 with pubescence restricted to marginal zone, forming a band of relatively short, mostly erect, simple setae, longest setae with 0.12-0.14 mm in length; pubescence of T6 mostly similar to that of T3-T5, its posterior margin, when seen from above, with a fringe of dense and short plumose hairs. Sterna with erect simple hairs, most of them with a gently curved apex; longest setae on S2 with 0.34-0.38 mm in length. Integumental surface : clypeus and supraclypeal area finely reticulate-rugulose and somewhat dull, piligerous punctures not evident. Lower parocular area smooth and shiny, except for fine piligerous punctures. Frons with relatively coarse punctures; puncture density about 1-3 pd on mid portion and upper frons; mid portion of frons, above antennal alveoli, upper frons around ocelli and vertex finely rugulose and somewhat dull; integument around basis of longer setae on upper frons and vertex distinctly raised in relation to remainder of surface; punctures on gena about as coarse as those on frons, but denser (about 0.5-1 pd). Punctures on mesoscutum with size and density similar to those on frons, interspace between them mostly smooth and shiny, except for conspicuous reticulation along anterior margin and along lateral yellow stripe; punctures on scutellum slightly larger and sparser than those on mesoscutum, interspace smooth and shiny, except for finely rugulose and somewhat dull integument along posterior margin of sclerite. Mesepisternum laterally mostly shiny, surface sparsely punctate and with some irregular and weak reticulation, integument around basis of longer setae distinctly raised in relation to remainder of surface; metepisternum finely rugulose-reticulate, somewhat dull. Punctures on lateral portion of propodeum with size and density similar to those on gena, interspace between smooth to finely reticulated; surface of posterior portion mostly shiny and finely reticulated. Metapostnotum finely rugulose-striate and mostly dull along anterior margin, remainder finely reticulate and mostly shiny. Outer surface of hind tibia finely reticulated and somewhat dull on basal one-third, reticulation gradually becoming weaker on remainder of surface, apical one-third entirely smooth and shiny. Terga mostly shiny, with fine reticulation visible along marginal zone of T1, on posterior half of T2 and on visible portions of T3-T6. Structure (measurements in mm): head about 1.2x wider than long (2.33:1.90); inner orbits slightly converging below (upper to lower interorbital distance, 1.55:1.27); clypeus 2.0x wider than long (1.13:0.57); F2 wider than long (0.15:0.125), and F3 as long as wide (0.15:0.15); minimum distance between clypeus and eye about 0.83x the width of F2 (0.125:0.15); malar space about 0.67x as long as F2 width (0.10:0.15); eye about 2.8x longer than its maximum width (1.48:0.53), in side view about as wide as gena (0.43:0.43). Intertegular distance subequal to mesoscutum length (1.50:1.43); scutellum about 1.9x wider than long (0.97:0.50), relatively short and not completely hiding the mid portion of metanotum in dorsal view, basal fovea lacking, but with a shallow emargination on the center of the slanted anterior margin. Hind wings with 6 hamuli. Corbicular depression occupying about distal half of hind tibia; anterior border of apex of tibia not raised in relation to remainder of surface; anterior margin of hind tibia following a gentle curve in side view.

Type material examined. Holotype worker of Trigona nigrifacies (ZMB), "Peru\Callanga\98" "Trigona [worker symbol]\nigrifacies\1900 Friese det.\Fr.", "Type" (plus additional labels, as shown in Fig. 1). The specimen is in good condition, except for lacking the right hind leg; the left mid leg is also broken between the femur and trochanter and has been glued back. Paratype worker of Trigona (Plebeia) intermedia (DZUP), "Yungas del Pal-\mar Boliva [sic] VI\10-1950 Zischka" "KU" "Paratype\Trigona intermedia\A. Wille".

Distribution. Northern portion of the Yungas, in Bolivia (Chapare, Larecaja) and Peru (Cusco).

DISCUSSION

The new genus proposed here certainly belongs to the lineage containing Plebeia and related genera. Traditionally, based on morphological evidence, this lineage has been considered to contain Plebeia , Friesella Moure, 1946, Mourella Schwarz, 1946, Schwarziana Moure, 1943, Scaura and Schwarzula Moure, 1946 (Moure 1951Moure JS (1951) Notas sôbre Meliponinae (Hymenopt. - Apoidea). Dusenia 2(1): 25-70.). Molecular evidence, however, has not corroborated such an arrangement, but indicated that two genera previously considered unrelated to the Plebeia line, Lestrimelitta Friese, 1903 and Nannotrigona Cockerell, 1922, should be added to it (Costa et al. 2003Costa MA, Del Lama MA, Melo GAR, Sheppard WS (2003) Molecular phylogeny of the stingless bees (Apidae, Apinae, Meliponini) inferred from mitochondrial 16S rDNA sequences. Apidologie 34: 73-84., Rasmussen & Cameron 2010Rasmussen C, Cameron SA (2010) Global stingless bee phylogeny supports ancient divergence, vicariance, and long distance dispersal. Biological Journal of the Linnean Society 99: 206-232.). In the topology recovered in the comprehensive study by Rasmussen & Cameron (2010Rasmussen C, Cameron SA (2010) Global stingless bee phylogeny supports ancient divergence, vicariance, and long distance dispersal. Biological Journal of the Linnean Society 99: 206-232.), the Plebeia line in its strict sense would include Plebeia , which resulted in two independent clades, with Friesella and Lestrimelitta coming out between them, plus a clade containing Nannotrigona as sister group to Mourella and Schwarziana . The clade formed by Scaura and Schwarzula was more remotely related to them. To facilitate further discussion, the smaller clade containing Plebeia , Friesella and Lestrimelitta is here referred as the Plebeia clade to differentiate it from the Plebeia line (see Fig. 12), as specified above based on the results of Rasmussen & Cameron (2010Rasmussen C, Cameron SA (2010) Global stingless bee phylogeny supports ancient divergence, vicariance, and long distance dispersal. Biological Journal of the Linnean Society 99: 206-232.).

Figure 12
Summary of the phylogenetic relationships, at genus level, recovered in the study of Rasmussen & Cameron (2010Rasmussen C, Cameron SA (2010) Global stingless bee phylogeny supports ancient divergence, vicariance, and long distance dispersal. Biological Journal of the Linnean Society 99: 206-232.) for the stingless bee taxa related to Plebeia . The color boxes highlight the Plebeia line and the Plebeia clade, two lineages discussed in the text. The putative placements predicted herein for Plectoplebeia gen. nov. are indicated by asterisks (see text for further details).

The positioning of Plectoplebeia within the Plebeia line has also been advocated by Wille (1960Wille A (1960) A new species of stingless bee (Meliponini) from Bolivia. Revista de Biologia Tropical 8(2): 219-223., 1979Wille A (1979) Phylogeny and relationships among the genera and subgenera of the stingless bees (Meliponinae) of the world. Revista de Biologia Tropical 27(2): 241-277.) when discussing the placement of his Trigona (Plebeia) intermedia , here treated as a junior synonym of Plectoplebeia nigrifacies . Wille recognized the unique features of his T. intermedia and argued that the species filled the gap between Plebeia and Schwarziana . In his opinion, the latter genus should therefore be subsumed under the former (both genera were treated by Wille then as subgenera of Trigona ). Wille's classification system, however, was very conservative and adopted broad genus-level concepts, which made most of his genera clearly non-monophyletic. Michener (1990Michener CD (1990) Classification of the Apidae (Hymenoptera). University of Kansas Science Bulletin 54(4): 75-164., 2007Michener CD (2007) The Bees of the World. Baltimore, Johns Hopkins University Press, 2nd ed.), who also advocates broad genus-level concepts, referred to the peculiar features of Wille's T. intermedia , but maintained it in his very inclusive and non-monophyletic Plebeia .

Evidence for the inclusion of Plectoplebeia in the Plebeia line comes from possession of a narrow depressed rim along the posterior margin of the inner surface of the hind tibia, as well as for a set of non-specialized features in the worker caste suggestive of the genera Plebeia and Mourella . Among the Neotropical genera, a narrow depressed rim in the hind tibia is present only in Scaura , Schwarzula and in the Plebeia line, although it is absent in Nannotrigona and at most only weekly indicated in Lestrimelitta . In Plebeia , Friesella and Mourella , the depressed rim continues almost to the basis of the tibia while in Plectoplebeia and Schwarziana it is lacking on the basal quarter of the tibia. Plectoplebeia departs from all these other genera for exhibiting a reduced difference in height between the rim and the keirotrichiate area. The transition between these two areas in the tibia is not strongly marked, their border being indicated by a shallow sulcus and not by a conspicuous step as in the other genera.

While the non-specialized features suggest its inclusion in Plebeia , the larger body size, the wider distance between the clypeus and the eye, the shorter, convex scutellum and the more elongate metasoma, with an unusually long first tergum, resemble more Mourella and Schwarziana . The somewhat coarse punctures on the head and mesosoma also resemble those on Mourella . The number of hamuli is also higher than that present in Plebeia , Friesella and Lestrimelitta , which all have 5, while Plectoplebeia has 6 to 7 (see also Wille 1960Wille A (1960) A new species of stingless bee (Meliponini) from Bolivia. Revista de Biologia Tropical 8(2): 219-223.). Nannotrigona has 5 (or sometimes 6) and Mourella and Schwarziana , 8 (most commonly 8 in Schwarziana , but varying from 7 to 10). Plectoplebeia , however, does not have the long plumose body pilosity, including the plumose sternal fimbria, and the modifications on the anterior distal part of the hind tibia, with an upturned border and a reticulate surface, characteristic of Mourella and Schwarziana .

The shallow emargination on the center of the slanted anterior margin of the scutellum is reminiscent of the basal fovea present in Nannotrigona and ScaptotrigonaMoure, 1942Moure JS (1942) Abelhas de Salobra (Hym. Apoidea). Papéis Avulsos [São Paulo] 2(21): 291-321.. A similar condition can be observed in some Plebeia and to a certain degree in Friesella and Mourella , and likely represents only a plesiomorphy.

Unique features are the shallow depression on the lower frons, the short scutellum, the elongate propodeum and metapostnotum, the rectangular first segment of the metasoma, the elongate and sinuous hindtibia, with a shallow rim on the inner surface, and the long wings. It is interesting to point out that long wings, in relation to body length, are also exhibited by workers of Parapartamona Schwarz, 1948, a genus containing only species restricted to cloud forests in Colombia and Ecuador (Moure 1995Moure JS (1995) Notas sobre o gênero Parapartamona Schwarz (Hymenoptera, Apidae). Acta Biológica Paranaense 21 (1992): 121-134.). Although a thorough study of the relative wing length in stingless bees is wanting, one can suggest that long wings possibly facilitate flying under a constantly dump atmosphere.

Taking into consideration the characters discussed above it is hard to predict if further evidence will favor a closer relationship of Plectoplebeia with the Plebeia clade or with that containing Mourella and Schwarziana . Judging from the high plasticity in the evolution of the external morphology of workers of stingless bees, as exemplified by major differences between the cleptobiotic Lestrimelitta and the related genera Friesella and Plebeia , both possibilities seem equally likely. An additional alternative position would be a sister group relationship with the Plebeia line. The putative placements predicted herein are indicated by asterisks in Fig. 12.

The recognition of Plectoplebeia as a new genus follows the pattern of the last two genera proposed for the Neotropical fauna, Meliwillea and Paratrigonoides (Roubik et al. 1997Roubik DW, Lobo-Segura JA, Camargo JMF (1997) New stingless bee genus endemic to Central American cloudforests: phylogenetic and biogeographic implications (Hymenoptera: Apidae: Meliponini). Systematic Entomology 22: 67-80., Camargo & Roubik 2005Camargo JMF, Roubik DW (2005) Neotropical Meliponini: Paratrigonoides mayri , new genus and species from western Colombia (Hymenoptera, Apidae, Apinae) and phylogeny of related genera. Zootaxa 1081: 33-45.). Like Plectoplebeia , these genera have each a single species, which represent isolated lineages that fall outside the genera to which they are related. After its proposal as sister group of Scaptotrigona based on morphological features, this positioning for Meliwillea has been corroborated also by molecular evidence (Costa et al. 2003Costa MA, Del Lama MA, Melo GAR, Sheppard WS (2003) Molecular phylogeny of the stingless bees (Apidae, Apinae, Meliponini) inferred from mitochondrial 16S rDNA sequences. Apidologie 34: 73-84.). In this sense, ideally a phylogenetic analysis should be carried out to support the proposal of Plectoplebeia as a new genus, but the current set of morphological characters used in the classification of the stingless bees is still limited and a deeper phylogenetic investigation would require dissection and thorough examination of a high number of taxa, preferably using both sexes and castes, something well beyond the scope of the present work. A study of the phylogenetic relationships within the Plebeia clade, using molecular data, is currently under way (H.A. Werneck, L.A.O. Campos & G.A.R. Melo, unpubl. data) and hopefully fresh specimens of Plectoplebeia nigrifacies will become available to be included in it.

ACKNOWLEDGEMENTS

I would like to thank Frank Koch and Michael Ohl for their kind help and support during my stay at the Museum für Naturkunde in Berlin. Brunno Rosa is thanked for taking the photographs of the paratype of Trigona intermedia housed in DZUP and Claus Rasmussen for reading a draft version of the manuscript. Financial support has been provided by Conselho Nacional de Desenvolvimento Científico e Tecnológico (process 205250/2014-9).

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Publication Dates

  • Publication in this collection
    2016

History

  • Received
    29 Sept 2015
  • Reviewed
    15 Nov 2015
  • Accepted
    02 Dec 2015
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