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

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.


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 (2005), with distinctive or autapomorphic characters highlighted in boldface.The general morphological terminology follows urban (1967), silveira et al. (2002) and miChener (2007).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 AND NOMENCLATURE
Plectoplebeia, a new Neotropical genus of stingless bees (Hymenoptera: Apidae) Gabriel A.R. Melo 1 1 Laboratório de Biologia Comparada de Hymenoptera, Departamento de Zoologia, Universidade Federal do Paraná. Caixa Postal 19020, 81531-980 Curitiba, PR, Brazil. E-mail: garmelo@ufpr.brABSTRACT.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.
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 (1900) 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 (2007).Based on personal communication by Claus Rasmussen, who examined the type specimen (Fig. 1), Camargo & Pedro (2007: 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 (2004) 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 (1912) 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.
As established below, Trigona (Plebeia) intermedia, a name proposed by Wille (1960) 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.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 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) (Friese 1900), Yungas del Palmar, Chapare and Mapiri, Larecaja, in Bolivia (Wille 1960, Camargo 1988).Based on information provided by gade (1999), rasmussen & vivallo (2014) 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 0.24-0.28mm 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 0.36-0.40mm in length, those on remainder of sclerite simple and shorter (0.18-0.22 mm); longest setae on scutellum about 0.40-0.44mm 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 0.12-0.14mm 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 0.34-0.38mm 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 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 and weak reticulation, integument around basis of longer setae distinctly raised in 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.

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 1951).Molecular evidence, however, has not corroborated such an arrangement, but indicated that two genera previously considered unrelated to the Plebeia line, Lestrimelitta Friese, 1903 andNannotrigona Cockerell, 1922, should be added to it (Costa et al. 2003, rasmussen & Cameron 2010).In the topology recovered in the comprehensive study by rasmussen & Cameron (2010), 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 (2010).
The positioning of Plectoplebeia within the Plebeia line has also been advocated by Wille (1960Wille ( , 1979) ) 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 (1990,2007), 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.number of hamuli is also higher than that in Plebeia, Friesella and Lestrimelitta, which all have 5, while Plectoplebeia has 6 to 7 (see also Wille 1960).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 Scaptotrigona Moure, 1942.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 1995).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. 1997(roubik et al. , Camargo & roubik 2005)).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. 2003).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.

Figure 12 .
Figure 12.Summary of the phylogenetic relationships, at genus level, recovered in the study of Rasmussen & CameRon (2010) 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).