The Trigonisca genus group clade, comprising the extant genus Trigonisca and the extinct genus Exebotrigona, is united by the combination of a minute body size, with a length typically 4.5 mm or frequently less, and a forewing length of 4 mm or less; a distinctly broadened base to the marginal cell, with a basal angle (angle formed within the marginal cell between pterostigmal margin and r-rs) of 68°–90°, and the marginal cell, at tangent of pterostigmal apex, broader than submarginal cell area; the posterior margin of the metatibia nodulose or tuberculate, sometimes weakly so (apparently not nodulose in Exebotrigona), owing to prominent bristle bases; and the setae of the inner surface of the metabasitarsus arranged in transverse rows (Michener, 1990, 2007).

Presently, there are 45 species contained in the Trigonisca genus group, including the species described herein, and these are arranged into four subgenera, which are sometimes treated as distinct genera (e.g., Moure, 1950). The analysis of Rasmussen and Cameron (2010) indicated the likelihood that Leurotrigona s.l. is paraphyletic, and so is treated as two distinct groups herein. Leurotrigona s.str. and Exochotrigona, new subgenus, each with two species (Pedro and Camargo, 2009; see below), while Celetrigona has four species (Camargo and Pedro, 2009) and Trigonisca s.str. (= Dolichotrigona Moure) has 37 (Albuquerque, 1990; Ayala, 1999; Albuquerque and Camargo, 2007; Camargo and Pedro, 2005; Alvarez and Lucia, 2018; herein). Five species of the group are currently recorded as occurring within Colombia: Trigonisca (Exochotrigona) crispula Pedro and Camargo, T. (Celetrigona) longicornis (Friese), T. (Trigonisca) schulthessi (Friese), T. (T.) buyssoni (Friese), and T. (T.) graeffei (Friese) (Nates-Parra, 2001; Smith-Pardo, 2003; Camargo and Pedro, 2009; Pedro and Camargo, 2009). Examination of numerous workers of Trigonisca in Colombian copal (Engel, personal obs.), individuals of which are not uncommonly encountered as inclusions, reveal that they are universally T. schulthessi, of which the injudiciously described T. ameliae Penney (Penney et al., 2013) is a junior synonym (new synonymy).

Type species: Leurotrigona pusilla Moure and Camargo in Moure et al., 1988.

Diagnosis: As for the genus as well as: Small bees, 2.30 mm or less in total body length, forewing length 1.90 mm or less; integument smooth, shining, largely black to dark brown throughout without true yellow maculation, with labrum, clypeus, mandible, scape, tegula, and mesoscutellum sometimes with yellowish to ferruginous areas.

Worker. Head slightly wider than long; clypeus with simple setae; vertex rounded; preoccipital area rounded; scape shorter than torulocellar distance; labrum simple; mandible bidentate; malar space short, as long as flagellar diameter. Transscutal sulcus between axillae shallowly impressed; mesoscutellum comparatively flat and low, acutely rounded apically in profile and slightly raised above level of metanotum; metatibia subtriangular, 2.5–2.6× as long as wide; posterior margin of metatibia somewhat sinuous, with distal angle projected; corbicular setae simple; inner surface with keirotrichiate zone faintly elevated, posterior glabrate zone not depressed; parapenicillum markedly sinuate; metabasitarsus subrectangular, without basal sericeous area on inner surface, with setae arranged in 6–7 transverse rows; forewing shorter than body; hind wing with 5 distal hamuli.

Drone. Metasomal sternum V with apical margin comparatively straight or concave (with deep, broad medial emargination in Leurotrigona); sternum VII relatively transverse (subtriangular, trapezoidal, or subrectangular in Trigonisca and Celetrigona).

Etymology: The new subgeneric name is a combination of the Greek exochos (meaning, “jutting out”), a reference to the projecting and prominent apical posterior angle of the metatibia, and the generic name Trigona Jurine. The gender of the name is feminine.

Included species: Trigonisca pusilla (Brazil, French Guiana, Peru) and T. crispula (Colombia). Both species are diagnosed and described in detail by Pedro and Camargo (2009).

Diagnosis: The new species can be distinguished in the worker caste from its congeners by the following combination of traits: mandible bidentate; setae of face and mesoscutum unmodified (fig. 3B) (lacking the modified pomponlike or plumose decumbent setae of species such as T. nataliae (Moure) or T. pediculana (Fabricius)); setae of scape shorter than diameter of scape (fig. 3B); sculpturing of mesoscutellum distinctly weaker than that of mesoscutum giving the former a shinier appearance (figs. 2A, 3A, C) (versus most other species in which the two are identically sculptured); presence of broad yellowish-orange areas of coloration on clypeus, lower face, paraocular areas, gena, and postgena (figs. 2A, 3B) (integument entirely sooty black in T. graeffei: Friese, 1900; Moure, 1950; Albuquerque, 1990); marginal cell not pronouncedly bulky, with r-rs forming slightly acute angle with pterostigma (fig. 4A) (e.g., similar to species such as T. mixteca Ayala, T. intermedia Moure, and others), i.e., r-rs not completely orthogonal to pterostigma (versus r-rs distinctly orthogonal to pterostigma and forming with 3Rs more pronouncedly bulky U-shaped base to marginal cell, such as in T. graeffei, T. meridionalis Albuquerque and Camarago, T. nataliae, and others: Albuquerque, 1990); R along wing margin beyond pterostigma equal to width of marginal cell at tangent of pterostigmal apex (fig. 4A).

Description: Worker. Total body length 2.73 mm (2.33–3.00 mm), forewing length (apex of costal sclerite to wing tip) 2.03 mm (2.00–2.07 mm). Head wider than long, width 1.00 mm (0.98–1.04 mm), length 0.92 mm (0.88–0.93 mm); compound eye length 0.64 mm (0.62–0.65 mm); upper interorbital distance 0.65 mm (0.65–0.69 mm), lower interorbital distance 0.60 mm (0.58–0.63 mm). Scape length 0.40 mm (0.38–0.40 mm), shorter than torulocellar distance, torulocellar distance 0.46 mm (0.46–0.50 mm). Clypeus broader than long, approximately 3.3–3.5× as wide as long, length 0.20 mm (0.20–0.21 mm), width 0.71 mm (0.69–0.71 mm). Malar area prominent, length approximately 1.6–1.8× flagellar diameter. Mandible bidentate, two small, acutely pointed preapical teeth. Metatibia 2.7–2.8× as long as wide, length 0.75 mm (0.75–0.83 mm), maximum width 0.28 mm (0.28–0.30 mm); outer surface gently concave in apical third, forming corbicula. Forewing with marginal cell base broad, basal angle 80°; R on wing margin beyond pterostigma as long as marginal cell width at pterostigmal apex; hind wing with 5 distal hamuli.

Integument of clypeus and lower face faintly and weakly microalveolate (fig. 3B), such sculpturing becoming more prominent on frons; vertex microalveolate as on frons, blending to weakly coriarious (sensu Harris, 1979) on gena, with such patterning becoming faint ventrally near postgena; postgena smooth. Pronotum faintly microalveolate; mesoscutum distinctly microalveolate (figs. 2B, 3A, C), with medial line present as weak impression about one-quarter mesoscutal midlength, parapsidal lines short, faintly impressed, about one-third length of medial line; tegula weakly and faintly imbricate; mesoscutellum with deep transverse depression bordering transscutal sulcus with mesoscutum and between axillae, surface faintly microalveolate to smooth; axilla weakly microalveolate, distinctly less sculptured than mesoscutum and appearing shinier; metanotum weakly microalveolate (as on axilla); mesepisternum and metepisternum tessellate (we consider tessellate to be on a gradation with microalveolate whereby the interspaces are larger and less impressed); propodeum tessellate (fig. 3A, C). Metasomal terga impunctate and smooth to weakly and exceedingly faintly coriarious, faintly evident coriarious areas more prominent on terga V and VI and on lateral, ventrally folded portions of terga; sterna weakly and faintly coriarious.

Integument generally black to dark brown (fig. 2A, B) except with yellowish orange on labiomaxillary complex, mandibles, labrum, clypeus, supraclypeal area, malar space, postgena, and lower gena, lower face (below tangent of antennal toruli), and in lower frons and paraocular areas, but not reaching to vertex of compound eye (fig. 3B); antennal scape yellowish orange on lower surface and brown on much of upper surface, particularly apically; pedicel and flagellum brown except light brown to yellowish orange on lower surface of first flagellomere and apex of apical flagellomere. Pronotum yellowish orange with areas of dark brown to black bordering mesoscutum and propleurae (fig. 2A); propleuron yellowish orange with dark brown along midline; mesoscutum black to dark brown; tegula translucent yellow; wing veins pale yellow to off-white, membranes hyaline clear, with iridescent reflections (fig. 4A); mesoscutellum as on mesoscutum except with narrow areas of lighter brown apicolaterally near margin with axillae; metanotum brown to dark brown; mesepisternum and metepisternum dark brown to black; propodeum dark brown to black; foreleg largely yellowish orange with areas of light brown to brown on upper or outer surfaces of profemur and protibia; midleg largely brown except mesotarsus yellowish orange, apical half of mesobasitarsus yellowish orange, and with areas of yellowish orange apically on mesocoxa, on mesotrochanter, basally and apically on mesofemur, and basally on mesotibia; hind leg largely brown to dark brown, except yellowish orange to light brown basally on metatibia, lighter brown on outer surface of metabasitarsus, and yellowish orange on metatarsus. Metasoma largely brown to dark brown, terga I–IV often lighter, either light brown or brown, than dark brown terga V and VI; terga II–IV variably with pale patch at lateral fold; sterna brown to dark brown.

Pubescence generally silvery white. Face with scattered minute, decumbent, silvery-white setae (fig. 3B), such setae largely simple except those of paraocular face below upper frons with some minute branches; vertex posterior to ocelli with a few more prominent, erect, longer, simple setae; setae of scape minute, simple, much shorter than diameter of scape, largely decumbent except a few suberect; gena and postgena sparsely setose, latter virtually bare. Mesoscutum with scattered, decumbent to suberect minute silvery setae (fig. 3C), similar to those of face, some with minute branches; intermixed along anterior borders with longer, erect simple, silvery-white setae, such longer erect setae more sparsely intermingled on mesoscutal disc; mesoscutellum with minute, decumbent setae sparse on disc, with more prominent, elongate, erect, simple, silvery-white setae posteriorly; metanotum with abundant, decumbent, silvery-white setae not obscuring surface; mesepisternum with minute to short decumbent setae similar to those of mesoscutum, such setae becoming sparser posteriorly and longer ventrally; metepisternum virtually bare, similar to posterior area of mesepisternum; propodeum largely bare except around propodeal spiracle. Setae of legs largely silvery white except more yellowish or yellowish orange on inner surfaces of tibiae and tarsi; elongate silvery, almost translucent, bristles of metatibial posterior margin simple, a few such setae on corbicular surface (fig. 4B); penicillus composed of long, pale yellow setae; rastellum composed of numerous, long, fine, soft setae; parapenicillus composed of elongate, pale yellow setae arching forward, some nearly meeting apex of penicillus. Metasoma sparsely setose; terga I–IV largely bare except for sparse, minute, decumbent, silvery white, simple setae apically; such setae becoming more abundant on more apical terga, most notably terga V and VI, intermixed with slightly longer suberect setae; sterna with similar subappressed to suberect setae apically, progressively setae more broadly present on more apical sterna.

Queen. Total body length 5.95 mm, forewing length (apex of costal sclerite to wing tip) 2.50 mm. Head slightly wider than long, width 1.04 mm, length 1.00 mm; compound eye length 0.65 mm; upper interorbital distance 0.73 mm, lower interorbital distance 0.71 mm. Scape length 0.50 mm, as long as torulocellar distance, torulocellar distance 0.50 mm. Clypeus broader than long, approximately 2× as wide as long, length 0.24 mm, width 0.50 mm. Malar area prominent, length approximately 1.8× flagellar diameter. Mandible narrower than that of worker, with a single, small preapical tooth. Intertegular distance 0.94 mm. Forewing with veins more yellowish than in worker, membrane hyaline, slightly tinged yellow like pale parchment; hind wing with 5 distal hamuli. Metatibia 3.1× as long as wide, length 0.69 mm, maximum width 0.22 mm; outer surface uniformly convex. Propodeum with exceedingly short basal area, broadly rounding into sloping posterior surface. Metasoma physogastric (fig. 5).

Integument of clypeus and face smooth and shining with minute, scattered setigerous punctures (fig. 6A); gena largely smooth and glabrous; postgena smooth and glabrous except setigerous punctures medially bordering hypostomal fossa, and at border with occiput. Pronotum smooth with scattered minute, setigerous punctures; mesoscutum smooth with scattered minute setigerous punctures (fig. 6B); mesoscutellum as on mesoscutum except punctures more widely spaced and those in posterior half slightly larger, axilla sculptured as on mesoscutum, preaxilla and mesoscutellar crest impunctate; metanotum with abundant minute, setigerous punctures; mesepisternum smooth with minute, setigerous punctures, such punctures becoming more widely spaced posteriorly with virtually glabrous space ventral to hypoepimeral area; metepisternum smooth with minute, setigerous punctures confined to upper quarter near wing base; basal area and posterior surface of propodeum smooth and glabrous, lateral surface with minute setigerous punctures as on anterior half of mesepisternum. Metasomal tergum I largely smooth and glabrous except some setigerous punctures anterolaterally and posteriorly; tergum II smooth with scattered, setigerous, postgradular punctures; terga III–VI smooth with more abundant and uniform setigerous punctures; sterna smooth to faintly coriarious with setigerous punctures in apical halves of discs, except sternum VI with more abundant and uniform postgradular setigerous punctures.

Integument generally yellowish orange to pale yellow (fig. 5), largely semitranslucent on mesosoma and portions of metasoma such that internal musculature can be observed in places; more brown on face above antennal toruli and between paraocular borders, apical half of pedicel, on vertex, uppermost gena, disc of mesoscutum, mesoscutellum, lower posterior mesepisternum, and ventral portion of metepisternum, with preaxilla, mesoscutellar crest, metanotum, and intercoxal region of metepisternum dark brown; wing veins pale yellow, membranes hyaline, clear.

Pubescence generally pale yellow to orange. Labrum with scattered elongate, erect, yellow setae; face with scattered minute, erect to suberect, yellow, simple setae; vertex posterior to ocelli with long, erect, simple setae; scape with minute, erect to suberect, simple setae, much shorter than diameter of scape; gena and postgena largely glabrous, except postgena with elongate, erect, simple, yellow setae bordering hypostomal fossa and long, erect, simple setae bordering occiput. Pronotum with numerous short, erect, fine, simple, white setae; mesoscutum with similar short setae as those on pronotum, intermixed with sparser elongate, erect, simple, white to yellowish setae; mesoscutellum with fine white setae slightly longer and sparser than those on mesoscutum, with elongate setae more numerous and somewhat longer, particularly along posterior border; metanotum with numerous exceptionally fine, short, white, simple setae; mesepisternum with short, erect, simple, yellowish setae, such setae becoming sparser posteriorly and slightly longer and paler ventrally, virtually glabrous posteriorly below hypoepimeral area; metepisternum virtually glabrous except with setae similar to mesepisternum in upper quarter near wing base; propodeum largely glabrous except laterally with scattered exceedingly fine, long, erect, simple, white setae, such setae more prominent around propodeal spiracle, with some longer, thicker, erect, simple, yellowish setae laterally bordering posterior surface. Setae of legs largely pale yellow to off-white; setae of tibiae and basitarsi particularly abundant; setae of metatibia long and rather uniformly distributed, those posteriorly greatly elongate; penicillum, rastellum, and parapenicillum absent (fig. 6C). Metasomal tergum I sparsely setose, with some fine, erect to suberect, simple, off-white setae laterally on upper anterior-facing surface; tergum II with abundant fine, erect to suberect, simple, off-white setae on postgradular disc, such setae slightly more numerous posteriorly than anteriorly and sparser basally and medially; terga III–V with uniformly dense fine, erect to suberect, simple, off-white setae forming distinctive setal mats; tergum VI with setae similar to preceding terga except slightly more spaced and gradually becoming thicker and greatly more elongate apically; sterna with sparse, long to elongate, erect, simple, yellowish to off-white setae in apical portions of discs; sternum VI with such setae more abundant somewhat longer and intermixed over entire disc with fine, short, erect, off-white setae.

Drone. Total body length 2.87–3.00 mm, forewing length (apex of costal sclerite to wing tip) 2.13–2.17 mm. Head wider than long, width 0.98–1.02 mm, length 0.83–0.90 mm; compound eye length 0.71–0.73 mm; upper interorbital distance 0.60–0.65 mm, lower interorbital distance 0.42–0.44 mm. Scape length 0.27–0.29 mm, much shorter than torulocellar distance, torulocellar distance 0.40–0.44 mm. Clypeus broader than long, approximately 1.8× as wide as long, length 0.21–0.24 mm, width 0.38–0.42 mm. Malar area linear, with mandibular base appearing to abut lower compound eye margin (fig. 8A). Metatibia 2.6–2.7× as long as wide (fig. 8B), length 0.77–0.78 mm, maximum width 0.28–0.30 mm; outer surface uniformly convex. Propodeum as in worker. Forewing as in worker except basal angle more acute, 73°, with R on wing margin beyond pterostigma slightly longer than marginal cell width at pterostigmal apex; hind wing with 5 distal hamuli. Modified sterna IV and V, hidden sterna VI and VII, and genital capsule as depicted in figure 9.

Integumental sculpturing as described for worker (fig. 7).

Coloration as described for worker except as follows: pale yellow on labiomaxillary complex, mandibles, and labrum (fig. 8A) (clypeus dark brown); antennal scape yellowish on lower surface and brown on much of upper surface; pedicel pale brown to brown; flagellum brown to dark brown. Pronotal collar brown to dark brown, with pronotal lobe yellow to pale brown (fig. 7A), sometimes with posterior borders and posterior dorsal ridge long mesoscutum yellow to pale brown; propleuron pale brown to brown; axilla dark brown to brown, mesoscutellum frequently lighter than axillae, brown to pale brown; metanotum brown to yellowish brown; procoxa, protrochanter, and profemur brown, protibia brown to light brown on outer surface and lighter basally and apically, with inner surface largely light brown to yellowish brown, protarsus yellow; midleg largely brown to dark brown except mesotrochanter lighter, mesofemur with light brown to yellowish-brown apex, mesobasitarsus dark brown to brown on outer surface except lighter basally and apically, with inner surface largely light brown to yellowish brown, mesotarsus yellow; hind leg largely brown to dark brown, except lighter on metatrochanter, yellowish brown to light brown at apex of metafemur, basally and apically on metatibia, and yellowish on metatarsus.

Pubescence as described for worker except as follows: metatibia with minute to short, decumbent to subappressed simple, silvery white to off-white setae on outer surface, except for nearly glabrous strip posteriorly from about midlength to apex, posterior to glabrous strip setae long, particularly along posterior margin, apical margin with a line of minute, fine, simple, silvery- to off-white setae; worker specializations (e.g., penicillus, rastellum, parapenicillus) absent. Metasoma sparsely setose; sternum III with small lunular patch of long, fine, yellow to off-white setae medially at apical margin, setae characteristically kinked medioposteriorly at apexes; sternum IV with larger lunular patch of similar setae medially at apical margin (figs. 7A, 8C, D), lunular patch proximally well separated from gradulus, surface of lunular patch more flattened than remainder of sternum, apical margin bordering lunular patch roughly straight; sternum V with similar lunular patch of setae encompassing majority of disc and proximally meeting gradulus (figs. 7A, 8C, D), proximal margin of lunular patch area slightly ridged and flattened relative to remainder of sternum, with apical margin of sternum broadly concave except short, medioapical projection; setae of gonostylus as depicted in figures 8C, 9C.

Holotype: , Colombia: La Guajira, Manaure, Pájaro, 11°31′43.91″N, 72°46′35.33″W, 20-xi-2016 [20 November 2016], M.S. Engel, V.H. Gonzalez, P. Sepúlveda, superior nest portion [taken from upper part of nest] (SEMC).

Paratypes (280, 1♀, 25♂♂): Workers: 101, Colombia: La Guajira, Manaure, Pájaro, 11°31′43.91″N, 72°46′35.33″W, 20-xi-2016 [20 November 2016], M.S. Engel, V.H. Gonzalez, P. Sepúlveda, superior nest portion [taken from upper part of nest] (91 SEMC, 2 AMNH, 2 BBSL, 2 LABUN, 1 ICNC, 2 PCYU, 1 IIRB); 123, Colombia: La Guajira, Manaure, Pájaro, 11°31′43.91″N, 72°46′35.33″W, 20-xi-2016 [20 November 2016], M.S. Engel, V.H. Gonzalez, P. Sepúlveda, inferior nest portion [taken from lower part of nest] (115 SEMC, 1 AMNH, 1 LABUN, 2 LIPI, 1 ICNC, 1 IIRB, 2 ZMHB); 8, Colombia: La Guajira, Manaure, Pájaro, 11°31′43.91″N, 72°46′35.33″W, 18-xi-2016 [18 November 2016], M.S. Engel and V.H. Gonzalez, Trigonisca from nest entrance (SEMC); 21, Colombia: La Guajira, Manaure, Pájaro, 11°31′43.91″N, 72°46′35.33″W, 18-xi-2016 [18 November 2016], M.S. Engel and V.H. Gonzalez (SEMC); 4, Colombia: La Guajira, Manaure, Pájaro, 11°31′43.91″N, 72°46′35.33″W, 19-xi-2016 [19 November 2016], M.S. Engel and V.H. Gonzalez, ex: white pan trap (SEMC); 1, Colombia: La Guajira, Maicao, Yutaho, 11°24′47.69″N, 72°24′28.32″W, 19-xi-2016 [19 November 2016], M.S. Engel, V.H. Gonzalez, P. Sepúlveda, ex: yellow pan trap (SEMC); 1, Colombia: La Guajira, Maicao, Yutaho, 11°24′47.69″N, 72°24′28.32″W, 19-xi-2016 [19 November 2016], M.S. Engel, V.H. Gonzalez, P. Sepúlveda, ex: white pan trap (SEMC); 3, Colombia: La Guajira, Albania, Aulaulia, 11°20′15.28″N, 72°26′57.22″W, 19-xi-2016 [19 November 2016], M.S. Engel, V.H. Gonzalez, P. Sepúlveda (SEMC); 1, Colombia: La Guajira, Albania, Aulaulia, 11°20′15.28″N, 72°26′57.22″W, 19-xi-2016 [19 November 2016], M.S. Engel, V.H. Gonzalez, P. Sepúlveda, ex: cactus nest (SEMC); 17, Colombia: La Guajira, Albania, Aulaulia, 11°20′15.28″N, 72°26′57.22″W, 19-xi-2016 [19 November 2016], M.S. Engel, V.H. Gonzalez, P. Sepúlveda, ex: double entrance nest (SEMC).

Queen: 1♀, Colombia: La Guajira, Manaure, Pájaro, 11°31′43.91″N, 72°46′35.33″W, 20-xi-2016 [20 November 2016], M.S. Engel, V.H. Gonzalez, P. Sepúlveda, superior nest portion [taken from upper part of nest] (SEMC).

Drones: 23♂♂, Colombia: La Guajira, Manaure, Pájaro, 11°31′43.91″N, 72°46′35.33″W, 20-xi-2016 [20 November 2016], M.S. Engel, V.H. Gonzalez, P. Sepúlveda, superior nest portion [taken from upper part of nest] (19♂♂ SEMC, 1♂ BBSL, 1♂ LABUN, 1♂ PCYU, 1♂ IIRB); 2♂♂, Colombia: La Guajira, Manaure, Pájaro, 11°31′43.91″N, 72°46′35.33″W, 20-xi-2016 [20 November 2016], M.S. Engel, V.H. Gonzalez, P. Sepúlveda, inferior nest portion [taken from lower part of nest] (1♂ SEMC, 1♂ AMNH).

Etymology: The epithet of this species is the local name in the Wayuunaiki language given by the Wayúu indigenous people of La Guajira, Colombia. The name is treated as a noun in apposition.

Comments: Among the large series of paratype workers and drones there are included several callow individuals, exhibiting those variations typical of early integumental coloration right after emergence.

No well-preserved eggs of T. mepecheu were discovered. However, much of a single damaged egg was identified and examined with an SEM (fig. 10A). It is obviously small and slender, and its posterior end appears to be slightly wider than the anterior one. At approximate midbody, its diameter measures 0.317 mm; its estimated length will probably be around 1.1 mm. Its chorionic surface pattern consists of elevated geometric figures (hexagons, pentagons, etc.: fig. 10) with the patterning becoming elongate where approaching the micropyle (fig. 10B, E). The egg's posterior end was torn away so that it is uncertain whether it has any chorionic patterning.

Material Studied: One egg; same locality and date as holotype.