Lisotrigona carpenteri Engel, 2000.

The new genus resembles both Lisotrigona and the smallest individuals of Austroplebeia. The presence of yellow maculation on the face and mesosoma of the worker differentiates this caste from those of Lisotrigona (Figs 1, 5–7), while in males the clypeus can be brownish to black (refer to Description, vide). In addition, workers of Lisotrigona have distinct erect bristles on the antennal scape (lacking in Ebaiotrigona) and have minute plumose facial setae covering the entire face, including the upper frons (in Ebaiotrigona the upper frons is lacking in plumose setae and instead covered by minute, fine, simple setae). While yellow maculation is shared between workers of Ebaiotrigona and Austroplebeia, the latter has a more complete wing venation (Fig. 1D for Ebaiotrigona venation), with 1Cu, 2Cu, and 3Cu present, at least as nebulous if not tubular veins, and thereby a more completely delimited subdiscoidal (= second cubital) cell. Additionally, Austroplebeia s.str. has 6 distal hamuli (versus 5 in Ebaiotrigona, Lisotrigona, and Anteplebeina), and Anteplebeina has 1M and 1cu-a confluent (versus 1M distad 1cu-a in Lisotrigona and Austroplebeia s.str.). Perhaps the most dramatic differences between Ebaiotrigona and other minute stingless bees are in the male terminalia. The male terminalia of Ebaiotrigona (Fig. 4) lack those distinctive features of Lisotrigona, that is, in the latter the gonocoxae are enormously expanded proximally into an incomplete ring, the slender gonostyli with apical setae are articulated at about midlength on the elongate gonocoxae, the genital capsule is schizogonal, and sterna VI and VII are entirely different (cf. Fig. 4 vs figs 4, 5 of Michener 2007a). Instead, in Ebaiotrigona the genital capsule is rectigonal, with more transverse gonocoxae in which the gonostyli articulate more distally. Furthermore, the gonostyli are uniquely modified: flattened laterally, with lamellate margins broadened proximally on both ventral and dorsal sides, and tapering apically to an acute point lacking setae. The bulb of the penis valve is enlarged and longer than broad, and abruptly tapers to a thin apical process that is shorter than the basal bulb. In Lisotrigona, the bulb is smaller and about as long as the apical process, the former gently tapering into the latter (Michener 2007a).

⚲: Minute, total length ca 3.95–4.15 mm, forewing length ca 2.96–3.10 mm; integument generally smooth and polished, some places with widely scattered minute punctures on head and mesosoma, with distinct pale yellow maculation on face, specifically undersurface of scape, supraclypeal area, and clypeus; pronotal lobe; and sometimes as small triangle on lower parocular area, as thin line on lateral margin of mesoscutum bordering tegula and as apicolateral spots on mesoscutellar apical margin (such yellow maculation absent in Lisotrigona and Pariotrigona, present but more extensive in Austroplebeia). Setae generally pale to white; those of body fine, short, and simple, face with minutely plumose setae except on upper frons with only minute simple setae (in Lisotrigona the minutely plumose setae distributed across face, including upper frons), scape with fine minute simple setae but without erect short bristles (erect short bristles present in Lisotrigona); mesoscutum with numerous erect, fine, short, simple setae; disc of mesoscutellum with similar setae to those of mesoscutum except twice as long or longer, particularly along posterior margin.

Head as broad as mesosoma, slightly broader than long, with face narrower than compound eye length; vertex gently rounded, not produced or ridged; preoccipital area rounded; scape shorter than antennal-ocellar distance, not reaching median ocellus; ocelli near top of vertex; flagellomere I trapezoidal, longer than flagellomere II; flagellomere II about as long as flagellomere III, each slightly broader than long; middle flagellomeres about as long as or slightly longer than broad; intertorular distance slightly shorter than torulocular distance; upper torular tangent below facial midlength; gena rounded, narrower than compound eye in profile; supraäntennal area with triangular medial elevation bordered laterally by converging furrows forming distinct scapal basins; frontal carina absent, indicated on supraäntennal triangle by weakly demarcated ridge, otherwise a narrowly polished line to median ocellus; malar area nearly linear, subequal to or shorter than 0.5× flagellar diameter (similar to Lisotrigona and Austroplebeia s.str.; Pariotrigona with malar space slightly longer than flagellar diameter; Anteplebeina with malar space as long as flagellar diameter); labrum transverse, simple, apical margin rounded; mandible with apical margin slightly oblique, largely edentate except for two small teeth on upper margin of margin (thus, bidentate), teeth well defined, acute, and incised, interdental spaces distinct but not broadly incised; labial palpomeres I and II with a few, scattered, elongate, apically arched to slightly wavy setae, such setae more clustered apically and sparse elsewhere (similar to that of Lisotrigona).

Mesoscutum with median sulcus faintly impressed, extending to slightly beyond mesoscutal midlength; notauli scarcely evident, not impressed; mesoscutellum short, acutely rounded in lateral aspect, overhanging metanotum and extreme base of propodeum, shining transverse depression on mesoscuto-mesoscutellar sulcus simple. Propodeum gently sloping; basal area slightly longer than mesoscutellum, shining, finely and faintly tessellate; propodeal spiracle elongate, nearly meeting metapostnotal lateral arms.

Forewing extending beyond apex of metasoma, with 2Rs, 1rs-m, 1m-cu, 3M, 4M, 1Cu, 2Cu, 3Cu, and 2cu-a absent or at most indicated by spectral traces; membrane hyaline, clear, with weak iridescent reflections apically; prestigma short, subequal to anterior width of 1Rs; pterostigma slender, subparallel margins slightly widening distally to point of 1r-rs, then arching to anterior margin along marginal cell base; marginal cell separated from wing apex by more than its maximum width, apex broadly open, opening about 0.75× maximum marginal cell width, 4Rs trace not angled apically (i.e., not appendiculate); 1M distad 1cu-a (thus, minute 2M+Cu present); submarginal slightly acute; 1M weakly arched; 2M not angled apically (i.e., angle between 2M and spectral 3M linear or at most faintly less than 180°); r-rs slightly longer than 3Rs. Hind wing with 5 distal hamuli; no closed cells and veins posterior to R absent except proximal arch of M+Cu.

Metatibia approximately triangular, approximately 2.8–3.0× as long as greatest width; retromargin gently curved with subangulate distal superior angle, retromarginal setae and superior prolateral surface setae simple; prolateral surface shallowly concave apically, with corbicula occupying slightly less than apical half; retrolateral surface with broad keirotrichiate zone and narrow superior subglabrous zone, without defined clivulus except proximally; keirotrichiate zone approximately 4× as broad as superior glabrate zone, keirotrichiate zone extending to apical margin, with keirotrichiate zone narrowing and superior glabrate zone broadening in apical-most portion of metatibia; inferior penicillum and rastellar comb present, each composed of fine soft setae. Metabasitarsus with proventral margin straight, retrodorsal margin generally paralleling proventral margin, apical margin weakly convex to comparatively straight, distal superior angle not projecting; retrolateral surface without basal sericeous area.

Metasoma subtriangular, about as wide as mesosoma, with metasomal terga smooth and shining except apical margins more matte and faintly and minutely imbricate, all terga almost glabrous, except by minute, erect, simple setae apically forming a narrow band on apical margin, such setae progressively longer, more abundant, and more spread on apical-most terga; sterna largely smooth and glabrous, with long to elongate, fine, erect, simple setae apically.

♂: Darker than worker, apparently without facial maculation of worker (Figs 2, 3), instead yellow areas of worker dark brown to black in drone [brown in Vietnamese male, wholly black in Chinese male (Li Yuran, pers. comm. and unpublished images to MSE)] [note that sometimes areas of yellow maculation start off brownish in individuals who are not fully pigmented and so brown areas of the male could eventually become fully yellow as in the worker; however, the fact that the Vietnamese male appears to be fully pigmented elsewhere on the body (Figs 2, 3) and that the Chinese male is wholly black tends to suggest that drones of Ebaiotrigona truly lack facial maculation, but this will require confirmation through extensive future sampling of males throughout the range of the species], except pronotal lobe consistently yellow. Scape shorter and broader than that of worker (Fig. 3); flagellomere I trapezoidal, shorter than pedicel or flagellomere II; flagellomere II about as long as flagellomere III, each slightly longer than broad. Metasomal sternum VI medioapically chamfered, bilobed; sternum VII medially broadly convex and slightly depressed, with shallow apicolateral concavities; genital capsule rectigonal (Fig. 4); gonobase somewhat transverse; gonocoxae broader than long, with gonostylus articulating somewhat proximally; gonostylus elongate and bladelike, flattened laterally, and broadened proximally and lamelliform mesally on dorsal and ventral sides, tapering apically to acute point with a single fine apical seta, seta simple (Fig. 4); penis valves elongate, bulb enlarged, longer than broad, well sclerotized, abruptly tapering to thin elongate apical process, process gently arched and acutely rounded apically, process slightly shorter than bulb, blub without elongate proximal apodeme, instead with short, twisted apodeme (Fig. 4).

Figure 2. 

Drone of Ebaiotrigona carpenteri (Engel), comb. nov. A lateral habitus B dorsal habitus.

The new generic name is a combination of the Ancient Greek adjective ēbaiós (ἠβαιός, meaning “small”) and the generic name Trigona Jurine. The gender of the name is feminine.

Figure 3. 

Drone of Ebaiotrigona carpenteri (Engel), comb. nov. A facial view B outer view of mandible C metatibia and metatarsus.

Currently, the genus includes only the type species, Ebaiotrigona carpenteri (Engel), new combination.

Figure 4. 

Male terminalia of Ebaiotrigona carpenteri (Engel), comb. nov. A genital capsule (left = dorsal, right = ventral) B metasomal sternum VII C sternum VI.

The worker of this species has been described by Engel (2000). We do not repeat that material here but instead provide descriptive details for the hitherto undocumented male.

♂: Body length 3.5 mm; forewing length 2.9 mm; head width 1.29 mm; head length (lower margin of clypeus to anterior margin of median ocellus and to summit of head) 1.04 mm, 1.19 mm, respectively; compound eye length, upper and lower interorbital distances 0.92 mm, 0.53 mm, 0.45 mm, respectively.

Compound strongly converging below, inner orbits only feebly concave above; compound eye length greater than upper interocular distance; antennae arising below lower third of face so that distance from lower clypeal margin to lower margin of antennal torulus is about one-half distance from upper margin of torulus to lower margin of median ocellus; clypeus about twice as broad as long, lower margin scarcely below lower ocular tangent, upper margin separated from antennal torulus by about one-half torular diameter; head surface in vicinity of antennal toruli depressed, not visible in profile; interocellar distance over twice ocellocular distance, almost 3× ocellar diameter; ocelli on submit of vertex, head surface declivitous immediately behind lateral ocelli with no ridge or carina; genal area much narrower than compound eye in profile; malar area linear (mandibular base almost in contact with lower compound eye margin); mandibles comparatively long, conspicuously crossing one another, mandibular apex slender, apical margin oblique with lower apical angle pointed, upper portion of apical margin faintly sinuous and simulating a faint preapical bump (scarcely large enough to denote as a “tooth”) (Fig. 3B); antennal scape short, its length less than half distance from antennal torulus to median ocellus; flagellum slightly tapering, covered with short, dense setae; flagellomere I shorter than pedicel, nearly 3× as broad as long; flagellomere II about 1.25× as broad as long, flagellomere III about as broad as long, subsequent flagellomeres progressively shorter so that flagellomeres IV–VI are shorter than broad, flagellomeres VII–X progressively longer, longer than broad, flagellomere XI with broadly rounded apex. Male terminalia as in Fig. 4.

Integument of head and mesosoma black except basal one-third of scape (grading into black distal half), mandible, labrum, clypeus, spot between antennae, mesoscutellum, metanotum, propodeum, legs except coxae and femora, and all metasomal segments, brown or suffused with brown ranging to black (darkest in Chinese male: Li Yuran, pers. comm. and image to MSE); pronotal lobe markedly yellow; protibia, meso- and metatibial apices, and tarsi light yellowish brown; tegulae yellowish brown; wings clear, veins light brown; stigma translucent, light brownish.

Integument shining, smooth, head and mesosoma with well separated, fine, small punctures, punctures on lateral part of mesoscutum denser; punctures on mesoscutellum much stronger and denser than those on mesoscutum, separated by 2–3× a puncture width; mesepisternum centrally with coarse punctures separated by 2–3× a puncture width, otherwise integument between punctures smooth; basal area of propodeum shining, minutely tessellate, glabrous; posterior surface smooth, shining. Metasomal terga smooth except minute punctures on narrow posterior margins.

Pubescence mostly exceptionally short, mostly yellowish white, setae of lower half of face white and conspicuously plumose, other setae simple or nearly so. Posterior part of mesoscutellum with zone of upcurved setae, longest on body except for some on apical margin of clypeus and mandible, about 2.5× as long as median ocellar diameter, otherwise long setae (nearly 2× ocellar diameter) sparse on apical margin of clypeus, vertex, coxae, and trochanters, rather numerous on mandibular lower margin. Setae of mesoscutum short, some setae at apicolateral corner longer, about as long as ocellar diameter. Metasomal terga I–IV glabrous except for minute erect setae on posterior margins.

Workers exhibit noticeable variation in overall coloration, and can loosely fall into a lighter and dark morph, although there are individuals who seemingly intergrade and so these morphs are not discrete (Figs 1, 5–7). Generally, areas of maculation on the clypeus, ventral surface of scape, mesoscutal lateral borders, axilla, apicolaterally on mesoscutellum, foreleg, and in isolated areas on the mid- and hind legs can vary from pale to vivid yellow, while the males the tarsi are more consistently yellowish brown to yellow and the podites basal to the tarsi are brown to black (darkest in the Chinese male: Li Yuran, pers. comm. and image to MSE). In addition, the width of the marks on the mesoscutum and mesoscutellum can be exceptionally narrow (mesoscutum) or faint (mesoscutellum), such that they can appear superficially absent. Most noticeably, areas of black on the mesosoma and legs can vary to dark brown (e.g., cf. Figs 1, 5, 6). The metasoma can range from being largely black to dark reddish brown, with lighter brown on the first tergum and basal sterna, to the same pattern but from pallid yellow on the basal sterna and first tergum, with ferruginous on the remaining terga, but blending from light proximally to dark apically, and within a given tergum darkening slightly toward each marginal zone. It should be noted that the holotype worker (AMNH) is of the darker morph.

Figure 5. 

Worker of Ebaiotrigona carpenteri (Engel), comb. nov., dark morph A lateral habitus B dorsal habitus.

Vietnam: 1♂, 67⚲⚲, Tân Thành [Village], Yên Thịnh [Community], Yên Thủy [District], Hòa Bình [Province] [20°21.35'N, 105°39.47'E], 22 June 2021, coll. Tuấn Anh Trương et al. [1♂, 6⚲⚲, nest #1; 5⚲⚲, nest #2; 5⚲⚲, nest #3; 3⚲⚲, nest #4; 2⚲⚲, nest #5; 12⚲⚲, nest #7; 8⚲⚲, nest #9; 8⚲⚲, nest #19; 12⚲⚲, nest #16; 6⚲⚲, nest #21] (IEBR); 18⚲⚲, Yên Hân [Community], Chợ Mới [District], Bắc Kạn [Province], 27 June 2021, coll. Tuấn Anh Trương et al. [11⚲⚲, nest #11; 1⚲⚲, nest #18; 6⚲⚲, nest #13] (IEBR); 53⚲⚲, Nam Cường [Community], Chợ Đồn [District], Bắc Kạn [Province], coll. Tuấn Anh Trương et al. (6⚲⚲, nest #9; 16⚲⚲, nest #11; 21⚲⚲, nest #21); 21⚲⚲, Lân Nghè, Hữu Liên Natural Reserve, Hữu Liên [District], Lạng Sơn [Province], 21°33'48.6"N, 106°24'36.4"E, ca 289 m, 11 June 2018, coll. Liên Thị Phương Nguyễn et al. (IEBR).

Figure 6. 

Worker of Ebaiotrigona carpenteri (Engel), comb. nov., intermediate light morph A lateral habitus B dorsal habitus.

Dark morph: 23⚲⚲, Vũ Quang National Park, Vũ Quang [District], Hà Tĩnh [Province], 18°17'44"N, 105°22'29"E, 12 December 2020, coll. Ngát Thị Trần & Cường Quang Nguyễn (IEBR).

Figure 7. 

Worker faces of Ebaiotrigona carpenteri (Engel), comb. nov., showing identical patterns in both dark and intermediate light morph A dark morph B intermediate light morph.

More than 10 nests were observed in a rocky wall in Yên Thủy, Hòa Bình Province, while six or seven were seen in one locality in limestone cliffs in Bắc Kạn Province (Figs 8, 9). The bees appear to prefer nesting in cavities between stones, either natural limestone cliffs or even amid the rocks of human-built walls, much like that of Pariotrigona (Bänziger et al. 2011). The bees were quite a nuisance and frequented human skin where they were lapping sweat, and attempted to approach the eyes of the collectors (Truong pers. obs.), although it is unclear if this was to collect tears or merely as a timid form of defense from a perceived threat near the nests. Similar observations on the behavior of the bees were made in southern China (Li et al. in press). It is possible that the bees rely on tears (lachryphagous) in the same manner as Pariotrigona and Lisotrigona, although no tear collection could be confirmed nor were bees observed visiting the eyes of cattle or other vertebrates. The bees and nests have a strong foul odor, and future work on the chemistry of their nests and stores is needed to determine their composition and the potential derivation of these smells. Future work will more fully explore the nesting biology, nest architecture, and immature stages of E. carpenteri.

Figure 8. 

Nests and habitat of Ebaiotrigona carpenteri (Engel), comb. nov., at Bắc Kạn Province, Vietnam A general habitat B nest entrance in limestone cliff C exposed nest from between limestone slabs.

Figure 9. 

Nests of Ebaiotrigona carpenteri (Engel), comb. nov., at Bắc Kạn Province, Vietnam A nest entrance B exposed nest from between limestone slabs.