Nannotrigona postica, (Latreille, 1807)

Engel, Michael S., 2022, Notes on South American stingless bees of the genus Scaptotrigona (Hymenoptera: Apidae), Part II: Subgroup A of the postica species group, Journal of Melittology 2022 (110), pp. 1-51 : 3-6

The postica species group

This group has metasomal terga III – V densely covered in yellow tomentum, completely obscuring the integument or with a narrow mediolongitudinal space with the tomentum more diffuse to absent such that the surface is exposed. In one species, however, the medial interruption is characteristically broad and the remaining tomentum is more diffuse. The typically dense tomentum gives the bees the appearance of having a yellow tail. The presence of this tomentum should not be confused with those species of other groups in which there is sometimes diffuse areas of whitish tomentum on terga III – VI, but in those species the tomentum never completely obscures the entire tergal surface as the tomentose patches are in diffuse patches, typically small oval areas, and with broad medial interruptions or even the vast majority of the terga without such tomentum. Often the patches on tergum III, and sometimes on the other terga as well, are so diffuse and small as to be largely obscured by the apical margin of the preceding tergum or are rubbed off entirely. The postica group as a whole is assuredly monophyletic although natural groups among the constituent species are unclear at this time.

The postica group is a large and diverse assemblage of species in South America, and to my current knowledge with only four species occurring in Central America. Given its number of species and scope, it is arranged into two informal subgroups for strictly practical purposes and it is not implied that these are clades, although the postica group as a whole certainly seems to be monophyletic. Subgroup A includes those species that are largely orange or yellowish orange in color or intermixed in color on the mesosoma, legs, and metasoma, while subgroup B covers the darker species, those that are entirely or largely dark brown to black. Species of subgroup A are predominantly found in the Andean region. These species are quite variable in many characters, making their identification rather challenging. Indeed, this variation is sometimes quite dramatic (e.g., Scaptotrigona magdalenae , n. sp., vide infra). Accordingly, I have tried to make the key to species as simple as possible by minimizing the use of extensive conditional statements.

Key to Species of Subgroup A in South America

(worker caste only)

1. Tegula orange, reddish orange, or translucent yellowish orange, sometimes with a small brown patch; mesepisternum often with extensive patches of yellowish orange, orange, or reddish orange with brown to dark brown patch ventrally, but sometimes wholly dark brown to black, or with orange restricted to hypoepimeral area or posterior half; legs with extensive areas of yellow orange to light reddish brown, brown, or even black [Subgroup A] .......................... 2

—. Tegula wholly dark brown or black; mesepisternum wholly black; legs largely dark brown to black ............................................................................ Subgroup B

2(1). Genal tooth absent .................................................................................................... 3

—. Genal tooth present ................................................................................................. 7

3(2). Dense yellow tomentum of metasomal terga III – V covering entire dorsal surface, or sometimes with narrow interruptions medially; length of genal concavity, if present, up to about 4× its depth ............................................................ 4

—. Tomentum of metasomal terga III – V broadly absent medially on discs; length of genal concavity about 5× its depth [ Brazil: Amazonas] .... S. faviziae , n. sp.

4(3). Concavity in lateral portion of preoccipital carina distinctly present and above with ventral extension of carina as translucent lamella entirely terminating in concavity or meeting lower margin of concavity .................................. 5

—. Concavity in lateral portion of preoccipital carina shallow, nearly absent, without lamellate extension of carina [ Ecuador: Pichincha] ....... S. extranea , n. sp.

5(4). Gena with large areas of orange and postgena wholly or nearly entirely orange; erect bristles of anterior margin of mesoscutum yellow to black; corbicular bristles dark fulvous to black ..................................................... 6

—. Gena and postgena almost wholly brown; erect bristles of anterior margin of mesoscutum bicolored, fuscous basally and off white apically; corbicular bristles individually bicolored, black basally and off white apically [ Ecuador: Morona-Santiago] ............................................................................ S. santiago , n. sp.

6(5). Erect bristles of vertex and anterolateral corners of mesoscutum dark fuscous to black; bristles of metabasitarsus entirely or nearly entirely black; malar space shorter, approximately 1.6× flagellar diameter [ Colombia: Valle del Cauca] .................................................................................................. S. ederi , n. sp.

—. Erect bristles of vertex and anterolateral corners of mesoscutum yellowish to fulvous; bristles of metabasitarsus entirely or nearly entirely fulvous; malar space longer, approximately 2× flagellar diameter [ Colombia: Cauca] ....................................................................................... S. gonzalezi , n. sp.

7(2). Head with extensive dark markings on at least upper half of frons, often covering majority of frons, and extending at least to vertex, sometimes separated from upper orbits by strip of orange to reddish orange integument ............... 8

—. Head with dark markings restricted to area around ocelli and not encompassing entire upper half of frons [ Colombia: Magdalena River Valley: Cundinamarca, Tolima] ................................. S. magdalenae , n. sp., partim [light morph]

8(7). Mesoscutum with conspicuous reddish orange stripes running along notauli to posterior border, sometimes portion anteriorly along notauli narrower and less conspicuous than posterior section of stripe ............................................ 9

—. Mesoscutum without conspicuous reddish orange stripes ........................... 12

9(8). Bristles of metatibial margins and corbicula wholly or nearly entirely black ..... ..................................................................................................................................... 10

—. Bristles of metatibial margins yellow to light fulvous, with those more apically sometimes darker fulvous and those of corbicular surface dark fulvous to fuscous [ Colombia: Meta: Macarena] .............................. S. macarenensis , n. sp.

10(9). Markings separated from upper inner orbits by strip of reddish orange integument; surface posterior to vertex with paired stripes of black to dark brown extending to dark marking bordering preoccipital ridge; bristles of vertex and anterior of mesoscutum almost wholly fulvous; small bees, head widths 2.27–2.48 mm ................................................................................ 11

—. Markings meeting inner eye margins and typically wrapping onto posterior orbit on upper gena, without dark stripes posterior to vertex extending to preoccipital ridge; preoccipital ridge not demarcated by dark brown; larger bees, head widths 2.67–2.73 mm [ Venezuela] ............ S. ochrotricha (Buysson)

11(10). Bristles of mesobasitarsus and metabasitarsal margins largely black; smaller bees, head widths 2.27–2.36 mm [ Colombia: Huila: Tatacoa Desert] ........ ................................................................................................. S. tatacoensis , n. sp.

—. Bristles of mesobasitarsus and metabasitarsal margins largely fulvous, sometimes with some dark fulvous to black setae intermixed; slightly larger bees, head widths 2.42–2.48 mm [ Colombia: Valle del Cauca: lower Anchicayá River Valley] ................................................................................... S. rosellae , n. sp.

12(8). Anterior border of mesoscutum with erect bristles black along entire margin ........................................................................................................... 13

—. Anterior border of mesoscutum with erect bristles along margin yellow to fulvous, if black bristles present, then restricted to anterolateral corners or with conspicuous white tips contrasting with remainder of rachis .......... 15

13(12). Mesepisternum with extensive areas of yellowish to reddish orange; bristles anteriorly on tegula yellow to light fulvous ..................................................... 14

—. Mesepisternum wholly black; bristles anteriorly on tegula black [ Colombia: Meta] ............................................................................................. S. caduceus , n. sp.

14(13). Metasomal terga III – V with abundant conspicuous thick, erect to subdecumbent black to dark fuscous bristles arising amid appressed yellow tomentum; larger bees, head widths 2.69–2.79 mm [ Brazil: Amazon Basin] ...... ...................................................................... S. nigrohirta Nogueira & Santos-Silva

—. Metasomal terga III – V with conspicuous thick, erect to decumbent yellow to light fulvous bristles arising amid appressed yellow tomentum; smaller bees, head widths 2.45–2.48 mm [north-central Ecuador: Pichincha] ....................... ........................................................................................................... S. kuperi , n. sp.

15(12). Metabasitarsus prolateral surface with scatered, erect to suberect, black bristles dominant amid finer yellow to light fulvous setae, margins with prominent black bristles ................................................................................................... 16

—. Metabasitarsus prolateral surface with yellow to light fulvous bristles dominant, sometimes with 1–4 black bristles, and margins typically with concolorous bristles, rarely with black bristles predominant on margins ............. 17

16(15). Protibial bristles light fulvous; forewing marginal apex with strong infumate spot at marginal cell apex and nebulous portion of Rs prominently darkened apically; orange on face extending upward along inner orbit to near summit [ Colombia: Magdalena River Valley: Cundinamarca] ........................................... ............................................................... S. magdalenae , n. sp., partim [dark morph]

—. Protibial bristles black, but if only a few black bristles, then forewing marginal apex with only weakly brownish area at marginal cell apex and nebulous portion of Rs not prominently darkened apically; orange on face not extending along inner orbit much, if at all, above upper tangent of antennal toruli [western Ecuador: Esmeraldas] ................................................. S. illescasi , n. sp.

17(15). Inferior and superior corbicular bristles concolorous ....................................... 18

—. Inferior corbicular bristles lighter than superior bristles, inferior bristles yellowish fulvous to fulvous, superior bristles dark fuscous to black [ Bolivia] ..... ..................................................................................................... S. yungasensis , n. sp.

18(17). Tegula with yellow to light fulvous bristles anteriorly; integument, where not dark brown to black, largely yellow; metasomal terga III – V with yellow to light fulvous bristles [ Peru: Madre de Dios] ............................. S. baldwini , n. sp.

—. Tegula with fuscous to black bristles anteriorly; integument, where not dark brown to black, largely orange to reddish orange; metasomal terga III – V with fulvous to dark fulvous bristles [ Brazil: southern and eastern Brazil] .... ................................................................................................... S. xanthotricha Moure