Heterotrigona (Sahulotrigona) tricholoma, Engel, 2019

Engel, Michael S., 2019, Notes on Papuasian and Malesian stingless bees, with the descriptions of new taxa (Hymenoptera: Apidae), Journal of Melittology 2019 (88), pp. 1-25 : 3-7

Heterotrigona (Sahulotrigona) tricholoma Engel, new species

ZooBank: urn:lsid:zoobank.org:act:28942BD5-85F6-4EFA-9B80-4D959CA6E2FA

( Figs. 1–7 )

DIAGNOSIS: The new species can be distinguished from other Sahulotrigona by the presence of a distinctive fringe of minute, erect, plumose setae along the posterior border and extending along the lateral borders to the level of the tangent between the anterior margins of the tegulae ( Fig. 7 ). In addition, the species is overall lighter in coloration, particularly the metasoma which is brown to almost yellowish brown, with more distinctive chestnut brown on the apical margins (giving the metasoma more of a banded appearance than in other Sahulotrigona ) (e.g., Figs. 3, 4 ). There is considerable variation in coloration, with individuals ranging from a dark morph to a lighter morph ( Figs. 1–6 ), but aside from color all other aspects of their morphology and setation, particularly the presence of the mesoscutal fringe, are identical.

DESCRIPTION: ⚲: Total body length approximately 5.13 mm (5.0– 5.2 mm), forewing length (including tegula) 5.4 mm (5.3–5.5 mm). Head wider than long, width 1.88 mm (1.83–1.92 mm), length 1.60 mm (1.56–1.65 mm); compound eye length 1.28 mm (1.23– 1.28) mm; upper interorbital distance 1.21 mm (1.10–1.21 mm), lower interorbital distance 1.15 mm (1.08–1.15 mm). Scape length 0.73 mm (0.69–0.73 mm), slightly shorter than torulocellar distance, torulocellar distance 0.76 mm (0.73–0.76 mm); flagellomeres about as long as wide except apical flagellomere longer than wide. Clypeus broader than long, approximately 2.1× as wide as long, length 0.46 mm (0.44–0.46 mm), width 0.96 mm (0.92–0.96 mm). Malar area short, length approximately subequal to flagellar diameter or 0.5× basal mandibular width. Intertegular distance 1.20 mm (1.20–1.33 mm). Hind wing with 7 distal hamuli (6–8 in H. paradisaea , 6 in H. taraxis , vide infra).

Integument generally dark brown to light chestnut brown or yellowish brown, except labiomaxillary complex yellow-brown, and darker reddish brown on mid and hind legs beyond trochanters; face with clypeus, supraclypeal area, and patches on lower face light brown to yellowish brown in darker individuals, face more extensively yellowish brown in lighter individuals with brown to back demarcating sulci and light chestnut brown patches on frons; mesosoma dark brown to light chestnut brown in lighter individuals, except with mesoscutellum (except axilla), metanotum, and propodeum dark brown; wing veins dark brown to brown, nebulous traces brown, membrane hyaline and clear except faint tinge apically; metasoma light brown to yellowish brown, with apical margins chestnut brown and giving banded appearance.

Integument largely smooth and shining, with exceedingly minute punctures at bases of setae but otherwise impunctate. Metasomal terga smooth, shining, and largely impunctate, faintly imbricate and more punctate in narrow apical zones owing to bases of minute, appressed, apically directed setae; sterna faintly imbricate, without impunctate apical margins.

Pubescence generally white to dark fuscous or black. Face with numerous fine, minute, appressed, silvery white, simple setae not obscuring integument; setae of upper frons gradually becoming more erect and in ocellar area intermingled with short, erect, simple setae, such erect, setae predominate on vertex; gena with setae as on face; postgena with long, erect, white, simple setae; scape with minute to short (shorter than diameter of scape), white, simple setae. Mesosomal dorsum with fine, minute, erect, light fuscous, simple setae intermixed with longer, erect, fuscous, simple setae, such longer setae sparser than minute setae, longer fuscous setae more numerous and elongate on mesoscutellum; mesoscutum with fringe of minute, erect, plumose setae along posterior border and lateral borders but not extending anterior of tangent between anterior margins of tegulae; metanotum with abundant, fine, minute, white setae; pleura with abundant, minute to short, subappressed, white, plumose setae, intermixed with longer, erect, simple, white setae, such setae becoming longer ventrally; basal area of propodeum glabrous except for sparse, apicolateral patches of fine, white setae, such setae with a few branches. Setae of legs white to dark fuscous. Metasoma with discs largely glabrous, with minute, suberect, simple, light fuscous setae laterally, such setae becoming progressively more present, albeit still sparse, over discs of fifth and sixth terga; apical margins with minute, simple, setae appressed vibrissae in narrow apical zones of second through fifth terga; longer, erect to suberect, simple, dark fuscous setae scatered laterally fifth and sixth tergum; fifth tergum with appressed to subappressed, minute, simple setae of apical zone extending more extensively posteriorly in apical portion of disc; sixth tergum with more extensive, suberect to subappressed, white setae intermixed with other more erect setae. Sterna with long, erect, simple, white setae on discs and extending to apical margins.

♀: Latet.

♂: Latet.

HOLOTYPE: ⚲, PNG [ Papua New Guinea]: Chimbu Prov., Wara Sera Research Sta., Crater Mtn. Conserv. Area , 6–10 Oct 2000, A.S. & M.F. Whiting ( AMNH).

Paratypes: 2⚲⚲, same data as holotype ( AMNH) .

ETYMOLOGY: The specific epithet is taken from the Greek words, trichós (τρῘΧΌς), meaning “hair”, and lôma (λῶμᾰ), meaning, “border” or “fringe”, and is a reference to the fringe of setae bordering the mesoscutum posterolaterally.

COMMENTS: It is interesting to note that many stingless bees in New Guinea seem to include a range of coloration that at the lighter end of the spectrum encompasses a patern of largely testaceous or aurantius individuals with darker middle and hind legs, and with similar facial paterning [aside from the current species, others include H. lamingtonia (Cockerell) , vide infra; H. keyensis (Friese) , and P. atricornis (Smith) , vide infra]. Whether this is some kind of mimicry complex remains to be explored.

Figures

Figure 7. Dorsal-posterior oblique view of mesosoma of worker of Heterotrigona (Sahulotrigona) tricholoma, new species, showing (arrow) distinctive plumose fimbria bordering the lateral and posterior margins of the mesoscutum.

Figures 1–2. Lateral habitus of workers of Heterotrigona (Sahulotrigona) tricholoma, new species, from Papua New Guinea. 1. Dark morph. 2. Light morph.

Figures 3–6. Workers of Heterotrigona (Sahulotrigona) tricholoma, new species, from Papua New Guinea. 3. Dorsal habitus of dark morph. 4. Facial view of dark morph. 5. Dorsal habitus of light morph. 6. Facial view of light morph.