Heterotrigona (Sahulotrigona)

Engel, Michael S. & Rasmussen, Claus, 2017, A new subgenus of Heterotrigona from New Guinea (Hymenoptera: Apidae), Journal of Melittology 2017 (73), pp. 1-16 : 3-8

Sahulotrigona Engel & Rasmussen , new subgenus

ZooBank: urn:lsid:zoobank.org:act:502099C0-FE8A-440B-A30B-BDE0C1AE8C9B

Trigona (Pacificotrigona) Tadauchi et al., 1998: 245 , nomen nudum.

TYPE SPECIES: Heterotrigona (Sahulotrigona) paradisaea Engel & Rasmussen, new species.

DIAGNOSIS: The subgenus Sahulotrigona is distinctive among species of Heterotrigona for the combination of a basal propodeal area that is largely glabrous ( Fig. 5 ), the basal vein (1M) postfurcal (i.e., distad 1cu-a) ( Fig. 7 ), and the posterior glabrate zone of the metatibial inner surface narrower than the raised keirotrichiate zone ( Figs. 9, 10 ). The subgenus includes the most easterly of the known species of Heterotrigona and is most similar to the subgenera Platytrigona and Sundatrigona , all three subgenera possessing a narrow glabrate to subglabrate zone on the posterior border of the inner surface of the metatibia. From the former, Sahulotrigona can be readily distinguished by the largely glabrous basal area of the propodeum, while both subgenera share a postfurcal basal vein (albeit in some Platytrigona the basal vein is confluent with 1cua). Species of Platytrigona are also larger than those of Sahulotrigona , the latter more closely approximate the smaller proportions of Sundatrigona . From the latter subgenus, Sahulotrigona can be distinguished by the postfurcal basal vein (antefurcal in Sundatrigona ), longer scape which is about as long as the torulocellar distance (scape distinctly shorter than torulocellar distance in Sundatrigona ), and the gena about as wide as compound eye in profile (gena narrower than compound eye in profile in Sundatrigona ).

DESCRIPTION: Workers of small size, forewing length (including tegula) approximately 5.6–6.0 mm; integument shiny, smooth, with scattered microscopic punctures; integumental maculation absent ( Figs. 1, 2 , 4–6 ); fine, minute, white to off-white plumose pubescence on face and clypeus and fine, plumose pubescence on lateral surfaces of mesosoma and somewhat obscuring integument; mesoscutum and mesoscutellum with evenly distributed, abundant, minute, erect, branched, fuscous to black setae (except pale in yellow morph of H. atricornis ), intermingled with more scattered, longer, erect, simple setae, neither of which obscure integument but are more abundant ventrally on mesopleuron; metasomal terga with sparse, minute, simple setae except apical tergum with numerous, fuscous, erect, short, apically plumose setae; sterna with long, erect, simple setae.

Head as broad as mesosoma, with face slightly broader than compound eye length; vertex short, rounded; ocelloccipital distance slightly greater than one ocellar diameter; interocellar distance approximately 2.0 times ocellar diameter; ocellocular distance 2.0 times ocellar diameter; scape almost as long as torulocellar distance; first flagellomere longer than second, second and third flagellomeres equal in length; second through tenth flagellomeres each about as long as wide; intertorular distance a little more than one-half torulorbital distance; upper torular tangent near facial midlength; frontal line weakly impressed, not carinate, extending from median ocellus to near upper torular tangent; inner orbit of compound eye weakly concave in upper third; gena about as broad as compound eye in profile, posterior border rounded; malar area of moderate length, about as long as flagellar diameter ( Fig. 2 ); labrum weakly convex, short, much wider than long, apical margin medially blunt to weakly convex; mandible bidentate, teeth well defined and incised (as in other Heterotrigona ), incision between first and second preapical teeth slightly less than orthogonal ( Fig. 3 ); first and second labial palpomeres with several elongate, apically wavy but simple setae.

Mesoscutum with median sulcus weakly impressed; notauli scarcely evident; parapsidal lines short, slightly shorter than ocellar diameter, and weakly impressed. Mesoscutellum short, ending at profile of metanotum and not overhanging propodeum ( Fig. 6 ), rounded ( Fig. 4 ), slightly swollen in profile, with shining transverse depression along mesoscuto-mesoscutellar sulcus. Propodeum long and sloping, with distinct angle between basal area and posterior surface ( Fig. 6 ), dorsal-facing surface about as long as posterior surface; basal area smooth, shining, largely glabrous except apicolateral patches of setae (but never largely pubescent as in Platytrigona Moure ) ( Fig. 5 ); propodeal spiracle elongate, approximately 4–4.5× as long as wide.

Forewing extending well beyond apex of metasoma ( Fig. 1 ), with 2Rs, 1rs-m, 1m-cu, apical half 3M, 4M, apical third 1Cu, 2Cu, 3Cu, and 2cu-a indicated by brownish nebulous traces ( Fig. 7 ); fenestrae demarcated by faint white spectral lines on otherwise infuscate wing membrane (lightly infuscate over most of membrane, darker in apical portion of radial cell and in and around marginal cell); membrane with dark brown microtrichia; prestigma short, about twice as long as anterior width of 1Rs; pterostigma slender; marginal cell approximately four times as long as maximum breadth, separated from wing apex by slightly more than its maximum width, with apex narrowly open, opening about one-fifth maximum marginal cell width, with nebulous, angled, appendiculate apex to 4Rs and nebulous 2r-rs (absent in H. atricornis ); 1M distad 1cu-a, thus minute M+Cuβ present, shorter than 1cu-a; submarginal angle (i.e., anterior angle between 1Rs and Rs+M), nearly orthogonal; M obtusely angled at 1m-cu (i.e., angle between 2M and 3M); 3M tubular in basal half, then nebulous; 2Rs weakly nebulous, angulate; 1rs-m faintly nebulous, almost spectral, straight; r-rs slightly longer than 3Rs. Hind wing with 6–8 distal hamuli (6 in H. atricornis , 6–8 in H. paradisaea ); radial and cubital cells closed by nebulous veins.

Metatibia slightly less than three times as long as greatest width, elongate subtriangular; posterior margin gently recurved with subangulate distal angle ( Figs. 8–10 ), setae along posterior margin and upper outer surface mostly plumose ( Figs. 8–10 ); outer surface weakly concave apically, with corbicula occupying apical third ( Fig. 8 ); apical margin transverse; inner surface with broad, elevated keirotrichiate zone and narrow subglabrous zone ( Figs. 9, 10 ), with abrupt clivulus (sensu Rasmussen et al., in press); keirotrichiate area broader than posterior glabrate zone, width of keirotrichiate zone in the subapical region (wider portion) slightly greater than length of apical glabrate zone and narrower than its width ( Fig. 9 ); penicillus and rastellar comb present, each composed of stiff setae. Metabasitarsus weakly trapezoidal, with posterior margin gently arched, distal angle not projecting ( Figs. 8–10 ); outer surface with fine basal posterior fimbriate field bordering depression; inner surface with short basal sericeous area ( Figs. 9, 10 ).

Metasoma narrow, with first metasomal tergum smooth and shining, second through fourth terga largely smooth and shining to faintly imbricate except exceedingly narrow apical marginal zones imbricate with appressed, minute, apically directed setae; postgradular surface of sixth tergum with short, erect, fuscous plumose setae.

ETYMOLOGY: The subgeneric name is a combination of Sahul, a reference to the occurrence of the known species within a distinct zoogeographic region relative to those Heterotrigona occurring in Sundaland, and the generic name Trigona Jurine. The gender of the name is feminine.

INCLUDED SPECIES: The subgenus as currently constituted contains only two species, both from New Guinea: Heterotrigona (Sahulotrigona) paradisaea , n. sp., and H. (S.) atricornis (Smith) .

Figures

Figures 4–6. Worker of Heterotrigona (Sahulotrigona) paradisaea, new subgenus and species, from eastern Papua New Guinea. 4. Dorsal view of head and mesosoma. 5. Detail of propodeum in oblique dorso-posterior view. 6. Lateral view of mesosoma, detailing mesoscutellar profile.

Figures 7–10. Worker of Heterotrigona (Sahulotrigona) paradisaea, new subgenus and species, from eastern Papua New Guinea. 7. Forewing. 8. Outer view of metatibia and metatarsus. 9. Inner view of metatibia and metatarsus with posterior glabrate (yellow), apical glabrate (blue), keirotrichiate (green), and sericeous (pink) areas colored (arrows indicate width of posterior glabrate and length of apical glabrate zones). 10. Unmodified view of inner surface of metatibia and metatarsus.

Figures 1–3. Worker of Heterotrigona (Sahulotrigona) paradisaea, new subgenus and species, from eastern Papua New Guinea. 1. Lateral habitus. 2. Facial view. 3. Outer view of mandible (P = preapical tooth).