Wallacetrigona Engel and Rasmussen, 2017

Rasmussen, Claus, Thomas, Jennifer C. & Engel, Michael S., 2017, A New Genus of Eastern Hemisphere Stingless Bees (Hymenoptera: Apidae), with a Key to the Supraspecific Groups of Indomalayan and Australasian Meliponini, American Museum Novitates 2017 (3888), pp. 1-36 : 5-11

Wallacetrigona Engel and Rasmussen , new genus

TYPE SPECIES: Trigona (Geniotrigona) incisa Sakagami and Inoue, 1989 .

DIAGNOSIS: The genus Wallacetrigona is most similar to Geniotrigona (see below), in which its type species was initially placed. The genus can be distinguished from Geniotrigona by the narrowly concave emargination (= interdental incision) separating the two preapical teeth (broadly concave interdental incision in Geniotrigona ); the absence of a strongly elevated ridge posteriorly on the vertex (present in Geniotrigona ); the presence of a deep, U- or V-shaped concave incision medially on the posterior border of the vertex (absent in all other Indomalayan and Australasian taxa); the absence of a dense covering of short, plumose setae on the mesoscutum (present in Geniotrigona ); the apical metasomal terga with short, scattered plumose setae amid longer, erect, black setae (plumose setae of Geniotrigona longer); keirotrichiate zone of metatibial inner surface about as broad as or slightly broader than posterior glabrate zone, and subequal to the length of the apical glabrate zone.

DESCRIPTION: Workers of moderate size, forewing length approximately 7.0–8.0 mm; integument fairly shiny (fig. 1A), smooth, with scattered microscopic punctures (some of which are setigerous) giving appearance of fine imbrication or tessellation on face (fig. 2A), gena, and apical margins of metasomal terga, but otherwise without distinctive sculpturing; integumental maculation absent; with fine, minute, plumose pubescence on face and clypeus and fine, plumose pubescence on mesosoma particularly numerous on metanotum, metepisternum, and propodeal lateral surfaces but not greatly obscuring integument; apical metasomal terga without dense, elongate, apically plumose setae (such setae present in Geniotrigona ).

Head as broad as mesosoma, with face broader than compound eye length (fig. 2A); vertex with faint depression immediately posterior to ocelli and with faint transverse ridge before occipital border but never elevated above level of ocelli (figs. 3A, 3B) (vertex with depression immediately posterior to ocelli and with posterior border greatly elevated as ridge above ocelli in frontal view in Geniotrigona : figs. 2C, 6A, 6B), with deep, concave, medial notch along bor- der with rounded preoccipital ridge (immediately posterior to median ocellus), notch approximately 0.3× ocellar diameter (notch shallow, narrow, and scarcely evident in Geniotrigona ); ocelloccipital distance slightly greater than one ocellar diameter; interocellar distance approximately 2.5× ocellar diameter; ocellocular distance 2.5× ocellar diameter; scape longer than torulocellar distance; second flagellomere longer than first, second and third flagellomeres subequal in length; second through 10th flagellomeres each longer than wide; intertorular distance a little less than one-half torulorbital distance; upper torular (“alveolar” in the terminology of Moure, 1961, and Sakagami, 1975) tangent at about facial midlength; frontal carina present but faint; inner orbit of compound eye weakly concave in upper third; gena slightly broader than compound eye in profile, posterior border rounded; malar area elongate, nearly twice as long as flagellar diameter (figs. 2A, 3A, 3B); labrum flat, large, wider than long, apical margin medially concave; mandible bidentate, teeth well defined and incised (i.e., interdental spaces distinct) (fig. 3C) (but not broadly concavely incised, i.e., with interdental spaces deep, as in Homotrigona Moure ), interdental incision between first and second preapical teeth (teeth of the pollex sensu Michener and Fraser, 1978) angulate (fig. 3C) (broadly orthogonal or concave in Geniotrigona : fig. 6D); galea with longitudinal rows of long, erect, apically hooked, brightly colored setae; first and second labial palpomeres with numerous, elongate, strongly apically wavy but simple setae (see also Michener and Roubik, 1993) (similar to those setae present in Geniotrigona : figs. 2D, 6C).

Mesoscutum with median sulcus weakly impressed; notauli short and scarcely evident; parapsidal lines short, length less than ocellar diameter, and weakly impressed. Mesoscutellum short, ending at profile of metanotum and not overhanging propodeum, rounded, swollen in profile, with shining transverse depression along mesoscuto-mesoscutellar sulcus. Propodeum declivitous, with shallow change in slope between basal area and posterior surface; basal area smooth, glabrous, and shining; propodeal spiracle elongate, 8× as long as wide.

Forewing extending beyond apex of metasoma (fig. 1A), with 2Rs, 1rs-m, 1m-cu, apical half 3M, 4M, apical half 1Cuβ, 2Cu, 3Cu, and 2cu-a indicated by brownish nebulous traces and fenestrae demarcated by white spectral lines on otherwise infuscate wing membrane (fig. 3D); membrane with dark brown microtrichia; prestigma short, scarcely longer than anterior width of 1Rs; pterostigma slender; marginal cell slightly less than 4× as long as maximum breadth, separated from wing apex by slightly more than its maximum width, with apex narrowly open, opening less than one-fifth maximum marginal cell width, with nebulous, angled, appendiculate apex to 4Rs; 1M basad 1cu-a (1M either basad or confluent with 1cu-a in Geniotrigona ), thus short 1Cuα present, 1Cuα 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 angulate; 1rs-m straight; r-rs about as long as 3Rs. Hind wing with 8–9 distal hamuli; radial and cubital cells closed by nebulous veins.

Metatibia slightly less than 3× as long as greatest width, elongate clavate (figs. 4A, 4B); posterior margin gently recurved with subangulate distal angle (fig. 4B) (recurved with rounded distal angle in Geniotrigona : figs. 4C, 4D), setae along posterior margin and upper outer surface mostly plumose; outer surface weakly concave apically, with corbicula occupying apical third (fig. 4A); apical margin transverse; inner surface with narrow, elevated keirotrichiate zone and broad subglabrous zone (figs. 4B, 5A), with abrupt clivulus 4; keirotrichiate zone about as broad as or slightly broader than posterior glabrate zone (figs. 4B, 5A) (narrower than posterior glabrate zone in Geniotrigona : figs. 4D, 5B), width of keirotrichiate zone subequal to length of apical glabrate zone (figs. 4B, 5A) (greater than length of apical glabrate zone in Geniotrigona : figs. 4D, 5B); penicillus and rastellar comb present, each composed of stiff setae. Metabasitarsus lightly concave and trapezoidal, with posterior margin arched, distal angle not projecting (figs. 4A, 4B, 5A); outer surface with small basal posterior fimbriate field; inner surface with short basal sericeous area (figs. 4B, 5A).

4 The term clivulus is introduced here (from Latin, diminutive form of clivus, meaning “sloping incline”) to refer to the slope between the elevated keirotrichiate plateau and the posterior glabrate zone. The condition of the clivulus varies between a gentle slope between these two surfaces in Lepidotrigona and Papuatrigona to an abrupt precipice in most Eastern Hemisphere genera.

Metasoma narrow, with first metasomal tergum smooth and shining, second through fourth terga largely smooth and shining except narrow apical marginal zones microscopically punctate; apical half of fifth and entire postgradular surface of sixth terga with short, plumose setae intermixed amid stiff, erect, black setae, plumose setae distinctly shorter than thicker erect, black setae and not densely covering integument (such setae as long as or longer than black setae, apically plumose, and dense in Geniotrigona ).

ETYMOLOGY: The generic name honors Alfred Russel Wallace (1823–1913), an intrepid and early explorer of the Indomalayan insect fauna and coauthor with Charles R. Darwin (1809– 1882) of the theory of evolution. The gender of the name is feminine.

INCLUDED SPECIES: Presently the genus is understood to only include the type species, Wallacetrigona incisa (Sakagami and Inoue) , new combination, from Indonesia (Sulawesi), east of the important faunal boundary known as the Wallace Line (and part of the biogeographic area known as Wallacea ) .