Tetragonula

Rasmussen, Claus, 2013, Stingless bees (Hymenoptera: Apidae: Meliponini) of the Indian subcontinent: Diversity, taxonomy and current status of knowledge, Zootaxa 3647 (3), pp. 401-428 : 409-413

Tetragonula species of the “ iridipennis ” species group

Diagnosis: Amongst Tetragonula species groups members of the “ iridipennis ” group are characterized by having a dark mesoscutum with four distinct hair bands separated by broad glabrous interspaces ( Fig. 1 d), and by their smaller body size, with the forewing length, including tegula, measuring 3.0 to 4.3 mm. In addition, Sakagami (1978) reported that the male gonostylus arises dorsad (not laterad) to the gonocoxite in all species of this group.

Comments: Besides the Indian species of Tetragonula (i.e., T. bengalensis ( Cameron) , T. iridipennis (Smith) , T. praeterita (Walker) and T. ruficornis (Smith)) , the group also includes the smallest member of the genus, the apparently widespread T. fuscobalteata ( Cameron 1908) and T. clypearis (Friese 1909) from Australia and New Guinea (Dollin et al. 1997). A last species in the group is T. pagdeni (Schwarz 1939) described based on the holotype (in USNM) male collected from Nakhon Si Thammarat in southern Thailand (Sakagami 1978), but widespread in all of southeast Asia (Sakagami et al. 1990). Sakagami (1978) reported that T. pagdeni workers were only statistically different from T. iridipennis s.l. from India (the former with paler coloration of the anterior corbicular fringe and more plumose frontal hairs), although males of T. pagdeni did differ in genitalic characteristics from the Indian specimens of T. iridipennis s.l. Preliminary molecular results (Rasmussen & Cameron 2007, 2010) placed four genetically distinct but morphologically “ iridipennis ”-like specimens from India in a highly supported clade together with specimens identified as T. pagdeni (from Malaysia), T. clypearis (from Australia) and, surprisingly, also T. minor (Sakagami 1978) (from Thailand). Tetragonula minor is a very small member of the genus and is tentatively placed in this species group, as the male is unknown and it cannot be assessed whether the male gonostylus arise dorsad from the gonocoxite. Workers of Tetragonula minor are distinguished from the other members by the darker hairs of the mesoscutum and corbicular fringe. The principal measurements of the species of this species group are given in table 1 (on average HW=1.6–1.8, WL=3.7–4.3, WD=0.9–1.2, HTL=1.4–1.7) and as follows for species not encountered in the Indian subcontinent: T. fuscobalteata : HW=1.35–1.5, WL=3.1–3.4, WD=0.9–1.0, HTL=1.2–1.4; T. clypearis : HW=1.57, WL=3.55, WD=0.97, HTL=1.46; T. minor : HW=1.6, WL=3.6–3.8, WD=1.0, HTL=1.5; T. pagdeni : HW=1.6–1.8, WL=3.9– 4.1, WD=1.0–1.2, HTL=1.4–1.7. The amber fossil Meliponorytes devictus Cockerell 1921 from the Hukawng Valley, Myanmar, has been placed under junior synonymy of T. iridipennis (Zeuner & Manning 1976) , but could represent an additional member of this species group. Although Hukawng amber generally is recognized as old (Cruickshank & Ko 2003), this particular piece is copal of much more recent but unknown age (Grimaldi et al. 1995).

......continued on the next page Problems: More than one hundred years ago four names were proposed for four very similar Tetragonula specimens from India and Sri Lanka. Those four species were poorly characterized in their time and they have never since been directly compared. This creates an uncertainty as to the true identity of these four validly proposed species. They might simply be synonymous, or they may be the correct names for some of the several species of Tetragonula that inhabit the Indian subcontinent. I have had the opportunity to examine and document with photographs the primary types of all four species. The external morphology of the primary types might provide sufficient and reliable characters for separating these species, but intraspecific variation (size, pubescence, and coloration) is at the same time obscuring the limits of each of the biological species. Ideally, additional characters from the male genitalia and molecular data will provide enough data to convincingly separate and define the species, but such data is not available at this point. It is beyond the scope of the present work to locate male specimens from the type localities or sample fresh specimens for use in molecular studies, to provide an assessment of the validity of each of these four species. Generalities about each of the species are provided below, in addition, detailed measurements of the type specimens are found in table 1, photographs of the type specimens are provided in figures 4–7, and lastly, table 2 provides direct comparison of each of the four primary types.

T. iridipennis T. praeterita T. ruficornis T. bengalensis

Erect setae on vertex dark brown dark brown light brown light or slightly darker

brown Tetragonula iridipennis (Smith 1854) ( Figs 4 a–j, map 2)

Trigona iridipennis Smith 1854: 413 –414: Lectotype (BMNH 17b.1114, worker): examined, “ Type ” (orange border), “ iridipennis / Type Sm.”, “B.M. TYPE / HYM. / 17B.1114”, “ TRIGONA / iridipennis / TYPE. Smith.”, “ Ceylon ” (reverse side “53 / 23”). In addition “ LECTOTYPE Trigona iridipennis Smith Design. JS Moure 1961 / C Rasmussen 2013”; Type locality: SRI LANKA, Central Province, Kandy [ca. 7.27°N, 80.60°E, ca. 467m a.s.l.].

Provenance: Frederick Smith (1805–1879) described this species merely as from Sri Lanka (then Ceylon). However, the label code of the lectotype indicates that the specimen was purchased by the Natural History Museum in London as part of lot 23 in 1853. According to the register at the museum, this lot was sold by Hugh Cuming (1791–1865), an insect dealer from London, and originated from Sri Lanka where it had been collected by George Henry Kendrick Thwaites (1811–1882). Thwaites went to Sri Lanka in 1849 as director or superintendent of the historical and important Royal Botanical Gardens of Peradeniya, near the city of Kandy in the Central Province (Anon 1882a, 1882b). Presumably the type specimen must have been collected around this area, although Thwaites also traveled to other parts of Sri Lanka during his time in Sri Lanka.

Lectotype: Smith (1854) did not state how many specimens he saw of T. iridipennis . In the case of additional type specimens (or syntypes) it is therefore necessary to designate a lectotype to stabilize the future use of the name. However, as Moure (1961) already referred to the above specimen as the holotype, the ICZN Article 74.6 (ICZN 1999) allows the inference by Moure (1961) as a valid lectotype designation, as the original description did not imply syntypes.

Figures

FIGURE 4. Tetragonula iridipennis (Smith): lectotype of Trigona iridipennis. 4 A. Habitus, dorsal view. 4 B. Frontal view of head. 4 C. View towards propodeum and metasoma. 4 D. Lower frontal view of head, including partially hidden mandibles. 4 E. Mesepisternum 4 F. Lateral view of head, including genal area. 4 G. Outer view of right hind tibia. 4 H. Inner view of right hind tibia. 4 I. Left fore- and hindwing. 4 J. Labels.

FIGURE 1. 1 A. Scanning electron microscope image demonstrating the inner surface of hind tibia and basitarsus, the latter with the differentiated basal sericeous area of short, dense, hairs characteristic of the genus Tetragonula of the Indian subcontinent (specimen is Heterotrigona itama Cockerell from Malaysia). 1 B. Close-up of the hind basitarsus with sericeous area of short, dense, hairs. 1 C. Lepidotrigona with diagnostic dense tessellation on head and thorax and densely plumose hairs on the margin of mesoscutum (Lepidotrigona cf. arcifera from India, Nagaland, collection 21). 1 D. The “ iridipennis ” species group is characterized by distinct bands of pubescence separated by broad glabrous interspaces on the mesoscutum (specimen from India, Tamil Nadu, collection 17). Notice that the latter two specimens are laterally glued directly to the entomological pin, thus, avoiding to pin through the mesoscutum and obscure characters from this area.