Lasiini Ashmead 1905
Creators: name: Boudinot, Brendon E.
name: Borowiec, Marek L.
name: Prebus, Matthew M.
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Hymenoptera
Formicidae

description: Tribe Lasiini Ashmead, 1905 (Figs 6, 7, 8A–K, 9A–J, 10A–D)
Type genus. Lasius.
Included genus groups. Cladomyrma, Lasius group, Metalasius, Prenolepis group.
Definition (worker).
1. With characters of Formicinae (see Bolton, 2003 and Note 1).
2. Mandible triangular, with 4–11 teeth; third tooth from apex reduced.
3. Dorsal mandibular groove, when present, running along lateral mandibular margin as seen in dorsal view (Note 2).
4. Palp formula usually 6,4, less often 3,4.
5. Frontal protuberance mediad antennal toruli with frontal carinae effaced, becoming broadly rounded posteriorly until continuous with face (Note 3).
6. Frontal protuberance raised above toruli or not.
7. Antennal toruli near or abutting posterior clypeal margin.
8. Antenna 12-, 11-, or 8-merous.
9. Compound eyes not enormous, that is, not longer than half the length of the head; eyes may be reduced to absent; long axis of eyes subparallel.
10. Ocelli present or absent (Note 4).
11. Metanotum differentiated or not.
12. Metapleural gland present, dorsal rim of metapleural gland curved inward.
13. Propodeal spiracle at or near posterolateral margin of propodeum.
14. Propodeal spiracle circular to elliptical, not slit-shaped.
15. Metacoxae wideset: Distance between mesocoxal bases less than between that between bases of metacoxae with mesosoma in ventral view and coxae oriented at right-angles to long axis of body.
16. Metatibiae without double row of ventral (inner) setae.
17. Petiolar foramen inprofile view low, not to barelyexceeding dorsal margin of metapleural gland, with or without dorsal margin or lip, but lip, when present, inconspicuous (Note 5).
18. Petiolar foramen in ventral view long, anterior margin exceeding metacoxal cavities anteriorly.
19. Petiolar node conspicuously shorter than propodeum, not reaching dorsal surface of propodeum (Note 6).
20. Petiolar apodeme (situated anteriorly on tergum) contiguous or nearly contiguous with petiolar node (Note 7).
21. Petiolar sternum U-shaped in cross-section (Note 8).
22. Abdominal segment III transverse sulcus absent.
23. Base of abdominal segment III with or without complete tergosternal fusion lateral to helcium, free sclerites commencing distantly up segment or near helcium; tergum III overhanging petiole or not.
24. Proventriculus sepalous (Note 9).
Notes on definition:
Note 1. The generic composition of the Lasiini has recently been reassessed following Blaimer et al. (2015) and Ward et al. (2016). The tribal definition proposed here is thus revised relative to Bolton (2003). It includes new characters and recognizes that several former plagiolepidines belong in the Lasiini.
Note 2. Previous studies have not focused attention on the dorsal mandibular groove. Here it was observed that the groove, as seen with the mandible in dorsal view, runs along the outer margin of the mandible toward the mandibular apex in the Myrmelachistini, Lasiini and most Melophorini. This contrasts with the state observed in the ‘formicoform radiation’ (i.e., the clade that includes Camponotini, Formicini and Melophorini, along with the monotypic tribes Gesomyrmecini, Gigantiopini, Oecophyllini, and Santschiellini; see the section † Kyromyrma, an ancestral formicine, under the section ‘ Incertae sedis in the Formicinae’ below). When the groove is present in the ‘formicoform radiation’, it is very close to the basal mandibular margin and is shortened, except in various plagiolepidines. The medial and shortened state may have arisen multiple times in the Formicini, Plagiolepidini, and Camponotini clade.
Note 3. The ‘frontal protuberance’ is the region between the antennal toruli, which is raised relative to the regions of the face laterad the toruli. To some degree, development of this condition accounts for the ‘laterally directed’ torular condition of Formicidae (Boudinot et al., 2020). In other formicine tribes, including the Melophorini (with Prolasius as an exception), the frontal protuberance is carinate above the toruli (i. e., ‘frontal carinae are present’), with these carinae continuing as a sharp ridge until their posterior terminus. Within the Lasiini, the frontal carinae are effaced; they are long in all groups except Cladomyrma, while in the Plagiolepidini the carinae are short in all genera except Anoplolepis.
Note 4. Ocellus presence–absence is arelatively weak character as expression of ocelli may be variable for genera in which ocelli are observed, such as Lasius and Nylanderia. However, this statement is included as ocellus expression is a traditional character which is easy to evaluate and may have value for future works defining tribes wherein ocelli may be consistently present or absent. Within the Lasiini, ocelli are always absent in Cladomyrma, Euprenolepis Emery, and Pseudolasius Emery, variably present among Lasius, Paraparatrechina Donisthorpe, and Prenolepis Mayr species, and consistently present in Myrmecocystus, Paratrechina Motschoulsky (except P. kohli; see comments under Prenolepis genus group), and Zatania LaPolla et al.
Note 5. The conformation of the dorsal region of the petiolar foramen is newly described here. There is complex variation of the form across the subfamily, but it appears at least that the form observed in the Lasiini is consistent; this form is also observed in the Myrmelachistini. In various lineages within the formicoform radiation, a raised and conspicuously carinate dorsal margin is observed.
Note 6. Short petiolar nodes are also observed in the Myrmelachistini and Plagiolepidini (excluding Anoplolepis). The node height is variable in the Melophorini, being short in Prolasius and Myrmecorhynchus André.
Note 7. The apodeme is clearly separated from the node in most Melophorini, except Prolasius.
Note 8. A U-shaped petiolar sternum was used by Bolton (2003) to diagnose the lasiine tribe group. This trait also occurs in the Myrmelachistini, Myrmoteratini Emery, Plagiolepidini, and four Melophorini (Lasiophanes, Prolasius, Stigmacros, Teratomyrmex); see ‘Ancestral state estimation’ results above and Figure S15.
Note 9. The proventriculus is weakly sepalous in Cladomyrma. The form of the proventriculus forms a natural division between the Plagiolepidini and the ‘plagiolepidiform’ Prenolepis genus group, as observed by Emery (1925). Due to uncertainty about the polarity of the sepalous condition – and whether this form arose multiple times (Eisner, 1957; Agosti, 1990, 1991) – Bolton (2003) lumped the two plagiolepidiform clades, plus the Myrmelachistini, into the Plagiolepidini.
Key to extant genera of Lasiini and primary clades of Lasius (workers)
1. Antenna with eight antennomeres. Mesonotum, metanotum, and propodeum more-or-less continuous, and metanotum undifferentiated (Fig. 6A). Propodeal spiracle distinctly situated in dorsal third of propodeum. Frontal carinae inconspicuous, being extremely short (<0.5 × anteroposterior antennal torulus diameter) or absent .............................................. ... Cladomyrma (seeAgosti, 1991; Agosti etal., 1999).
– Antenna with 11 or 12 antennomeres. Mesonotum, metanotum, and/or propodeum discontinuous, and metanotum differentiated (Fig. 6A–G, I–L), rarely mesosomal dorsum continuous and metanotum undifferentiated (few Paraparatrechina) (Fig. 6H). Propodeal spiracle situated somewhat below or above midheight of propodeum, but not in dorsal third. Frontal carinae conspicuous (≥1.0 × anteroposterior antennal torulus diameter) .................... .................... 2
2. Petiole posteriorly elongated. Node reduced, apex not or barely projecting dorsally above metapleural gland when observed in profile view (Fig. 6F–L). Abdominal tergum IV with anterolateral corners directed anterodorsally from helcium and forming lateral margins of concavity, which receives entire posterior region of petiole when gaster raised (Fig. 7A); petiole largely obscured by abdominal tergum IV in dorsal view. Facial region between antennal toruli flat, effaced frontal carinae not raised above toruli (Fig. 7C)........................... Prenolepis genus group (see LaPolla etal., 2012; LaPolla & Fisher, 2014).
– Petiole without posterior elongation. Node squamiform, not reduced, apex projecting dorsally above metapleural gland when observed in profile view (Fig. 6B–E). Abdominal tergum IV with anterolateral corners weakly or not raised anterodorsally from helcium, corners not forming lateral margins of concavity and not concealing entire posterior region of petiole when gaster raised (Fig. 7B); petiole visible in dorsal view, not obscured by abdominal tergum IV. Facial region between antennal toruli bulging to concave, frontal carinae raised above toruli (Fig. 7D) .......................................... 3
3. Eyes situated in anterior half of head as measured in full-face view (Fig. 10A). Metapleural gland orifice reduced, with opening directed posteriorly. Propodeal spiracle situated in lower half of propodeum in profile view. Antennomere III broader than long. Hypostoma lacking carina along lateral margins ................... ......................... Metalasius gen.nov. (notall states observable for † M. pumilus comb. nov., see below).
– Eyes situated in posterior half of head as measured in full-face view (Fig. 9). Metapleural gland orifice small to very large, opening laterally as well as posteriorly. Propodeal spiracle situated at or above midheight of propodeum in profile view. Antennomere III usually longer than broad. Hypostoma with carina along lateral margins ...................... 4 (Lasius genus group).
4. Maxillary palpomeres III and IV strongly flattened and greatly elongated, length of each exceeds length of apical antennomere. Ventral surface of head with psammophore, that is, margined by long setae (Fig. 6D). Mesothorax and metathorax elongated, mesonotum meeting metanotum at very low angle (Fig. 6D). Compound eyes set at or near extreme posterior margin of head in full-face view; eyes often separated from this border by <1 eye diameter .................................. ............ Myrmecocystus (see Snelling, 1976, 1982).
– Maxillary palpomeres III and IV circular to elliptical in cross-section and not elongated, length of each is less than length of apical antennomere. Ventral surface of head without psammophore (Fig. 6B, C). Mesothorax not elongated and metathorax very rarely elongated, mesonotum usually meeting metanotum at steep angle (Fig. 6B, C). Compound eyes set further away from posterior head margin in full-face view; eyes usually separated from this border by> 1 eye diameter.................................. 5 (Lasius).
5. Metapleural gland enlarged internally, atrium (internal chamber of gland) bulging (forming bulla) and conspicuously visible from external view in profile (Fig. 7E)*. Usually, distance between atrium and propodeal spiracle <2 spiracular diameters as viewed with spiracle and gland in same plane of focus (Fig. 7E). Compound eyes usually somewhat- to very-reduced; if compound eye large, then offset basal tooth present on mandible and body yellowish brown........................................... ................................ Lasiusflavus clade.
– Metapleural gland small, atrium flat to concave, inconspicuous from external view in profile (Fig. 7F). Usually, distance between atrium and propodeal spiracle> 2 spiracular diameters as viewed with spiracle and gland in same plane of focus (Fig. 7F). Compound eyes relatively large and offset basal tooth absent; if offset basal tooth present, then body jet black ............................. Lasiusniger clade.
*Note: The enlarged state of the metapleural gland bulla is a defining synapomorphy of the flavus clade. Aslightly enlarged bulla is observable in the fuliginosus species group, but these jet-coloured ants are otherwise highly distinct.
description: Published as part of Boudinot, Brendon E., Borowiec, Marek L. & Prebus, Matthew M., 2022, Phylogeny, evolution, and classification of the ant genus Lasius, the tribe Lasiini and the subfamily Formicinae (Hymenoptera: Formicidae), pp. 113-151 in Systematic Entomology 47 on pages 128-134, DOI: 10.1111/syen.12522, http://zenodo.org/record/5975346