Camponotini, Forel, 1878

Ward, Philip S. & Boudinot, Brendon E., 2021, Grappling with homoplasy: taxonomic refinements and reassignments in the ant genera Camponotus and Colobopsis (Hymenoptera: Formicidae), Arthropod Systematics & Phylogeny 79, pp. 37-56 : 37

3.3.1 . Identification of male Camponotini

Diagnosis.

Camponotini are well-defined morphologically based on the female castes ( Bolton 2003). Males are identifiable as Formicinae by their long scapes, the strongly oblique gonocoxal-gonostylar articulation, absence of constriction between the third and fourth abdominal segments, and failure of the clypeus to extend between the antennal toruli, among other features (see subfamily key in Boudinot 2015). Given the available sample, male Camponotini are distinguishable from those of other formicine tribes by the following combination of traits (Fig. 10 ): (1) antennal toruli posteriorly-situated (i.e., anterior margins of torular rims distant from posterior clypeal margin); (2) antennae 13-merous; (3) arolia grossly enlarged; (4) gonostyli usually distinctly digitate (finger-like in shape and proportions); (5) waist simple, i.e., (5a) petiolar node usually vertical (except, e.g., Ca. (Myrmopytia) longicollis , which lacks a node altogether), (5b) petiole is not elongate posteriorly (e.g., anterior and posterior faces of node subequal in length), (5c) tergosternal articulation of abdominal segment III (AIII) is unfused, (5d) AIII articulation not raised dorsally above helcium, and (5e) the anterior surface of abdominal tergum III is convex, without a median longitudinal groove for reception of the petiole when “gaster” flexed anteriorly; (6) in most species, the first free abscissae of the radial sector and media veins (Rsf1 and Mf1) are characteristically aligned, forming a more-or-less straight line, although they may be kinked at the juncture of Rs+M, or have some other curvature; in rare cases, e.g., Colobopsis pylora (alate gyne examined), the abscissae meet at a distinct angle; (7) fore wing crossvein 1m-cu is usually absent (although loss within the group may have occurred in parallel, see Remarks below); and (8) head with distinct shape, resembling an inverted pear in full-face view: (8a) posterior head margin broadly convex, (8b) posterior head margin continuous or nearly so with the strongly bulging compound eyes (rarely the head is posteriorly elongate, e.g., Camponotus gouldi ), (8c) malar area from the compound eyes to the mandibular insertion in full-face view strongly narrowed lateromedially, usually with parallel to subparallel malar margins that are almost orthogonal to the anterior eye margin.

Genera included.

Calomyrmex Emery, Camponotus , Colobopsis , Dinomyrmex Ashmead, Echinopla F. Smith, Opisthopsis Dalla Torre, Overbeckia Viehmeyer, Polyrhachis F. Smith.

Remarks on distinguishing the genera.

Camponotus and Colobopsis are globally distinguished from one another in the key to males provided below (section 3.3.2), and are the only camponotine genera occurring in the New World. In the Old World, these genera can be confused with Calomyrmex , Dinomyrmex , Echinopla , Opisthopsis , Overbeckia , or Polyrhachis , for which differentiating features are noted below. In general, Colobopsis is the only genus among these with antennal toruli situated at midlength of the frontal carinae, although some male Camponotus can be hard to evaluate due to poor development of the carinae. Further scrutiny of this condition is necessary.

Dinomyrmex males are readily identified by the following combination of states: (1) body massive, ~2 cm long; (2) head oddly shaped, with concave malar regions in full-face view; (3) propodeal spiracles long, slit-shaped; (4) petiolar node broadly wedge-shaped in profile view; (5) gonapophyses lateromedially flattened and weakly lobate; (6) golden pubescence present on pronotum; and (7) numerous long, reddish macrosetae present on pronotum, lateral mesonotum, and propodeum.

Polyrhachis is easily distinguished. Based on examination of a sample of males from nine of the 13 current valid Polyrhachis subgenera ( Campomyrma Wheeler, Chariomyrma Forel, Cyrtomyrma Forel, Hagiomyrma Wheeler, Hemioptica Roger, Myrma Billberg, Myrmatopa Forel, Myrmhopla Forel, Polyrhachis ), the following differential characters were observed for the genus: (1) head posteriorly truncate in posterior/posterodorsal view, with the posteromedian margin carinate; (2) frontal carinae usually robust, especially broad dorsoventrally dorsal to medial torular arch as seen in lateral view (orientation assuming prognathy), and often strong and well-marked; (3) third abdominal tergum often > 1/3 the total length of the gaster; and (4) helcial tergite elongate, with a very shallow notch or even an anteromedian lobe (e.g., in Polyrhachis sensu stricto), although the medial notch may be extremely long and narrow, reaching the helcial base, as in some Myrmatopa . None of the helcial states observed in Polyrhachis have been seen in Camponotus . While the genitalia and ninth abdominal sternum of Camponotus tend to be rather uniform, those of Polyrhachis vary considerably from species to species and subgenus to subgenus, in ways which are distinct from Camponotus and which deserve special attention.

The boundaries of Calomyrmex , Echinopla , Opisthopsis , and Overbeckia remain largely unexplored due to limited sampling. At least one species of Opisthopsis and one of Calomyrmex (in UCDC), and at least Colobopsis vitrea (male unknown) have the forewing crossvein 1m-cu enclosing and forming a discal cell. A discal cell is absent in Echinopla , Camponotus (including the recently demoted subgenus Camponotus Phasmomyrmex ), most Colobopsis , Overbeckia , and Polyrhachis . Opisthopsis (when 1m-cu present) and Calomyrmex (when 1m-cu present) may be distinguished from one another by the shape of the discal cell, being isosceles-shaped in Opisthopsis and subrectangular in Calomyrmex ; however, this should be validated with a broader taxonomic sample. The examined male of Opisthopsis , that of O. haddoni ( MHNG), was observed to have an exceptionally sharp and long ventroapical point of the penial sclerite; this species also has small ocelli, a very shallow and short posterior head margin posterad the compound eyes, and a large and convex anterior clypeal lobe. Among Echinopla , only E. striata was available for examination; the male of this species lacks 1m-cu, has a short third abdominal tergum, has a posteriorly-truncate head as in Polyrhachis , and is extremely hairy with both standing pilosity and pubescence. The male of Overbeckia has short scapes which are shorter than the head length, very close-set antennal toruli (separated by slightly more than one torular diameter), a small clypeus without an anterior lobe, and a long head posterior to the compound eyes.

Figures

Figure 10. Habitus of male Colobopsis and Camponotus; (A, B) heads in full-face (dorsal) view; (C, D) genitalia in dorsolateral oblique view; (E, F) bodies in profile view; (G, H) wings in ventral view; scale bars: A, B = 0.5 mm, C, D = 0.1 mm, E-G = 1.0 mm. A, C, E, G: Colobopsis species indet., from Fijian radiation (CASENT 0171201). B, D, F, H: Camponotus planus (CASENT 0173220, image from AntWeb [www. antweb. org], photographed by April Nobile). Abbreviations: atVIII = abdominal tergum VIII (metasomal VII), asIX = abdominal sternum IX (metasomal VIII), ce = cerci, gc = gonocoxa, gs = gonostylus, Mf 1 = first free medial vein abscissa, psa = penial sclerite ventral apex, Rsf 1 = first free radial sector vein abscissa, vo = volsella.