Key to Dacetini

This key to genera is based on: Bolton, B. 2000. The ant tribe Dacetini. Memoirs of the American Entomological Institute. 65:1-1028. It was constructed at a time when Dacetini was considered to be a valid tribe within the subfamily Myrmicinae. Our understanding of the higher level relationships within Myrmicinae have changed since 2000 (Ward et al. 2015) and all of the genera in this key are now considered to belong to the large tribe Attini. A group of genera within this tribe, the Daceton genus-group, contains most of the genera of the former Dacetini. The few exceptions collectively include a large number of species. Pyramica is a synonym of Strumigenys and the latter is no longer considered to be part of the Daceton genus-group. Both of these genera are retained in the key below. The genus Lenomyrmex is also now added to the Daceton genus-group. This genus is not included in this key.

Ward et al. (2015) states the following in regards to these changes:

The trap-jaw ants of the old tribe Dacetini are not monophyletic: species placed in Strumigenys form a separate clade that is sister to phalacromyrmecine ants, represented in our study by Phalacromyrmex and Pilotrochus. The phalacromyrmecines and Strumigenys are in turn sister to basicerotine ants. This arrangement receives strong support (PP 1.00 BS 98–100) at the relevant nodes. Species of long-mandibulate Strumigenys with kinetic action are nested within groups of short-mandibulate species formerly assigned to the genus Pyramica. This justifies the synonymy of the latter under the former (Baroni Urbani & De Andrade, 2007), and supports the hypothesis (Bolton, 1999) that kinetic mandibles are a derived state in the genus.

The true dacetine ants (PP 96 BS 41) comprise all genera currently placed in this group except Strumigenys, but they also include the enigmatic genus Lenomyrmex, whose affinities were previously unclear (Fernández & Palacio, 1999). Dacetine ants are sister to the fungus-growing ants, hereafter referred to as the Atta genus-group (PP 1.00 BS 59 for the larger clade; PP 1.00 BS 95 for the Atta genus-group). Previous analyses (Schultz & Brady, 2008) also hinted at a relationship between the Atta genus-group and dacetine ants, but without significant support. Our results motivate a search for features in common between these two groups that might provide insight into the origins of specialized biology in both clades.

Baroni Urbani and de Andrade (2007) also provide a key to the Dacetini genera. The key given there is prefaced by further discussion of the former tribe and its genera.

Key to Dacetine Genera based on workers

1

 * Limbus absent from first gastral tergite. With the head in profile the eye not situated at the ventrolateral margin. Spongiform tissue absent from postpetiole but if a narrow waxy border present (extremely rare) it is not arranged in discrete lateral and ventral lobes in profile view . . . . . 2


 * Limbus present on first gastral tergite. With the head in profile the eye situated at the ventrolateral margin or rarely eye absent. Spongiform tissue usually present on postpetiole (only extremely rarely absent); when present it is arranged into discrete lateral and ventral lobes in profile view . . . . . 8

2
return to couplet #1
 * With head in profile the scape, when laid back in its normal resting position, passes above the eye. Mandible always linear, with 3 apical teeth in a more or less vertical or oblique series that interlock at full closure . . . . . 3


 * With head in profile the scape, when laid back in its normal resting position, passes below the eye or across the ventral margin of the eye. Mandible triangular or linear, if linear then with 2 apical teeth in a more or less vertical or oblique series that overlap at full closure . . . . . 5

3
return to couplet #2
 * Basal process of mandible passes below the labrum at full mandibular closure. Labrum vestigial, a minute Y-shaped sclerite between the mandibular insertions. Trigger hairs arise from mandible. Maxillary palps absent. Apex of metapleural gland bulla level with dorsal most point of propodeal spiracle. Antenna with 11 segments. Transverse sulcus present on mesopleuron. (Neotropical) . . . . . Acanthognathus


 * Basal process of mandible passes above the labrum at full mandibular closure. Labrum large, a conspicuous transverse sclerite between the mandibular insertions. Trigger hairs arise from labrum. Maxillary palps with 3-5 segments. Apex of metapleural gland bulla far below level of dorsalmost point of propodeal spiracle. Antenna with 5 or 6 segments. Transverse sulcus absent from mesopleuron . . . . . 4

4
return to couplet #3
 * Second funicular ( = third antennal) segment extremely elongate, at least approaching the combined length of the apical plus preapical segments. Antenna with 5 segments in total. Basimandibular gland absent. Palp formula 5, 3. Labral trigger hairs paired, lateral. Anterolateral margin of head with a minute gap or no gap between head capsule and base of mandible when the latter fully closed. Pronotal cervix dorsally without a thickly rounded anterior collar. (New Guinea, Australia, New Caledonia, New Zea1and) . . . . . Orectognathus


 * Second funicular (= third antennal) segment short, only a fraction of the combined length of the apical plus p r eapical segments. Antenna with 6 segments in total. Basimandibular gland present. Palp formula 3, 2. Labral trigger hair single, median. Anterolateral margin of head with a large U-shaped gap between head capsule and base of mandible when the latter fully closed. Pronotal cervix dorsally with a thick rounded anterior collar. (Afrotropical) . . . . . Microdaceton

5
return to couplet #2
 * Frontal lobes absent; antennal socket surrounded only by an extension of the torulus. Antenna with 11 segments. Base of scape shaft continuing line of main length of shaft, straight or nearly straight to the level of the small flange or rim that immediately follows the neck of the articulatory condyle, not abruptly downcurved. Propodeal spiracle in profile close to dorsal margin of sclerite, widely separated from metapleural gland bulla. Suture between first gastral tergite and sternites rounded laterobasally. (Neotropical) . . . . . Daceton


 * Frontal lobes present; torulus visible ventral to the lobe. Antenna with 4-8 segments. Base of scape shaft not continuing line of main length of shaft, instead scape abruptly downcurved before reaching the small flange or rim that immediately follows the neck of the articulatory condyle. Propodeal spiracle in profile low on side of sclerite, abutting metapleural gland bulla. Suture between first gastral tergite and stemite angled laterobasally . . . . . 6

6
return to couplet #5
 * Labrum very large, shield-like, at full reflex ion capable of covering the entire buccal cavity and completely concealing the labio-maxillary complex. Mandible triangular to elongate-triangular . . . . . 7


 * Labrum not a large shield, at full reflex ion not capable of covering the entire buccal cavity, leaving much of the labio-maxillary complex exposed. Mandible linear. (Australia) . . . . . Epopostruma

7
return to couplet #6
 * Mandible edentate from basal process to preapical tooth. In ventral view outer margin of mandible without an inflected basal angle; in profile mandible not sharply angled downward near base. Basal process of mandible large, in same plane as the masticatory margin. Petiole node without lateral laminar outgrowths. (Australia) . . . . . Mesostruma


 * Mandible denticulate from basal process to preapical tooth. In ventral view outer margin of mandible with an inflected basal angle; in profile mandible sharply angled downward near base. Basal process of mandible small, depressed below plane of masticatory margin. Petiole node with lateral laminar outgrowths. (Solomon Is, New Guinea, Australia) . . . . . Colobostruma

8
return to couplet #1
 * Labrum with reduced distal lobes and specialised proximal shield. Labral lobes small, papilliform or vestigial, not arising from across entire width of labrum. Shield of labrum proximal of lobes with laterally extended margins that are thick in anterior view; whole sclerite usually roughly T-shaped. Buccal cavity relatively long and narrow, lateral margins of cavity converging anteriorly and the mandibles in ventral view apparently arising from the apex of the labio-maxillary complex. Maximum gape of mandibles 170° or more. (World wide) . . . . . Strumigenys


 * Labrum with exaggerated elon gate distal lobes and unspecialised proximal shield. Labral lobes variously shaped but always well developed and prominent, arising from across entire width of labrum. Shield of labrum proximal of lobes without laterally extended margins; whole sclerite never T-shaped. Buccal cavity relatively short and wide, lateral margins of cavity not converging anteriorly and the mandibles in ventral view not arising from the apex of the labio-maxillary complex. Maximum gape of man dibles 90° or less. (World wide) . . . . . . Pyramica