Key to Crematogaster brevis group workers

This worker key is based on: Hosoishi, S. & Ogata, K. 2012. Revision of the Crematogaster brevis complex in Asia (Hymenoptera: Formicidae). Zootaxa. 3349:18-30.

In the course of classifying Asian Crematogaster species to subgenus using a traditional subgeneric classification (Santschi, 1918; Emery, 1922; Wheeler, 1922), we found that the species complex treated in this paper could not be clearly assigned to subgenus. The Crematogaster brevis complex can be distinguished from other Asian Crematogaster species by the following characters: (1) anterolateral margin of clypeus produced anteriorly; (2) antenna 11-segmented; (3) antennal club 2-segmented (exceptionally seems 3-segmented in the larger workers within a species); and (4) postpetiole weakly bilobed. Workers of the subgenus Orthocrema share features (2) and (3), but they do not share feature (1) for Asian fauna.

The species complex mostly falls in the old subgenus Mesocrema, but the taxonomy of the subgenus is quite confusing because of the vague subgeneric diagnosis established by Santschi (1928).

We divide the C. brevis complex into two species groups: the C. brevis group has a developed occipital carina and the petiole is rectangular in dorsal view; the C. treubi group has an undeveloped occipital carina and the petiole is broader anteriorly than posteriorly in dorsal view.

Crematogaster brevis group
 * Crematogaster brevis
 * Crematogaster overbecki

Polymorphism unknown (C. treubi group is monomorphic). The occipital carina developed as distinct ridge (Fig. 2a). Pronotal shoulders developed as ridges (Fig. 4). The petiole in dorsal view rectangular, with angular anterolateral corners (Fig. 3a). Postpetiole bilobed behind. Mesosoma with standing hairs sparse.

This species group seems to be most similar to the Malagasy Mesocrema species, C. rasoherinae.

Crematogaster treubi group
 * Crematogaster bouvardi
 * Crematogaster kojimai
 * Crematogaster treubi
 * Crematogaster treubi apilis
 * Crematogaster walshi
 * Crematogaster yappi

Workers monomorphic. The occipital carina undeveloped, not forming a distinct ridge (Fig. 2b). Pronotal shoulders not developed as distinct ridges. The petiole in dorsal view broader anteriorly than posteriorly, with rounded, not angular, anterolateral margins (Fig. 3b). The postpetiole weakly bilobed, but without distinct longitudinal median sulcus. Mesosoma with abundant standing hairs.

This species group is easily defined by the undeveloped occipital carina and generally 2-segmented antennal club, not only from C. brevis group, but also from other Asian Crematogaster species.

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Crematogaster

1

 * Clypeus with distinct rugulae. Petiole rectangular, with angular corners in dorsal view (Fig. 3a). Occipital carina developed as distinct ridge (Fig. 2a) . . . . . 2


 * Clypeus relatively smooth and shining without distinct rugulae. Petiole broader  anteriorly than posteriroly, but without angular corners (Fig. 3b). Occipital carina undeveloped, without distinct ridge (Fig. 2b) . . . . . 3

2

 * Clypeus with one longitudinal rugula on the median portion and two distinct pairs of longitudinal rugulae laterally. Dorsal promesonotum with dense reticulate sculpture (Fig. 4a) . . . . . Crematogaster brevis


 * Clypeus with two distinct pairs of longitudinal rugulae, but lacking median rugula. Dorsal promesonotum with more open reticulate sculpture with shiny interspaces (Fig. 4b) . . . . . Crematogaster overbecki

3

 * Propodeal spines undeveloped . . . . . Crematogaster yappi


 * Propodeal spines developed . . . . . 4

4

 * Postpetiole strongly bilobed behind (Fig. 3c) . . . . . Crematogaster walshi


 * Postpetiole weakly bilobed (Fig. 3b) . . . . . 5

5

 * Metanotal groove distinct and deep (Fig. 5a) . . . . . Crematogaster bouvardi


 * Metanotal groove less distinct and deep (Fig. 5b) . . . . . 6

6

 * Propodeal spines short and stout, their length shorter than the diameter of propodeal spiracles (Fig. 5b) . . . . . Crematogaster kojimai


 * Propodeal spines long and slender, their length longer than the diameter of propodeal spiracles (Fig. 5c) . . . . . Crematogaster treubi