Crematogaster ranavalonae group

Based on: Blaimer, B. B. 2012c. A subgeneric revision of Crematogaster and discussion of regional species-groups (Hymenoptera: Formicidae). Zootaxa 3482:47-67. and Hosoishi, S. 2015. Revision of the Crematogaster ranavalonae-group in Asia, with description of two new species (Hymenoptera, Formicidae). Journal of Hymenoptera Research 42, 63-92..

Blaimer (2012c) established this Paleotropical group and Hosoishi (2015) subsequently revised the group's Asian members.

Asian species of the ranavalonae-group

Additional ranavalonae-group species

The species of the group that occur beyond the geographic area treated in Hosoishi's 2015 study:

Identification

The Asian species of the group are easily separated from other Asian Crematogaster in having a steeply raised pronotum, a smooth and shiny body surface, and short and appressed body setae.

Key to Asian Crematogaster ranavalonae group species

The Crematogaster ranavalonae group

Blaimer (2012a) Distributed in the Old World tropics, with species described from Madagascar, Africa, India and Indonesia/Malaysia. Little is known about the biology of these enigmatic ants, and they are rarely encountered compared with other Crematogaster species. It has been hypothesized that the queen caste is adapted to temporary social parasitism. This is inferred from the morphology of their queens. They are generally smaller than other Crematogaster species and have falcate mandibles. A single anecdotal record exists documenting the discovery of a dealate queen in a nest of a different Crematogaster species; in this case, however, the host queen was still present in the nest (Forel, 1913). Based on the limited biological data accompanying collections of species in the group, it appears that arboreal carton nest building is a common nesting habit (Forel, 1891, 1910, 1915; Santschi, 1934; M. Janda, personal communication; S. van Noort, personal communication; personal observation).

In Malagasy the species occur in both humid as well as in dry forest habitats and seem to only nest arboreally. Crematogaster ranavalonae is known to build carton nests housing very large colony sizes (Dejean et al., 2010; personal observation), but the relatively few collections in Madagascar suggest a generally lower abundance and population sizes of species in this group in comparison with other Crematogaster species.

Hosoishi (2015) - Members of the Crematogaster ranavalonae-group have been differentiated based on characters found in the worker and queen castes (Blaimer 2012a, 2012b). Although workers of the Asian members also possess the taxonomic characters identified by her, the propodeal spines in some of the Asian species are not well developed, appearing instead as small tubercles. However, I have identified a unique character among the members of the Asian C. ranavalonae-group; that is, while the ridge separating the lateral and ventral portions of the mesopleuron is distinct in most Crematogaster species, it is not distinct in the Asian members of the C. ranavalonae-group. Furthermore, the queen caste of some members of the species group has falcate mandibles, suggesting the occurrence of temporal social parasitism in those species (Forel 1910; Santschi 1934; Hölldobler and Wilson 1990; Blaimer 2012a). However, among the Asian fauna, falcate mandibles are found only in the queen of C. augusti and are unknown in other species due to the rarity with which they are encountered in the field. In this study, I do not treate the queen caste because it is not represented in my collections.

Hosoishi 2015. Figure 7.

The Crematogaster ranavalonae-group consists of twenty-two species, including eleven species from Africa and Madagascar, ten from Asia, and one from New Guinea (Blaimer 2012b). Among the Asian fauna (ten species and four subspecies), four species and three subspecies have been described from India. It is considered that India is the center of diversity in this species-group, but this may be an overestimate attributable to the rarity of this species group in the field. This paper provides a revision of the Asian members of C. ranavalonae-group, based on the morphological characters of the worker caste.

An important character in the Asian Crematogaster ranavalonae-group is the ventrolateral katepisternal ridge (Fig. 7). The ridge separates the mesopleuron lateral surface from ventral surface. Most Asian Crematogaster species have a well-defined ridge separating the two surfaces (Fig. 7B), but in some species the ridge is absent or vestigial (Fig. 7A). The ridge is visible in pinned specimens from lateral or ventrolateral view.

Diagnosis

Worker

Blaimer (2012c) summarized her earlier worker diagnosis (Blaimer 2012a) for the group:

1. Number of maxillary and labial palps reduced in workers: palp formula 3,3, 3,2 or 2,2 (versus 5,3 in other examined members of the genus).

2. In lateral view, median portion of clypeus more or less prominently convex and in fullface view medially protruding over mandibles.

3. Fronto-clypeal suture impressed, often anterior portion of frons (above suture) transversely concave.

4. Head usually rounded and equally long as wide or slightly wider than long.

5. Promesonotal suture often complete and distinct.

6. Subpetiolar process absent.

7. Postpetiole with median impression.

Asian members of the group have workers with the features listed by Blaimer (above) plus the following (Hosoishi 2015):

(i) Pronotum steeply raised in lateral view.

(ii) Ventrolateral katepisternal ridge indistinct, but weakly developed anteriorly in some species.

(iii) Integument essentially smooth and shiny.

(iv) Erect pilosity almost absent. Some erect setae are developed on the clypeus or dorsal surface of petiole and postpetiole, but absent on the dorsum of head, mesosoma and fourth to seventh abdominal tergites.

(v) Dorsum of head, mesosoma and fourth abdominal tergite with short and appressed setae.

Queen

Blaimer (2012a)

1. Mandibles with apical tooth enlarged and acute, other teeth, if present, relatively reduced.

2. Anterior portion of clypeus flat and at least slightly projecting over mandibles.

3. Head significantly longer than wide or about equal length and width, cephalic index 0.84–1.11.

4. Mesosoma with the following characteristics: thorax reduced in size, shortened, mesonotal index 0.74–1.12. Propodeum in contrast elongate, its dorsum meeting metanotum at ∼30◦ angle. Propodeal spines present or absent.

5. Postpetiole with distinct median impression, and width usually significantly exceeding petiole width, petiole–postpetiole index 0.94–1.69.

6. Leg length highly variable, very long to short, leg–body index 1.05–2.45, length of hind tibia 0.61–2.55 mm.

7. Body size highly variable, head width 0.81–1.82 mm and Weber’s length 1.16–2.98 mm.

8. Erect pilosity often abundant.

References