Physocrema

The species in this group were revised (Hosoishi and Ogata, 2009) when they were considered to form a subgenus. The subgenus is now synonymized under the subgenus Crematogaster (Blaimer 2012c). Some of these species have been assigned to the current Crematogaster inflata species-group.


 * Crematogaster ampullaris - now a member of the Crematogaster inflata species-group
 * Crematogaster aurita
 * Crematogaster bakeri
 * Crematogaster difformis
 * Crematogaster inflata - now a member of the Crematogaster inflata species-group
 * Crematogaster mucronata
 * Crematogaster onusta - now a member of the Crematogaster inflata species-group
 * Crematogaster physothorax
 * Crematogaster sewardi
 * Crematogaster tanakai
 * Crematogaster vacca
 * Crematogaster yamanei

Identification
Workers of the subgenus Physocrema are distinguished by these features: (1) anteromedian margin of clypeus convex with slightly impressed median portion; (2) anterolateral margins of clypeus produced anteriorly; (3) 4-jointed antennal club (but, 3-jointed in mucronata); (4) propodeum swollen; (5) metapleural gland orifice circular; (6) petiole elliptical; (7) petiole without node-like process posteriorly. The subgenus is unique among Asian Crematogaster ants in having features (4), (5), (6) and (7). The workers of the subgenus Physocrema share features (1), (2), (3) and (7) with the subgenus Paracrema (= subgenus Crematogaster). In Asian Crematogaster specimens examined, the workers of the subgenera Crematogaster, Decacrema, Mesocrema, Oxygyne, Paracrema, Physocrema and Xiphocrema share features (2) and (7) (constituent species in these subgenera are now all considered to be in the subgenus Crematogaster, with the exception of Mesocrema. Its species are split between the subgenera Crematogaster and Orthocrema)

Most Physocrema species show strong polymorphism in size and sculpture and it is especially pronounced in C. (P.) ampullaris, C. (P.) aurita, C. (P.) difformis, C. (P.) sewardi, C. (P.) yamanei and C. (P.) vacca, and weakly so in C. (P.) inflata, C. (P.) mucronata, C. (P.) onusta and C. (P.) physothorax. In the especially pronounced group, small workers are very different from large workers. For example, in C. (P.) aurita, the scape clearly exceeds the posterior corner of the head in small workers, but it does not in large workers. In general, the mandible has 5 teeth on the masticatory margin, but in some species smaller specimens have only 4 teeth. The postpetiole lacks a longitudinal median sulcus, but it is weakly bilobed posteriorly in large workers of some species. To diagnose Physocrema species, large workers are more useful than smaller workers, particularly in closely similar species.

Key to Crematogaster Physocrema species

Distribution
Southeast Asia: Vietnam (southern parts), Laos, Cambodia, Thailand, Myanmar (southeastern parts), Malaysia (Peninsula and Borneo), Singapore, Indonesia (Sumatra, Mentawai, Java, Bali, Lombok, Kalimantan, Sulawesi, Timor), Philippines.

Biology
Workers in some Physocrema species release defensive secretions from their metapleural glands when they are disturbed (Bushinger & Maschwitz, 1984). Two arthropods were reported to be possible Batesian mimics of Crematogaster inflata, because of the defensive mechanism. A Camponotus ant nests and forages near the nest of C. (P.) inflata and has similar body coloring pattern and walking behavior (Ito et al. 2004). The other is a staphylinid beetle, Drusilla inflatae, collected near colonies of C. (P.) inflata (Maruyama et al. 2003). The color pattern of the beetle closely resembles that of C. (P.) inflata. The secretions contain a mixture of phenols in Crematogaster difformis and C. (P.) inflata (Attygalle et al. 1989; Jones et al. 2005). Jones et al. (2005) suggest that analyses of the secretions may be useful for taxonomic and phylogenetic studies.

Some species of the subgenus Physocrema are reported to be mutualistic ants in ant plants. Several Lecanopteris fern species are inhabited by these ants in Malay Peninsula, Borneo, Sumatra and Sulawesi (Gay & Hensen, 1992). The rubiaceous tree, Neonauclea cyrtopoda, was occupied by these ants in North Sumatra (Maschwitz & Fiala, 1995). The authors identified the black Crematogaster ants with an inflated propodeum as C. (P.) difformis, but those identifications are doubtful because of the similar species. The reported associations were probably opportunistic, and there is no indication that any species of Physocrema form obligate associations with ant plants. This study should facilitate future studies of mimicry and mutualism.

Diagnosis of worker
Hosoishi and Ogata (2009) - Head subquadrate, slightly broader than long, with weakly concave posterior margin, angular posterior corners and subparallel sides. Occipital carinae developed. Mandible striate, with four teeth in small workers and five in larger workers, apical and subapical teeth large. Anterior margin of clypeus convex with slightly impressed median portion (Figs 1, 2); anterolateral margins of clypeus protruded anteriorly, resulting in an appearance of the anterolateral and anteromedian margins being at about the same level (Figs 1, 2); posterior margin of clypeus rounded between frontal lobes. Frontal carinae almost parallel. Antennae 11 segmented; antennal club 4-jointed. Compound eyes large but not distinctly projecting beyond lateral margins of head in full face view.

Pronotum and mesonotum usually without defined suture, rarely promesonotal suture present in large workers. Mesothoracic spiracle reduced to form small pit dorsoventrally. Variable extent of posterior mesosoma enlarged and swollen (Figs 3, 4). Metapleural gland opening circular; propodeal spiracle facing posterolaterally (Figs 3, 4).

Petiole flattened without node nor subpetiolar process; spiracle situated anteriorly midway between dorsal and ventral margins of petiole in lateral view, directed laterally; in dorsal view, elliptical with convex sides, longer than broad (Fig. 5). Postpetiole without distinctly longitudinal median sulcus, weakly bilobed behind in large workers (Fig. 5); spiracle situated distinctly anteriorly on the lateral surface.

Nomenclature

 * PHYSOCREMA [junior synonym of Crematogaster (Crematogaster)]
 * Physocrema Forel, 1912f: 220 [as subgenus of Crematogaster]. Type-species: Crematogaster inflata, by subsequent designation of Wheeler, W.M. 1913a: 82.
 * Physocrema raised to genus: Soulié, 1964: 398.
 * Physocrema junior synonym of Crematogaster: Hölldobler & Wilson, 1990: 13.
 * Physocrema subgenus of Crematogaster: Bolton, 1995b: 42.
 * Physocrema junior synonym of Crematogaster (Crematogaster): Blaimer 2012: 53.