Rotastruma

Luo and Guénard (2016) - Rotastruma is a rarely collected arboreal genus with two species. They exhibit a limited distribution in the Indomalayan region. Rotastruma recava is known from Borneo and the Malaysian Peninsula, and Rotastruma stenoceps is reported from China (Hubei, Hunan, Guangdong, Yunnan) (antmaps.org). The latter was described in 1991 from Guangdong (China) on the basis of the worker caste, with virtually no information reported on its ecology since its original description. Recently, during attempts to collect additional Paratopula specimens, a single queen identified as Rotastruma stenoceps was collected in Hong Kong, less than 200 kilometres South East from the site of the holotype (Bolton 1991).

Identification
Rotastruma is a marginal leptothoracine genus. It falls into an assemblage of small and little-understood genera on the periphery of what is currently understood as tribe Leptothoracini. Rotastruma appears to have affinities with the genera Paratopula and Romblonella, which form part of this marginal group. Little more can be said of this enigmatic small genus until a detailed survey can be made to define with some accuracy where the limits of tribe Leptothoracini really lie. The respective species pages of the ants that comprise this genus explain how to identify the two known species.

Distribution
Southern China, Singapore and Sarawak (East Malayasia).

Biology
Little is known about the two species of Rotastruma. R. recava has been collected from dead twigs. R. stenoceps is only known from the types and there are no habitat or other biological details associated with their collection.

Hosoishi et al. (2015) collected one colony of an uncertain Rotastruma sp. in regrowth forest in Kampong Thom Province, Cambodia. Two species are currently recognised: Rotastruma recava from Singapore and Borneo, and Rotastruma stenoceps from China (Bolton, 1991). According to a key to species (Bolton, 1991), the collected specimens are similar to R. stenoceps in having the occipital margin transverse and sides of head straight, but differ slightly by having propodeal spines curving upward.

Nomenclature

 *  ROTASTRUMA [Myrmicinae: Formicoxenini]
 * Rotastruma Bolton, 1991: 8. Type-species: Rotastruma recava, by original designation.

Worker Monomorphic subarboreal to arboreal myrmicine ants with the following combination of characters.

1. Palp formula 5, 3.

2. Mandible triangular, with 6 teeth which decrease in size from apical to basal.

3. Clypeus with a median longitudinal carina; anterior clypeal margin with a pair of hairs which straddle the midpoint.

4. Median portion of clypeus broad posteriorly, broadly inserted between the frontal lobes.

5. Frontal lobes narrow, each lobe distinctly narrower than the portion of the clypeus that is inserted between them.

6. Torulus not freely projecting.

7. Frontal carinae very weakly present; antennal scrobes represented only by extremely shallowly depressed areas running above the eyes.

8. Eyes large, situated at or just behind the midlength of the sides.

9. Antennae 12-segmented, the 3 apical segments forming a strongly defined club.

10. Alitrunk low in profile and with a shallowly evenly convex dorsum; promesonotum not domed-convex; metanotal groove absent; propodeum bispinose; sides of alitrunk marginate, especially on mesonotum and propodeum.

11. Propodeal spiracle set low on the side at about the midlength of the sclerite, very close to the dorsalmost point of the metapleural gland bulla.

12. Metapleural lobes present, small and rounded.

13. Metasternal process absent; cuticle between anterior halves of metacoxal cavities depressed.

14. Tibial spurs absent from middle and hind legs.

15. Petiole nodiform, with a short anterior peduncle; petiolar spiracle located at about the midlength of the peduncle.

16. Postpetiolar sternite reduced, small in profile.

17. Sting functional, strong and simple.

18. Cuticle thick and armoured. Pilosity present on all dorsal surfaces of head and body.

Female As worker but only very slightly larger in size. Ocelli present. Alitrunk with full complement of flight sclerites and certainly winged when virgin.