Oligomyrmex Mayr

Eguchi, K., Viet, B. T. & Yamane, S., 2011, Generic synopsis of the Formicidae of Vietnam (Insecta: Hymenoptera), Part I - Myrmicinae and Pseudomyrmicinae., Zootaxa 2878, pp. 1-61 : 22

Oligomyrmex Mayr , 1867

Taxonomy. The genus Oligomyrmex is assigned to the tribe Solenopsidini (Bolton 2003). Fernández (2004) placed Afroxyidris, Oligomyrmex and Paedalgus as junior synonyms of Carebara , but here we do not follow Fernández 's treatment because of his insufficient consideration of Old World taxa. Workers of Vietnamese species have the following features (see Bolton 2003; Ettershank 1966).

Worker dimorphic; head in full-face view subrectangular or subtrapezoidal; major with posterolateral corners more or less produced into preoccipital lobes; minor with round posterolateral corners; frontal carina and antennal scrobe absent; median portion of clypeus margined laterally by conspicuous carinae in minor (median portion of clypeus usually but not always margined laterally in major); posteromedian portion of clypeus narrowly to relatively broadly inserted between frontal lobes; median clypeal seta absent; mandible triangular, with 5-6 teeth on masticatory margin (teeth often rounded or worn in major); antenna with 9- or 11-segments, with 2-segmented club; eye small to much reduced, or rarely absent; major of some species with mesosomal segmentation developed to a fairly high degree; promesonotum in lateral view usually weakly to strongly raised, but sometimes dorsal outline of mesosoma almost straight; promesonotal suture completely absent dorsally in minor, but sometimes well developed in major; metanotal groove conspicuous, usually impressed deeply on dorsum; propodeum unarmed or armed with a pair of propodeal spines or angles; propodeal lobe slightly to strongly roundly expanded, or present as a carina or lamella attaining the base of propodeal spine or angle; petiole pedunculate and with node, often with subpetiolar process; gastral shoulder usually conspicuous.

The minor worker of Oligomyrmex is similar to that of Pheidologeton , and the workers of Parvimyrma and Solenopsis . However, the minor of Pheidologeton does not have the median part of clypeus laterally margined by carinae. The workers of Parvimyrma and Solenopsis have a median clypeal seta. Oligomyrmex and Pheidologeton are hardly distinguishable from each other by the morphology of the major worker but the body is much larger in the latter genus.

Vietnamese species. Three species of Oligomyrmex have been described from Vietnam: bouvardi Santschi (type locality: Mi Tho, Ho Chi Minh City); capreolus Wheeler (type locality: Van Phu); cribriceps (Wheeler) (type locality: Dong Mo). Twelve additional species have been recognized by us from Vietnam: sp. eg-1 (Chua Yen Tu, Cuc Phuong, Tay Yen Tu, Van Ban); sp. eg-2 (Sa Pa); sp. eg-3 [= sp. 23 of SKY: Yamane et al., 2003] (Cuc Phuong, Nam Cat Tien, Van Ban); sp. eg-4 [= sp. 22 of SKY: Yamane et al., 2003] (Cuc Phuong, Nam Cat Tien, Phu Quoc, Pu Mat, Sa Pa, Van Ban); sp. eg-5 [= sp. A: Eguchi et al. 2005] (Ba Be, Sa Pa, Tay Yen Tu); sp. eg-6 (Ba Be, Binh Chau-Phuoc Buu, Nam Cat Tien); sp. eg-7 [= sp. 24 of SKY: Eguchi et al., 2005] (Cuc Phuong, Tam Dao, Tay Yen Tu); sp. eg-8 (Binh Chau-Phuoc Buu, Phu Quoc); sp. eg-9 (Nam Cat Tien); sp. eg-10 (Van Ban); sp. eg-11 (Phu Quoc); sp. eg-12 (Nam Cat Tien, Phu Quoc).

Bionomics. Species richness and colony density of Oligomyrmex seems to be highest in humid forests. Nests are found in rotten twigs, wood fragments and logs, inside the outer walls of termite mounds and in the soil. Most species probably forage both on and under the ground (Eguchi & Bui 2009).