Solenopsis Westwood

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 : 28-29

Solenopsis Westwood , 1840

Taxonomy. The genus Solenopsis is assigned to the Solenopsis genus group of the tribe Solenopsidini by Bolton (1987). Workers of Vietnamese species have the following features.

Worker monomorphic or polymorphic (worker of the introduced S. geminata polymorphic); head in full-face view subrectangular; frontal carina and antennal scrobe absent; median portion of clypeus expanded anteriad, usually defined laterally by clypeal carinae which form clypeal teeth; median clypeal seta present (sometimes absent in major of S. geminata); posteromedian portion of clypeus moderately or narrowly inserted between frontal lobes; mandible usually narrow and subtriangular, with apical tooth followed by 2 distinct teeth and then one or more small or inconspicuous denticles on masticatory margin (major of S. geminata with massive mandible lacking teeth on masticatory margin); antenna 9- or 10-segmented, with 2-segmented club; apical antennal segment much longer than preapical segment; eye moderately developed, reduced or absent; promesonotum in lateral view usually weakly or strongly domed; promesonotal suture absent or weak dorsally; metanotal groove conspicuous dorsally, usually a deeply impressed groove on dorsum; propodeum unarmed; propodeal lobe roundly expanded, or reduced to a carina; petiole pedunculate with distinct node; gastral shoulder inconspicuous to well developed; sting well developed.

Solenopsis sp. eg-3 (Vietnam), sp. eg-4 (W. Malaysia) and sp. eg-5 (Vietnam and Thailand) show characteristics seen in the minor worker of the Carebara lignata species complex sensu Fernández (2004): antenna 9-segmented, with 2-segmented club; eye completely absent; median portion of clypeus in profile roundly and strongly swollen; clypeal carina evanescent or absent; clypeal teeth completely absent; promesonotum in profile rather flat dorsally. However, Solenopsis sp. eg-3, sp. eg-4 and sp. eg-5 have a median clypeal seta which is distinguishable from the background hairs on the anterior clypeal margin.

The worker of Solenopsis is similar to the minor worker of Oligomyrmex , and the worker of Parvimyrma and Monomorium (for distinguishing characters see under the relevant genera).

Vietnamese species. Four species are known from Vietnam: geminata (Fabricius) (Ha Noi, Nam Cat Tien, Nui Chua, Phu Quoc), sp. eg-2 [= sp. 12 of SKY: Eguchi et al., 2005] (Binh Chau - Phuoc Buu, Cuc Phuong, Nam Cat Tien, Pu Mat), sp. eg-3 [= sp. 3 of SKY: Eguchi et al., 2005] (Cuc Phuong, Tay Yen Tu), sp. eg-5 (Binh Chau - Phuoc Buu, Nam Cat Tien, Phu Quoc).

Bionomics. Solenopsis sp. eg-2 and sp. eg-3 are found in the soil or under stones. Their reduced or absent eyes and pale body color suggest that they are subterranean nesters and foragers or even lestobiotic in the nest of other ants or termites. Solenopsis geminata is an introduced species from the Neotropics. Commerce has accidentally introduced the species to urban and rural areas and other open habitats (including agricultural fields) in North America, South America, Asia, Australia, Oceania and Africa. The species is omnivorous and nests in the soil often beneath objects such as stones, concrete blocks, etc. This is one of the notorious pest ants in Asia (named the tropical fire ant) because well-developed colonies include a huge number of aggressive workers armed with a powerful sting. Detailed bionomics of S. geminata and other fire ants are provided by Taber (2000).