Pseudolasius

Pseudolasius are perhaps best known for possessing a polymorphic worker caste, with most species having completely dimorphic majors (soldiers) and minors (LaPolla, 2004).

Identification
Mandible with 4 to 7 teeth; maxillary palps 2-to 5-segmented; labial palps 2- to 4-segmented; mandalus small and inconspicuous. Setae on dorsum of head randomly placed; with erect setae on scapes, legs and dorsum of mesosoma, including propodeum; body often covered in dense pubescence. Eyes often poorly developed, typically placed below midlength. Workers strongly polymorphic, with a major caste present; posterior margin of head in majors typically emarginate. Propodeum with a low- to high-domed dorsal face; overall mesosoma shape compact. (LaPolla et al. 2010)

Distribution
This genus is restricted to southern Asia, from India to China, stretching southwards to northern Australia. It appears to be restricted to tropical localities.

Biology
All species are apparently hypogeic. They convergently resemble Acropyga and especially subterraneous Lasius in colour and morphological characters, but are, however, polymorphic. The sociobiology of Pseudolasius is virtually unknown. In Malaysian lowland rainforests, three Pseudolasius species are involved in mutualistic relationships with a total of eight scale insect species in six genera feeding at the roots of plants (Malsch et al. 2001). The ants feed on honeydew excreted by the mealybug partners, and these (both adults and immature instars) are kept in chambers with and without ant brood. All three species carry their mealybugs (1) when disturbed, (2) during nest movements, and (3) to feeding sites. Ants build flat soil pavilions around their mealybug feeding sites and tend their trophobiosis partners. It is assumed that Pseudolasius queens do not co-disperse with their associated mealybugs during mating flight.

These Pseudolasius spp. are highly polydomous, which results in an extremely decentralized colony structure. Numerous small nest chambers were either widely distributed in the top soil (Pseudolasius sp.2 and sp.3) or predominantly in small decaying twigs (Pseudolasius sp.1). Pseudolasius sp. 1 and Pseudolasius sp. 2 are polygynous.

Castes


Major worker of Pseudolasius from Queensland.



Minor worker of Pseudolasius from Queensland.

Worker Morphology
Palp formula 5,3 in an undescribed species from Vietnam.

Nomenclature

 *  PSEUDOLASIUS [Formicinae: Plagiolepidini]
 * Pseudolasius Emery, 1887a: 244. Type-species: Formica familiaris, by subsequent designation of Bingham, 1903: 337.
 * Pseudolasius senior synonym of Nesolasius: Bolton, 1994: 50.
 * NESOLASIUS [junior synonym of Pseudolasius]
 * Nesolasius Wheeler, W.M. 1935b: 50 [as subgenus of Pseudolasius]. Type-species: Pseudolasius (Nesolasius) typhlops, by original designation.
 * Nesolasius junior synonym of Pseudolasius: Bolton, 1994: 50.

The polymorphic nature of this genus is well known, but overall this is a fairly heterogeneous group that is in need of taxonomic revision. There are clearly some lineages that have taken a hypogaeic evolutionary route and look quite different from the larger, presumably epigaeic species. (LaPolla et al. 2010)