Rhopalothrix

The genus Rhopalothrix is a rare inhabitant of wet forest leaf litter and soil.

Identification
Rhopalothrix belong to the tribe Basicerotini. This tribe is taxonomically problematic as there is no single accepted classification of its species into genera. Baroni Urbani and de Andrade (2007) synonymized the tribe Basicerotini with the Dacetini and proposed that all basicerotine genera be placed in the genus Basiceros. Longino and Boudinot (2013) revised a distinctive Rhopalothrix isthmica clade and recognized 13 species. The Rhopalothrix isthmica clade was defined by two synapomorphies: (1) absence of squamiform setae on the face, and (2) development of shallow arcuate grooves and ridges on the face. All the species share a similar habitus, being small, nearly eyeless, pale brown, with uniformly matte surface, and a characteristically broad, lumpy face. The R. isthmica clade is strictly Neotropical, with the greatest abundance and diversity in Central America. They also noted there were an additional 3 species, outside of this clade, in the genus: Rhopalothrix ciliata from Colombia, Rhopalothrix diadema from New Guinea, and Rhopalothrix orbis from Australia. These latter three species all have squamiform setae on the face and their heads are more elongate and less flattened, more like other basicerotines.

Key to Rhopalothrix isthmica clade Rhopalothrix workers

Biology
Longino (2013) - Knowledge of the biology of the Rhopalothrix isthmica clade of Rhopalothrix is conjectural; a nest has never been recovered and a live specimen never seen. What we know is based on locations and frequencies of capture using various mass-sampling methods. Specimens are known from wet to moderately seasonal forest, from sea level to 2140 m elevation. At higher elevation, they are found in diverse mesophyll forest and in forests with various combinations of Liquidambar and montane oak. In Costa Rica, they are restricted to the wet forests of the Atlantic slope, to 1500 m on the Barva Transect in the Cordillera Volcánica Central and to 800 m in the Cordillera de Tilarán. The genus is unknown from the Monteverde cloud forest at 1500 m, the lowland wet forests of the Osa Peninsula, and the lowland tropical dry forests of Guanacaste, in spite of intensive collecting efforts in these areas. Further north in Central America they can occur at higher elevations.

In quantitative sampling at La Selva Biological Station, in the Atlantic lowlands of Costa Rica, occurrences were relatively more frequent in soil/litter cores than in samples of sifted litter from the soil surface. This suggests that nests are subterranean, with workers only occasionally venturing up into the litter layer. Dealate queens are known for a few species, occurring occasionally in Winkler or Berlese samples. Alate queens of one La Selva species were found in canopy fogging samples, one each in two separate fogging events. Oddly, alate queens have not been found in the many Malaise samples from La Selva. Males remain unknown.

Nomenclature

 *  RHOPALOTHRIX [Myrmicinae: Basicerotini]
 * Rhopalothrix Mayr, 1870a: 415. Type-species: Rhopalothrix ciliata, by subsequent designation of Wheeler, W.M. 1911f: 172.
 * Rhopalothrix senior synonym of Acanthidris, Heptastruma: Brown & Kempf, 1960: 230.
 * Rhopalothrix junior synonym of Basiceros: Baroni Urbani & De Andrade, 2007: 88.
 * ACANTHIDRIS [junior synonym of Rhopalothrix]
 * Acanthidris Weber, 1941a: 188. Type-species: Acanthidris isthmicus, by original designation.
 * Acanthidris junior synonym of Rhopalothrix: Brown & Kempf, 1960: 230.
 * HEPTASTRUMA [junior synonym of Rhopalothrix]
 * Heptastruma Weber, 1934a: 54. Type-species: Heptastruma wheeleri (junior secondary homonym in Rhopalothrix, replaced by Rhopalothrix weberi), by original designation.
 * Heptastruma junior synonym of Rhopalothrix: Brown & Kempf, 1960: 230.