Pseudomyrmex nigrocinctus

An obligate acacia mutualist that can inhabit a few different species of Vachellia

Identification
Ward (1993) - Workers and queens of P. nigrocinctus are easily distinguished from all other acacia ants, except Pseudomyrmex particeps (see below), by their small size (HW < 0.86 in both castes), elongate head in the worker (worker CI < 0.85), and narrow petiole and postpetiole (worker PWI3 0.50, worker PPWI 1.30, queen PWI2 0.57-0.63). The orange color and short eyes are also characteristic.

Distribution
Guatemala to Costa Rica, with most records coming from the southern end of its range.

Distribution based on Regional Taxon Lists
Neotropical Region: Costa Rica, El Salvador, French Guiana, Guatemala, Guyana, Nicaragua, Suriname.

Biology
Ward (1993) - Colonies are monogynous, and have been collected from Acacia collinsii, A. cornigera and A. hindsii. Records from Acacia gentlei and A. globulifera (Beulig & Janzen 1969: 59) need to be confirmed because of possible confusion with Pseudomyrmex peperi. Janzen's (1967b) observations on "P. nigrocincta" in Mexico refer to P. peperi. On the other hand descriptions of the biology and behavior of P. nigrocinctus in Costa Rica (Janzen 1973, 1974, 1975, 1983; Beulig & Janzen 1969) are reliably attributed to P. nigrocinctus.

Amador-Vargas (2019) found that Pseudomyrmex spinicola made larger clearings around the trees they occupied than Pseudomyrmex flavicornis and Pseudomyrmex nigrocinctus. Pseudomyrmex spinicola workers also pruned thicker vegetative tissue, and their workers had broader heads - presumed to allow more robust pruning due to larger muscles in the head providing greater mandibular force. More generally, this study and its findings are unusual in examining plant pruning differences provided by ants involved in acacia mutalisms. Most studies of ant-provided benefits to plants in these ant-plant mutualisms focus on herbivory.

Nomenclature

 *  nigrocinctus. Pseudomyrma nigrocincta Emery, 1890b: 64, pl. 6, fig. 3 (w.q.) COSTA RICA. [Also described as new by Emery, 1894k: 52.] Combination in Pseudomyrmex: Kempf, 1972a: 221. Senior synonym of alfari, bicincta, peltata: Ward, 1993: 144.
 * alfari. Pseudomyrma alfari Forel, 1906d: 228 (w.) COSTA RICA. Combination in Pseudomyrmex: Kempf, 1972a: 215. Junior synonym of nigrocinctus: Ward, 1993: 145.
 * bicincta. Pseudomyrma nigrocincta var. bicincta Santschi, 1922b: 347 (w.) COSTA RICA. Combination in Pseudomyrmex: Kempf, 1972a: 221. Junior synonym of nigrocinctus: Ward, 1993: 145.
 * peltata. Pseudomyrma peltata Menozzi, 1927c: 273, fig. 2 (w.m.) COSTA RICA. Combination in Pseudomyrmex: Kempf, 1972a: 222. Junior synonym of nigrocinctus: Ward, 1993: 145.

Description
Ward (1993) - Worker measurements (n =21). —HL 0.89- 1.08, HW 0.74-0.85, MFC 0.035-0.051, CI 0.75-0.84, REL 0.40-0.45, REL2 0.51-0.56, OOI 1.39-2.76, VI 0.62-0.78, FCI 0.044-0.065, SI 0.44-0.48, SI2 0.81-0.89, NI 0.58-0.64, PLI 0.59-0.68, PWI 0.49-0.61, PPWI 1.10-1.30.

Worker diagnosis. —Small species with elongate head and short eyes (REL O.45, REL2 0.56, EL/LHT 0.61). Palp formula 5,3. Median clypeal lobe rather narrow, its surface and anterior margin convex. Frontal carinae separated by about basal scape width (FCI 0.055). Metanotal groove well marked; basal and declivitous faces of Propodeum subequal. Petiole short (PLI > 0.57), its anterior peduncle broad in dorsal view (PWI3 0.50-0.61) and not well differentiated from the node. Petiole lacking expanded posterolateral corners. Postpetiole less broad than in most other species in the P. ferrugineus group (see PPWI values). Head densely punctulate and subopaque, becoming sublucid posteriorly where the punctulae are separated by shiny interspaces. Mesosoma punctulate to (laterally) coriarious-imbricate, sublucid, becoming subopaque on the propodeum. Standing pilosity moderately common; pubescence dense and closely appressed. Orange-brown, often with anterolateral fuscous patches on abdominal tergite IV (these form a distinct transverse black band in queens).

Type Material
Ward (1993):

Syntype workers, queens, males, Alajuela, Costa Rica (A. Alfaro) [Examined]. One syntype worker from MCSN here designated LECTOTYPE.

Pseudomyrma alfari Forel 1906:228. Two syntype workers, Tivives, embouchure de Jesus-Maria, Costa Rica (A. Alfaro) (MHNG) [Examined]. One syntype here designated LECTOTYPE.

Pseudomyrma nigrocinta var. bicincta Santschi 1922: 347. Syntype workers, Costa Rica (MHNG, NHMB) [Examined]. One syntype from NHMB here designated LECTOTYPE.

Pseudomyrma peltata Menozzi 1927a:273. Three syntype workers, San Jose, Costa Rica (H. Schmidt) (NHMB) [Examined].