Tapinoma atriceps

Tapinoma atriceps is an arboreal ant which can be found from the understory layer to the canopy and rarely on the ground. Escárraga et al. (2021) found nests of this ant in hollow cavities of the vegetation or dry hanging branches, in plants of the families Poaceae (Bambusoideae), Melastomataceae, Piperaceae, and Urticaceae. Workers are commonly found foraging on the leaves of plants near the nest. The colony can be moderately large, with more than 312 workers, and in a couple of nests we found four dealate queens, evidencing polygyny as in other species of Tapinoma (e.g., Bustos and Cherix 1998; Buczkowski and Bennet 2008) (Escárraga et al., 2021).

Identification
Escárraga et al., 2021 - Tapinoma atriceps and Tapinoma breviscapum can be differentiated from other Neotropical Tapinoma species by their particular bicolored pattern. Other Tapinoma can be mostly pale yellow or uniform brown, with yellow antennal scapes and coxae, but never with a spot on the mesopleuron, nor the bicolored pattern of T. atriceps and T. breviscapum. Only two other ant species that occur in South America, Tapinoma melanocephalum and Linepithema leucomelas, have similar colors and size that could lead to confusion. In the case of T. melanocephalum, a common invasive species, the head and mesosoma is dark brown and the gaster is pale yellow (Guerrero 2018). Linepithema leucomelas can be differentiated by the characters that define the genus: presence of a well-developed petiolar scale and mandibular dentition which presents teeth alternating with denticles (Wild 2007b).

The most readily recognizable morphological diagnostic traits that permit separation of T. atriceps and T. breviscapum workers and queens are the relative length of the scape (i.e., SI), the shape of the propodeum, and differences in the degree of cephalic pubescence. In T. atriceps the worker scape is almost as long as the HL or greater (SI >93; Fig. 1A), in contrast with T. breviscapum, where it is relatively short (SI < 85; Fig. 1B), sometimes reaching or barely surpassing the posterior head margin by a distance shorter than the pedicel length. SL shows significant differences between the workers of each species (T = 7.51, p < 0.0001). Although there is a certain degree of overlap in the absolute measure (0.50–0.63 in T. atriceps and 0.44–0.56 in T. breviscapum) the relationship from SL to HL for each species showed non-overlapping ranges (Fig. 7). Other morphometric traits, such as HL, HW, and WL were also evaluated; however, each of their paired distributions overlapped, showing no statistical differences. The SL partially overlaps in queens of both species (0.58–0.62 in T. atriceps and 0.49–0.59 in T. breviscapum); however, differences between species were found (T = 2.29, p = 0.0257). These differences are notable in the non-overlapping ranges of the relative length of the scape (82–83 and 70–76, respectively). Statistical differences were also found in the HW of both species (T = 2.26, p = 0.0268); even without measuring, these differences are evident when they are compared under a stereoscope (Fig. 2B vs 2E), as T. breviscapum queens have a more elongate head as reflected in CI values that do not overlap those of T. atriceps queens.

The worker propodeum in both species differs markedly in shape and in the proportions between the dorsal and the posterior faces (Fig. 4B vs 6B). The dorsal propodeal margin when seen laterally in T. atriceps forms a distinct blunt angle with the declivity, contrasting with the rounded convexity formed in T. breviscapum. Additionally, the dorsal margin in T. atriceps is about 1/4 the length of the declivitous margin, while in T. breviscapum it is longer, about 1/2 that of the declivity (Figs 1B, D, 4B, 6B). The dorsal surface of the head in T. atriceps workers (Fig. 4A) is covered by appressed pubescence that is relatively longer and sparser than in T. breviscapum, where it is abundant and relatively shorter (Fig. 6A). The males of both species are relatively similar in morphology (Fig. 3), but the male of T. breviscapum can be differentiated from T. atriceps males because the former is on average slightly larger (0.63 ± 0.02 mm) and the scutellum is glabrous, while males of T. breviscapum are slightly smaller (0.62 ± 0.02 mm) and have decumbent hairs on the scutellum.

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina, Brazil, Paraguay.

Nomenclature

 *  atriceps. Tapinoma (Micromyrma) atriceps Emery, 1888c: 363 (w.q.m.) BRAZIL. Current subspecies: nominal plus breviscapum.

References based on Global Ant Biodiversity Informatics

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