Tapinoma pulchellum Cover & Rabeling, 2024

Cover, Stefan P. & Rabeling, Christian, 2024, Four new inquiline social parasite species in the dolichoderine ant genus Tapinoma (Hymenoptera, Formicidae), ZooKeys 1202, pp. 111-134 : 111-134

Tapinoma pulchellum Cover & Rabeling sp. nov.

Diagnosis.

An apparently workerless, inquiline social parasite of Tapinoma sessile exhibiting morphological traits of the inquiline syndrome. Queens and males are tiny, much smaller than the host workers, and are very similar to each other in size and habitus (Fig. 3 , Table 2). Females are apparently alate, but males are brachypterous. Both sexes have a reduced (5, 4) palp formula and twelve antennal segments. Females have a flat anterior clypeal border, edentate mandibles, and a petiole with a small, dorsally rounded node in side view. Females most similar to but are readily distinguished from T. incognitum by differing palp count, edentate mandibles, anterior clypeal border, petiole shape, and propodeal profile (subangulate with short dorsal face and long, weakly concave posterior face versus rounded convexity in T. incognitum ).

Description.

Holotype queen: HL 0.44, HW 0.50, SL 0.44, ML 0.76, CI 113, SI 88. Parasite queen notably smaller than host workers. Head in full-face view nearly square, dorsal margin straight with corners evenly rounded. Anterior margin of clypeus flat, median impression absent, posterior margin rounded, not projecting forward between antennal insertions. Mandibles reduced, apical tooth well developed, barely touching each other when mandibles are closed; other mandibular teeth absent. Antennae with 12 segments, scapes relatively short, surpassing the dorsal margin of head by less than their own width. Palp count 5, 4. Mesosoma fully developed with typical modifications related to wing bearing. Propodeum in side view rounded, with short dorsal face and longer, slightly concave posterior face. Propodeal spiracles slightly elevated and conspicuous. Metapleural gland orifice reduced. In side view petiole with low, blunt node; viewed from the rear subrectangular in shape with dorsal margin flat to slightly convex. In dorsal view, four gastric tergites visible. Integument thin. Body surface covered with short, appressed pubescence; posterior margin of all gastric sternites and fourth gastric tergite with long erect setae. Color dark brown to yellowish brown, appendages pale yellow.

Paratype male: HL 0.44, HW 0.50, SL 0.44, ML 0.76, CI 100, SI 113. Specimen damaged, but largely intact. Head glued on to point next to body. Male small, approximately the same size as the queen, brachypterous, closely similar to the conspecific queen in habitus. Head square. Eyes small, maximum diameter ~ ¼ of head length. Individual ommatidia partly fused, lacking the distinct convex surface of each ommatidium; compound eyes appear as if coated with a translucent resin. Ocelli slightly elevated above the surface the head. Anterior margin of clypeus with a broad, median, shallow impression. Mandibles reduced in size, with a single large apical tooth but lacking other teeth or denticles. Antennae with 12 segments, scapes short. Palp count 5, 4. Mesosoma well-developed with typical modifications related to wing bearing. In sideview, propodeum rounded, divided into dorsal and posterior surfaces of approximately equal length. Metapleural gland orifice absent / reduced. Petiole small, overhung by first gastric tergite, not entirely visible in dorsal view. In dorsal view, five gastric tergites visible. Wings vestigial, distorted, lacking venation. Body surface densely covered with short, appressed pubescence, except for the antennal scapes and flagellum, which are covered by a dense, very short, suberect pubescence. Color medium brown, appendages yellowish brown.

Etymology.

Tapinoma pulchellum is a beautiful ant (Fig. 3 ) and also beautifully embodies the hallmark morphological traits of the inquiline syndrome. The specific epithet pulchellum is the singular nominative neuter of the Latin adjective pulchellus, which is the diminutive of pulcher, meaning pretty or beautiful.

Type locality.

U. S. A., North Carolina, Orange County, Eno River State Park, 8 miles northwest of downtown Durham; open field adjacent to the Eno Trace trailhead. GPS: 36.073 ° N, 79.008 ° W; elevation 460 ’ (140 m). Large, maintained open field surrounded by mature secondary oak-hickory forest. The field was dominated by scattered Juniperus virginiana to 30 ’ tall plus a few young Pinus virginiana . Dense, grassy-herbaceous vegetation plus young Sweetgum ( Liquidambar styraciflua ) up to 8 ’ tall. Sandy clay soil. The holotype queen was found in pitfall sample 13 F 4, 2. The paratype male was found in pitfall sample 13 F 5, 1. There is also a worker of the potential host from pitfall sample 13 F 5, 3. Collected by Amy Arnett in June 1997.

Type material.

Holotype queen ( MCZENT 00806459 ) . Paratype male ( MCZENT 00806460 ; same collecting locality as holotype) . Holotype and paratype deposited in the MCZC.

Discussion and biology.

Tapinoma pulchellum is known from only two specimens: a dealate female and a damaged male, which both exhibit typical characters of the morphological inquiline syndrome (Fig. 3 , Table 2). Tapinoma pulchellum is closely similar to T. incognitum , from which it can be readily distinguished by the palp formula of both queens and males, the edentate mandibles, the flat anterior clypeal border, the petiole shape, and the unique propodeal profile. This striking similarity makes it highly probable that T. pulchellum is a workerless inquiline, similar in its life-history to T. incognitum .

Both specimens were recovered from adjacent pitfall traps at the type locality in Eno River State Park in North Carolina. Accordingly, T. pulchellum has not been observed in mixed colonies with its host. However, T. sessile is the only Tapinoma species at the type locality, so T. sessile is almost certainly the host of T. pulchellum . Visits to the type locality in 2011 and 2012 failed to turn up additional specimens of T. pulchellum but allowed observations of the putative host at that site. The field contained a dense population of Tapinoma sessile , and nests were located at the base of grass clumps or in the dense grassy thatch that covered the ground under the living vegetation. The T. sessile population was unusual. Colonies were large, with more than 4,000 –5,000 ants, and uniformly monogynous. Both workers and queens were larger than the average size for T. sessile . Sexuals were not present, indicating that the mating flights had taken place already in early July.

Figures

Figure 3. Morphological comparison of the Tapinoma pulchellum holotype queen A, C, E and a paratype male B, D, F in lateral A, B dorsal C, D and full-face E, F view. The type series was collected in two adjacent pitfall traps at Eno River State Park in North Carolina. Scale bars 0.5 mm (A, C – E); 0.25 mm (B, F).