Tapinoma inflatiscapus 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 inflatiscapus Cover & Rabeling sp. nov.

Diagnosis.

A unique, workerless, host-queen-intolerant inquiline social parasite of Tapinoma sessile with relatively few morphological adaptations to its parasitic lifestyle. Inquiline females and males are equal in size, smaller than the host females and males, and approximately the size of host workers (Fig. 2 , Table 2). Both females and males are winged and seem capable of flying. Females have a reduced 5, 4 palp formula whereas males have the same palp formula (6, 4) as host males. Both sexes of T. inflatiscapus are easily distinguished from those of all other North American congeners by the presence of short, erect hairs on the dorsal surface of the head, the mesosomal dorsum, and the first gastric tergite. In addition, the antennal scapes are covered by short, dense, suberect pubescence and may have one or two erect hairs near the distal end. Lastly, in females, the scape reaches its maximum diameter between the mid-point and the antennal insertion, not posterior to the mid-point as in many other Tapinoma species.

Description.

Holotype queen: HL 0.76, HW 0.76, SL 0.74, ML 1.15, CI 100, SI 96. Head distinctly heart shaped, approximately as wide as long. Clypeus broad, anterior margin flat or slightly convex, median impression absent; posterior margin rounded, projecting between antennal insertions. Mandibles well developed, overlapping when closed; first three apical teeth well developed, continually decreasing in size from apex to base. Eleven teeth and denticles present, most denticles on cutting edge of mandible ill defined. Antennae with 12 segments, scapes relatively long, easily surpassing the dorsal margin of head; scape somewhat dorsoventrally flattened, basal third slightly curved. Scape widest between the insertion and the mid-point. Palp count 5, 4. Mesosoma robust with typical modifications related to wing bearing. In side view, propodeum with dorsal surface approximately one third as long as posterior surface. Metapleural gland orifice large and rounded in oblique view; orifice guarded by long setae pointing inwards. Petiole reduced, overhung by first gastric tergite. In dorsal view, four gastric tergites visible. Integument thin. Body surfaces with micro-sculpture resembling a honeycomb. Entire body with dense, short, suberect to erect pubescence, including head and antennal scapes. Short erect hairs present on dorsal surface of head and mesosoma. Color pale to medium brown, legs and antennae paler, yellowish brown. Paratype queens (n = 8): HL 0.65 – 0.76, HW 0.65 – 0.76, SL 0.68 – 0.76, ML 1.03 – 1.15, CI 92 – 100, SI 96 – 113.

Paratype male: HL 0.62, HW 0.62, SL 0.62, ML 1.12, CI 100, SI 100. Males similar in size to the females, head as wide as long (CI). Eyes large, maximum diameter ~ ⅓ of head width. Ommatidia clearly separated from each other; each ommatidium with a distinct convex surface. Ocelli slightly elevated above the surface of the head, but forming a raised, triangular turret in side view. Anterior margin of clypeus flat, median impression absent; posterior margin rounded, projecting between antennal insertions. Mandibles well developed with a single large apical tooth and ~ 18 denticles on cutting edge of mandible. Antennae with 13 segments, scapes surpassing the posterior border of the head by a bit less than ½ their length. Palp formula 6, 4. Mesosoma robust with typical modifications related to wing bearing. In side view, propodeum with dorsal surface ~ ⅓ as long as the posterior surface. Metapleural gland orifice pointing backwards, circular in posterior view. Petiole visible in dorsal view. In dorsal view, six gastric tergites visible. Front and hind wings well developed. Dorsal body surfaces with short, suberect to erect pubescence, including head and antennal scapes. Short, erect hairs present on dorsal surfaces of head and mesosoma, long erect hairs irregularly dispersed over the body. Color uniformly pale to yellowish brown. Paratype males (n = 6): HL 0.53 – 0.71, HW 0.53 – 0.71, SL 0.59 – 0.65, ML 0.91 – 1.12, CI 90 – 100, SI 92 – 117.

Etymology.

In T. inflatiscapus females, the antennal scape reaches its maximum diameter between the mid-point and the antennal insertion instead of posterior to the mid-point as in other Tapinoma . This unique, diagnostic morphological character is emphasized in the species epithet, which is a compound Latin noun in the nominative case used in apposition (inflati is the participle in the genitive case of inflatus + scapus, the noun in the nominative singular case).

Type locality.

U. S. A., Utah, Sevier County, Cove Mountain, 13.4 miles south of Glenwood Fish Hatchery on FSR 068. GPS: 38.649 ° N, 111.950 ° W; elevation 9350 ’ (2850 m). Enormous, grazed sagebrush ( Artemisia tridentata ) meadow around Big Lake. Superficial nest under rock and in adjacent grass clump in open on gentle south facing slope; fine silty sand. Small colony (~ 400 ants). No host queens. Brood, mostly eggs and larvae, plus a few parasite queen pupae. Collected by SPC (SPC 7816), 20 July 2008.

Type material.

Holotype queen ( SPC 7816 , MCZENT 00806458 ) . Paratype male ( SPC 7816 , MCZENT 00806458 ) , and the following paratypes: 63 queens, 4 males [20 - VII- 2008, SPC 7816 ] . Holotype and paratypes deposited in the MCZC. Additional paratypes deposited at CASC, CRC, LACM, and UCDC.

Additional material.

(i) U. S. A., Colorado, El Paso County, Black Forest, 4.5 miles south of Hodgen Rd. on Meridian Rd. GPS (from Google Maps): 39.01 ° N, 104.61 ° W; elevation 7350 ’ (2240 m). Open Ponderosa Pine ( Pinus ponderosa ) forest, 20 – 40 ’ (6 – 12 m) tall with grassy understory and bearberry ( Arctostaphylos sp. ) in spots; medium sandy soil. Both colonies were under pine branches half buried in soil and litter. Collected by SPC (SPC 4117, 4120), 16 July 1994.

(ii) U. S. A., Colorado, Montrose County, 2.1 miles southeast of junction with Rt. 50 on P 77 Road. GPS: 38.420 ° N, 107.628 ° W; elevation 8200 ’ (2500 m). Rich, mixed shrubby northeast facing slope with some sagebrush ( Artemisia tridentata ), 3 – 4 ’ (0.9 – 1.2 m) tall; fine sandy soil; sparse ground cover. Small colony consisting of two parasite females, ~ 30 host workers and no brood. Collected by SPC (SPC 7388), 16 July 2006.

(iii) One other collection from the type locality: SPC (SPC 8076), collected 18 July 2009, same collection data as type series, under rock in open, ~ 1000 ants, no host brood, a few inquiline pupae only.

Discussion and biology.

Tapinoma inflatiscapus is a host-queen-intolerant inquiline that parasitizes T. sessile colonies in mid to high elevation habitats in the mountains of Utah and Colorado. So far it has been found in sagebrush meadows ( Artemisia tridentata ), mixed shrub and sagebrush, and Ponderosa Pine ( Pinus ponderosa ) woodlands. Morphologically, T. inflatiscapus is most similar to T. shattucki from Massachusetts from which it can be easily distinguished by the unique shape of the antennal scape, the presence of short, erect hairs on the dorsal body surfaces, and its comparatively robust habitus. In addition, the male palp formula is 6, 4. All other Tapinoma inquiline males have reduced palp formulae (Table 2).

Tapinoma inflatiscapus has been collected from two localities in Colorado and a single locality in Utah. On all occasions, T. inflatiscapus was found in mixed colonies with its host, T. sessile . In every case these colonies lacked a host queen and any host brood, suggesting that T. inflatiscapus either kills the host queen (s) or can only colonize queenless host colonies. Parasite workers have not been observed, so T. inflatiscapus appears to be a workerless inquiline. We could not observe whether T. inflatiscapus is mono- or polygynous, although collection SPC 7388 contained two dealate queens.

The morphology of T. inflatiscapus queens and males reflects some characteristics of the inquiline syndrome (Fig. 2 , Table 2), but the degree of specialization is not nearly as pronounced as in T. incognitum and T. pulchellum . Tapinoma inflatiscapus alates are smaller than those of the host and approximately the size of host workers. The number of antennal segments is not reduced, and the palp count is reduced in the queens (palp formula 5, 3), but not in males. The mandibles are normal in size and dentation. Both queens and males are winged and mesosomal development is robust, thus the wings appear to be functional and dispersal by flight probable. Mating may take place outside of the nest. If so, there may be less inbreeding and much better dispersal than in inquilines where mating takes place inside the host nest and where flight is problematic or impossible.

Figures

Figure 2. Morphological comparison of the Tapinoma inflatiscapus holotype queen A, E and a paratype male B, F in lateral A, B and full-face E, F view. For the dorsal views of T. inflatiscapus C, D dealate queen C and male D paratypes were photographed. The type series was collected at Cove Mountain in Utah and belongs to a single nest series with the collection code SPC 7816. Scale bar: 0.5 mm (A – F).