Solenopsis interrupta

The sting poison constituents have not been elucidated, but the sting of this insect is reported by Dr. Blum (personal communication) to be excruciatingly painful, much more so than any of the other species encountered by Dr. Blum in South America or in his experience with the two imported species in North America. (Buren 1972)

Identification
Pitts et. al. (2018) - A member of the Solenopsis saevissima species-group. The gynes of S. interrupta superficially resemble Solenopsis pythia and Solenopsis metallica in both coloration and sculpture of the head. Both S. pythia and S. metallica have other derived characters, however, and thus are easily distinguished from S. interrupta.

The gynes of S. interrupta and Solenopsis richteri are similar in coloration and both sometimes have a distinct orange tergal maculation with a demarcated posterior margin. In many cases, the gynes of these two species are difficult to differentiate, but they may be separated by the sculpture of the postpetiole. The gynes of S. interrupta are typically slightly lighter in coloration. In addition, the OOI of S. interrupta gynes is much greater than that of the S. richteri gynes. The workers of these species, however, are relatively easy to separate from the other members of this species-group.

The male is dark in coloration as are males of most species in this group. The pubescence of the males is longer and denser than that of Solenopsis saevissima males. Often, the head of the male is shagreened as it is in S. invicta males.

The larvae of S. interrupta are similar to those of S. invicta and S. saevissima. They differ, however, in the size and shape of the body setae. Also, the setae ventral to the antennal level are typically longer in S. interrupta than in Solenopsis invicta or S. saevissima.

Distribution
Pitts et. al. (2018) - There is some question concerning the exact type locality for S. interrupta. Santschi (1916) merely lists the type locality as “Argentine: Bajo Hondo, Monte Hermeso”. But there are at least two locations in Argentina called Bajo Hondo. Buren (1972) placed the type locality in Buenos Aires Province and he considered the nominal S. interrupta range to span Uruguay and Buenos Aires, Entre Rios, Santa Fe Provinces, Argentina. He excluded the northwestern Argentinian and Bolivian forms from the species. Trager (1991) placed the type locality in La Rioja Province, since he considered Buenos Aires to be well outside the range of his concept of the species (Cordoba and Mendoza Provinces in Argentina northward into Bolivia) and he considered Santschi’s description to fit well within his image of S. interrupta. Here, we follow Trager’s (1991) interpretation.

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

Nomenclature

 *  interrupta. Solenopsis saevissima var. interrupta Santschi, 1916e: 379 (w.) ARGENTINA. Subspecies of saevissima: Creighton, 1930b: 89. Raised to species: Wilson, 1952b: 51. See also: Buren, 1972: 22; Trager, 1991: 178.

Worker
Buren (1972) - Head length .81 to 1.67 mm, width .69 to 1.79 mm; in majors length 1.59 to 1.67 mm, width 1.63 to 1.79 mm. Thorax 1.73 to 2.14 mm. long in majors. Scapes 1.06 to 1.12 mm. in majors.

Head strongly cordate in large workers, much broader behind than in front; with large, well developed occipital robes, and strong occipital excision. Ocellar pit deep, in large workers a developed ocellus often present. Scapes very short in large workers, often reaching only about mid-way between eyes and occipital lobe peaks. Eyes much smaller than in blumi, comparing workers of the same head wdth. The cordate head shape occurs down through the polymorphic series to about the medium sized workers; only small media with heads with elliptical sides, only minors with heads even slightly wider in front than behind. Scapes in minors slightly surpassing occipital borders.

Thorax of large workers; promesonotum in profile strongly convex as in Solenopsis quinquecuspis and in Solenopsis blumi, but with a different set, primarily in shape of propodeum whose base in large workers slopes downward toward rear, becoming gradually rounded into the declivity. Thorax in profile singular in one point in having mesonotum slope very gradually into the mesopropodeal impression without a sharp break in outline; but propodeum in front arising very sharply and precipitously. Thorax from above robust and very wide but with only weak pronotal shoulders. In large workers mesonotum well developed, sometimes approaching condition seen in blumi; often promesonotal suture distinct and angulate or semi-angulate medially. Petiole and postpetiole large and robust, postpetiole often.47 to.49 mm long, .70 to .73 mm wide in large workers, larger than in any other species of the complex known to me. Postpetiole from above often wider behind than in front, or sides straight and parallel; anterior border feebly to more strongly convex.

Striae on genae similar to those on blumi, usually not reaching the antennal striae mesally. Piligerous foveoli and punctures on head less developed than in either blumi or quinquecuspis, so that the cephalic integument appears much smoother than in those species. Several fine striae and a weak integumental fold often evident immediately mesad to eye. Mesopleura in large workers with very fine striae, these often obliterated and integument smooth and shining on the lower part of this sclerite. Metapleura with somewhat coarse striae, especially toward the rear. Sides of petiole finely punctate. Sides of post petiole densely punctate and opaque. On posterodorsal face, postpetiole shagreened in front, finely punctate in middle and behind, the transverse striae common in other species very weak or absent.

Erect hairs short and stout, not very flexuous; long hairs of head and thorax, usually greatly longer than remainder of pilosity in most species in the saevissima complex, not so clearly differentiated in this species. Pubescent hairs on front face of petiole sparse.

Color distinctive. Gaster very similar to that of Solenopsis richteri, with a large reddish yellow spot on first gastric tergite, remainder of gaster very dark brown or black. Remainder of body largely the same color as the gastric spot; the head, thorax, scapes and legs all reddish yellow, integument somewhat transparent. Mandibles, a small bar mark on front, and petiole and postpetiole somewhat deeper in color, usually brown or reddish brown. Smallest workers may lack gastric spot, otherwise its presence throughout polymorphic series appears uniform. The colors of preserved specimens brighter, i.e., somewhat more reddish, than in Solenopsis saevissima.

Pitts et. al. (2018) - Head weakly to strongly cordate. Head and mesosomal sculpture with small piligerous foveolae, <0.01 mm in diameter. Median frontal streak mostly absent, but sometimes distinctly darkened. Median ocellus in largest major workers absent. Mandibular costulae dense, present throughout, rarely partially obsolescent. Mesonotum with 20–25 setae. Promesonotal suture in largest major workers gently curved medially, never projecting upward. Propodeum sculpture glabrous posteroventral to spiracle. Postpetiole shape as high as or higher than broad. Postpetiole sculpture in posterior view weakly transversely rugose, weakly granulate, reaches dorsum only in largest workers. Color generally red yellow to brown yellow, with head and mesosoma dorsum darker. Gaster dark brown. T1 with maculation red yellow to brown yellow.

Queen
Pitts et. al. (2018) - Head: broader than long, quadrate, slightly wider dorsal to eyes than ventral to them, sides of head convex from eyes to occipital angles, straight to nearly straight ventral to eyes. Eyes sometimes with 3–4 setae protruding from between ommatidia, setal length ≤3X width of ommatidium. Ocelli large, prominent. Median ocellus circular, lateral ocelli slightly ovate. Clypeus projecting, carinal teeth stout and sharp, carinae well defined, less so dorsally, slightly divergent ventrally, edge of clypeus between carinae with shallow concave depression, depression deepest between carinal teeth. Paracarinal teeth poorly defined to absent. Median clypeal tooth usually well developed; sometimes less developed. Approximately 0.50 of eye dorsal tomidpoint of head.

Mesosoma. Parapsidal lines present on posterior half of disk. Mesonotum with indistinct to distinct median furrow, usually on posterior 0.25–0.33 of disk. Propodeum sometimes with median longitudinal depression. Median bidentate process present on metasternum. Wing venation as in Figure.

Metasoma. Lateral faces of postpetiole weakly concave to straight sided. Petiolar spiracle tuberculate in some cases. Postpetiolar spiracle usually not tuberculate.

Coloration, Sculpturing, and Pilosity. Piligerous foveolae moderate to small, sparse, width 0.01–0.03 mm in diameter on head, smaller on meso- and metasoma. Pubescence golden and erect, longer and denser on head than elsewhere, longest on anterior edge of clypeus. Pubescence darker on darkly maculated areas. Mesosoma with longest pubescence (length 0.30 mm or greater) 3X longer than shortest pubescence. Mandible with several coarse, 6–8, distinct costulae present throughout. Propodeum with fine striae posteriorly, anterior 0.25 polished to finely striate. Petiolar node posterior surface with lower 0.75 coarsely striate, dorsum finely striate. Postpetiolar node posterior surface with middle 0.50 striate (with 7–10 striae), finely granulate, lower 0.25 coarsely granulate. Interfoveolar spaces on head finely striate when piligerous foveolae are large. Remaining integument smooth and polished. Two color varieties exist. Dark form brown with katepisternum, metasoma and medial area of legs dark brown. Light form orange to yellow orange, except vertex and T2-4, T1 laterally and apically and sternites apically dark brown. Light form also with posterior margin of orange maculation of T1 distinct. Both color forms with dark brown maculations anteriorly on pronotum, anteromedian area of mesonotum, area around parapsidal lines, sometimes on median area of axillae, anteromedian and triangular posteromedian area of scutellum, medially on anepisternum, and medially and laterally on propodeum. Internal margins of ocelli dark brown. Median frontal streak present. Wings hyaline with pale yellow to hyaline veins.

L ~7.8–8.4, HW 1.35–1.60, VW 0.89–1.01, HL 1.20–1.35, EL 0.40–0.51, OD 0.10–0.15, OOD 0.15–0.20, LOW 0.10–0.12, MOW 0.10–0.12, CD 0.15–0.20, MFC 0.18–0.23, EW 0.30–0.35, SL 0.90–1.10, PDL 0.15–0.20, LF1 0.10–0.12, LF2 0.08–0.11, LF3 0.08–0.10, WF1 0.06–0.08, FL 1.10–1.21, FW 0.21–0.31, MW 1.30–1.40, DLM 2.49–2.62, PRH 1.00–1.11, PL 0.59–0.75, PND 0.55–0.65, PH 0.60–0.72, PPL 0.30–0.40, DPW 0.61–0.82, PPW 0.59–0.73, PHB 0.41–0.50, N=5.

Male
Pitts et. al. (2018) - Head. Eyes sometimes with 3–4 setae protruding from between ommatidia, setal length ≤ 3X width of ommatidium. Ocelli large and prominent, median ocellus circular, lateral ocelli elliptical. In lateral view, clypeus with blunt, central lobe with indistinct anterior transverse carina. Mesosoma. Propodeum rounded, declivous face perpendicular, flat except with distinct to indistinct median longitudinal depression, basal face strongly convex transversely and longitudinally. Metapleuron broad almost 0.66 as wide as high. Wing venation as in Figure.

Metasoma. In cephalic view, dorsum of node transverse to having weak median depression and weakly bilobate. Petiolar and postpetiolar spiracles slightly tuberculate to not tuberculate. Genitalia as in Figure.

Coloration, Sculpturing, and Pilosity. Pubescence sparse, yellow to yellow orange, erect to suberect, not of uniform length over body (0.10–0.35 mm long), longer on gena and vertex. Mesonotal pubescence dense. Base of propodeum striato-granulate. Propodeum with anteromedial area glabrous. Area between eye and insertion of antenna, and lateral faces of scutellum finely striate. Area between ocelli granulate. Remainder of head weakly to coarsely granulate throughout, shagreened in some cases. Lower surface of petiolar nodes coarsely striato-granulate, dorsum finely striatogranulate. Postpetiole often with fine striations present dorsomedially. Metapleuron with dorsal longitudinal region finely striate. Gena granulate. Remaining integument smooth and polished. Color red brown to dark brown. Mandible brown anteriorly changing to yellow brown at apex. Flagellum yellow brown and legs segments brown medially grading to yellow towards base and apex.

L ~5.6–6.0, HW 1.00–1.10, VW 0.30–0.55, HL 0.81–0.92, EL 0.40–0.51, OD 0.10–0.15, OOD 0.15–0.20, LOW 0.11–0.14, MOW 0.11–0.15, CD 0.15–0.25, MFC 0.15–0.21, EW 0.32–0.40, SL 0.15–0.20, SW 0.10–0.15, PDL 0.05–0.10, PEW 0.11–0.15, LF1 0.20–0.25, LF2 0.13–0.16, LF3 0.16–0.22, WF1 0.08–0.10, FL 1.09–1.22, FW 0.20–0.30, MW 1.35–1.50, DLM 2.30–2.51, PRH 0.90–1.00, PL 0.60–0.75, PND 0.50–0.65, PH 0.39–0.52, PPL 0.29–0.41, DPW 0.60–0.71, PPW 0.55–0.75, PHB 0.18–0.30, N=6.

Larva
Pitts et. al. (2018) - Fourth instar worker larva. Head. Large, subpyriform in anterior view (height 0.44 mm, width 0.51 mm). Cranium slightly broader than long. Antenna with 2 or 3 sensilla, each bearing spinule. Occipital setal row with 8–12 bifid setae, base 0.5 to 0.8X total length of seta, 0.067–0.010 mm long. First setal row on vertex with 1–2 bifid setae, base ;0.66X total length of seta, 0.07–0.09 mm long. Second setal row on vertex with 4 simple setae, 0.13 mm long. Setae ventral to antenna level simple, 0.15–0.21 mm long. Clypeus with transverse row of 4 setae, inner setae shorter than outer setae, 0.07–0.12 mm long. Labrum small, short (breadth 2X length). Labrum with 4–6 minute sensilla and 2 setae on dorsal surface of each half and apical margin with 5–6 sensilla on each half. Each half of epipharynx with 2–4 isolated sensilla. Straight medial portion of mandible with 2–5 teeth that decrease in size dorsally. Maxilla with apex conical, palpus peg-like with 5 sensilla, each bearing one spinule. Galea conical with 2 apical sensilla, each bearing one spinule. Labium with patch of spinules dorsal to each palpus, spinules in short rows of 2–3. Labial palpus slightly elevated with 5 sensilla, each bearing one spinule.

Body. Spiracles small, first spiracle larger than others. Body setae of 2 types. Simple setae (0.05–0.11 mm long) arranged in transverse row of 5–10 on ventral surface of each thoracic somite and on each of 3 anterior abdominal somites, some with short denticulate tips. Bifid setae (0.07–0.10 mm long) occur elsewhere, base 0.5–0.75X length. Some bifid setae on thoracic dorsum with base 0.33X length of seta.

Length. 3.2–3.4 mm.

Type Material
Pitts et. al. (2018) - Syntype (?) workers. Argentina. La Rioja. Bajo Hondo. .

References based on Global Ant Biodiversity Informatics

 * Buren W. F. 1972. Revisionary studies on the taxonomy of the imported fire ants. Journal of the Georgia Entomological Society 7: 1-26.
 * Creighton W. S. 1930. The New World species of the genus Solenopsis (Hymenop. Formicidae). Proceedings of the American Academy of Arts and Sciences 66: 39-151.
 * Cuezzo, F. 1998. Formicidae. Chapter 42 in Morrone J.J., and S. Coscaron (dirs) Biodiversidad de artropodos argentinos: una perspectiva biotaxonomica Ediciones Sur, La Plata. Pages 452-462.
 * Kempf, W.W. 1972. Catalago abreviado das formigas da regiao Neotropical (Hym. Formicidae) Studia Entomologica 15(1-4).
 * Kusnezov N. 1978. Hormigas argentinas: clave para su identificación. Miscelánea. Instituto Miguel Lillo 61:1-147 + 28 pl.
 * Trager J. C. 1991. A revision of the fire ants, Solenopsis geminata group (Hymenoptera: Formicidae: Myrmicinae). Journal of the New York Entomological Society 99: 141-198
 * Vittar, F. 2008. Hormigas (Hymenoptera: Formicidae) de la Mesopotamia Argentina. INSUGEO Miscelania 17(2):447-466
 * Vittar, F., and F. Cuezzo. "Hormigas (Hymenoptera: Formicidae) de la provincia de Santa Fe, Argentina." Revista de la Sociedad Entomológica Argentina (versión On-line ISSN 1851-7471) 67, no. 1-2 (2008).
 * Wheeler W. M. 1925. Neotropical ants in the collections of the Royal Museum of Stockholm. Arkiv för Zoologi 17A(8): 1-55.
 * Wilson E. O. 1952. The Solenopsis saevissima complex in South America (Hymenoptera: Formicidae). Memórias do Instituto Oswaldo Cruz. Rio de Janeiro 50: 60-68.