Linepithema leucomelas

An arboreal species inhabiting Brazil's Atlantic forest.

Identification
Wild (2007) - Worker Strikingly bicolored, dark head contrasting with pale whitish yellow on all or part of the mesosoma and appendages; antennal scapes long (SI 106–125).

Linepithema leucomelas is unlikely to be confused with any other Linepithema species owing to its striking coloration. Workers of the closely-related Linepithema iniquum have a strong constriction of the mesonotum, while males of L. iniquum are nearly identical but the petiolar node is concolorous with the mesosomal dorsum.

Some worker specimens from Santa Catarina are darker in color than specimens from elsewhere, with a dark propodeum and more extensive infuscation. A few specimens from São Paulo state are larger and bear more than one pair of pronotal setae.

Male Forewing with 1 submarginal cell; petiolar node bearing a relatively low, rounded scale; propodeum with posterior face convex; antennal segment 3 more than twice as long as antennal scape; dorsum of petiole much lighter in color than mesosomal dorsum.

Distribution based on Regional Taxon Lists
Neotropical Region: Brazil.

Biology
Wild (2007) - This species is an Atlantic forest ant. Most records are from rainforest or wet forest. Linepithema leucomelas is one of only two primarily arboreal species in the genus, the other being L. iniquum. Kempf (1969: 294) observes that L. leucomelas nests “under bark, also in the cavities of bamboo, gourd trees, and arboreal ferns.” Leuderwaldt (1926) reports several nests from bamboo and one from a Hemitelia fern. Ketterl et al. (2003) note L. leucomelas nesting in bromeliads in Araucaria trees in Rio Grande do Sul. Among museum records, one nest is from under Jacaranda bark and two separate Port-of-Entry intercepts into the United States report the ant from orchid plants. Alate queens have been collected from nests in May and October, and alate males have been collected in October.

As noted in Emery’s original description and again by Kempf (1969), this ant shows similar coloration to an unrelated arboreal Atlantic forest species, Tapinoma atriceps Emery. The significance of this convergence is unknown.

Nomenclature

 *  leucomelas. Iridomyrmex leucomelas Emery, 1894g: 378 (footnote) (w.q.) BRAZIL. Wild, 2007a: 83 (m.). Combination in Linepithema: Shattuck, 1992a: 16. Senior synonym of aspidocoptus: Wild, 2007a: 81.
 * aspidocoptus. Iridomyrmex aspidocoptus Kempf, 1969: 295, figs. 10, 11 (w.) BRAZIL. Combination in Linepithema: Shattuck, 1992a: 16. Junior synonym of leucomelas: Wild, 2007a: 81.

Wild (2007):

Worker
Lectotype: HL 0.69, HW 0.60, MFC 0.16, SL 0.70, FL 0.60, LHT 0.61, PW 0.37, ES 1.79, SI 116, CI 88, CDI 27, OI 26.

Worker: (n = 22) HL 0.60–0.78, HW 0.52–0.74, MFC 0.14–0.18, SL 0.64–0.79, FL 0.51–0.68, LHT 0.58–0.71, PW 0.33–0.58, ES 1.22–2.00, SI 106–125, CI 85–96, CDI 24–28, OI 20–26.

Head in full face view varying from relatively narrow to relatively broad (CI 85–96), lateral margins convex, posterior margin slightly convex to concave. Compound eyes of moderate size (OI 20–26), comprised of 55–80 facets. Antennal scapes long (SI 106–125), as long or longer than head length. In full face view, scapes in repose exceeding posterior margin of head by a length greater than the length of the first funicular segment. Frontal carinae narrowly to moderately spaced (CDI 24–28). Maxillary palps very long, well more than ½ HL, ultimate segment (segment six) longer than segment 2.

Mesosoma in lateral view with pronotum and mesonotum forming a single continuous convexity, mesonotal profile straight to very slightly impressed mesally. Metanotal groove slightly impressed to not at all impressed, propodeum low and quadrate-forward.

Petiolar scale sharp and inclined anteriorly, in lateral view falling short of the propodeal spiracle.

Cephalic dorsum (excluding clypeus) bearing 4–6 erect setae. Pronotum bearing 1–4 erect setae. Mesonotum without erect setae. Gastric tergite 1 bearing 1–3 erect setae (mean = 2.0), tergite 2 with 2–4 erect setae, tergite 3 with 4–6 erect setae. Venter of metasoma with scattered erect setae.

Surface of head and mesosomal dorsum finely reticulate-punctate and relatively dull. Pubescence dense on head and mesosomal dorsum. Mesopleura with pubescence fading to absent anteroventrally, surface smooth and shining. Metapleural bulla with moderate to sparse pubescence thinner than on propodeal dorsum but never completely absent. Gastric tergites 1–4 with dense pubescence, surface only slightly shining.

Body color variable, but always bicolored with head and part of gaster dark brown and with at least pronotum, petiole, and some appendages a pale whitish-yellow. Some specimens pale whitish yellow except for dark head and gastric infuscation, others dark except for light pronotum, petiole, funiculus, tibiae and tarsi. Most specimens show mesopleural infuscation.

Queen
(n = 2) HL 0.85, HW 0.78–0.79, SL 0.79–0.83, FL 0.78–0.80, LHT 0.88, EL 0.26–0.27, MML 1.65–1.66, WL 5.01, CI 92–94, SI 100–106, OI 31–32, WI 30, FI 47–49.

Moderately small species (MML < 1.7). Head longer than broad in full face view (CI 92–94), posterior margin slightly concave to slightly convex. Eyes small (OI 31–32). Ocelli small. Antennal scapes long (SI 100–106), in full face view scapes in repose surpassing posterior margin by a length greater than length of first funicular segment.

Forewings of moderate length relative to mesosomal length (WI 30). Forewings with Rs+M somewhat longer than M.f2. Legs moderately long relative to mesosomal length (FI 47–49).

Dorsum of mesosoma and metasoma with abundant standing setae. Mesoscutum bearing more than 10 standing setae. Head, mesosoma and metasoma medium to dark brown, trochanters, tibiae, and tarsi testaceous.

Male
(n = 2) HL 0.48–0.52, HW 0.44–0.47, SL 0.11–0.12, FL 0.52–0.55, LHT 0.49–0.54, EL 0.19–0.20, MML 0.87–0.94, WL 2.23, PH 0.19–0.21, CI 91–92, SI 23, OI 38–41, WI 26, FI 58–59.

Head relatively narrow in full face view (CI 91–92), lateral margins continuing to expand posterior of compound eyes. Eyes moderately small (OI 38–41), occupying much of anterolateral surface of head anterior of midpoint and separated from posterolateral clypeal margin by a length less than width of antennal scape. Ocelli small and in full frontal view emerging only slightly above adjoining posterolateral margins. Antennal scape short (SI 23), only 40–50% length of 3rd antennal segment. Anterior clypeal margin convex medially. Mandibles small, masticatory margin slightly longer than inner margin, apical tooth enlarged and followed by a series of 8–12 denticles. Inner margin and exterior lateral margin parallel to slightly diverging.

Mesosoma not well developed and subequal in length to metasoma. Mesoscutum not greatly enlarged, not projecting forward over pronotum. Propodeum in lateral view not well developed and not overhanging petiole, posterior face slightly convex and rounding gradually into dorsal face. Forewings of moderate length (WI 26) and bearing one submarginal cell. Wings transparent, with pale brown wing veins and stigma. Legs of moderate length relative to mesosoma (FI 58–59).

Petiolar node bearing a low, rounded scale, node height shorter than node length. Venter of node bearing a convex posteriorly-pointing process. Gaster ovoid in dorsal view, about 2 times as long as broad. Gonostylus produced as triangular pilose lobe. Volsella with cuspis present, digitus short and downturned distally.

Dorsal surfaces of body with erect setae sparse, mesoscutum with 0–4 fine erect to suberect setae. Venter of gaster with scattered setae. Pubescence dense on body and appendages, becoming sparse only on medial propodeal dorsum. Sculpture on head and mesoscutum not well developed, surface shining through pubescence.

Head, mesosoma, and metasoma medium brown. Mandibles, petiole, antennae, and legs pale whitish-yellow to light brown, much lighter than head and mesosoma.

Type Material
Lectotype worker, by present designation, examined, and 1 worker paralectotype, Rio Grande do Sul, Brazil USNM, examined.