Linepithema pulex

Linepithema pulex has been collected in a variety of habitats in the Atlantic coastal rainforest region, including mata atlântica, humid subtropical tall forest, forest edge, coffee plantation, and Restinga habitats. This species appears to be patchy in distribution and not commonly encountered (A. Wild pers. obs, R. Silva, pers. comm.) Nests of L. pulex were observed only at the type locality in Paraguay, where one superficial nest was in soil and leaf litter to a depth of 5cm, another nest fragment was found in the leaf litter, and the type series was found nesting 1m above ground in litter, at the junction between a small Philodendron bipinnatifidum Schott vine and tree trunk. This species has been recorded recruiting to tuna, sardine, and honey baits in Brazil and in Paraguay, and several records result from Winkler or Berlese litter sampling methods. Males were observed in the nest in November, and one nest was found to have a single dealate queen. (Wild 2007)

Identification
Wild (2007) – Worker Sculpture on head densely punctate-reticulate, surface dull and opaque; metanotal groove deeply impressed; propodeum raised; gastric tergites 3–4 with sparse pubescence; size small (HL < 0.65; FL < 0.47); antennal scapes short (SI 87–100); body color yellow to reddish brown.

Some Brazilian worker specimens have less extensive sculpture on the head, so that the sides of the head are relatively shining compared to Argentinean and Paraguayan specimens. A few specimens from Minas Gerais and São Paulo are darker in color than the type series. The shape of the mesonotum and the propodeum is also rather variable between localities, but this variation does not appear to show any broad geographic structure.

Workers of Linepithema angulatum are larger, the head less opaque, and the gaster with dense pubescence on all tergites. Workers of Linepithema cryptobioticum have much shorter antennal scapes (SI < 85) and smaller eyes.

Male Forewing with 1 submarginal cell; eyes relatively small (EL < 0.20) propodeum with posterior face slightly concave, not strongly overhanging petiole; petiolar node bearing a tall dorsal scale; surface of head densely punctate and opaque.

Distribution
Southeastern Brazil, northeastern Argentina, and eastern Paraguay.

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

Biology
Rosumek (2017) assessed trophic resource use and period of activity within the ant community in a southern Brazil Atlantic forest. He found a number of Linepithema, reporting "None of these species showed statistically significant preferences, due to low number of records and use of several resources. Linepithema micans and Linepithema pulex seem to use resources more broadly than Linepithema iniquum, which might descend to the ground mostly to scavenge animal resources. The small L. pulex may have stronger carnivorous tendencies and, in fact, twice they were able to recruit a few dozens of workers and predate crickets just by themselves, a remarkable feat considering its size. Linepithema pulexwas found to mostly be a diurnal forager.

Nomenclature

 *  pulex. Linepithema pulex Wild, 2007a: 105, figs. 45, 46, 69, 105 (w.q.m.) PARAGUAY.

Santschi’s (1923) name pulex is not available under ICZN rules (ICZN, 2000) as it was published as a quadrinomen. This study marks the first available use of pulex in Linepithema. Santschi’s specimens from Santa Catarina (NHMB, examined) are clearly conspecific with the Paraguayan type series. The type series was chosen from a recent Paraguayan collection because Brazilian collection and specimen loan regulations render scientific study in that country difficult.

Worker
Holotype: HL 0.57, HW 0.52, MFC 0.16, SL 0.48, FL 0.41, LHT 0.38, ES 1.26, PW 0.32, CI 91, SI 92, CDI 31, OI 22.

Worker: (n = 14) HL 0.48–0.65, HW 0.42–0.58, MFC 0.13–0.16, SL 0.42–0.54, FL 0.34–0.47, LHT 0.33–0.46, ES 0.82–1.76, PW 0.26–0.36, CI 86–95, SI 87–100, CDI 27–31, OI 16–27.

Head in full face view slightly longer than broad (CI 86–95), lateral margins convex, posterior margin concave. Compound eyes small to moderate (OI 16–27), comprised of 40–60 facets (usually < 50). Antennal scapes short (SI 87–100), shorter than head length. In full face view, scapes in repose surpass posterior margin of head by less then the length of the first funicular segment. Frontal carinae moderately to broadly spaced (CDI 27–31). Maxillary palps about ½ HL or less, ultimate segment longer than either of the preceding two segments, ultimate segment (segment six) longer than segment 2.

Mesosoma in lateral view with pronotum and mesonotum forming a single convexity, mesonotum relatively angular in most specimens, without central saddle or indentation. Mesonotal angle sometimes approaches 90º in larger workers. Metanotal groove deeply impressed, propodeum raised, dorsal face straight or with medial saddle-like impression, posterior margin concave.

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

Cephalic dorsum (excluding clypeus) either lacking erect setae or bearing a single pair of short setae near posterior margin. Pronotum with at least one pair of long erect anterior setae and often with a second or rarely a third shorter pair near the mesonotal suture. Mesonotum sometimes with a small pair of erect setae in the posterior quarter anterior of metanotal suture. Erect setae on gastric tergites 1–4 ( = abdominal tergites 3–6) relatively abundant, tergite 1 bearing 3–8 erect setae (mean = 5.8). Venter of metasoma with scattered erect setae.

Sculpture on head and mesosomal dorsum densely and finely punctate, surface dull and opaque. Pubescence dense on head and mesosomal dorsum. Mesopleura and metapleura anterior of metapleural gland orifice without pubescence, surface glabrous. Gastric tergites 1–2 with moderate pubescence, becoming dilute on tergites 3–4, surface moderately shining.

Color testaceous to medium reddish brown, gaster often darker, light brown to dark brown.

Queen
(n = 1) HL 0.72, HW 0.67, SL 0.57, FL 0.57, LHT 0.63, EL 0.23, MML 1.37, WL n/a, CI 94, SI 84, OI 32, WI n/a, FI 41.

Small species (MML 1.37). Head longer than broad in full face view (CI 94), posterior margin slightly concave. Eyes moderately small (OI 32). Ocelli moderately small. Antennal scapes relatively short (SI 84), in full face view scapes in repose surpassing posterior margin by a length less than that of first funicular segment.

Wings unknown (not present on single examined queen). Legs short relative to mesosomal length (FI = 41).

Dorsum of mesosoma and metasoma with short, scattered standing setae. Mesoscutum with more than 10 standing setae. Body and appendages concolorous light reddish brown.

Male
(n = 4) HL 0.45–0.47, HW 0.44–0.48, SL 0.11–0.12, FL 0.44–0.45, LHT 0.37–0.39, EL 0.17–0.19, MML 0.78–0.82, WL 2.21–2.26, PH 0.17–0.18, CI 97–103, SI 24–26, OI 37–41, WI 28–29, FI 55–58.

Head about as broad as long in full face view (CI 97–103). Eyes relatively small (OI 38–41), occupying much of anterolateral surface of head anterior of midline and separated from posterolateral clypeal margin by a length less than width of antennal scape. Ocelli of moderate size and in full frontal view set above adjoining posterolateral margins. Antennal scape short (SI 24–26), about 2/3 length of 3rd antennal segment. Anterior clypeal margin convex medially. Mandibles small, masticatory margin broad, longer than inner margin, usually bearing a small apical tooth followed by a much longer subapical tooth and a series of 7–10 denticles. Inner margin and exterior lateral margin parallel to slightly diverging.

Mesosoma moderately developed and subequal in length to metasoma. Mesoscutum not greatly enlarged, projecting slightly forward over pronotum, dorsal margin in lateral view relatively flat. Scutellum equal in height to mesoscutum and well above level of propodeum. Propodeum in lateral view not strongly overhanging petiole, posterior face slightly concave. Forewings long relative to mesosomal length (WI 28–29) and bearing one submarginal cell. Wings transparent, with pale brown wing veins and stigma. Legs of moderate length relative to mesosoma (FI 55–58).

Petiolar node bearing a blunt erect scale, node height taller than node length. Venter of node bearing a strong, posteriorly-projecting process. Gaster ovoid in dorsal view, about 2 times as long as broad. Gonostylus produced as a pointed, triangular pilose lobe. Volsella with cuspis present, digitus short and downturned distally.

Dorsal surfaces of body with scattered erect setae, mesoscutum with more than 4 erect 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 finely and densely punctate, surface opaque.

Head dark brown. Mesosoma and metasoma pale brown to medium brown. Mandibles, antennae, and legs pale whitish-yellow.

Type Material
Holotype worker. Paraguay. Canindeyú: Reserva Natural del Bosque Mbaracayú, Jejuimi, 24º08’S 055º32’W 12.xi.2002. Humid subtropical semideciduous forest, nest 1m above ground in litter between Philodendron bipinnatifidum vine and tree trunk, and in tree bark. A.L.Wild acc. no. AW1678. 1 worker,.

Paratypes. Same collection data as holotype, A. L. Wild acc. nos. AW1677–1678, 13 workers, 9 males, and 1 queen,, , , , , , , , , ,.

Etymology
Santschi’s name pulex probably refers to the small size of this species.

References based on Global Ant Biodiversity Informatics

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 * Nascimento Santos M., J. H. C. Delabie, and J. M. Queiroz. 2019. Biodiversity conservation in urban parks: a study of ground-dwelling ants (Hymenoptera: Formicidae) in Rio de Janeiro City. Urban Ecosystems https://doi.org/10.1007/s11252-019-00872-8
 * Santos Lopes J. F., N. Martins dos Reis Hallack, T. Archanjo de Sales, M. Silva Brugger, L. F. Ribeiro, I. N. Hastenreiter, and R. da Silva Camargo. 2012. Comparison of the Ant Assemblages in Three Phytophysionomies: Rocky Field, Secondary Forest, and Riparian ForestA Case Study in the State Park of Ibitipoca, Brazil. Psyche doi:10.1155/2012/928371
 * Santos P. P., A. Vasconcelos, B. Jahyny, and J. H. C. Delabie. 2010. Ant fauna (Hymenoptera, Formicidae) associated to arboreal nests of Nasutitermes spp. (Isoptera, Termitidae) in a cacao plantation in southeastern Bahia, Brazil. Revista Brasileira de Entomologia 54(3): 450-454.
 * Santos-Junior L. C., J. M. Saraiva, R. Silvestre, and W. F. Antonialli-Junior. 2014. Evaluation of Insects that Exploit Temporary Protein Resources Emphasizing the Action of Ants (Hymenoptera, Formicidae) in a Neotropical Semi-deciduous Forest. Sociobiology 61(1): 43-51
 * Santschi F. 1923. Pheidole et quelques autres fourmis néotropiques. Annales de la Société Entomologique de Belgique 63: 45-69.
 * Shattuck S. O. 1994. Taxonomic catalog of the ant subfamilies Aneuretinae and Dolichoderinae (Hymenoptera: Formicidae). University of California Publications in Entomology 112: i-xix, 1-241.
 * Silva R.R., and C. R. F. Brandao. 2014. Ecosystem-Wide Morphological Structure of Leaf-Litter Ant Communities along a Tropical Latitudinal Gradient. PLoSONE 9(3): e93049. doi:10.1371/journal.pone.0093049
 * Siqueira de Castro F., A. B. Gontijo, P. de Tarso Amorim Castro, and S. Pontes Ribeiro. 2012. Annual and Seasonal Changes in the Structure of Litter-Dwelling Ant Assemblages (Hymenoptera: Formicidae) in Atlantic Semideciduous Forests. Psyche doi:10.1155/2012/959715
 * Siqueira de Castro F., A. B. Gontijo, W. Duarte da Rocha, and S. Pontes Ribeiro. 2011. As comunidades de formigas de serapilheira nas florestas semidecíduas do Parque Estadual do Rio Doce, Minas Gerais. MG.BIOTA, Belo Horizonte 3(5): 5-24.
 * Wild A. L. 2007. Taxonomic revision of the ant genus Linepithema (Hymenoptera: Formicidae). University of California Publications in Entomology 126: 1-151
 * Wild, A. L.. "A catalogue of the ants of Paraguay (Hymenoptera: Formicidae)." Zootaxa 1622 (2007): 1-55.