Linepithema dispertitum

Linepithema dispertitum prefers woodland habitats at high altitudes (Wild, 2007). Specimens have been collected with pitfall traps and manually in a paramo landscape, where the annual precipitation is 1300–1400 mm, and the average temperature between 10–12°C (Hijmans et al. 2004a). Workers forage on the soil and under rocks, and most commonly nest in soil or rotting wood, but can also be found nesting in other situations. This behavior contrasts with its sister species, Linepithema iniquum, which is considered an arboreal ant. (Escarraga & Guerrero, 2016)

Identification
Wild (2007) - Workers of the closely related species Linepithema iniquum usually have a much stronger mesonotal impression and always bear at least five and usually more erect setae on the cephalic dorsum posterior of the clypeus. Separating worker specimens without reference to geography can be difficult as both species are among the most variable in the genus over their full distribution. They overlap in nearly all measured morphometric characters, but in general L. iniquum specimens tend to have longer antennal scapes and a narrower pronotum in dorsal view than L. dispertitum. Additionally, L. iniquum is normally arboreal while L. dispertitum tends to nest in soil or rotting wood. These ants co-occur only in southern Central America where they may be reliably differentiated by the sparse pubescence on gastric tergite 2 in L. iniquum versus moderate to dense pubescence on gastric tergite 2 in L. dispertitum, although these characters do not always hold elsewhere.

Distribution
Northern Mexico to Panama, with an isolated population above 2400 meters in the Cordillera Central of Hispaniola (Wild 2007).

Distribution based on Regional Taxon Lists
Neotropical Region: Colombia, Costa Rica, Dominican Republic, El Salvador, Guatemala, Honduras, Mexico, Panama, Trinidad and Tobago.

Biology
Wild (2007) - Linepithema dispertitum is primarily a montane forest ant but has been recorded across a broad range of habitats. This species has been collected from 130 to over 3,000 meters in elevation, with more than 90% of records across the range of L. dispertitum being from above 1,000 meters. Where habitat information has been recorded, 15 collections are from montane pine forest, five from montane rain forest, three from oak woodland, two from coffee plantations, and one each from tropical dry forest and rainforest.

Unlike the largely arboreal and closely related Linepithema iniquum, L. dispertitum is more frequently found nesting in soil or rotting wood. 28 nest records are from under stones, nine are from rotting wood, eight are from orchids, two are from moss on a tree trunk, and one is from under bark. Several of the orchid records were overland port-of-entry intercepts of full colonies with dealate queens into the United States from southern Mexico, suggesting the potential of this species to spread beyond its native range. Alate males have been recorded in April and June in Veracruz, Mexico, in November in Guatemala, in January in El Salvador, and in July and September in the Dominican Republic.

Linepithema dispertitum is probably monogynous in some populations. Of ten nest excavations that I conducted in Guatemala and in the Dominican Republic, four nests contained a single dealate queen, and the remainder uncovered no queens. Molecular genetic data will be needed to confirm monogyny, and given the extensive interpopulation variation in male morphology it is possible that mating system and colony structure vary correspondingly.

I observed Pseudacteon sp. phorid flies attacking L. dispertitum at nest excavations in Baja Verapaz and Sololá, Guatemala. The flies appeared within a few minutes as I broke into the ant nests. Voucher specimens of the phorids were identified by Brian Brown and have been deposited at.

In the Dominican Republic, L. dispertitum appears to be confined to a single population inhabiting pine forests above 2400 meters on Pico Duarte and neighboring mountains in the Cordillera Central. In these areas, L. dispertitum is abundant and apparently found to the exclusion of most other ant species.

Nomenclature

 *  dispertitum. Iridomyrmex dispertitus Forel, 1885a: 351 (w.m.) GUATEMALA. Wild, 2007a: 44 (m.). Combination in Linepithema: Shattuck, 1992a: 16.

Wild (2007) - Linepithema dispertitum is one of the more difficult species to diagnose owing to extensive variation among localities. This variation appears to be entirely allopatric, as there are no regions where more than one form is known to occur. Worker specimens from Costa Rica, the Dominican Republic, El Salvador, and Guatemala, including Forel’s types of L. dispertitum from Tecpán, are relatively large-eyed ( > 60 ommatidia), lack standing setae on the pronotum and often on the cephalic dorsum, show strong impression of the metanotal suture, and have dense pubescence on gastric tergites 1–4. Specimens from central Mexico have smaller eyes (OI < 26; < 60 ommatidia), a less-impressed metanotal suture, often with pubescence fading to sparse on abdominal tergites 3–4, and occasionally bear erect setae on the pronotum. Ants from the single northerly Chihuahuan collection have well developed pilosity, usually bearing more than 4 erect setae on the cephalic dorsum, a single pair of pronotal setae, and extensive pilosity on the gaster. The single collection from Baja California Sur is large (HW > 0.65), dark colored, and relatively pubescent, with a sparse pubescence extending onto the mesopleura and metapleural bulla.

Variation among the few known male specimens in this species is extraordinary and would suggest that this species be more finely divided if it were not for the continuous and allopatric nature of the variation. Guatemalan specimens from the type locality and from Sololá have an unusually worker-like head with short wings and long antennal scapes that easily surpass the posterior margin of the head in full face view. Specimens from Baja Verapaz, Guatemala and from La Libertad, El Salvador are similarly worker-like but with antennal scapes that are somewhat shorter. An unassociated male from Cuernavaca, Mexico has an even shorter first antennal scape that approaches the common condition of other Linepithema. The Hispaniolan collections are similar to the Mexican specimen in scape length but have much longer wings and a lower, more rounded petiolar node.

In spite of the extensive variation, it is unlikely that L. dispertitum is paraphyletic. Males share a number of apparently derived similarities, including the size and placement of the eyes, the long first antennal scape, the worker-like mandibles, and the relatively reduced structure of the mesosoma. Molecular data at several loci from populations in Baja California, Guatemala, and Hispaniola (Wild, unpublished) also support the monophyly of this species with respect to the close relative L. iniquum.

Worker
Wild (2007) - (n = 44) HL 0.58–0.81, HW 0.49–0.75, MFC 0.15–0.22, SL 0.53–0.76, FL 0.43–0.65, LHT 0.47–0.71, PW 0.31–0.47, ES 1.26–2.18, SI 97–113, CI 83–94, CDI 26–33, OI 20–30.

Worker diagnosis: Cephalic dorsum with 6 or fewer erect setae (often lacking entirely); mesonotum with a slight medial impression; mesopleura and metapleura smooth and shining, with pubescence sparse to absent; medium brown to piceous in color; Central America and Hispaniola.

Head in full face view oval to heart-shaped, varying from relatively narrow to relatively broad (CI 83–94), lateral margins convex, posterior margin slightly convex in some smaller specimens to distinctly concave in medium to larger specimens. Compound eyes of moderate size (OI 20–30), comprised of 47–80 (mean = 61) facets. Antennal scapes relatively long (SI 97–113), slightly shorter to slightly longer than head length. In full face view, scapes in repose exceeding posterior margin of head. Frontal carinae moderately to broadly spaced (CDI 26–33). Maxillary palps of moderate length, approximately 1⁄2 HL, ultimate segment (segment six) subequal in length to, or slightly longer than, segment 2.

Mesosoma in lateral view with pronotum and mesonotum forming a more or less single convexity, usually interrupted by a slight mesal impression on mesonotum. Mesothorax at impression wider than widest diameter of fore coxa. Metanotal groove slightly to deeply impressed. Propodeum variable in shape, from raised and evenly rounded to somewhat flattened dorsally. Metapleural bulla relatively swollen and protruding.

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

Cephalic dorsum (excluding clypeus) bearing 0–6 (mean = 1.9) erect setae. Pronotum bearing 0–2 (mean = 0.4) erect setae. Mesonotum without erect setae. Gastric tergite 1 ( = abdominal tergite 3) bearing 0–6 (mean = 0.6) erect setae, tergite 2 with 0–9 (mean = 2.8) erect setae, tergite 3 with 0–8 (mean = 3.9) erect setae. Venter of metasoma with scattered erect setae.

Surface of head and mesosomal dorsum smooth and relatively shining. Pubescence dense, short, and often subdecumbent to suberect on dorsum of head and mesosoma, sometimes presenting a distinct gray velvety sheen. Pubescence dense on gastric tergites 1–2, often dense to sometimes dilute on tergites 3–4. Mesopleura and metapleural bulla without pubescence or rarely with a few appressed hairs, surface strongly shining.

Concolorous medium brown to piceous.

Queen
Wild (2007) - (n = 4) HL 0.80–0.94, HW 0.71–0.88, SL 0.67–0.83, FL 0.65–0.84, LHT 0.72–0.95, EL 0.23–0.26, MML 1.48–1.70, WL 4.20–4.36, CI 89–94, SI 90–95, OI 28, WI 28–30, FI 43–49.

Moderately small species (MML < 1.7). Head longer than broad in full face view (CI 89–94), posterior margin slightly concave. Lateral margins often somewhat impressed anterior of eyes. Eyes small (OI 28). Ocelli small. Antennal scapes of moderate length (SI 90–95), in full face view scapes in repose surpassing posterior margin by a length greater than or equal to length of first funicular segment.

Forewings moderately short relative to mesosomal length (WI 28–30). Forewings with Rs+M more than twice as long as M.f2. Legs moderately long relative to mesosomal length (FI 43–49).

Pilosity variable on dorsum of mesosoma and metasoma, sparse to relatively abundant. Mesoscutum with 0–10 standing setae. Body color medium brown to piceous. Antennal scapes, legs, and mandibles concolorous with body.

Male
Wild (2007) - (n = 6) HL 0.55 –0.62, HW 0.47–0.58, SL 0.17–0.53, EL 0.20–0.23, MML 0.93–1.01, WL 2.27–3.50, FL 0.57–0.65, LHT 0.57–0.65, CI 85–96, SI 32–86, OI 32–40, WI 24–35, FI 60–69.

Male diagnosis: Forewing with 1 submarginal cell; first antennal segment relatively long (SI > 31); propodeum with convex posterior face; eye separated from posterolateral clypeal margin by a distance greater than or equal to width of antennal scape; color medium to dark brown.

Male description: Extremely variable across range and difficult to characterize (see discussion). Head relatively narrow in full face view (CI 85–96), head shape ovoid or in some populations (Guatemala and El Salvador) approaching a chordate worker-like shape. Eyes small (OI 32–40) and separated from posterolateral clypeal margin by a length less than or equal to width of antennal scape. Ocelli small and in full frontal view emerging only slightly or not at all above adjoining posterolateral margins. Antennal scape long to very long (SI 32–86), approaching the worker condition in some populations (Guatemala and El Salvador), varying from 70% to 320% length of 3rd antennal segment. Anterior clypeal margin convex medially. Mandibles large and worker-like, masticatory margin broad, much longer than inner margin, bearing 1–2 apical teeth followed by alternating series of teeth and denticles, as in worker dentition. Inner margin and exterior lateral margin strongly diverging.

Mesosoma not well developed and subequal in length to metasoma. Mesoscutum not greatly enlarged, not projecting forward over pronotum. Propodeum in lateral view low and not overhanging petiole, posterior face slightly convex and rounding gradually into dorsal face. Forewings normally of moderate length (WI 24–26), rarely very long (WI 35, Hispaniola), and bearing one submarginal cell. Wings clear to slightly smoky with medium brown wing veins and stigma. Legs moderately long relative to mesosoma (FI 60–69).

Petiolar node bearing a sharp, worker-like forward inclined scale (Guatemala and El Salvador) or a low, rounded scale with node height shorter than node length (Hispaniola), or intermediate, with sharp, upright scale (Mexico). Venter of node bearing a convex lobe or downward-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 to absent, mesoscutum lacking standing 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, legs, antennal scapes, mesosoma and metasoma medium brown to dark brown. Tibiae, trochanters, and antennal apices lighter.

Type Material
Wild (2007) - Lectotype worker, by present designation, examined], 13 worker and 2 male paralectotypes, Tecpán 7000’, Chimaltenango, Guatemala, M. Stoll. (MHNG, {{NHMW}), examined].