Myrmelachista plebecula

Wheeler (1934) collected specimens from Tillandsia. In Costa Rica  Myrmelachista plebecula occurs throughout the country, from sea level to 1400m elevation cloud forest. It is also found in many different habitats.

Identification
Longino (2006) - Worker and queen with 9 antennal segments; maxillary palpus of worker 5-segmented; queen mandible and clypeus largely smooth and shining; queen HL 0.67–0.82mm, CI 85–90; queen often sharply bicolored, with red orange head and mesosoma, dark gaster (occasionally uniform dark red brown); worker HW up to 0.6mm; worker in full face view with pilosity on side of head fully appressed, with no projecting setae or erect pubescence; basiparamere of male with very short, subtriangular lobe, or lobe absent; paramere elongate and linear, with parallel sides; cuspis completely absent; digitus elongate, curving, scimitar-shaped.

Workers of plebecula and Myrmelachista joycei cannot always be distinguished.

Distribution based on Regional Taxon Lists
Neotropical Region: Costa Rica, Ecuador, Guatemala.

Biology
Longino (2006) - This species occurs in a wide variety of habitats, from moist to wet forest, lowlands to mid-montane elevations, weedy roadside vegetation, second growth forest, or mature forest. It is nearly always in highly insolated areas, being relatively common near ground level in scrubby vegetation but restricted to the high canopy in mature forest.

Nests are in narrow galleries in dead or live stems of a variety of plant species. The dead stems are usually narrow gauge, hard, and woody, not fibrous. Colonies may be olydomous, occupying multiple dead or live stems in a tree or shrub. I have found colonies nesting in live stems of Cordia alliodora, Cecropia obtusifolia, Callophylum brasiliense, Sloanea, and Ficus. It is unknown whether workers do any excavation of galleries on their own or just occupy preexisting chambers in myrmecophytes or chambers left by stem-boring insects.

Workers can be observed foraging on exposed stem and trunk surfaces in full sun, often moving in files. Pseudococcidae may occur in nest chambers in live stems (pers. obs.).

Alate queens may be in nests at any time of year. Alate queens have been collected in Malaise traps and one was collected at a blacklight sheet.

Nomenclature

 *  plebecula. Myrmelachista plebecula Menozzi, 1927d: 338 (w.) COSTA RICA. Longino, 2006a: 43 (q.). Senior synonym of costaricensis: Longino, 2006a: 43.
 * costaricensis. Myrmelachista costaricensis Wheeler, W.M. 1934g: 196, fig. 3 (w.m.) COSTA RICA. Junior synonym of plebecula: Longino, 2006a: 43.

Worker
Longino (2006) - HL 0.432–0.539, HW 0.418–0.512, SL 0.225–0.281, EL 0.102–0.119, CI 92–97 (n=5).

Antenna 9-segmented; maxillary palpus 5-segmented (may be 6-segmented in very large workers); mandible, clypeus, and face smooth and shining (mandible may be weakly striate in very large workers); in full face view, side and rear margins of head with very sparse, very short, fully appressed to subdecumbent pubescence, no projecting erect setae; ventral surface of head with very sparse, very short subdecumbent pubescence, no erect setae; hind tibia usually with sparse, appressed pilosity, occasionally more abundant and subdecumbent, pilosity short, about 1/4 width of tibia; typically bicolored, with orange red head and mesosoma, dark brown gaster, but in montane wet forest areas may be completely dark red brown.

Queen
Longino (2006) - HL 0.674–0.815, HW 0.601–0.696, SL 0.330–0.385, EL 0.197–0.227, OW 0.032–0.056, OD 0.127–0.166, CI 85–90, OI 32–35, OcI 4–7 (n=9).

Antenna 9-segmented; maxillary palpus 5 or 6-segmented, with varying degrees of fusion of terminal two palpomeres; mandible and clypeus largely smooth and shining with sparse small piligerous puncta; face entirely smooth and shining; face, sides of head, and ventral surface of head with sparse short appressed to subdecumbent pubescence, longer erect setae sparse, 6–8 across posterior margin of vertex, a pair at about mid-face, about 5 on clypeus; hind tibia usually with sparse, appressed pilosity, occasionally more abundant and subdecumbent, pilosity short, about 1/4 width of tibia; coloration often bicolored, with light red orange head and mesosoma, contrasting dark brown gaster; grading to forms with uniform red brown coloration.

Male
Wheeler (1934), for the synonomized M. costaricensis - Length 1.8-2.3 mm.

Head through the eyes somewhat broader than long, semicircularly rounded behind, with short, straight, anteriorly converging cheeks. Eyes and ocelli large and prominent. Clypeus like that of the worker, but with only an indistinct trace of the median denticle. Mandibles narrow, somewhat broadened apically, bidentate, the apical tooth acute, the basal short and blunt. Antennae 10-jointed; scapes fully 5 times as long as broad; first funicular joint nearly twice as long as broad; joints 2-5 small, nearly as long as broad; club very distinctly 4-jointed, the 3 basal joints sub equal, longer than broad, together much longer than the somewhat more swollen terminal joint. Thorax large, broader than the head; mesonotum large, subcircular, as broad as long, very convex in front, flattened behind. Epinotum small, lower than the mesonotum, shaped somewhat as in the worker. Petiolar scale lower and thicker, its summit much less acute, from behind straight, transverse and entire. Gaster shaped as in the worker; genitalia large and exserted. Legs long and slender.

Wings longer than the body, with well-developed pterostigma and closed marginal cell; discoidal cell lacking.

Smooth and shining; mandibles sub opaque, finely and densely punctate.

Pilosity pale, shorter and less abundant than in the worker.

Head deep castaneous, clypeus, mandibles, and scapes somewhat paler; funiculi, thorax, petiole, venter, legs and genitalia brownish yellow; femora and tibiae somewhat darker; dorsum of gaster brown, paler than the head; wings colorless, with very pale yellow veins and pterostigma.

Longino (2006) - Antenna 10-segmented; maxillary palpus 6-segmented; pygostyles minute, in the form of weakly sclerotized papillae without setae; basiparamere with very short, subtriangular lobe or lobe completely absent; paramere elongate and linear, with parallel sides; cuspis completely absent; digitus elongate, curving, scimitar-shaped; apodeme of penial valve curving into dorsal margin at obtuse angle.

Type Material
Longino (2006) - Syntype workers: Costa Rica, San José (Schmidt) [] (examined).

References based on Global Ant Biodiversity Informatics

 * INBio Collection (via Gbif)
 * Longino J. T. 2006. A taxonomic review of the genus Myrmelachista (hymenoptera: Formicidae) in Costa Rica. Zootaxa 1141: 1-54
 * Longino J. et al. ADMAC project. Accessed on March 24th 2017 at https://sites.google.com/site/admacsite/