Mexico to Colombia (type locality Costa Rica) (Fernandez 2003). Costa Rica: montane forests throughout country, becoming less common at lower elevations. Very common in Monteverde cloudforest; rare at La Selva. Material I have seen from Mexico is from cloud forest above 1800m.
Inhabits wet forest floor litter. Known from Winkler and Berlese samples.
Fern‡ndez C., F. 2003. Revision of the myrmicine ants of the Adelomyrmex genus-group (Hymenoptera: Formicidae). Zootaxa 361: 1Ð52.
Menozzi, C. 1931. Contribuzione alla conoscenza del "microgenton" di Costa Rica. III. Hymenoptera - Formicidae. Boll. Lab. Zool. Gen. Agrar. R. Sc. Super. Agric. 25:259-274.
Fernández, F., 2003:
Apsychomyrmex tristani Menozzi , 1931:260 (w); Borgmeier, 1937:240 (w); M.R. Smith, 1947:472 (worker redescription). [Holotype not seen, presumably in Deutsches Entomologisches Institut].
Adelomyrmex tristani : Kempf, 1972:18 ( New combination ); Bolton, 1995:58 (w.).
Worker measurements (n=40). HL 0.53 - 0.73 HW 0.45 - 0.65 SL 0.29 - 0.41 EL 0.05 - 0.08 WL 0.53 - 0.73 GL 0.63 - 0.92 TL 2.00 - 2.84 CI 90 - 91 SI 55 - 63.
Worker diagnosis: Head with posterior margin weakly flat to feebly concave. Mandibles with 5 to 6 teeth decreasing in size from the apical teeth. Tooth of basal margin of mandible not protuberant, smaller than subapical masticatory tooth. Eyes small, with 7 to 22 facets. Hypostomal tooth small but visible. Promesonotum slightly convex, higher than propodeal dorsum; metanotal groove well marked. Lateral sides of pronotum angulated. Propodeal spiracle rounded. Propodeum sloping, with the spines variable in size and shape, from low, triangular to long and narrow. Petiole high, with anterior side sloping and posterior side more or less feebly convex; sometimes petiole nearly quadrate, with anterior and posterior faces nearly parallel. Postpetiole campaniform with a ventral transverse ridge toothlike as seen in profile. Sting well developed. Mandibles dorsally with moderate longitudinal rugulations. Clypeal plate smooth and shining. Head frons longitudinally rugulate, head sides irregularly rugulated and mixed with punctures. Promesonotal dorsum variously sculptured, from longitudinal fine rugulae to longitudinal to strong coarse costae, in some workers the rugae or striae mixed, anteriorly oblique to transverse, in a few workers only a very few central longitudinal rugae visible. Promesonotal rugae or striae mixed with punctures. Propodeal declivity transversely rugulated between propodeal spines. Declivitous face of propodeum from smooth to covered with transverse rugae. Petiole and postpetiole normally transversely rugulated, sometimes times dorsally smooth and shining. Legs and gaster smooth and shining.
Hairs yellowish, long and flexuous on the body, more short and appressed on antennae and legs. Body black, dark brown or brown, legs light brown, tarsi yellowish.
Queen measurements: HL 0.75 HW 0.66 SL 0.45 EL 0.11 WL 0.84 GL 1.05 TL 3.22 CI 88 SI 68.
As worker with the following differences: Mandibles with all teeth of masticatory border of similar size. Three ocelli present. 12 - 13 ommatidia in the largest diameter of eye. Pronotum laterally costulated. Promesonotum longitudinally costulated with areas smooth and shining variable, from anterior half to nearly all promesonotum. Metanotum longitudinally costulated. Mesopleurae with longitudinal costulation and areas smooth and shining. Propodeum costulated longitudinally in the sides, transversely in the declivitous face.
Material examined: MEXICO : 3 w, Chiapas , 17.3 km NWBochi, 1800 m. , 24.ix.1992 , R.S. AndersonNo. 92-115 ( INBio ) ; 6 w, 10 q, Chiapas , 7.4 km SSWMotozintla de Mendoza, 2000 m. , 21.ix.1992 , R.S. AndersonNo. 92-110 ( INBio , IAvH ) ; 2 w, Chiapas , km N Unión Juarez, Volcán Tacana, lower slopes, 2000 m , 19.ix.1992 , R.S. AndersonNo. 92-110 ( INBio ) ; 9 w, Puebla , Tezitlán , 18.iv. 46 , F. BonnetNo. 1350 ( LACM , USNM ) ; 6 w, Veracruz , Fortin Canyon, Metlac River , 5.viii. 69 , S. & J. Peck ( BMNH ) ; GUATEMALA : 1 w, San Francisco , 19.iii. 46 No. 20342 , in Odontoglossum sp. Lot. No. 46-3094 ( MZSP ) ; COSTA RICA : 2 w, Alajuela , 6.5 km EMonteverde , 10°18’N84°45’W , 950 m. , 22.viii.1985 , J. LonginoNo. 861-s ( INBio ) ; 3 w, 1 q, Alajuela , 3 km EMonteverde , 10°18’N84°47’W , 1400 m. , 26.iv.1990 , J. LonginoNo. 2674-s ( INBio ) ; 2 w, Guanacaste , Cerro Cacao , 10°56’N85°27’W , 1500 m. , 9- 11.ii.1989 , J. LonginoNo. 2339-s ( INBio ) ; 13 w, Heredia , 18 km NVolcán Barba , 10°17’N84°05’W , 800 m , 14.vii.1986 , J. LonginoNo. 1383-S ( INBio ) ; 1 w, Heredia , La Selva Biological Station , 10°26’N84°01W , 50-150 m , x.1992 , OET ( INBio ) ; 14 w, 1 f., Puntarenas , Monteverde , 10°18’N84°48’W , 1560 m , 15.vii.1984 , L. Longino ( LACM ) ; 24 w, 7 q, Puntarenas , Monteverde , 10°18’N84°48’W , 1300-1800 m , 15.vii.1984 - 14.v.1991 , J. LonginoNos. 1572 - 2888-s ( INBio , IAvH ) ; 15 w, Puntarenas , Monteverde , 10°18’N84°48’W , 1400 m. , iv.- v.1987 , S. Little ( INBio , IAvH ) ; 14 w, 5 q, Puntarenas , Monteverde , 10°18’N84°48’W , 1550 m , 8.iv.1988 - 10.xii.1987 , J. LonginoNo. 1994-s to 1973-s ( INBio ) ; 6 w, 1 q, Puntarenas , Monteverde , 10°18’N84°48’W , 1600 m. , 30.iv.1989 , L. LonginoNo. 2486-s ( INBio ) ; 3 w, 1 f, Puntarenas , Monteverde , 10°18’N84°48’W , 1600 m. , 1.v.1991 , U. California EAP ( INBio ) ; 1 w, Puntarenas , Estación Pittier , 9°02’N82°55’W , 1670 m. , 2.vii.1989 ( INBio ) ; 2 w, Puntarenas , Fila Cruces , 8°47’N83°03’W , 1200 m. , 29.vi.1995 , J. LonginoNo. 3693-s ( INBio ) ; 3 w, San José , Laredo, en Philodendron , tunnel , 8.v. 57 , ( USNM ) ; 1 w, " From México or Costa Rica, in orchid, intercepted in Brownsville , Texas , 1 w, ( ICN ) . COLOMBIA : 2 w, Antioquia , El Retiro, Fca. El Barcino, 2100 m , 11°51’N83°95’W , winkler trap , 13.xii.1993 , A. Vahos leg. ( ICN ) ; 1 w, Quindío , Filandia, 1870 m , 1.vi.2002 , J. Sossa leg. ( IAvH ) ; 11 w, Santander , Encino, Cachalú Natural Reserve , 06°04’N73°07’W , 2000 m , winkler trap , 20.iii.1999 , E.L. Gonzalez leg. ( IAvH , ICN ) ; 4 w, Valle , Alto Anchicaya, Farallones de Cali National Park, 650 m , winkler trap , S. Sarria leg. ( IAvH , ICN ) ; 1 w, Valle , Cali, El Ensueño , 27 km road Cali-Buenaventura, 1780 m , in litt., 8.xii.1993 , P. Chacón leg. ( ICN ) .
Comments. This species is highly variable in size, color, pilosity, configuration of the propodeal spines, and to a lesser extent, petiole configuration. Relative to other groups of monomorphic myrmicines, there is a great deal of size variation, with worker HW ranging from 0.45 to 0.65 mm. The eyes vary from 7-8 to 20-22 ommatidia, with this number correlated with size. In color, the majority of the specimens are black with brown appendages and yellowish extremities. The normal pilosity is moderately long, although very long in some small brown workers (Costa Rica, Barbas Volcano, 800 m). The petiole typically has a short peduncle, curving continuously into the dorsal rounded face; in some workers, the petiole is somewhat more square, with the anterior and posterior faces almost parallel. The characteristics with the greatest variability are the sculpturing of the promesonotum and the size and form of the propodeal spines. The most typical tendency in worker sculpturing is the formation of rugulae or longitudinal carinae, either moderately or strongly marked, which form 14-15 coarse costulae over the dorsal area. Most of the time these costae or rugulae do not touch the anterior border of the pronotum, instead being replaced by oblique or transverse rugae. In a few cases these rugae reach the anterior margin of the pronotum, and in some workers they are concentric around a few central longitudinal rugae. In a few other workers, they are mostly oblique, almost transverse. Figures 23, 39 and 40 show some examples of the sculpturing. The teeth or propodeal spines are variable as well, from low and triangular (shorter than their bases), to elongated and slender in shape.
With such wide variation it would be easy to interpret the endpoints (in isolation) as different species, and in fact at the beginning of this revision some of the extreme examples seemed to represent new species, based especially on the size and sculpturing of the promesonotum. Nevertheless, critical examination of wider samples, from México to Colombia, reveals a continuum of size, sculpturing, and color mixtures. There are samples from the same locality and even the same nest in which the workers are different in size and promesonotum sculpturing. Under these circumstances, it is a challenge to identify characteristics by which species can be unambiguously separated. It is possible that A. tristani is actually a complex of closely-related species that have very recently undergone (or are undergoing) speciation. Populations in valleys or isolated mountains might be in the process of becoming discontinuous from neighboring populations, with accompanying differences in size, color, pilosity, or habits. Males associated with workers (lacking to date) could provide important information for evaluating these alternatives. Bigger samples, males, and genetic study should elucidate whether A. tristani is an extremely variable species or a set of closely-related species.
Some of the biggest specimens of A. tristani look like A. robustus . Nevertheless, the latter has a typical HW equal or greater than 0.83 mm, and most are around 0.85 mm. The rugulae of the head and promesonotum in A. robustus are more irregular, never straight, with more abundant and marked piliferous punctures. The tooth of the basal margin is large and robust, as big as or bigger than the subapical tooth of the masticatory margin; the clypeal teeth are also conspicuous. The propodeal spines are always low and black.
A. robustus is known only from Mexico.