The fungus-growing ants (Hymenoptera: Formicidae: Attini) of northeastern Mexico are poorly known. Herein new distributional records in NE Mexico and habitat observations are provided for the fungus-growing ants Apterostigma mexicanum Lattke, Atta texana (Buckley), Cyphomyrmex rimosus (Spinola), Mycocepurus smithii Forel, Mycetosoritis hartmanni Wheeler, Sericomyrmex aztecus Wheeler, Trachymyrmex smithi Buren, and Trachymyrmex turrifex Wheeler.
Fungus-growing ants of the tribe Attini are important model systems in studies on behavioral ecology, coevolution, mutualism, parasitism and biogeography (Currie et al. 2003; Munkacsi et al. 2004; Mikheyev et al. 2007). Attine ants are a predominantly Neotropical group with few successful extensions into the Nearctic ecozone (Weber 1972). Species of Cyphomyrmex, Atta texana (Buckley) and particularly Trachymyrmex septentrionalis (McCook) are the northernmost distributed of all attine ants (Weber 1972). Northeastern (NE) Mexico (states of Coahuila, Nuevo León, San Luis Potosí, and Tamaulipas) includes the distribution limits of several attines; this region, and particularly the state of Tamaulipas encompasses the contact of the Nearctic and Neotropical realms. The attines of NE Mexico are poorly known. Along the Gulf of Mexico coastal plain, the northernmost colonies of the Mexican leaf-cutting ant, Atta mexicana (Smith) have been reported in Tamaulipas, in San Fernando, and in the state of Nuevo León at Sabinas Hidalgo and Cerralvo, at the piedmont of the Sierra Madre Oriental (Sánchez-Peña 2005). In Tamaulipas state, Flores-Maldonado et al. (1999) reported Apterostigma pilosum Mayr and Trachymyrmex turrifex Wheeler in Cañón del Novillo, near Ciudad Victoria. Trachymyrmex saussurei (Forel) a neotropical species, exists in Gómez Farías, Tamaulipas (Rabeling et al. 2007). The present paper includes distribution records and habitat observations for attine species, some of which were not expected to occur or are not frequently reported in NE Mexico.
MATERIALS AND METHODS
With the exception of some specimens of Cyphomyrmex rimosus Spinola from Matamoros caught with pitfall traps, all specimens were collected by hand by the author during directed searches for workers. Descriptions used for identification are listed with each species. Records are reported by state (uppercase) and municipality (municipio); more specific localities are mentioned when pertinent. Voucher specimens are deposited at the Entomological Collection of Universidad Autónoma Agraria Antonio Narro, (UAAAN), Saltillo, Coahuila, Mexico. Specimens of taxa marked with an asterisk (*) have been deposited at the Bohart Museum of Entomology, University of California at Davis (UCDC).
RESULTS AND DISCUSSION
Table 1 is a summary of collected attine ants. These are detailed below.
Apterostigma mexicanum Lattke (*). SAN LUIS POTOSI: Municipio of Aquismón. 11.IV.2008. N 21°35'59”, W 99°06'12”, 980 masl (meters above sea level). About 200 m above the Sótano de las Golondrinas (Pit of Swallows). Apterostigma includes the most basal extant attines along with Myrmicocrypta and Mycocepurus (Currie et al. 2003). Workers of A. mexicanum were collected on soil in extensive clearing in medium-tall rainforest that included the trees Brosimum alicastrum Sw. (ojite, ramón), Bursera simaruba (L.) Sarg. (chaká, gumbo-limbo), Ficus cotinifolia H.B.K. (higuerón, strangler fig) near the transition to cloud forest. Apparently previously known from 5 specimens, all from tropical forest in Veracruz state, near Córdoba (Lattke 1997).
ATTINE ANTS COLLECTED IN NORTHEASTERN MEXICO, THEIR LOCALITIES AND GENERAL HABITATS.
Atta texana (Buckley) (*). COAHUILA: Municipio of Jiménez, town of Jiménez. 22.IX.2006. 29°03'04”N, 100°40'11”W, 240 masl. Municipio of Múzquiz, town of Múzquiz, Sabinas River. 5.VII.2008. 27°58'09”, W 101°34'53”, 490 masl. At Jiménez town, the Texas leaf-cutting ant was collected within 200 m from the Rio Grande (Rio Bravo) river, and also 15 km to the south, down the river. In both sites A. texana lives on the deeper soil flats (“Vegas”) along the river, in woods and clearings with pecans [(Carya illinoinensis (Wangenh.) K. Koch)], walnut (Juglans sp.), and huisache, (Acacia farnesiana (L.) Willd.). Mature colonies form nest mounds 5–10 m in diameter. At Múzquiz, A. texana was in a riparian forest of baldcypress (Taxodium cf. mucronatum Ten.), willow (Salix nigra Marshall) and sycamore (Platanus sp.).The Múzquiz locality is near the southwestern distribution limit for A. texana. There are few reports of this ant in Mexico, and no recent records of the reported populations of A. texana along the Gulf of Mexico, in the states of Tamaulipas, Veracruz, and Tabasco (Smith 1963). There is an unexpected, extremely disjunct record from Tehuacán, central Mexico (Ríos-Casanova et al. 2004). Coronado-Padilla et al. (1972) reported it from Allende, Coahuila (about 100 km NE from Múzquiz). The distribution of Atta spp. is quite fragmented in Northeastern Mexico; the factors responsible are possibly lack of moisture and soil type.
Cyphomyrmex rimosus (Spinola). Widespread morphospecies, known from Texas (San Marcos) and southern USA to Argentina (Wheeler 1907; Longino 2008) thus coordinates are not given here. Collected in mesic microhabitats, mainly springs and streams between 10 and 500 masl. NUEVO LEON: municipios of Cerralvo, at the spring; Guadalupe: La Pastora State Park, 10.VII.2006; Montemorelos: Rancho Marrufo, km 6 Montemorelos-General Terán highway, in wooded area along fencerow, 8.XII.2007; Pesquería: Santa María la Floreña, along tree-covered irrigation channel from Río Pesquería, 24.VIII.2008; Sabinas Hidalgo, at the spring, 18.VII.2006. TAMAULIPAS: municipios of Gómez Farias, San Pedrito town, in garden, 25.VIII.2008; Matamoros, Ejido (community) El Longoreño, gallery forest and grassy areas near the Rio Grande and ponds, 31.VIII.2007.
Mycetosoritis hartmanni Wheeler. NUEVO LEON: Municipio of Cadereyta, Rancho El Escape, Ejido Jerónimo Treviño. 8.XII.2007. N 25°32'25”, W 99°54'7”', 504 masl. TAMAULIPAS: Municipio of Llera, El Encino-La Libertad road, near Sabinas River (Río Sabinas), 23.IX.2006. N 23°08'09”, W 99°08'53”, 110 masl. The Nuevo León locality is an irrigated, organic vegetable farm at a semiarid site, on alluvial soils near the Santa Catarina river. There, several small plots (<1 ha) were grown to cover crops (Fabaceae), providing full shade. Mycetosoritis hartmanni workers were foraging under the cover crop, at the northern edge of one plot, at noon. The Tamaulipas location is disturbed tropical gallery forest with the trees T. mucronatum, Ficus sp., and Inga vera Willd., about 20 km north of Gómez Farias. Mycetosoritis hartmanni is an infrequently collected species (Mackay 1998; Longino 2009). In Mexico, this ant is known from the humid, medium-height tropical forest at Gómez Farias, Tamaulipas (Jusino-Atresino & Phillips 1992). The type locality is warm-temperate (Austin, Texas) (Wheeler 1907). Longino (2009) lists M. hartmanni from south Texas (Laguna Atascosa Wildlife Refuge) in coastal, low shrubby vegetation. Mycetosoritis hartmanii has not been reported living in the ephemeral habitat of annual agricultural crops.
Mycocepurus smithii Forel. NUEVO LEON: Municipio of Guadalupe, La Pastora State Park.10.VII.2006 and 28.XII.2006. N 25°39'53”, W 100°15'15”, 500 masl. This 200-ha park includes a remnant patch of old forest with interior live oaks (Quercus fusiformis Small) and anacua (Erethia anacua (Terán & Berland.) I. M. Johnst.) and gallery forest of sycamores (Platanus sp.), walnut (Juglans sp.) and bald cypress (T. mucronatum), on intermittent creeks running into the La Silla river. This park has been engulfed by the metropolitan area of Monterrey since at least 20 years ago. An aggregation of nest entrances of Mycocepurus colonies were in the gallery forest, on the flat surface of sandy banks along shallow dry creeks. Workers were observed at 5:00 PM on 10.VII.2006 at 30 m from the dry creek, foraging in the forest litter. Workers of C. rimosus were present also. On 28.XII.2006, foraging was observed at 13:00 h, after night temperatures of 510°C; the species apparently does not become inactive in winter here, as the attine Trachymyrmex septentrionalis does further north (Weber 1972). Local Mycocepurus appears to be mainly riparian, foraging in the same areas (moist microhabitats) as the ponerine ants Pachycondyla villosa (F.) and Odontomachus cf. laticeps Roger. Ants of open and disturbed habitats (Pogonomyrmex barbatus (Smith), Solenopsis geminata (Fabricius) and Dorymyrmex sp.) nested within 20 meters of M. smithii, in clearings. Rosas-Mejía et al. (2008) reported Mycocepurus sp. as an urban ant in Ciudad Victoria, 300 km south of Monterrey. Jusino-Atresino & Phillips (1992) collected M. smithii from the subdeciduous tropical forest of Gómez Farias, Tamaulipas, about 400 km south of Monterrey. Also reported from more distant tropical sites in Mexico to the south (states of Jalisco, Nayarit, San Luis Potosí, Tabasco, and Veracruz) (Mackay et al. 2004; Vázquez-Bolaños 2007), in deciduous and subdeciduous tropical forests, oakpine forest, and secondary vegetation in urban areas (Vázquez-Bolaños 2007). The report herein is the northernmost for the species; it is in the Nearctic ecozone at almost the same latitude of Brownsville, Texas, and in the Rio Grande Basin as well. This locality is apparently the most xeric (annual average precipitation 551 mm) and temperate (SAGARPA 2002) known for Mycocepurus in most of its range. Ants of the genera Mycetosoritis and Mycocepurus are small, cryptic, and infrequently collected (Mackay 1998).
Sericomyrmex aztecus Forel (*). SAN LUIS POTOSI: Municipio of Aquismón. 10.IV.2008. N 21°48'09”, W 99°10'49”, 200 m masl. Rio Santa María, Tamul. Undercover of tropical gallery forest including trees of B. simaruba and F. cotinifolia. Municipio of Ciudad Valles, N 21°56'11”, W 98°53'23”, 100 masl. Near gardens of hotel at Taninul. This is a mesic microhabitat in secondary low and medium-height tropical forest with B. simaruba and F. cotinifolia. The northernmost species of Sericomyrmex is S. aztecus from Mexico. Longino (2008) collected S. aztecus in Chiapas, near the Guatemala border. The Taninul, Ciudad Valles location reported herein, about 40 km from the state of Tamaulipas, is probably the northernmost record for the genus. Both Wheeler (1925) and Longino (2008) consider that Mesoamerican (or most) species of Sericomyrmex are very similar, and probably describe intraspecific variation.
Trachymyrmex smithi Buren. COAHUILA: Municipio and city of Saltillo. 19.VII.2005. N 25°21'36”, W 100°58'42”, 1680 masl. Lomas de Lourdes, Sierra de Zapalinamé. Workers foraging after summer rains on reddish-soil hills, above SE Saltillo. The habitat is temperate, an ecotone of xerophilous brush and forest with oaks (Quercus laeta Liebm. and the endemic Q. saltillensis Trel.), madrone (Arbutus xalapensis Kunth), and pistache (Pistacia mexicana H.B.K.). The type locality for T. smithi is La Rosa, General Cepeda, Coahuila, about 50 km W, in rocky Chihuahuan desert habitats (Buren 1944). Mackay & Mackay (2002) list it from Chihuahua state, Mexico. From the records, this species appears to occur in high, temperate deserts where summer temperatures are usually below 33C.
Trachymyrmex turrifex Wheeler. NUEVO LEON: Municipio of Pesquería, town of Santa María la Floreña, 24.VIII.2008. N 25°44'06”, W 99°49'44”, 320 masl. Nest in shaded sandy soil in garden; natural vegetation is thorny brush with honey mesquite (Prosopis glandulosa Torr.), huisache, palo verde (Parkinsonia texana (A. Gray) Watson), and desert hackberry (Celtis pallida Torr.). Municipio of García. 17.IX.2009. N 25°42'38”, W 100°32'53”, 840 masl. On sandy soil in thorny brush as above. TAMAULIPAS: Municipio of Matamoros. N 25°51'25”, W 97°30'31”, 10 masl. 22.VII.2009. Under trees in urban garden in sandy soil; nest aggregations (6 nests/10 m2). Known from matorral at Vallecillo, Nuevo León (40 km S of Laredo, Texas) (Buren (1944). This is possibly the most common Trachymyrmex species in the lower, hotter arid areas of NE Mexico.
W. Mackay, P. Ward, and C. Rabeling kindly verified the identification of specimens. W. Mackay and 2 reviewers also improved the manuscript. Thanks to those persons responsible for the wonderful web-available identification materials for ants. Supported by Universidad Autónoma Agraria Antonio Narro (Dirección de Investigación, item 01-04-0206-39).