In general, poneromorph ants (Bolton 2003), previously part of the subfamily Ponerinae, have been considered “primitive” both in terms of their morphology and habits. These ants have a wide, mainly Pantropical distribution (Smith 1979; Hölldobler & Wilson 1990). Most species live in small colonies formed by a few dozen to a maximum of some hundred individuals, with workers that tend to be monomorphic. They are generally predators, although some also feed on sugary nectars, fruit, and the secretions of certain homopterans. Most species forage alone, although some exhibit recruiting behavior. Hölldobler & Wilson (1990) provide additional information on their biology and habits.

On the American continent, 25 genera of these ants are known, of which 17 have been recorded for Mexico (Bolton 1994; Brandão 1996; Lattke 2003). At present, 76 species of poneromorphs are recognized for the Mexican Republic, of which only 5 have been recorded for Morelos (Kempf 1972; Smith 1979; Rodríguez 1986; Brandão 1991, 1996; Cartas 1993; Bolton 1995; Lattke 1995; Quiroz & Valenzuela 1995, 2002; Castaño 1996; Rojas 1996; Longino 1998; Lachaud & García-Ballinas 2001; Durou et. al. 2002). Baroni-Urbani (1983), Hölldobler & Wilson (1990), and Bolton (1994) provide keys for the identification of Neotropical genera, and MacKay & MacKay (1989) for those found in Mexico.

The state of Morelos is situated in south central Mexico between 2 important geographic zones: the Transverse Neovolcanic Belt and the Rio Balsas Basin. The state's rugged topography favors several climatic domains and an important floristic diversity. In addition, Morelos is characterized by the presence of Neartic, Neotropical, and some autochthonous faunal components (Anonymous 1981; Aguilar 1990).

The present study provides an inventory of the poneromorph ant species that occur in the state. It also includes some information on the distribution, nesting, and foraging habits of these species.

Description of the Study Area

The state of Morelos is located between 18°22'06”N and 19°07'10”N, and 98°03'W and 98°30'08”W. Its region (covering a surface area of 4,958 km²) is divided into 33 municipalities, with the state capital located in the city of Cuernavaca. The 2 highest points in Morelos, Chichinautzin Mountain and the Popocatepetl Volcano, are located in the northern region at altitudes of 3,450 m and 5,452 m above sea level, respectively. From these heights, the state's topography descends southward to 890 m in the Jojutla Valley and then climbs again to 1,500 m in the Sierra de San Gabriel in southern Morelos, near Guerrero (Vidal 1980).

The climate is hot and sub-humid in most parts of the state. Temperate and sub-humid conditions predominate on mountain slopes, whereas semi-cold to cold conditions characterize altitudes above 2,800 m (Anonymous 1981). Tropical deciduous forest (TDF) is the most widely distributed vegetation type in the state, ranging between 890 m and 1,800 m above sea level and covering more than 50% of the state's surface area. Some disturbed areas of TDF have been transformed into thorn forests (“huizacheras”), which are generally characterized by a great number and variety of Acacia species. Among the ravines and canyons of the mountainous zone, small patches of temperate cloud forest can be found. Stands of pine, oak, and fir occur from 1,800 m to 4,000 m. In the highest part of the state, bordering the slopes of Popocatepetl, mountain prairie is prevalent. The average frost line is located at approximately 5,000 m (Miranda & Hernández 1963; Rzedowski 1978; Anonymous 1981).

Materials and Methods

We collected ants at 2-4 sites in each of the 33 municipalities of Morelos, in 7 vegetation types at elevations ranging from 890-3500 m (Fig. 1 and Table 1). Ants were collected from pitfall traps and also captured directly with entomological forceps and aspirators. Direct collection was conducted by following a 100 m transect at each sampling site, with ants captured from soil, under rocks, on fallen trunks, inside trunks, and on vegetation (grass, shrubs, and trees) to a height of approximately 2 meters. Two people carried out this procedure, which lasted 3 h at each of the 77 sites (Table 1).

For trapping, we placed 2 pitfall traps in each of the selected areas. They consisted of 1-L capacity plastic containers with a diameter of 13 cm. These were half-filled with commercial anti-freeze diluted 30% with water as a preservative and buried so that their openings were at soil level. Finally, they were covered with a plastic plate to prevent desiccation and contamination by garbage and/or water if it rained. Traps were emptied every 48 h after placement.

We preserved specimens in 70% ethanol. We mounted vouchers and identified them using MacKay & MacKay (1989), MacKay & Vinson 1989, Bolton 1994, and Longino's (1998) web page. We deposited vouchers of all species at the Institute of Ecology, Xalapa, Veracruz (IEXA).

Results and Discussion

A total of 139 poneromorph ant samples were obtained, with 56.3% collected directly and 46.3% from traps. From all samples, 576 specimens were obtained. Compared with the capture of other ant subfamilies, relatively few poneromorph specimens were obtained; for example, over 5000 Ecitoninae ants were collected under similar conditions (Quiroz & Valenzuela 2006). Poneromorphs tend to form low-population colonies, and individuals generally forage alone. They can, however, represent a substantial percentage of ant biomass in tropical regions due to the abundance of certain species and to the relatively large size of some (e.g., Cartas 1993).

Preliminary data show that in the state of Morelos the subfamily Myrmicinae has the greatest richness in terms of genera (41.5%), followed by poneromorphs (19.5%), Formicinae (17.1%), Dolichoderinae (12.2%), Ecitoninae (7.2%), and Pseudomyrmecinae (2.5%).

Table 2 lists the species collected. The genus with the greatest species richness is Gnamptogenys (4 species), followed by Hypoponera, Pachycondyla, Odontomachus, and Ectatomma (2 species each); and Anochetus, Belonopelta, Leptogenys, and Platythyrea (1 each).

A total of 16 species of poneromorph ants were found in Morelos. Two other species, Hypoponera foeda and Leptogenys wheeleri, were not collected by us but have been reported for the state (Brandão 1996). With the new recordings, the number of poneromorph ant species reaches 18 for Morelos. None is endemic to the state: O. clarus is distributed in the United States and Mexico; L. mexicana and L. wheeleri have been recorded only from Mexico; H. foeda is known for Mexico, Central America, and some Caribbean Islands; H. opaciceps, P. stigma, P. villosa, and E. tuberculatum are distributed from South America to the United States; G striatula and G. regularis are known from Mexico to Argentina; A. mayri, G. strigata, G. sulcata, O. laticeps, and E. ruidum are distributed in Mexico, Central America and northern South America; B. deletrix is distributed from Mexico to Costa Rica. One species, Pl. punctata, is known from the United States, Mexico, Central America, and some Caribbean Islands. Finally, H. punctatissima is a pantropical tramp species, probably of African origin (Wilson & Taylor 1967; Kempf 1972; Brandão 1991, 1996; Bolton 1995; Lattke 1995, 2003; Longino 1998).

Of the 16 species collected during this study, 13 are new records from the state of Morelos: A. mayri, B. deletrix, E. ruidum, E. tuberculatum, G. strigata, G. sulcata, G. regularis, H. punctatissima, L. mexicana, O. laticeps, P. stigma, P. villosa and Pl. punctata.

Poneromorphs are widely distributed throughout Morelos. Only four of the 33 municipalities in Morelos (Huitzilac, Tlalnepantla, Ocuituco, and Tétela del Volcán) failed to produce samples of these ants. Failure to yield samples could occur because these municipalities are located in the mountainous northern part of the state.

The most abundant and widely distributed species were O. clarus (37.4% of the total number of samples obtained), G. striatula (12.2%), E. tuberculatum and H. opaciceps (7.1%), and E. ruidum and P. stigma (6%). These 6 species represent 75.8% of the samples collected (Table 2 and Table 3). Next in frequency were G. strigata and O. laticeps (5%), Pl. punctata (4.3%) G. sulcata and L. mexicana (3%), and A. mayri (1.4%). The remaining 4 species (B. deletrix, G. regularis, H. punctatissima, and P. villosa) were collected only once each, suggesting that they are uncommon in Morelos or that our sampling methods were ineffective in detecting them. Due to the methods used, we could be underestimating the species abundance of tree inhabitants, subterranean habits, and ants that nest and forage in litter.

The greatest abundance and diversity were found between 890 and 1600 m; 86.1% of samples and all species were found in this altitudinal range. Only 4 species (H. opaciceps, O. clarus, Pl. punctata, and P. stigma) were obtained above 1600 m. The highest collection altitude recorded (1,890 m) corresponds to O. clarus, which was found in Nepopualco, in the municipality of Totolapan (Fig. 2 and Table 2).

Poneromorphs were encountered in a great diversity of vegetational associations (Table 2) including tropical deciduous forest (TDF), ecotonal areas between TDF and pine-oak forests, thorn forests, pastureland, urban and suburban vegetation, and a variety of agroecosystems (including mango, avocado, and guava orchards).

Most species were found in TDF, the most extensive vegetational association in Morelos and one that is especially common in the central and southern portions of the state. Other landscape elements, including pastureland, cultivated fields, and thorn forest (mainly Acacia spp.), are often interspersed with the more abundant TDF. Pine-oak forests are encountered in the mountainous, northern part of the state, and a transitional ecotone is a common occurrence between TDF and the pine-oak forest. This transitional zone appears to establish the distributional limit for poneromorphs within the state of Morelos.

We found that most species are epigeal foragers (except for G. regularis and P. villosa). However, some can forage underground (L. mexicana, G. strigata), in litter (G. strigata, G. sulcata, and B. deletrix), and others on trees (E. tuberculatum, G. regularis, P. stigma, P. villosa, and Pl. punctata).

Most species nest in soil (except for A. mayri, G. sulcata, H. punctatissima, P. stigma, and P. villosa), in some cases preferentially under rocks (O. clarus). Others nest in hollow branches (A. mayri, B. deletrix, G. regularis, H. punctatissima, H. opaciceps, G. strigata, and P. stigma), in litter (B. deletrix), in pre-existing cavities in dead and living trees (G. sulcata, P. villosa), and at the base of epiphytic plants (P. villosa). Our observations regarding foraging and nesting sites coincide with those of Lachaud (1990), Lattke (1995), Longino (1998), and Durou et al. (2002). Data for B. deletrix and L. wheeleri were taken from Longino (1998), Wilson (1955), and Durou et al. (2002).

Of the 76 species of poneromorphs reported from Mexico,18 (23.7%) are known for Morelos, even though this state is relatively small (4,958 km²; 0.25% of the entire area of the country).

Poneromorphs are Pantropical, although in America they have made some degree of penetration into the Nearctic region (Brown 1976). Of the 18 species of poneromorphs found in Morelos, 7 are recorded from the United States. The remaining 11 species are distributed only in the Neotropics. This composition of poneromorph ants may result from the location of the state at the juncture of these 2 biogeographic zones (Brown 1976; Anonymous 1981; Aguilar 1990).