A SURVEY OF GROUND-DWELLING ANTS (HYMENOPTERA: FORMICIDAE) IN GEORGIA

Headnote

ABSTRACT

Ground-dwelling ants (Hymenoptera: Formicidae) were sampled at 29 sites in 26 counties in Georgia with pitfall traps, leaf litter extraction, visual searching, and bait stations. We found 96 ant taxa including nine species not previously reported from Georgia: Myrmica americana Weber, M. pinetorum Wheeler, M. punctiventris Roger, M. spatulata Smith, Pyramica wrayi (Brown), Stenamma breuicorne (Mayr), S. diecki Emery, S. impar Forel, and S. schmitti Wheeler, as well as three apparently undescribed species (Myrmica sp. and two Stenamma spp.). Combined with previous published records and museum records, we increased the total number of ground-dwelling ants known from Georgia to 144 taxa.

Key Words: ground-dwelling ants, Formicidae, survey, Georgia, species.

RESUMEN

Hormigas que habitan en el suelo (Hymenoptera: Formicidae) fueron recolectadas en 29 sitios en 26 condados del estado de Georgia con trampas de suelo, extracion de hojarasca, busqueda visual, y trampas de cebo. Nosotros encontramos 96 taxa de hormigas incluyendo nueve especies no informadas anteriormente en Georgia: Myrmica americana Weber, M. pinetorum Wheeler, M. punctiventris Roger, M. spatulata Smith, Pyramica wrayi (Brown), Stenamma brevicorne (Mayr), S. diecki Emery, S. impar Forel, y S. schmitti Wheeler, además de tres especies aparentemente no descritas (Myrmica sp. y dos Stenamma spp.). Al juntar estos datos con las publicaciones y registros de museos, nosotros aumentamos el número de hormigas conocidas que habitan el suelo en Georgia a un total de 144 taxa.

The state of Georgia in the southeastern United States is characterized by a relatively wide range of soil, topographic and climatic conditions. The eight Major Land Resource Areas (MLRAs) identified in the state are (1) Atlantic Coast Flatwoods, (2) Southern Coastal Plains, (3) Carolina and Georgia Sand Hills, (4) Black Lands, (5) Southern Piedmont, (6) Southern Appalachian Ridges and Valleys, (7) Sand Mountains, and (8) Blue Ridge (USDA-SCS 1981). Each MLRA is characterized by a unique combination or pattern of soils, climate, water resources, and land use. These factors, in turn, affect the biotic communities and habitats as well as the floral and faunal characteristics of each.

The diversity and abundance of ants (Hymenoptera: Formicidae) in Georgia are relatively unknown. Wheeler (1913) published a list of 72 ant species collected in Georgia by J. C. Bradley and W. T. Davis; taxonomic revisions have since decreased this list to 62 species. Since that publication, museum records and collections have been the primary sources of occurrence and distribution of ant species in the state; these data are limited in scope. With the exception of Florida (Johnson 1986; Deyrup 2003) and South Carolina (Smith 1934), surveys for ant species are also limited from areas bordering Georgia.

The objective of the study reported herein was to collect, identify, and catalog ground-dwelling ant species from representative MLRAs in Georgia. Undisturbed habitats were purposely sampled to avoid high population levels of two invasive ant species-Solenopsis invicta Buren and Llnepithema humile (Mayr)-that occur throughout the state and reportedly compete with and displace other ant species (Porter & Savignano 1990; Holway 1999).

MATERIALS AND METHODS

Sample Methods and Sites

Twenty-nine sites were sampled 1 to 4 times between June 2000 and September 2002 for ground-dwelling ants (Fig. 1). Most sites were located in state parks; others were on state-owned properties. The sites represented six of the eight MLRAs identified in Georgia. Information and characteristics of each collection site are listed in Table 1.

Each site was 600 m^sup 2^ and was located in wooded areas and at least 60 m from any paths, roads, or right-of-ways. Sampling methods employed were pitfall trapping, extraction from leaf litter collections, visual searching, and baiting as described by Agosti & Alonso (2000) and Bestlemeyer et al. (2000). For each sampling event, 20 pitfall traps were placed individually at 1-m intervals along a transect. Traps were 40-ml plastic vials filled to 60% of container volume with propylene glycol. The vials were placed in the ground with the upper opening level with the soil surface. The traps remained in the ground for 7 d when they were removed, capped, and transported to the laboratory for processing. Leaf litter was gathered by hand from several locations within the 600 m^sup 2^ site. These were combined and placed in a 50-L plastic bag, stored on ice, and transported to the laboratory. In the laboratory, litter samples were divided and placed in Berlese funnels (Agosti & Alonso 2000) for 24 h to separate ants. Bait stations used were those described by Brinkman et al. (2001). Tuna packaged in oil, was placed in a thin layer over the surface of a 2.5-cm diam filter paper disk (Whatman no. 1) in a plastic Petri dish (10 × 35 mm). Ten stations were placed individually at 2-m intervals along a transect. The stations remained uncovered on the ground for 2 h. They were then covered, placed on ice, and transported to the laboratory for processing. The ground, tree trunks, fallen trees, and other surfaces were visually searched for ants at each sampling time. The total amount of time spent on visual searching was 1.5 h, but varied based on the number of individuals involved in the search. Ants discovered in the visual searches were collected, placed in 70% ethyl alcohol, and transported to the laboratory for processing.

Fig. 1. Georgia sites sampled for ground-dwelling ants, 2000-2002.

TABLE 1. LOCATIONS AND CHARACTERISTICS OF SITES SAMPLED FOR GROUND-DWELLING ANTS IN GEORGIA, 2000-2002. ALL STUDY SITES IN STATE-OWNED PROPERTY (STATE PARKS OR UNIVERSITY OF GEORGIA).

TABLE 2. LIST OF GROUND-DWELLING ANTS COLLECTED IN GEORGIA 2000-2002 SURVEY WITH COLLECTION SITE (S) NOTED.

TABLE 2. LIST OF GROUND-DWELLING ANTS COLLECTED IN GEORGIA 2000-2002 SURVEY WITH COLLECTION SITE (S) NOTED.

In the laboratory, ant specimens were separated and placed in 95% ethyl alcohol. Identifications were made with keys by Bolton (1994, 2000); Buren (1968); Creighton (1950); Cuezzo (2000); Deyrup et al. (1985); DuBois (1986); Gregg (1958); Holldobler & Wilson (1990); Johnson (1988); MacKay (2000); Smith (1957); Snelling (1973, 1988); Snelling & Longino (1992); Taylor (1967); Trager (1984, 1988); Ward (1985, 1988); Wilson (1955); and Wing (1968), and by comparison with specimens housed in the University of Georgia Natural History Museum (Athens, GA). Stefan Cover (The Museum of Comparative Zoology, Harvard Univ., Cambridge, MA) and Mark Deyrup (Archbold Biological Station, Lake Placid, FL) confirmed species identifications. Voucher specimens have been deposited in the University of Georgia Natural History Museum and the Museum of Comparative Zoology at Harvard University.

TABLE 3. SPECIES OF GROUND-DWELLING ANTS PREVIOUSLY REPORTED TO OCCUR IN GEORGIA BUT NOT COLLECTED IN THE 2000-2002 STATE SURVEY.

RESULTS AND DISCUSSION

Ninety-six species of ground-dwelling ants representing 33 genera were collected and identified in this 2-year survey (Table 2). Of those collected, 9 species have not been previously reported from Georgia. These are Myrmica americana Weber, M. pinetorum Wheeler, M. punctiventris Roger, M. spatulata Smith, Pyramica wrayi (Brown), Stenamma brevicorne (Mayr), S. diecki Emery, S. impar Forel, and S. schmitti Wheeler.

Of those previously unreported species, M. americana was collected from 3 sites, M. pinetorum was collected from 1 site, M. punctiventris was collected from 7 sites, and M. spatulata was collected from 2 sites. Ants of this genus nest in soil and in rotting wood and are primarily carnivorous, but they will feed on plant exudates such as nectar (Creighton 1950). In addition, P. wrayi and S. brevicorne were each collected from 1 site, S. diecki was collected from 8 sites, S. schmitti was collected from 5 sites, and S. impar was collected from 2 sites. All Stenamma species are carnivorous, and Pyramica are specialized predators of collembolans (Holldobler & Wilson 1990).

Eleven individuals of Myrmica and 3 individuals of Stenamma, possibly representing two species, were collected from Amicalola State Park in Dawson Co. (site 6) and represent as yet undescribed species (S. Cover, pers. comm.). Those specimens were collected on 2-V-2000, primarily by pitfall trapping and leaf litter collection.

A review of ant specimens deposited in the Archbold Biological Station (ABS), the University of Georgia Natural History Museum (UGANHM), the lists of ants published by Wheeler (1913), and a survey conducted by Jouvenaz et al. (1977) reveal that 48 species of ground-dwelling ants representing 21 genera have been reported from Georgia but were not collected in the survey reported herein (Table 3). To date, these two lists (Tables 2 and 3) comprise the ground-dwelling ant species reported from Georgia. Species collected within the Aphaenogaster picea/rudis/texana complex and the Solenopsis molesta complex are footnoted in Table 2.

In terms of occurrence and distribution, Prenolepis imparis (Say) was collected from 17 of the 29 sites sampled, the Aphaenogaster picea/rudis/ texana complex from 21 sites; the Solenopsis molesta complex from 17 sites, and Crematogaster ashmeadi Mayr from 16 sites in this survey. All other species were collected from less than one-half of the sites. Members of the genus Pheidole were most numerous with 2,765 individuals representing 10 species collected at 14 sites. Dorymyrmex burnei (Trager), D. insanus (Buckley), and Cyphomyrmex rimosus (Spinola) were collected only at southern sites, while Amblyopone pallipes (Haldeman), Ponera pennsylvanica Buckley, and Tapinoma sessile (Say) were collected from sites in northern Georgia. Pseudomyrmex ejectus (Smith) was collected from pitfall traps at one site. Pseudomyrmex spp. are characteristically arboreal in their habits. These specimens most likely dropped to the forest floor, and thus were collected as ground-dwellers. Three species the seed harvester Pogonomyrmex badius (Latreille), the obligate slave raider Polyergus lucidus Mayr, and the generalist Aphaenogaster miamiana Wheeler-were recovered only on Sapelo Island, a barrier island on Georgia's coast.

The survey reported herein provides a basis for various ecological studies and assessments. Ant assemblages, species composition, and community structure are important in terms of community ecology. For example, in Australia, ants are one of the most functionally important faunal groups (Matthews & Etching 1984; Anderson 1992) and are model organisms for studies in community ecology (Anderson 1983,1988,1991; Greenslade & Halliday 1983). Ants also have been used as bio-indicators in mine site rehabilitation (Majer 1983,1985).

Schultz & McGlynn (2000) noted the many interactions that occur between ants and other organisms within habitats. They further postulated that if these interactions are understood, one could predict ecological conditions within a given habitat based upon the presence or absence of specific ants. Furthermore, one could correlate the presence of a specific ant species with specific ecological conditions, and these correlations could be used as predictors of ant biodiversity and interactions among ant species (Alonso 2000).

This survey is the first published listing of ground-dwelling ants in Georgia since Wheeler (1913). This compilation will serve to support biodiversity, systematics, and ecological studies for Georgia and surrounding environs.

ACKNOWLEDGMENTS

Stan Diffie, Vanessa Hammons, and Jeremy Davidson provided technical support. Georgia Department of Natural Resources provided permission to use state parks for collection sites. Stefan Cover (The Museum of Comparative Zoology, Harvard University) and Mark Deyrup (Archbold Biological Station, Lake Placid, FL) verified species identifications, and Cecil Smith of the Georgia Natural History Museum supplied equipment and allowed access to ant specimens.

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