Pheidole bicarinata

From Wilson (2003): P. bicarinata is highly adaptable across its range in both habitat and nest site. In Colorado, Gregg (1963) recorded bicarinata between 1000 and 2100 m, nesting in rotten logs as well as various types of soil beneath stones. The habitats occupied were very diverse, comprising pinyon-cedar and mixed deciduous woodland, canyon-bottom meadows, shortgrass prairie, and sagebrush desert. In Utah and Nevada, bicarinata occurs from sagebrush desert to montane woodland, nesting under stones and pieces of wood, as well as crater nests in open soil (Ingham 1959, 1963; Cole 1966b; Allred and Cole 1979). In western Texas, it has been found in xeric habitats in open soil and under stones, cow dung, a bale of hay, and in cracks in asphalt. Beck et al., studying scavenging ants of Utah, observed workers feeding on dead rodents. Males were found in one Colorado nest in early July. In the eastern United States the species favors sandy soils with some clay content. It is often abundant in open, disturbed grassy areas, such as lawns, golf courses, and abandoned fields (Stefan Cover, personal communication). It is omnivorous in diet, and regularly harvests seeds. Diana E. Wheeler and Frederik Nijhout used bicarinata in their pioneering studies to demonstrate the role of juvenile hormone in the determination of the major and minor subcastes; they traced development through four larval instars (see Wheeler 1991).

Identification
See the description in the nomenclature section.

Distribution
New Jersey to northern Florida and west through Nebraska, Colorado, and Texas to Utah and Nevada. (Wilson 2003)

This taxon was described from the United States.

Habitat
This species has a preference for open sites with sandy soils and habitats that are at the moister end of dry (e.g., grasslands and valley bottoms in arid areas), at least in the west. It also inhabitats sites that have some but not all of these characteristics. Gregg (1963) stated Pheidole bicarinata in Colorado was a Sonoran Zone species. In the eastern US (Carter, 1962; Wilson 2003) this ant is common in fields and open grassy locations, including in ruderal sites (sidewalks, lawns, and along the shoulder of roads).

Nesting Biology
Nests are found underneath ground-covering objects, within rotten downed wood, or in open ground with a small crater mound. Mounds are typically incomplete, resembling a wedge or crescent.

Colony Attributes
Colonies are small, often just a few hundred workers.

Foraging/Diet
Seeds are collected and may be stored in underground granaries that are part of the nest. Workers also visit extraflora nectories.

Other Insects
The two Oresema wasps shown below were found by Stefan Cover with a colony of P. bicarinata  in Arizona (Specimen Labels)

The general biology of Eucharitid wasps are summarized nicely here (Lachaud, J., Cerdan, P. and Pérez-Lachaud, G. 2012 - see the original paper for the citations indicated by the numerals doi:10.1155/2012/393486):

"Within Hymenoptera, the family Eucharitidae (subdivided in three subfamilies: Oraseminae, Eucharitinae, and the Indo-Pacific Gollumiellinae) is the most numerous and diverse group of ant parasitoids [1, 2]. All of the members of this family have a highly modified life cycle [3–6]. Unlike most parasitic wasp species, eucharitid females deposit their eggs away from hosts, in or on plant tissue [2, 7]. The active first instar larva, termed planidium, is responsible for gaining access to the host ant larvae by using various phoretic behaviors including either attachment to an intermediate host (most often a potential ant prey) or to foraging ant workers, with on occasion the presence of attractive substances in or on the eggs [2, 8]. Within the nest, planidia attach themselves to ant larvae, but development is only completed when the host pupates [6, 7, 9, 10]. In almost all of the cases, adults emerge among ant brood (but see [11]) and have to leave the host nest to reproduce. Ants show only moderate aggression to newly emerged eucharitids [7, 12–17] and transport them outside as if they were refuse [11, 15, 17], ultimately enhancing wasp dispersal. Parasitism is very variable and localized in time and space [13, 18, 19]. A very high local prevalence may lead to only a very low impact at the regional scale, suggesting that these parasitoids do not have a major influence on the dynamics of their host population [19]. However, they constitute a remarkable example of both host-parasitoid coevolution and host behavior manipulation."

Description
From Wilson (2003): DIAGNOSIS A member of the “bicarinata complex” belonging to the larger pilifera group and comprising Pheidole agricola, Pheidole aurea, Pheidole bajaensis, Pheidole barbata, Pheidole bicarinata, Pheidole centeotl, Pheidole cerebrosior, Pheidole ceres, Pheidole defecta, Pheidole macclendoni, Pheidole marcidula, Pheidole paiute, Pheidole pinealis, Pheidole psammophila, Pheidole xerophila, Pheidole yaqui and Pheidole yucatana, which complex is characterized by large to very large, forward-set eyes, especially in the minor; and in the major, the occipital lobes lacking any sculpturing (exception: aurea), the posterior half of the head capsule smooth and shiny, and the postpetiole from above oval, elliptical, or laterally angulate (conulate in cerebrosior). P. bicarinata is distinguished within the subgroup by the following combination of traits.

Major: humerus in dorsal-oblique view dentate to subangulate; propodeal spine moderately long and stout; petiolar node in side view tapered; lateral margins of postpetiolar node seen from about acute-angular; anterior fringe of pronotal dorsum transversely carinulate, remainder mostly smooth and shiny; lateral margins of pronotal dorsum carinulate or not; mesonotal dorsum foveolate and opaque to mostly smooth and shiny; dorsum of propodeum foveolate and opaque and carinulate or not.

Minor: humerus in dorsal-oblique view obtusely subangulate; petiole variable in size and shape, from small and equilaterally triangular to moderately elongate. P. bicarinata is a taxonomically difficult species (or, possibly, complex of closely similar species). It is highly variable, especially geographically, in propodeal and pronotal sculpturing, and as suggested above, in development of the propodeal spine, and in color. The variation among different characters is discordant to some degree, and intermediates within the respective characters occur. I believe it prudent for the present to leave the described infraspecific forms as a single species (I am indebted to Philip S. Ward for valuable information and advice on the variation and status of bicarinata).

MEASUREMENTS (mm) Major (Brown Co. State Park, Indiana): HW 1.04, HL 1.14, SL 0.54, EL 0.14, PW 0.52. Minor (Brown Co. State Park): HW 0.54, HL 0.58, SL 0.50, EL 0.12, PW 0.34.

COLOR Major: body varying geographically, from clear yellow in the western parts of the range to brownish yellow to dark brown in the east.

Minor: clear yellow to medium brown.



'''Figure. Upper: “typical” bicarinata major. Lower: “typical” bicarinata minor. INDIANA: Brown County State Park, col. E. O. Wilson. (Lower propodeum is of “vinelandica” variant major from Calvert Cliffs State Park, Calvert Co., Maryland; see description of other variation in Diagnosis and Color.) Scale bars = 1 mm.'''

Type Material
- as reported in Wilson (2003)

Type Locality Information
USA. Illinois.

Etymology
L bicarinata, double-ridged, two-carinal, possibly referring to the carinae of the clypeus. (Wilson 2003)