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|Revived from synonymy: Quinet, Hamidi, et al. 2009: 45.|
A wingless third caste exists in several species of Orthocrema. Eyes, ocelli, thorax and overall size are intermediate between winged queens and workers. Ovaries are bigger than in workers but there is no spermatheca. Many unfertilized eggs are laid which suggests a trophic function in colonies.
Fig. 1 (A -E)
Accepted by J. Pitts: 19 Mar. 2009; published: 17 Apr.
Taxonomic conclusions are based on abundant collections and natural history observations from Fortaleza, State of Ceará, Brazil. These collections were compared directly with the types of C. pygmaeaHNS. These are the only collections of C. pygmaeaHNS known to date. Crematogaster pygmaeaHNS is very close to the widespread C. abstinensHNS. Both species occur sympatrically in Fortaleza, where they are clearly distinct.
FIGURE 1. Crematogaster pygmaeaHNS worker: (A) face view, (B) lateral view; queen: (C) face view, (D) lateral view. Imaged worker and queen from one colony, Fortaleza, unique pin code JTLC000003537. E. comparison of worker mesosoma of C. pygmaeaHNS (left) and C. abstinensHNS (right). Note shorter propodeal spine and shinier lateral pronotum of C. pygmaeaHNS.
Crematogaster pygmaeaHNS and C. abstinensHNS are uniquely characterized by the combination in the worker of (1) shiny face, (2) subquadrate dorsal face of petiole, (3) appressed tibial pilosity, (4) very wide postpetiole, (5) abundant short stiff setae on face that curve toward the median axis, and (6) complete absence of an anteroventral petiolar tooth. Crematogaster pygmaeaHNS differs from C. abstinensHNS in shorter propodeal spines. The propodeal spines of C. pygmaeaHNS are relatively triangular in shape, not spiniform, and slightly longer than the maximum diameter of the propodeal spiracle. The propodeal spines of C. abstinensHNS are spiniform and about twice as long as the maximum diameter of the propodeal spiracle (Fig. 1G). Another difference in the zone of sympatry is that C. abstinensHNS has a more heavily sculptured promesonotum, particularly near the juncture of dorsal and lateral surfaces. However, in other parts of the range of C. abstinensHNS this character is variable and approaches the condition seen in C. pygmaeaHNS. Crematogaster obscurataHNS is also similar to these species but has a punctate face.
Measurements of a worker and a queen were made with a micrometer stage with accuracy to the nearest 0.01 mm.
Worker: HL (head length; perpendicular distance from line tangent to rearmost points of vertex margin to line tangent to anteriormost projections of clypeus, in full face view) 0.565, HW (head width; maximum width of head in face view, including eyes if they project beyond the sides of the head) 0.604, SL (scape length; length of scape shaft from apex to basal flange, not including basal condyle and neck) 0.436, EL (eye length, measured along maximum diameter) 0.174, WL (Weber's length; viewing mesosoma in lateral profile, distance from approximate inflection point, where downward sloping pronotum curves into anteriorly projecting neck, to posteroventral propodeal lobes) 0.609, SPL (propodeal spine length; measured from tip of propodeal spine to closest point on outer rim of propodeal spiracle) 0.076, PTH (petiole height; viewed in lateral profile, perpendicular distance from ventral margin to highest point of posterolateral tubercles) 0.124, PTL (petiole length; viewed in lateral profile and measured in same plane as anterodorsal face, distance from inflection point marking juncture of posterolateral lobes and cylindrical posterior portion of segment to anterior inflection point where petiole curves up to condyle) 0.217, PTW (petiole width; maximum width of petiole in dorsal view) 0.217, PPL (postpetiole length; viewed dorsally, perpendicular distance from narrowest point of peduncle joining postpetiolar node and helcium, to line tangent to posteriormost lobes) 0.155, PPW (postpetiole width; maximum width of postpetiole, in same view as and perpendicular to postpetiole length) 0.201.
Queen (previously undescribed): HL 0.998, HW 1.330, SL 0.671, EL 0.364, WL 2.402, PTH 0.399, PTL 0.538, PTW 0.574, PPL 0.431, PPW 0.643.
Natural History Observations
The state of Ceará belongs to the "caatinga" domain, a 750,000 km2 area of northeastern Brazil with a semi-arid climate. Temperature varies little, with an annual average of approximately 26oC, and rainfall is low (less than 750 mm/year). Rainfall is concentrated in three consecutive months during the southern hemisphere summer (November until June). Crematogaster pygmaeaHNS occurs in two phytogeographic zones: the littoral zone stricto sensu and the adjacent savana-like formation called "tabuleiro." The first is a narrow strip of coastal vegetation along the seashore, with dune and mangrove formations. The tabuleiro is a savanna-like formation that occurs close to the coast, on flat sandy plains of northeastern Brazil. The physiognomy of the "tabuleiro" is characterized by dense patches of trees and shrubs surrounded by a grassy cover with scattered low shrubs (Oliveira-Filho 1993). All the observed C. pygmaeaHNS colonies were found in these two zones. Colonies could be found very near the sea, in completely sandy areas with only grassy cover. Crematogaster pygmaeaHNS was never found in the "caatinga" zone, a seasonal xerophilous thorn woodland/shrubland that prevails on the semi-arid lowlands and covers most of Ceará state.
Detailed observations were made of four C. pygmaeaHNS colonies (I, II and III, IV) at sites situated on or near the campus of the State University of Ceará (3o 47' S - 38o 33' W), in Fortaleza (state of Ceará, northeastern Brazil), about 7 km from the coast. The campus itself is located in the tabuleiro zone. In the study sites the original vegetation was modified by human activities, being in the campus and Fortaleza urban areas.
Colony I was located on the campus, in a sandy/clayey area with patches of mango or cashew trees surrounded by dense herbaceous cover. Very close to colony I and physically separated from it by an asphalt road, colony II was in a more open area. The area had rows of square beds with fodder plants (see Fig. 2) separated by sandy/clayey areas covered with sparse herbaceous vegetation. Patches of mango trees, sugar cane and dense herbaceous vegetation surrounded it. Colony III was located on the campus, some 800m from colonies I and II, in an open sandy/clayey area with only herbaceous cover. Colony IV was located outside, but close to the campus, in an open area covered with dense herbaceous vegetation and patches of low shrubs surrounding sports (football) grounds.
Detailed maps of colonies I and II were made in July 1999 and October 2006, respectively. To facilitate mapping of colony I, a grid of 0.5m squares was marked out on the whole colony area, using string. The rows of square beds served as references to map colony II (see Fig. 2). All the nest entrances and trails of the two colonies, as well as the plants visited by C. pygmaeaHNS workers for food sources, were precisely mapped. Each plant visited by C. pygmaeaHNS workers was carefully inspected to identify the food sources explored by the ants.
Colony I extended over an area about 26 by 10m (Fig. 2). It consisted of 36 nest entrances connected by nearly 104m of trails that also led the workers to plants where they explored liquid sugary food sources (nectar or honeydew). One hundred herbaceous plants were visited by ants. Nearly 50 % of them (N = 46) were Borreria verticillata G. Mey. plants (Rubiaceae) whose floral nectaries were explored by C. pygmaeaHNS workers. Some B. verticillata plants also had scale insects ( CoccidaeHNS) colonies attended by ants for their honeydew production. The second and third most visited plants (N = 27 and 12 respectively) were two unknown Cyperaceae species where C. pygmaeaHNS workers attended scale insect colonies. On the remaining plants (N = 15) (Commelina sp. - Commelinaceae; Mimosa sensitiva L. - Mimosaceae; Turnera subulata Smith - Turneraceae; one unknown species of Papilionaceae; one unknown species of Cyperaceae; one species of unknown family) ants explored sugary secretions from scale insects, aphids ( AphididaeHNS), and/or extrafloral nectaries.
Colony II had roughly the same size (about 30 by 8m) and consisted of 62 nest entrances connected by nearly 75m of trail network (Fig. 2). More than 50% of the 97 herbaceous plants visited by ants (N = 54) were T. subulata plants (white alder), a common ruderal plant in northeastern Brazil. The petiole of T. s ubu la ta leaves has two large apical extrafloral nectaries that were explored by C. pygmaeaHNS workers. The second most visited plant was B. verticillata (N = 27) whose floral nectaries and, sometimes, aphids or scale insect colonies were explored by ants. The remaining plants belonged to Asteraceae, Euphorbiaceae, Fabaceae, Plumbaginaceae and Poaceae families and had scale insect colonies attended by ants.
In each colony, one or two groups of nest entrances were disconnected from the main group (Fig. 2). They probably represented colony disjunctions, since preliminary observations showed that the trail network of a C. pygmaeaHNS colony is an unstable structure that undergoes size and shape modifications with time. For example, during the dry season the trail network undergoes a great size reduction.
In order to investigate nest architecture and composition, 72 C. pygmaeaHNS nests were excavated: 20 from colony I, in June and July 2002; 37 from colony II, in June 2003; and 25 from colony IV, in May 2006. For the nests of colony I and the first ten nest excavations of colony II, only queen number and brood presence (colony I), or number and depth of chambers per nest were recorded (colony II). More detailed observations were made with the remaining nests of colony II and those of colony IV: nest depth, number of chambers per nest, depth and size of chambers, number of queens per chamber and presence of brood in chambers. Nest excavation was carried out by digging a deep soil parallelepiped (20 x 20 x 40 cm), with the nest entrance in its center. The whole parallelepiped was carefully laid down on a plastic sheet, and then cut into thin slices with a spatula, starting from the side with the nest entrance. Depth and, when possible, size of each chamber was recorded, as well as the queen number and presence of brood. Thirteen of the 34 active nests (i.e. with at least workers) excavated in June 2003 were brought to the laboratory to count the queens and workers. Finally, the diameter of 52 nest entrances from 4 colonies (colony I, II, I V, and a fifth one) was measured in March 2003 and April 2008.
Eleven to 40% of the excavated nests were inactive (Table 1), meaning that there was neither gallery nor chamber below the nest entrance, in spite of workers entering and exiting the nest entrance. Of the remaining, active, nests (i.e. with gallery, chambers, and at least workers in the chambers), almost all (92-100%) contained brood, and 47-71% contained at least one queen (Table 1). Colonies were clearly polygynous (Table 1), with some nests containing more than 10 queens.
Number of excavated nest
Specimen Habitat Summary
Found most commonly in these habitats: 1 times found in tabuleiro' (savanna).
Found most commonly in these microhabitats: 1 times ex soil, 1 times nesting in ground in sandy soil.
Elevations: collected at 30 m
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