Cyphomyrmex costatus Mann

Kempf, W. W., 1966, A revision of the Neotropical fungus-growing ants of the genus Cyphomyrmex Mayr. Part II. Group of rimosus (Spinola) (Hym. Formicidae)., Studia Entomologica (N. S.) 8, pp. 161-200 : 172-177

4. Cyphomyrmex costatus Mann

(Figs. 10, 19, 38, 48)

Cyphomyrmex costatus Mann , 1922: 44-5 (Worker; Honduras: Lombardia) - Weber 1940: 408, figs. 1-2 (Worker; key). - Weber, 1941: 104-6, pl. 2 (Panama Canal Zone: Barro Colorado Island; Bion.). - Weber, 1956 (1958): 723 (Bion.). - Weber, 1957a: 480-94, figs. 1-5 (Panama Canal Zone: Barro Colorado Island; Panama; Cerro Campana; Bion.). - Weber, 1957b: 638 (Bion.).

Cyphomyrmex colombianus Weber , 1940: 408, 413-4 (Worker; Colombia: Rio Porce, El Hormiguero Mine). - NOV. SYN.

Cyphomyrmex strigatus : G. C. Wheeler, 1948 (nec Mayr, 1887): 669-70, pl. 2, figs. 7-8 (Larvae; Panama Canal Zone).

Types. - 3 workers collected by W. M. Mann in rotten wood, presumably deposited in the U. S. National Museum; not seen. Holotype worker (unique) of colombianus in the N. A. Weber collection; not seen. One of the three isolated females of colombianus , not described but mentioned by Weber (1940: 414), taken at the same locality as holotype, was examined (NAW).

Worker. - Total length 2.1-2.4 mm; head length 0.56- 0.61 mm; head width 0.51-0.56 mm; thorax length 0.67-0.75 mm; hind femur length 0.48-0.56 mm. Light brown; dorsum of head and gaster fuscous reddish brown. Integument densely granulose, opaque, with larger, shallow, scattered pits, visible on head and gaster. Antennal scrobe superficially reticulate-punctate and somewhat shining.

Head as shown in Figs. 10 and 19. Anterior apron of clypeus flattened, gently convex, mesially notched, laterally acutely dentate. Frontal lobes semicircular, greatly expanded, covering cheeks in full-face view. Frontal carinae moderately diverging caudad. Occipital corners lobate, not foliaceous, somewhat projecting. Vertex with a pair of carinae that diverge cephalad. Preocular carina fading out above eyes. Postero-inferior border of antennal scrobe bluntly marginate between upper orbit of eye and occipital lobe. Lower border of cheeks bluntly marginate. Eyes with 5-6 facets across greatest diameter. Supraocular tumulus either vestigial or distinct. Scape greatly attenuated at base, strongly incrassate apicad, not projecting beyond scrobe when in repose. Funicular segments II-VIII rather broader than long, IX about as long as broad.

Thorax as shown in Fig. 19. Pronotum lacking mesial tubercles on disc, a small tubercle postero-laterally on each side, just behind the vestigially marginate lateral border of disc; antero-inferior corner of pronotum rectangular. Mesonotum dorsally with a shallow longitudinal impression, flanked on each side by a prominent, bluntly edged carina, which is slightly sigmoidal in dorsal view. In side-view, the carina is feebly impressed just behind the half. Mesoepinotal groove broadly and rather deeply impressed. Basal face of epinotum with a similar longitudinal impression, flanked on each side by a blunt ridge, which slightly diverges caudad; its posterior corner forming a rectangular tooth in side-view. Declivous face laterally unarmed. Epinotal spiracle situated on a vestigial oblique carina. Femora, especially hind femora, postero-ventrally crested, bearing at basal third a broader foliaceous lobe (Fig. 48). Tibiae subprismatic.

Pedicel as shown in Figs. 19 and 38. Petiolar node trapezoidal in dorsal view, broadest in front with rounded corners, its dorsum flattened, with a short, prominent median laminule on posterior border. Postpetiole also slightly broader than long, with a distinct anterior face at right angle to dorsal face, haying a median oval depression flanked by blunt, divergent ridges, bearing a vestigial tumulus on anterior, a more distinct and flat one, on posterior end. Tergum I of gaster with four longitudinal, coarse and blunt carinae; both lateral and median carinae becoming obsolete somewhat in front of posterior border.

Pilosity scarce, consisting of minute, decumbent, silvery hairs on body and appendages.

Female (undescribed). - Total length 2.8-3.0 mm; head length 0.64-0.72 mm; head width 0.59-0.64 mm; thorax length 0.83-0.88 mm; hind femur length 0.62-0.64 mm. Quite similar to the worker, with the following differences of the caste: Compound eyes with about 10 facets across greatest diameter. Ocelli small, anterior ocellus between anterior end of carinae on vertex, lateral ones on the outer face of the same carinae. Lateral pronotal tubercles well developed. Mesothoracic scutum with a pair of short antero-mesial ridges, starting at anterior border and fading out at the half of the length of scutum. Postero-laterally, a pair of ridges that start at the transcutal suture going forewards to the antero-lateral border, lateral border slightly upturned. Scutellum not separated by sutures from the tubercular and slightly prominent paraptera; posteriorly, the scutellum is bilobate. Epinotal spines prominent, in side-view as long as deep at base, compressed, bluntly tipped. Postpetiole more transverse than in worker. Wings somewhat infuscated, with the usual venation.

Male still undescribed. I leave the diagnosis of this caste for another occasion, when it will be possible to treat it comparatively.

Distribution. - The territory inhabited by costatus , as presently known, extends from Honduras in Central America to the Cordillera Central in northern Colombia.

Specimens examined: 9 worker, 5 females and 7 males, as follows: Panama Canal Zone: Barro Colorado Island, June 1955, N. A. Weber leg. 4 workers, 1 female (NAW n. 3483, 3488); same locality, June-October 1943, Zetek leg. 3 workers (MCZ); same locality, January 1960, W. L. Brown, Jr. & E. S. McCluskey leg. 2 workers, 3 females, 7 males (the latter taken in nuptial flight) (MCZ, WWK). - Colombia, Cordillera Central, Rio Porce, 1020 m, 1938, N. A. Weber leg. 1 female (paratype of colombianus ) (NAW n. 981).

Discussion. - This is the smallest species of the genus, easily recognized, being the only form in the rimosus-group having four longitudinal carinae on tergum.1 of gaster. The closest relative is wheeleri , from which it was already distinguished on a foregoing page.

Synonymy. - Prof. Weber based his colombianus on a lone worker found at El Hormiguero Mine, on the slope of the Cordillera Central bordering the Rio Porce, Colombia. A little later, he also discovered three dealate females, not yet described, apparently belonging to the same species. The colombianus worker is said to differ from costatus is somewhat larger size, darker color and shallower mesoepinotal groove. One of the females, received on loan, proved quite similar to the known costatus females, except for larger size: total length 3.2 mm; head length 0.78 mm; head width 0.67 mm; thorax length 0.88 mm; hind femur length 0.69 mm. Inasmuch as size alone seems so far to be the only palpable difference between both forms, and as such not very impressive, 1 propose to place colombianus into synonymy of costatus .

Bionomics. - The types of the species were found by Mann in rotten wood. No further detail is given.

The bulk of our information has been gathered by Weber, who, in successive studies (1941-57), was able to elucidate many aspects of its biology, so that in this regard costatus is one of the best known species of the genus.

Weber's observations were made in Panama, principally on Barro Colorado Island. There, the ants are not uncommon, although seasonal scarcity, due to dry seasons and different stages of the wet season, has been observed. The nests are found in the soil, under stones or rotten wood. The cells, elliptical in shape, are of variable size, according to colony development. 8X5, 15X10, 32X13 and 30X20 mm with a maximum height of 10 mm are the dimensions obtained by actual measurements in the field.

The fungus garden is bluish gray in color, friable, and crumbles easily. In nature, the garden, though sessile, is in part supported by rootlets. The substrate, consisting of vegetable debris, is strengthened by quartz sand grains, parts of insect skeletons, notably of ants (Weber gives a list of parts from a variety of species), forming the frame work of the fungus-garden.

In artifical cultures, the ants accepted as substrate dried fecal pellets of caterpillars, rose stamens, and cassava granules dusted with yeast extract. The material collected in Panama, in June 1955, was taken to the U. S. by Prof. Weber, who studied the factors responsible for the production and maintenance of thriving cultures of fungi in ant gardens, despite continual possibilities for contamination. The most striking result of this important research consisted in the development, from artifical cultures, of the sporophore or fruiting stage of the fungus cultivated by costatus . This was identified by two specialists as a new species belonging to the agaric genus Lepiota.

Individual colonies, always monogynous, may contain from 20 up to nearly 100 workers. Individual behavior, like "jigging" and grooming was likewise observed (cf. Weber, 1957: 484).

Finally, the ant Megalomyrmex wheeleri Weber was found living in symbiotic relationship with Cyphomyrmex costatus . The former, apparently feeding on the fungus, occurred in 4 nests of the latter. In two nests, there was only a queen of Megalomyrmex , in the remaining nests a queen with numerous workers of her own species. In all cases, the guests lived in a separate cell which, however, communicated with the cell containing the fungus garden. The host species did not disturb the guest. Due to adverse conditions, the study of this relationship could not be carried to completion.

Notes. - The larvae described under the name of C. strigatus by G. C. Wheeler (1948: 669-670) certainly belong to the present species. Both strigatus and costatus have four longitudinal costae on gaster, but the former does not occur in Panama.

The figures for this species have been drawn to a larger scale, as compared with the rest of the drawings. So the striking difference in size is not readily apparent.