Megalomyrmex symmetochus Wheeler

Longino, John T., 2010, A taxonomic review of the ant genus Megalomyrmex Forel (Hymenoptera: Formicidae) in Central America, Zootaxa 2720, pp. 35-58 : 55-56

Megalomyrmex symmetochus Wheeler

( Figs 1 B, 3A, 3C)

Megalomyrmex symmetochus Wheeler, W.M. 1925: 168 , fig. 5. Lectotype worker (designated by Brandão, 1990: 445): Barro Colorado Island, Panama, July 1924 (Wheeler) [MCZ] (not examined). Wheeler,1925: 168, description of queen, male. Wheeler, G. & Wheeler, J., 1955: 126, description of larva. See also: Brandão, 1990: 445.

Measurements. Worker: HW 0.60–0.84, HL 0.75–0.89, SL 0.72–0.82, EL 0.21–0.25, ML 1.03–1.31, CI 88–95, SI 90–93 (n=30, from Brandão, 1990; n=5, current study).

Geographic range. Costa Rica to Panama.

Biology. This species appears to be a specialized associate of small Attini ( Wheeler 1925, Brandão 1990, Adams et al. 2000), a habit shared with other species of Megalomyrmex such as wettereri , mondabora , and adamsae . As defined here, M. symmetochus specializes on Sericomyrmex amabilis Wheeler. Wheeler (1925) found numerous colonies nesting with Sericomyrmex on Barro Colorado Island, Panama. He observed a number of colonies in the lab, and made the following observations (in Wheeler's account M. symmetochus is referred to as Cepobroticus Wheeler, a subgenus erected by Wheeler to contain the single species M. symmetochus , later synonymized with Megalomyrmex by Ettershank [1966]):

“The colonies of the Cepobroticus so frequently found living with Sericomyrmex amabilis were decidedly less populous than those of their host. The largest comprised less than 75 individuals, and often the number did not exceed 40 or 50. In every nest a dealated mother queen was present. She usually took up her station, surrounded by a group of her workers, in one of the crypts of the fungus garden a short distance - half to three quarters of an inch - from the Sericomyrmex queen. The guest ants kept their brood in small clusters scattered through the garden and each cluster was cared for by a few workers. Although the ants and their brood were thus intermingled, the workers of each species lavished their attention exclusively on their own eggs, larvae and pupae and were never seen even to transport the progeny of the other species from one part of the garden to another.

The workers and queens of Cepobroticus are rather alert and move about more rapidly than their hosts. They devote so much time to licking and fondling one another that the observer is somewhat astonished to find them paying little or no attention to the fungus-growers. As a rule the two species are indifferent to one another. One may watch them for hours without observing anything more than rather distant, mutual antennal salutations. On rare occasions a worker Cepobroticus may be seen licking the gaster of a Sericomyrmex worker or of the sluggish queen. More frequently one of the host workers may be observed in the act of lavishing similar but more elaborate attentions on a Cepobroticus worker. The fungus-grower begins by licking the feet or tarsi, the tibiae and femora, then the thorax or abdomen and finally the head and even the mandibles of the guest. During this operation the latter remains motionless and inclines its body somewhat to one side.

The Sericomyrmex never feed their guests by regurgitation. This is not surprising because they never feed one another thus, but resort individually to the growing fungus bromatia. When hungry the Cepobroticus workers and queen also crop the fungus mycelium, but they do this rather roughly, using their mandibles and even shaking or disturbing the substratum. The guests very rarely transport or rearrange the particles of the substratum or take the slightest interest in the garden, except as a source of nourishment. Only on one occasion did I see a Cepobroticus carry a particle of the substratum to another spot, insert it and pat it down with her fore feet. When fresh fruit was introduced into the nest, it was much less frequently visited and eaten by the guests than by their hosts.”

Numerous collections from Pipeline Road and vicinity ( Panama) by R. Adams and colleagues have all been from nests of Sericomyrmex amabilis . At La Selva Biological Station in Costa Rica, alate queens and males have been collected at blacklights. Males and queens were common at the lab clearing blacklight on 4 Aug 1992. A lone worker was obtained by Ronald Vargas, during general collection of ants from trail surfaces and low vegetation.

Material examined. COSTA RICA: Heredia: La Selva Biological Station, 10°26'N, 084°01'W, 50 m, 1 May 1994 (J. Longino); Puntarenas: 15 km SSW Pto. Jimenez, 08°24'28"N, 083°19'41"W, 170 m, mature wet forest, 7 Mar 2010 (J. Longino); PANAMA: Canal Zone: Pipeline Road, 09°09'36"N, 079°44'42"W, 50 m, wet forest, 29 Jul 2005 (R. Adams); Barro Colorado Island, 09°09'N, 079°51'W, 100 m, 12 Dec 2003.

Figures

FIGURE 1. Variation in mandibular dentition among (A) foreli, (B) symmetochus, (C) drifti, (D) incisus, (E) mondaboroides, and (F) silvestrii.