Megalomyrmex wallacei Mann, 1916

Brandão, Carlos Roberto F., 2003, Further Revisionary Studies On The Ant Genus Megalomyrmex Forel (Hymenoptera: Formicidae: Myrmicinae: Solenopsidini) C R F. B Abstract, Papéis Avulsos de Zoologia (São Paulo) 43 (8), pp. 145-159 : 149-150

Megalomyrmex wallacei Mann, 1916

This species has been previously recorded only in the states of Amazonas and Rondônia in Brazil. Recently the MZSP received several samples from this species after the publication of my 1990 revision, extending M. wallacei known distribution. I had already commented on the extreme variation of the sculpturing pattern shown by specimens of M. wallace i, but should add that even the mandibles can be completely shiny and smooth, especially in samples from the northern part of its distribution.

From the Brazilian state of Amazonas I studied the following new material: twelve workers from Lago Jacaré , Manacapuru (3°28’S, 45°18’W), collected by Boris Malkin in March 26 to 28, 1963, ( MZSP); four workers from Rio Tarumã-Mirim , Igapó (3°02’S, 60°11’W), collected by Joaquim Adis in January 6, 1977 (pitfall traps BoF-TM # 42 and 32) (determined as M. wallacei by Roy R. Snelling) ( LACM), two workers, one collected in Novo Airão, Rio Unini , right margin of Igarapé Acajuri (01°38’25”S, 61°39’19”W), “mata primária”, in November, 20 to 23, of 1995 by Bindá & Alencar (pit-fall trap # 8), and the other from the same locality, date and collectors, at the left margin of a lake (Lago Pedras, 01 38’25”S, 61°39’19”W), also in “mata primária” (pit-fall trap # 10) ( INPA). From the CPDC collection (# 794), I studied a worker collected by Dr. Forbes Benton in Reserva Ducke , Manaus, in April, 1991 .

From Pará state, I studied two workers from Tucurui (Berro d’Água) (3 42’S, 49°27’W), collected in August 18, 1979 by W.L. Overal .

I collected several workers, four gynes and three males (see description below) from four colonies, in September 27, 1987, Maracá Island (3°25’S, 61 40’W), near “Furo do Igarapé Firmino”, more precisely near the mouth of this small creek into the Uraricoera river , state of Rodônia , Brazil. The colonies with up to 300 workers, one gyne, and immatures, live under dead leaves of the litter. Workers keep the larvae in between the mandibles. When disturbed, they spread out to rejoin after some minutes under a different leaf .

R. R. da Silva and N.L. de Albuquerque obtained three workers of M. wallacei from a 1 m 2 sample of litter, submitted to Winkler extractor, taken from a gallery forest inside the savanna (cerrado) in Palmeirante, Tocantins state (formerly the northern half of Goiás state), Brazil (07 52’25”S, 47°57’07”W) in December 10 to 15, 2001. This sample represents the eastern record of the species and shows the smallest values in all measurements for workers of M. wallacei .

From J. Longino, I received ten workers and a male from Estación Biologica La Selva, Heredia, Costa Rica, 50 to 150 m of altitude (10 26’N, 84°01’W); eight workers with the same label: “ Apr. 1994, INBIO-OET (N. Barger & J. Longino baiting study NNB/PLT 02)” ; one worker bears the label “ J. Longino # 3733”, and the male label says: “ 17 Ene 1993 bosque secundario M/00/002”. Longino has also collected 2 workers from Rupununi , Karanambo, Guyana (3 45’N, 59°20’W), 100 m elevation, in January 16, 1981 .

From the CPDC collection (# 991), I studied a worker collected in Cerro Pirre, Darien, Panamá in August 26-30, 1991 by R. Ruiz .

F. Fernández ( IHVL) kindly loaned me the first Colombian samples of M. wallacei : four workers collected in Parque Nacional Utria, Chocó province (06 01’01”N 77°20’66”W) Ensenada, Bosque Abierto, in May 21, 1991 by M. Baena (labels says 77°20’66”N, instead of W), and Caparu Igapo, Vaupes province 100 m elevation, “Ex humus 1 cm ”, by D. Forero in December 1, 1995. One additional worker from the same locality bears a label saying: Colombia, Guajira?, collected from March to June, 1981 by J. Rincón. Also from IHVL collection, I studied a worker from Valle del Cauca, Parque Nacional Farallones de Cali, Embalses de alto Anchicaya (03 26’N, 76°48’W), 750 m, W2, collected in October 13, 2000 by S. Sarria and others. The integument of the specimen is completely smooth and it is rather small for a M. wallacei . However, the specimens show all the other characters diagnosing this species, being now also known from Eastern Colombia. Megalomyrmex modestus from the Modestus species group was recorded at this site, but M. modestus workers are easily separated from M. wallacei workers by the characters discussed by Brandão (1990).

Gynes

In the 1990 revision, I stated that the gyne bodies are totally covered by rough punctures. However the samples studied and described herein furnished gynes with bodies mostly smooth and shining, while other individuals from other localities have bodies totally sculptured, or with intermediates between these conditions. In general, workers and gynes from the same colony share the same sculpturing pattern. In Maracás, for instance, the propodeal faces of both workers and gynes are covered by coarse transverse reticulations.

Males (first description)

Clypeus not swollen, smooth; mandibles smooth with four large teeth in the cutting edge, with some small denticles superimposed on the large ones; three equally developed ocelli with surrounding coarse sculpture; head otherwise smooth and shining, as the rest of the body; 2 nd to 5 th funicular segments darker than the others; mesonotum with parapsidial furrows, and notaulus; propodeum declivity much longer than basal face, declivity bears 3-4 concentric rugosities over the foramen and a complete epipetiolar carina; petiolar node compressed antero-posteriorly, with the lateral angles produced laterally; ventral process of postpetiole globose.

Leoninus group

In my 1990 paper, I said that instead of true winged gynes, members of this group present gamergates as the sole female reproductives. Although true winged gynes of the Megalomyrmex of the Leoninus group of species have never been found, yet the current nomenclature for wingless gynes in the Myrmicinae applies the term “ergatoids” to similar cases, meaning they are modified evolutionary descendants of winged gynes (see revision in Hölldobler & Wilson, 1990). However, until now I am not aware of any detailed study of the reproductive biology of any species of Myrmicinae in which the female reproductives are similar in size and shape to the sterile workers – a phenomenon that seems to be more common than previously believed.

In any case, permanent wingless female reproductives affect speciation, dispersion rates, and intraspecific variation, making the specific recognition rather problematic in this group of species. I would like to point out what I consider to be one of the most important results of wingless females, namely that colonies of Megalomyrmex of the Leoninus group of species do not construct or excavate nests, but rather occupy pre-formed spaces among rocks, under bark or within the leaf litter, readily moving away immatures when disturbed. This behavior also prevents their establishment in laboratory nests; in my experience there are no other myrmicine ants as difficult to keep in laboratory conditions as the species belonging to this group. As soon as they are transferred to artificial nests, each worker grabs an immature (or a group of them [if they are small enough]), and runs away to the nearest hiding place without any apparent coordinated behavior, to join nestmates only by chance afterwards.

In relation to the brief characterization provided in 1990 for females of this group, I should add that in larger specimens it is often possible to observe the small mesonotum spiracle openings, at the anterolateral dorsal border of the metapropodeal sulcus.

Jones et al. (1999) described the pyrrolidine alkaloids found in extracts of two species in this group, M. cyendyra Brandão and M. latreillei Emery. Pyrrolidines are well known venom components of other myrmicine ants in general and have been detected also in M. leoninus .