Hymenoptera: Formicidae: Myrmicinae), with the Description of Two New Species
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J. HYM. RES. Vol. 17(1), 2008, pp. 64–82 Revisionary Studies on the Enigmatic Neotropical Ant Genus Stegomyrmex Emery, 1912 (Hymenoptera: Formicidae: Myrmicinae), With the Description of Two New Species RODRIGO M. FEITOSA,CARLOS R. F. BRANDA˜ O AND JORGE L. M. DINIZ (RMF, CRFB) Museu de Zoologia da Universidade de Sa˜o Paulo, Av. Nazare´ 481, Sa˜o Paulo, SP, 04263-000, Brazil; RMF email: [email protected]; CRFB email: [email protected] (JLMD) Campus Jataı´, Unidade Jatoba´, Universidade Federal de Goia´s, BR 364, km 192, Jataı´, GO, 75800-000, Brazil; email: [email protected] __________________________________________________________________________________________________________________________________________________________ Abstract.—The recent increase in leaf litter ants sampling effort in Neotropical wet forests has revealed new and interesting records of the highly specialized myrmicine ant genus Stegomyrmex Emery, previously considered as extremely rare. We present a modified diagnosis for the genus and describe Stegomyrmex bensoni n. sp. and S. olindae n. sp., based on, respectively, workers, males, and gyne (central-north Brazil) and on a single worker (northern Brazil). Stegomyrmex vizottoi Diniz (southeastern Brazil) is redescribed and compared with S. olindae n. sp.; these species present significant differences in size, sculpturation, and sting apparatus morphology. The males of S. vizottoi are described for the first time. A key for workers and queens and a distribution map for the five know Stegomyrmex species are provided. __________________________________________________________________________________________________________________________________________________________ Stegomyrmex is the sole representative of species, S. manni, from Barro Colorado the peculiar and exclusively Neotropical Island, Panama, and agreed with Wheeler’s myrmicine tribe Stegomyrmecini (Bolton placement of the genus in an individual 2003). These ants have been considered tribe. extremely rare by many authors, perhaps Bernard (1951) and Lenko (1965) com- due to their cryptobiotic habits enhanced mented on the morphological resemblance by peculiar soil-binding pilosity (Ho¨lldo- of Stegomyrmex to some Attini. However, bler and Wilson 1986), and by the foraging Brown (1949), Brown and Kempf (1960), technique they employ (Diniz and Branda˜o and Ho¨lldobler and Wilson (1986) consid- 1993). However, recent collections employ- ered stegomyrmecine ants more closely ing large-scale sampling (e.g. Agosti et al. related to Basicerotini than to Attini or 2000) have revealed that they are relatively Dacetini, mainly by the presence of deep common inhabitants of the dense leaf litter antennal scrobes and the soil-binding of Neotropical forests. pilosity. Dlussky and Fedoseeva (1988) Emery (1912) described Stegomyrmex considered Stegomyrmex as incertae sedis with a single species, S. connectens, based in Myrmicinae, without further discus- on a gyne and a male from Peru and sion. However, in the last proposals of Bolivia respectively. Emery included Ste- Bolton (1994, 2003, 2006 et al.), Stegomyr- gomyrmex in the Dacetini based on gyne mex is placed in its own tribe within the characters. Wheeler (1922) established a Myrmicinae. Bolton (2003) commented new tribe, Stegomyrmicini (sic), with Ste- that the structure of the promesonotum gomyrmex as its only member. He separat- may suggest a relationship between Ste- ed it from the Dacetini mainly by the shape gomyrmecini and Pheidolini, but that of mandibles and wing venation. Smith there is no undisputed evidence for this (1946) described the second Stegomyrmex yet. VOLUME 17, NUMBER 1, 2008 65 Lenko (1965) found a worker of S. METHODS vizottoi (identified by him as S. manni)in This study was based on the available the gizzard of a Conopophaga lineata Wied specimens in the collection of the Museu (Aves, Conopophagidae). Ho¨lldobler & de Zoologia da Universidade de Sa˜o Paulo, Wilson (1986) commented on the pre- Sa˜o Paulo, Brazil, which is believed to hold sumed role of the soil-binding hairs of most of the known Stegomyrmex specimens. basicerotine and stegomyrmecine ants in Depository collections are referred to by enhancing their camouflage to predators. the following acronyms: Diniz (1990) was the first to revise the BMNH – The Natural History Museum, taxonomy of Stegomyrmecini, describing London, UK. the third species of the genus, Stegomyrmex CASC – California Academy of Sciences, vizottoi, based on workers and a gyne from San Francisco, California, USA. Brazil and Paraguay. In the same work, CPDC – Centro de Pesquisas do Cacau, Diniz commented on the relatively slow Itabuna, Bahia, Brazil. movements of stegomyrmecine ants. JLMD – Laborato´rio de Zoologia, Cam- Diniz and Branda˜o (1993) were the first to pus Jataı´, Universidade Federal de Goia´s, describe the nesting habits of Stegomyrmex, Brazil. based on observations on colonies of S. vizottoi LACM from Mirassol, state of Sa˜o Paulo, Brazil, – Los Angeles County Museum describing nest architecture, population dis- of Natural History, Los Angeles, Califor- tribution among nest chambers, different nia, USA. workerbehaviorsateachpartofthenest, MCSN – Museo Civico di Storia Natur- and the foraging habits of the workers, which ale ‘‘Giacomo Doria’’, Genoa, Italy. exploit the environment surrounding their MPEG – Museu Paraense Emı´lio Goeldi, nests singly, searching for myriapod eggs. Bele´m, Para´, Brazil. Recent surveys of leaf litter ants in the MZSP – Museu de Zoologia da Uni- Brazilian Atlantic forest and in sparse versidade de Sa˜o Paulo, Sa˜o Paulo, Brazil. localities of central and northern Brazil USNM – National Museum of Natural revealed several Stegomyrmex specimens, History – Smithsonian Institution, Wash- including a remarkable new species de- ington, DC, USA. scribed here, and extending considerably The terms for external morphology and the known distribution range of S. vizottoi. surface sculpturing follow, respectively, Our analysis of S. vizottoi along its distri- Bolton (1994, 2000) and Harris (1979). The bution shows, however, that, as presently terms for wing venation follow Brown and accepted, it includes two distinct species, Nutting (1950). The reproductive females recognizable by the surface sculpture, by are here called ‘‘gynes’’, as suggested by morphometry, and by differences in the De Andrade and Baroni Urbani (1999). sting apparatus, as we fully describe and Measurements were obtained with a comment on below. micrometric reticule and using the scale In this paper we offer taxonomic notes of a scanning electron microscope (SEM). on the peculiar ant genus Stegomyrmex, All measurements are given in mm, and based on the study of the specimens the abbreviations used are: deposited in the Museu de Zoologia da HW: head width; the maximum width of Universidade de Sa˜o Paulo ant collection, the head capsule, measured in full face literature information, and enriched by view, at a median transverse line that unpublished observations. We also de- touches the superior margins of the com- scribe two new species and comment on pound eyes. new records and information regarding HL: head length; the maximum measur- these seldom collected ants. able length of head capsule excluding the 66 JOURNAL OF HYMENOPTERA RESEARCH mandible, measured in full face view, in a in xylene, and then mounted in Canada straight line from the midpoint of the balsam for observation and illustration anterior clypeal margin to the midpoint of under optical microscope. The terms for the vertexal margin. sting apparatus morphology follow Kugler SL: antennal scape length; the chord (1978). length of the antennal scape, excluding Coordinates of localities were obtained the basal condyle and its peduncle. from the information on the specimens WL: mesosoma length (Weber’s length); labels and after consulting the ENCARTA the diagonal length of mesosoma in profile, World AtlasH (Microsoft); they were plot- from the midpoint of the anterior pronotal ted on the distribution map generated by declivity to the posterior basal angle of the the software ArcView 3.2 GISH. metapleuron. When citing label data, we present PL: petiole length; the longitudinal axis additional information between brackets, of petiole in lateral view. explanation of codes on the labels, eventual PPL: postpetiole length; the longitudinal corrections to the misprints, and reference axis of postpetiole in lateral view. to the notebooks from which we took GL: gaster length; the maximum length information regarding the localities and/ of gaster in lateral view, excluding sting. or the biology of the species. TL: total length; the summed length of HL (plus the closed mandibles), WL, PL, RESULTS PPL, and GL. CI: cephalic index. HW x 100/HL. Stegomyrmex Emery, 1912 SI: scape index. SL x 100/HW. Stegomyrmex Emery, 1912: 99. Gyne. Type The SEM images of Stegomyrmex speci- species: Stegomyrmex connectens, by mono- mens were obtained from a single speci- typy. Emery, 1912: 101 (placement in Dace- men of each species. The specimens were tini); Emery, 1914: 42 (placement in Dace- previously cleaned in acetone, critical- tini); Forel, 1917: 246 (placement in Dacetini); point dried in a Balzer (Bal-TecH CPD Emery, 1924: 314 (placement in Dacetini, 030), and sputtered over with gold (Bal- diagnosis, catalogue); Wheeler, 1922: 668 TecH SCD 050). After that, the specimens (establishment of Stegomyrmecini [as Stego- were mounted on the tip of metallic myrmicini]); Donisthorpe, 1943: 727 (place- triangles