Nest descriptions of Megalopta aegis (Vachal) and M. guimaraesi Santos & Silveira (Hymenoptera, Halictidae) from the Brazilian Cerrado

Descrição dos ninhos de Megalopta aegis (Vachal) e M. guimaraesi Santos & Silveira (Hymenoptera, Halictidae) do Cerrado

SHORT COMMUNICATION

Nest descriptions of Megalopta aegis (Vachal) and M. guimaraesi Santos & Silveira (Hymenoptera, Halictidae) from the Brazilian Cerrado

Descrição dos ninhos de Megalopta aegis (Vachal) e M. guimaraesi Santos & Silveira (Hymenoptera, Halictidae) do Cerrado

Leandro M. Santos^I,III; Simon M. Tierney^II; William T. Wcislo^II

^ILaboratório de Biologia Comparada de Hymenoptera, Departamento de Zoologia, Universidade Federal do Paraná, Caixa Postal 19020, 81531-980 Curitiba-PR, Brazil. [e-mail]

^IISmithsonian Tropical Research Institute, Apartado Postal 0843-03092, Balboa, Ancón, República de Panamá. [e-mail]; [e-mail]

^IIIPrograma de Pós-Graduação em Entomologia, Departamento de Zoologia, Universidade Federal do Paraná, Caixa Postal 19020, 81531-980 Curitiba-PR, Brazil

ABSTRACT

We present the first data on the nesting biology of Megalopta aegis and M. guimaraesi from southeastern Brazil. Nests were collected in the Área de Proteção Ambiental Água Limpa, Bauru, São Paulo state. Our data suggest that nest architecture is conserved throughout all species of Megalopta. Two nests of M. guimaraesi consisted of a single female with brood. Of three M. aegis nests, two contained single females with brood and the third nest contained three adult females, with three times more brood than any single female nest. This observation suggests that social behavior in M. aegis is facultative, as known for other Megalopta species.

Keywords: Augochlorini; bees; nesting biology; nocturnal.

RESUMO

Apresentamos os primeiros registros da biologia de nidificação de Megalopta aegis (Vachal) e de M. guimaraesi Santos & Silveira, do sudeste do Brasil. Os ninhos foram coletados na Área de Proteção Ambiental Água Limpa, Bauru, estado de São Paulo. Os dados sugerem que a arquitetura do ninho em Megalopta seja conservada entre suas espécies. Dois ninhos de M. guimaraesi continham apenas uma única fêmea com imaturos. Dos três ninhos de M. aegis, dois possuíam uma única fêmea com imaturos e o terceiro ninho continha três fêmeas adultas com três vezes mais imaturos do que nos ninhos com apenas uma fêmea. Essa observação sugere que o comportamento social em M. aegis seja facultativo, semelhante a outras espécies de Megalopta.

Palavras-chave: Abelhas noturnas; Augochlorini; biologia de nidificação.

Megalopta Smith 1853 is a genus of sweat bees (Halictinae, Augochlorini), widespread in the Neotropics below ~1300 m, from central Mexico through northern Argentina (Moure et al. 2007 and references therein). Megalopta are unusual bees in that they forage in dim-light conditions (post-sunset and pre-sunrise) when most other bees do not forage (reviewed in Wcislo & Tierney 2009). Individuals of Megalopta utilize dead wood as nesting substrates, a habit also known in some other augochlorine genera: Augochlora Smith 1853 (Wcislo et al. 2003 and references therein); Neocorynura Schrottky 1910 (Brosi et al. 2006 and references therein) and Xenochlora Engel, Brooks & Yanega 1997 (Tierney et al. 2008a). Xenochlora and Megalopta form a monophyletic group (Engel 2000), which is not closely related to the remaining augochlorine wood nesters, suggesting that this behaviour has independently evolved in Augochlorini at least three times (for a comparative study of augochlorine nesting, see Eickwort & Sakagami 1979).

In Central America, the nesting biology of Megalopta atra Engel 2006, M. ecuadoria Friese 1926 and M. genalis Meade-Waldo 1916 has been described (see Wcislo et al. 2004; Tierney et al. 2008b). The genus shows its highest species richness in South America, yet very little is known about the natural history of Megalopta from this region. Sakagami & Moure (1967) briefly described the nesting habits of one species of Megalopta collected in Jataí, Goiás State, Brazil, although the authors assert that: " it is virtually impossible to make correct identifications of most Megalopta species, because of poor original descriptions by earlier writers, difficulty in comparing type specimens and occurrence of cephalic polymorphism" (op cit., p. 128). Apart from this record, no other work has described the nests of South American Megalopta.

Santos & Silveira (2009) recently concluded a taxonomic review of the Megalopta of Minas Gerais State and here we provide the first description of the nesting biology of Megalopta aegis (Vachal, 1904) and M. guimaraesi Santos & Silveira, 2009 from Brazilian Cerrado. We present these notes as a contribution to understanding the biology and ecology of these dim-light bees.

We collected nests at the end of the dry season (8–11 October 2008) from a protected area of Cerrado habitat, adjacent to the Bauru campus of the Universidade Estadual Paulista São Paulo State, Brazil (Área de Proteção Ambiental Água Limpa: 22°21'S; 49º00'W; altitude: 580m). The Cerrado biome largely consist of tropical savannah interspersed with mosaic patches of forest, woodland and scrubland (Silva & Bates 2002), and we found nests in the understory of Cerradão, a closed canopy forest, typical of the Bauru region (Cavassan et al. 1984).

Collections were made during daylight hours when all nest members were assumed to be present, beginning no less than two hours after sunrise and ceasing at least two hours before sunset. Nests were identified by searching for circular entrance collars (constructed from pith) at the terminal end of dead stems, lianas, and branches (Fig. 1) hanging in the bottom two meters of the forest understory; the entrance collar often has a slightly different colour from the surrounding wood, so nests are often characterized by a conspicuous series of differently-coloured concentric circles. Presence of Megalopta within wood substrates was initially verified in the field, using a medical otoscope to observe the inner nest tunnel. If the tunnel was very clean (with no visible signs of decomposition, fungi or other arthropods) and/or we observed brood cells or an adult bee we then plugged the entrance. Intact nests were cooled to ~ 5º C, to anaesthetize adults, prior to being split longitudinally with a knife. Nest substrate and tunnel dimensions were measured and the number of adults and immatures were recorded and then preserved in ethanol. Substrates were discarded and vouchers of adults were deposited in "Coleção Entomológica Padre Jesus Santiago Moure", Departamento de Zoologia, Universidade Federal do Paraná (UFPR). Photographs were taken using a camera Leica DFC 500 attached to a stereomiscroscope Leica MZ16 and images were treated using the software Auto-Montage Pro (Syncroscopy) of the Projeto Taxon line, Rede Paranaense de Coleções Biológicas of the UFPR.

Five nests of Megalopta were collected in dead tree stems/branches (Fig. 2) ranging in diameter from 29–35 mm (n = 3) for M. aegis, and 19–23 mm (n = 2) for M. guimaraesi. Nests consisted of linear tunnels excavated from the pith (M. aegis: 74–335 mm long, 9–16 mm wide; M. guimaraesi: 54–115 mm long, 8 mm wide), and except for size did not differ from nests of other known Megalopta (see illustrations in Wcislo et al. 2004). Members of this genus possess relatively robust mandibles, and massive mandibular adductor muscles, presumably adapted for the manipulation of wood particles. Most tunnels were un-branched (tunnel width slightly larger than the body width of an adult bee), but for Nest #5 of M. aegis there were two adjacent tunnels (stem diameter = 29 mm). Brood cells were constructed from pith and lined interiorly with a hydrophobic coating. Cells are usually adjacent to and aligned along the same longitudinal axis as the main tunnel, and are accessed via a circular opening, of similar diameter to the nest entrance collar. Multiple cells were often constructed next to each other in a linear end-to-end manner, which together form part of the tunnel wall, even though each cell maintains it own form, which is surrounded and packed with additional pith.

Four of the five nests collected (Nests # 1–4) contained one adult female. No adult males were present in any of the collected nests. All single female nests contained at least two brood cells (maximum of three), one of which was open (in two nests the open cell was being provisioned with pollen), and the remainder contained immature brood. M. aegis single female: Nest #1—one open empty cell, one large larva (Fig. 3); Nest #4—one open cell with pollen being provisioned, one egg. M. guimaraesi single female: Nest #2—one open cell with pollen being provisioned, one pre-pupa; Nest #3—one open empty cell, one large larva, one male pupa (Fig. 4).

The only social colony (Nest #5) contained three M. aegis adult females and seven brood cells with immatures of mixed stages: one open empty cell, one egg, one medium larva, one large larva, one female pupa (Fig. 5) and two male pupae. This latter nest was approximately triple the length (335 mm) of any solitary nest (M. aegis: 74–103 mm; M. guimaraesi; 54–115 mm), with at least a threefold increase in the number of brood (six immatures) compared with solitary female nests (< two immatures—all but one solitary nest contained a single immature).

The nest architecture of M. aegis and M. guimaraesi does not differ in substantial ways from that of other known Megalopta (cf. Wcislo et al. 2004; Tierney et al. 2008b). Thus, it seems that nest architecture is consistent throughout the geographic range of this genus and conserved within the genus. Likewise, the census data from our collections are comparable with data on social organization from other Megalopta (e.g., Smith et al. 2007; Wcislo et al. 2004; Wcislo & Gonzales 2006; Tierney et al. 2008b), in that some nests contained solitary females while one nest contained a small social group, indicating that this behavior is also flexible in this species.

We hope that these data will spur further interest in these bees, as well as other dim-light bee taxa, in particular the rare con-generic social parasite Megalopta (Noctoraptor) Engel, Brooks & Yanega 1997 of which very little is known (Biani & Wcislo 2007), as well as the closest diurnal relative Xenochlora, which also nests in dead tree stems and is restricted to the Amazonian basin (Tierney et al. 2008a). The systematics of the genus Megalopta are currently complicated by the fact that taxonomic descriptions have historically been derived from specimens collected at light traps, rather than from intact nests, and thus intra-specific morphological variation has confounded taxonomic identifications (Sakagami & Moure 1965; Tierney et al. 2008a), and has made it difficult to associate conspecific males and females.

Acknowledgments. We are most grateful to Fátima Knoll, Gabriel A. R. Melo for their hospitality and assistance with fieldwork and Vitor A. Nardino (Taxon line – UFPR) for taking photographs. This work was supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Ministério da Ciência e Tecnologia, Brazil by Masters Fellowship to LMS, an Earl S. Tupper Postdoctoral Fellowship from the Smithsonian Tropical Research Institute (STRI) awarded to SMT and a National Geographic Society Research and Exploration Grant to WTW and SMT, and general research funds from STRI to WTW.

Received 06/03/2009; accepted 16/04/2010

Editor: Eduardo Andrade Botelho de Almeida

• Biani, N. B. & W. T. Wcislo. 2007. Notes on the reproductive morphology of the parasitic bee Megalopta byroni (Hymenoptera: Halictidae), and a tentative new host record. Journal of the Kansas Entomological Society 80: 392394.
• Brosi, B. J.; A. H. Smith-Pardo & V. H. Gonzalez. 2006. A new wood-nesting Neocorynura (Hymenoptera: Halictidae: Augochlorini) from Costa Rica, with notes on its biology. Zootaxa 1189: 5568.
• Cavassan, O.; O. Cesar & F. R. Martins. 1984. Fitossociologia da vegetação arbórea da Reserva Estadual de Bauru, Estado de São Paulo. Revista Brasileira de Botânica 7: 91106.
• Eickwort, G. C. & S. F. Sakagami. 1979. A classification of nest architecture of bees in the tribe Augochlorini (Hymenoptera: Halictidae; Halictinae) with a description of a Brazilian nest of Rhinocorynura inflaticeps Biotropica 11: 2837.
• Engel, M. S. 2000. Classification of the bee tribe Augochlorini (Hymenoptera: Halictidae). Bulletin of the American Museum of Natural History 250: 189.
• Moure, J. S.; D. Urban & G. A. R. Melo. 2007. Catalogue of Bees (Hymenoptera, Apoidea) in the Neotropical Region Curitiba, Sociedade Brasileira de Entomologia, 1058 p.
• Sakagami, S. F. & J. S. Moure. 1965. Cephalic polymorphism in some Neotropical halictine bees. Anais da Academia Brasileira de Ciências 37: 303313.
• Sakagami, S. F. & J. S. Moure. 1967. Additional observations on the nesting habits of some Brazilian halictine bees (Hymenoptera: Apoidea). Mushi 40: 119137.
• Santos, L. M. & F. A. Silveira. 2009. Taxonomic notes on Megalopta Smith, 1853 (Hymenoptera: Halictidae) with a synopsis of the species in the state of Minas Gerais, Brazil. Zootaxa 2194: 120.
• Silva, J. M. C. & J. M. Bates. 2002. Biogeographic patterns and conservation in the South American Cerrado: a tropical savanna hotspot. BioScience 52: 225233.
• Smith A. R.; W. T. Wcislo & S. O'Donnell. 2007. Survival and productivity benefits to social nesting in the sweat bee Megalopta genalis (Hymenoptera: Halictidae). Behavioral Ecology and Sociobiology 61: 11111120.
• Tierney, S. M.; T. Gonzales-Ojeda & W. T. Wcislo. 2008a. Nesting biology and social behavior of Xenochlora bees (Hymenoptera: Halictidae: Augochlorini) from Peru. Journal of the Kansas Entomological Society 81: 6172.
• Tierney, S. M.; T. Gonzales-Ojeda & W. T. Wcislo. 2008b. Biology of a nocturnal bee, Megalopta atra (Hymenoptera: Halictidae: Augochlorini), from the Panamanian highlands. Journal of Natural History 42: 18411847.
• Wcislo, W. T.; L. Arneson; K. Roesch; V. Gonzalez; A. R. Smith & H. Fernández. 2004. The evolution of nocturnal behaviour in sweat bees, Megalopta genalis and M. ecuadoria (Hymenoptera: Halictidae): an escape from competitors and enemies? Biological Journal of the Linnean Society 83: 377387.
• Wcislo, W. T. & V. H. Gonzalez. 2006. Social and ecological contexts of trophallaxis in facultatively social sweat bees, Megalopta genalis and M. ecuadoria (Hymenoptera, Halictidae). Insectes Sociaux 53: 220225.
• Wcislo W. T.; V. H. Gonzalez & M. S. Engel. 2003. Nesting and social behavior of a wood-dwelling Neotropical bee, Augochlora isthmii (Schwarz), and notes on a new species, A. alexanderi Engel (Hymenoptera, Halictidae). Journal of the Kansas Entomological Society 76: 588602.
• Wcislo W. T. & S. M. Tierney. 2009. Behavioural environments and niche construction: the evolution of dim-light foraging in bees. Biological Reviews 84: 1937.

Publication Dates

• Publication in this collection
  19 July 2010
• Date of issue
  June 2010

History

• Received
  06 Mar 2009
• Accepted
  16 Apr 2010