Nests of Centris tarsata Smith, 1874 were obtained from trap-nests in areas of dry semi-deciduous forest (Baixa Grande) and caatinga (Ipirá), in the State of Bahia. Nesting occurred in bamboo canes and in tubes of black cardboard with 5.8 cm (= small tube) and 10.5 cm (= large tube) in length and 0.6 and 0.8 cm in diameter, respectively. In both areas C. tarsata nested during the wet season producing four generations in Baixa Grande and three generations in Ipirá. The immatures of one generation underwent diapause at both sites. The bees constructed their nests with a mixture of sand and oil. In general, the cells were elongated and arranged in linear series with its opening pointing towards the nest entrance. Completed nests had two to three cells in small tubes, one to seven cells in large tubes, and two to 13 cells in bamboo canes. The nest plug resembled an uncompleted cell and was externally covered with oil. The cells were provisioned with pollen, oil, and nectar. Nests were parasitized by Mesocheira bicolor (Fabricius, 1804) (Hymenoptera: Apidae) and other not identify bee species.
Ninhos de Centris tarsata Smith, 1874 foram obtidos através da utilização de ninhos-armadilha, em áreas de floresta estacional semi-decídua (Baixa Grande) e de caatinga (Ipirá), no Estado da Bahia. A nidificação ocorreu em gomos de bambus e em tubos de cartolina preta, estes com comprimentos de 5,8 cm (= tubos pequenos) e 10,5 cm (= tubos grandes), e diâmetro de 0,6 e 0,8 cm, respectivamente. Em ambas as áreas C. tarsata nidificou durante a estação úmida, produzindo quatro gerações anuais em Baixa Grande e três em Ipirá. Os imaturos de uma das gerações passaram por diapausa em ambos os locais. As abelhas construíram seus ninhos com uma mistura de areia e óleo. Em geral, as células foram alongadas e arranjadas em série linear, com sua abertura dirigida para a entrada do ninho. Os ninhos completados tinham de duas a três células nos tubos pequenos, de uma a sete células nos tubos grandes e de duas a 13 nos gomos de bambu. A parede de fechamento do ninho lembrava uma célula incompleta e era coberta externamente com óleo. As células foram aprovisionadas com pólen, óleo e néctar. Os ninhos foram parasitados por Mesocheira bicolor (Fabricius, 1804) (Hymenoptera, Apidae) e por outra espécie de abelha não identificada

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Plants Visited by Centris spp.

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ABSTRACT. In this study were examined the species richness and seasonal abundance of cavity-nesting bees in areas of dry semi-deciduous forest and caatinga in the State of Bahia, Brazil. Sampling was done employing two types of trap-nests: bamboo canes and tubes made of black cardboard with dimensions of either 58 x 6 mm or 105 x 8 mm. The traps were inspected once a month. One hundred and forty-six nests of 11 bee species were collected in the forest, and 121 nests of seven species were collected in the caatinga. Five species of cleptoparasitic bees were also reared from these nests. The highest nesting frequencies occurred in the wet season in both areas. Nests parasitism was important only for Centris tarsata Smith, 1874, and was higher at the caatinga site than in the forest. The mortality of pre-emergent adults was high, especially in C. tarsata, Tetrapedia diversipes Klug, 1810 and Euglossa cordata (Linnaeus, 1758). Information on the number of cells per nest, the size, shape, and arrangement of brood cells in the nests, as well as the number of adults produced and the number of generations per year are also presented. Species richness, temporal patterns of nesting, and percentage of parasitism were compared with other habitats.

-Wasps and bees are important components of fl ower visitor guilds in the Neotropical region. The abundance of social wasps and bees, collected during fl ower visits, was used to calculate niche breadth and niche overlap indices, in order to characterize the utilization of the fl oral resources by those insects. Samples were taken monthly, for 13 months (156h), by two collectors which captured the specimes on fl owers using entomological nets, while walking along a way in an area of caatinga at Itatim, State of Bahia, Brazil. Wasps and bees heavily visited a few sources of fl oral resources, but the most visited plants by each group were different, and few plant species were important for both groups, resulting in low niche overlap between bees and wasps. The niche overlap among wasp species was generally higher than among bee species. The general overlap, which takes into consideration all species together was low (< 30%).KEY WORDS: Niche, overlap, fl ower visitor, semi-arid region RESUMO -Vespas e abelhas são importantes componentes da guilda de visitantes fl orais nos Neotrópicos. A abundância de vespas sociais e abelhas visitando fl ores foi utilizada para calcular os índices de amplitude e sobreposição dos nichos trófi cos e para caracterizar o uso das fontes de recursos fl orais por aqueles insetos. A amostragem foi realizada mensalmente, durante 13 meses (156h), por dois coletores que capturaram os espécimes com redes entomológicas, ao longo de uma trilha em uma área de caatinga em Itatim, BA. As vespas e abelhas concentraram as visitas em poucas fontes de recursos. As plantas mais visitadas por cada um desses grupos foram distintas e poucas espécies de plantas foram importantes para ambos os grupos, resultando em baixos índices de sobreposição entre abelhas e vespas. A sobreposição do nicho trófi co entre espécies de vespas foi em geral mais elevada do que entre espécies de abelhas. A sobreposição geral entre todas as espécies foi baixa (< 30%).PALAVRAS-CHAVE: Nicho, sobreposição, visitante fl oral, região semi-árida

Trophic niche breadth and niche overlap of bees were studied in a region of Caatinga (a deciduous dry thorn scrub forest) in Brazil with the lowest mean annual rainfall of the country, highly seasonal environmental variation, and an unpredictable rainy season. A null model approach was used to determine if the observed niche overlap in the community differed from that expected by chance. In general, even bee species with wider trophic niches concentrated foraging efforts on flowers of only a few of the available plant species, with low trophic niche overlap between pairs of species and among all species in the community. A randomization test showed niche overlap among the 10 common species in the guild to be significantly less than expected by chance, suggesting the existence of functional complementarity. The structure of communities defined by high functional complementarity is likely to be more sensitive to variation in available resources (e.g., richness and abundance of floral resources for bees). Ecosystem services provided by such communities may be more greatly affected by environmental changes (anthropogenic activities and climate change) than are services provided by communities with greater functional redundancy. stingless bees / Apoidea / solitary bees / Caatinga / semiarid / niche overlap