Suchergebnisse

Oil bees exploit host plants for resources to feed the adults and offspring, as well as for the construction of their nests. The aim of the current study is to investigate how the species in this guild distribute their foraging effort, and the range in their niche overlap levels. The bees were sampled for six months, during their visits to the flowers in a savanna ("cerrado"). These oil-bee species explored the floral resources provided by 13 plant species. The trophic niche of the most abundant species, Centris aenea Lepeletier, was relatively narrow, similarly to those of Epicharis species. Low overlap of trophic niches (TrNO≤30%) was most commonly found. The distribution of bee visits to the host plants revealed redundancy in the floral resource exploitation. However, the foraging concentration levels in some key plants were different for distinct oil-bee species, and it contributed to the low overlap of niches between many pairs of species

This study aimed to assess the efficiency of Centris aenea Lepeletier as pollinator of Malpighia emarginata DC. The pollination efficiency was determined according to three criteria: 1) the pollen deposition rate of M. emarginata and other plant species on the thorax ventral region of females, 2) the rate of M. emarginata fruit set after a single visit, and 3) the pollen deposition rate on the stigma after one single visit. 59% of the pollen grains deposited on the ventral region of C. aenea came from flowers of M. emarginata. The fruit set after a single visit by C. aenea (21%) was much higher than that reported previously for Centris tarsata Smith. We argue that pollination efficiency of C. aenea can be related to its body size, since that females of C. aenea can carry larger amounts of pollen grains of M. emarginata than C. tarsata, as well females of C. aenea are able to touch a larger stigma area, resulting in higher fruit sets after a single visit. Our study suggests that only one visit by C. aenea ensures fruit set in M. emarginata.

Due to deforestation and fragmentation of ecosystems, the management of bee populations targeting pollination services is increasingly urgent. Because urban environments are stressful, the dietary knowledge in such areas can help to cope with this issue in the near future. Using palynological analysis the floral resources used by Centris flavifrons, an important pollinator of crops and native plants was studied in an urban area. Byrsonima sericea type, Solanum paniculatum type, Cestrum type, and Myrcia type 1 together accounted for more than 93% of pollen grains foraged by females. It is noteworthy that this bee population depends on few plant species both for pollen and for oil. Furthermore, females showed flexibility to replace the primary pollen source in different breeding seasons, as well as one female could provision different cells in the same nest with different predominant pollen types. It is highlighted the importance of wastelands for keeping bee populations in urban areas.

Geometric morphometrics is a tool capable of measuring the response of organisms to different environmental pressures. We tested the hypothesis that E. cordata wing morphometry, as an indicator of response to environmental pressure, it would vary depending on habitat changes, in the Atlantic Forest, Savanna and dry forest (Caatinga). For analysis of wing shape and size, 18 landmarks were digitized at the intersections of the wing veins 348 individuals. Except for the two populations sampled in Chapada Diamantina, the wing shape had significant statistical variations among the populations (p < 0.05). The wing size variation was also statistically significant among populations (p < 0.05). Although E. cordata is a species tolerant to different environments, the observed morphometric variability may be related to population adaptations to the conditions of each phytophysiognomy.

The conservation of the fauna of bees inhabiting the Brazilian savanna is threatened due to changes in land use in the last decades. We investigated the composition, species richness and abundance of a bee assemblage in the vicinity of the Chapada Diamantina National Park. In addition, we compiled data on composition and diversity from another bee assemblage located in the same portion of the Cerrado, which was previously investigated by one of us almost 30 years ago, in order to produce a more complete panorama on beta diversity of bees in this region. We used a non-metric multidimensional scaling ordination analysis (NMDS) to compare composition of bee assemblages from diff erent types of open vegetation. We recorded 77 bee species (H' = 2.95; J = 0.68), 42% of them were singletons. We collected slightly more than half of the species and 60% of the genera recorded in the bee assemblage studied three decades ago. H' was signifi cantly lower in our area than in the previous study (t = 8.588, p <0.001), but equitability (J) was very similar. Several factors may contribute to these diff erences, including local diff erences in bee assemblage composition, diff erences in the probability of capturing the diff erent species (many rare species), factors affecting the sampling itself, and perhaps species loss over the three decades separating the two studies. The magnitude of species loss is difficult to assess because the two studies were not carried out exactly in the same area and there were differences in sampling time and sampling effort.

Variations in abundance and species richness among communities are often determined by interactions between biotic and abiotic factors. However, for communities composed of species that share a common specialization (such as similar foraging adaptations) it may be a key ecological factor involved in the common specialization that affects community variations. To evaluate this possibility, we characterized the guild of oil-collecting bees of a Neotropical savanna in Brazil and tested whether differences in Byrsonima abundance and availability of floral oil explain differences in species richness and abundance of oil-collecting bees of different tribes. Both the number of species and total abundance of Centridini species increased with the abundance of Byrsonima. One plausible explanation for the stronger adjustment between the abundance of Centridini and Byrsonima is that the abundance of these plants affects not only the availability of floral oil, but also of pollen. These findings indicate that the existence of a common specialization among different species does not homogenize their response to variations in a common explored resource.

Products based on entomopathogenic fungi are extensively used to control insect pests. These biopesticides can result in lethal or sublethal effects on non-target organisms. This study aimed to evaluate the survival of Melipona scutellaris Latreille workers exposed to commercial products based on Beauveria bassiana (IBCB 66), Metarhizium anisopliae (IBCB 425), and Isaria fumosorosea (ESALQ 1296). Fifty foragers were exposed to B. bassiana at 8.25 x 106 conidia/mL, M. anisopliae at 1.1 x 107 conidia/mL, and I. fumosorosea at 2.5 x 109 conidia/mL, using three routes of exposure (ingestion, contact with a surface, and topical application). Kaplan-Meier survival curves were estimated to determine the proportion of workers surviving after each application of the biopesticides. Workers exposed to B. bassiana, M. anisopliae, and I. fumosorosea presented survival rates of 74%, 34%, and 42%, respectively, after 168 hours of exposure by ingestion. For exposure via contact with a contaminated surface, survival rates were 64%, 70%, and 78%; for topical application, 68%, 66%, and 72% of the workers survived, respectively. The results highlight the variability in toxicity of biopesticides based on M. anisopliae, B. bassiana, and I. fumosorosea for M. scutellaris workers. Although all biopesticides resulted in mortality, bee survival rates varied depending on the exposure route. Understanding the effect of entomopathogenic fungi-based products on M. scutellaris may facilitate the development of strategies (such as timing and frequency of spraying) to reduce their impact on bees.

In this study we investigated the group of floral resources that support bee populations from a bee assemblage in a savanna, and the way in which bee species use these food resources, with an emphasis on the breadth and overlap of trophic niches. The interactions between 75 species of bees and 62 species of plants visited to obtain floral resources were recorded on a Brazilian savanna site. The bee species explored a diverse set of plant species, but concentrated the collection of resources in a few plant species. The distribution of the samples over a long period favored a robust characterization of the food niche of the bee populations. Byrsonima sericea, Serjania faveolata, and Stigmaphyllon paralias were the plant species with the highest number of links with bees. In general, the trophic niche overlap was low, with 75% of pairs of bee species having a niche overlap (NO) less than 0.33. Only four pairs showed high overlap (NO>0.70) and all cases were related to the exploitation of floral resources provided by B. sericea, a key resource for the maintenance of the local bee fauna, an oil and pollen provider.