Genetic differentiation between two host “races” and two species of cleptoparasitic bees and between their two hosts

In this paper we test the following two hypotheses: (1) that apparently conspecific samples of the cleptoparasitic beeCoelioxys funeraria, differing markedly in size and reared from different host species, do indeed represent one panmictic population; (2) that bees that nest in holes in wood or twigs have higher levels of genetic variation than those nesting in the ground. Based upon 41 loci, the genetic differences between the two samples ofC. funeraria could be explained entirely in terms of sampling error. In contrast, the sympatricC. moesta showed 16 fixed allelic differences from theC. funeraria samples. Similarly, the two hosts ofC. funeraria, Megachile relativa andM. inermis, had 21 fixed allelic differences between them out of 42 presumptive gene loci. Heterozygosities among the wood-nesting bees were not particularly high for Hymenoptera, ranging from 0.045 to 0.054. Comparisons of heterozygosity estimates among bees remain ambiguous as to whether soil nesting confers sufficient environmental buffering effects to reduce possible advantages of heterosis in ground-nesting species.     

Effects of neonicotinoid seed treatments on wild bee populations in soybean and corn fields in eastern Ontario

1. Neonicotinoid-coated corn and soybean seeds are a common crop in Canada and the US. A growing body of research is demonstrating that, through various exposure routes, neonicotinoids can impact a suite of nontarget organisms including beneficial insects such as bees. However, to date, only a few studies have examined the effects of neonicotinoids in field settings.
2. We assessed the relationship between agricultural crop soil neonicotinoid levels and wild bee abundance and diversity at 16 agricultural sites representing different soil neonicotinoid levels. We detected clothianidin at 11 sites, thiamethoxam at three sites; imidacloprid was not detected.
3. Hedgerow and crop soils were consistent in terms of where clothianidin was detected; thiamethoxan was not detected in hedgerow soils. Based on model outcomes, fields with higher levels of soil neonicotinoids exhibited significantly lower wild bee abundance and diversity than those with low or no neonicotinoids detected.
4. Crop soil neonicotinoid level, hedgerow floral resource abundance and crop type were consistent predictors of bee abundance across models; only neonicotinoid level and crop type were significant predictors of diversity.
5. Our results are consistent with recent findings in the midwestern US, and underscore the potential risk of soil neonicotinoids to wild bee populations across regions and crop systems.

     

Pollen use by Megalopta sweat bees in relation to resource availability in a tropical forest

1. Spatial and temporal availability of pollen helps shape bee foraging behaviour and productivity, which has been studied in great detail at the landscape level, but never in a diverse tropical forest. 2. To study the effect of spatio‐temporal variation in resource distribution on pollen use and productivity, we identified pollen from spatially explicit nest collections of two generalist sweat bees, Megalopta genalis Meade‐Waldo and M. centralis Friese, from Barro Colorado Island, Panama, a 50‐ha forest dynamics plot during the 2007 dry and early wet seasons. Pollen from nests collected in 1998–1999 without spatial information was also identified. 3. Bees used pollen of at least 64 species; many of these occurred in only one collection. The 2007 collections contained pollen of 35 different species, but were dominated by five species, especially Hura crepitans L. and Pseudobombax septenatum (Jacq.) Dugand. 4. Temporal availability, but not distance from nest, influenced flower use at a 50‐ha scale. 5. Body size was not associated with minimum flight distance as inferred from pollen collections. 6. Nest productivity and pollen diversity decreased from the dry to wet seasons, mirroring community‐level availability of floral resources. 7. Results suggest that on a scale of 50 ha, bees are choosing certain host plant species regardless of distance from the nest, but adjusting foraging behaviour opportunistically based on the temporal availability of host flowers.     

Nest preference and ecology of cavity-nesting bees (Hymenoptera: Apoidea) in Punjab,Pakistan

Among bees, 85 % are solitary species, most of them are ground-nester and some are cavity-nesting and construct their nests in pre-existing cavities. This work was conducted to evaluate the substrate preference and nest architecture (acceptance, occupation percentage, seasonality and parasitism) of cavity-nesting bees in different substrates. Trap nests offered comprised five different materials (drilled cavities in wood, bamboo, cardboard tubes, plastic soda straws, and mud blocks). These were installed in four districts for two years. The nesting cavities of five different diameters (6, 8, 10, 12 and 14 mm) were provided in each nesting material with an average length of 180 ± 9.92 mm. In all the materials, 5400 nesting cavities were offered, out of which 628 were colonized by bees from two families (Megachilidae and Apidae) and six species (Megachile cephalotes, M. lanata, M. bicolor, Xylocopa basalis, X. fenestrata and Ceratina smaragdula), including one parasitic bee (Euaspis carbonaria). The bee species differed significantly in occupying five nesting materials. The most preferred diameters were 8 mm and 10 mm, with 52.20% and 29.45% of colonization, respectively. Nesting was done throughout the year except in winter. This study will serve as a baseline for future studies and conservation programs of cavity-nesting bees in Pakistan.     

Salt marsh elevation is a strong determinant of nest‐site selection by Clapper Rails in Georgia,USA

As sea levels rise, birds nesting in coastal marshes will be particularly vulnerable to increased tidal inundation. Understanding how marsh birds select their nesting habitat along the elevational gradient of these marshes will provide insight into how these species might be affected by rising sea levels. Clapper Rails (Rallus crepitans) are coastal marsh‐nesting birds whose nests are vulnerable to flooding, but it is not clear if they select for habitat along the elevational gradient or only use other habitat cues. Our objective was to determine if Clapper Rails select higher‐elevation nest sites, while also controlling for selection of other habitat variables at both landscape and territory levels, by comparing nest habitat to habitat in other areas of territories and at random points in the marsh landscape. At the landscape level, Clapper Rails did not exhibit selection for the elevational gradient, with nests and random points at similar elevations. At the territory level, however, nest‐site selection was most influenced by elevation and plant height, with Clapper Rails selecting nest sites with higher elevations and in areas with taller plants. However, the strength of the elevation effect was uncertain, suggesting the importance of precise elevation measurements in the field. Given this selection for higher‐elevation nest sites, Clapper Rails may be somewhat resilient to increased tidal inundation. However, the potential for increased intra‐ and interspecific competition for high‐elevation marshes should make conservation of these habitats a priority.     

Landmark orientation during the approach to the nest in the stingless beeTrigona (Tetragonisca) angustula (Apidae,Meliponinae)

Summary We displaced a small nest box containing stingless bees (Trigona (Tetragonisca)angustula) over distances of up to 1.6 meters in different directions and counted the numbers of returning foragers to measure the effects of this manipulation on the homing ability of bees. Bees find it hard to locate the nest box when it was displaced more than about 1 m backwards, forwards or sideways relative to the direction into which the nest entrance pointed. They do not find the nest when its height above ground is changed. The bees use landmarks in the vicinity of the nest to locate it: When the nest box is displaced and landmark positions are changed so that their angular position at the new nest site is the same as at the normal nest position their homing ability is less impaired than it is without changes in landmark positions. Our results show that the bees do not use the nest box itself as a landmark until they have approached the nest position to within about 1 meter with the aid of surrounding landmarks.     

Comparative resistance in Buckfast and Canadian stocks of honey bees (Apis mellifera L.) to infestation by honey bee tracheal mites (Acarapis woodi (Rennie))

The results of bioassay and colony evaluation demonstrated that British and Texas Buckfast honey bee stocks had one-third to one-half the mean prevalence and abundance of tracheal mites as Canadian standard stock, indicating that Buckfast stocks are less susceptible to tracheal mites than Canadian standard stock. Hybrid Canadian and Buckfast stocks exhibited resistance characteristics similar to only one of their parental stocks, suggesting the colony has an unknown effect on the expression of a bee's resistance to mites. A high correlation (r _s=0.66) between abundance values from the bioassay and colony evaluations indicates that the bioassay can be used to screen bees for mite resistance.     

Tropical pollinators in the canopy and understory: Field data and theory for stratum “preferences”

Claims have been made for a canopy preference by large bees pollinating tropical flowers—without data or tests that support or refute this opinion. The working hypothesis for bee foraging behavior in three dimensions is that forager experience can produce stratum fidelity, just as rewarding foraging produces floral fidelity. Wideranging search behavior should allow bees to track spatiotemporal distribution of resources. A systematic study of 20 bee species and 10 genera: Apis, Trigona, Eulaema, Centris, Euglossa, Scaptotrigona, Partamona, Megalopta, Rhinetula,and Oxytrigonawas made in two forests in Panama. Two traps were operated simultaneously at canopy height and in the understory to test whether there were consistent stratum associations. Studies were continuous for 1 and 8 years. The only high-canopy foragers were two nocturnal bees, all the rest flew at both heights with similar probability or consistently came to lower traps. Large euglossines showed a tendency to forage high, which was directly related to their capacity for heat loss during flight, compared to smaller euglossines. They are also more conspicuous in warning coloration, another expected correlate of foraging more often in the open. Although large variance in stratum association predominates, some medium-sized diurnal forest bees avoid the exposed upper canopy, while some nocturnal bees tend to forage there.     

Morphology of reproductive and trophic eggs and their controlled release by workers in Trigona (Tetragonisca) angustula llliger (Apidae, Meliponinae)

Abstract. To study the reproductive potential of workers in the stingless bee Trigona (Tetragonisca) angustula Illiger (Apidae, Meliponinae), we examined the morphological quality of their eggs. Worker-eggs were all placed on the inside of the upper wall of brood cells. Normally, such eggs are consumed by the queen and are therefore referred to as trophic. The provisioning and oviposition processes in queenright colonies are characterized by the occurrence of circular aggregations of workers, 'rosettes', around the broodcell opening immediately after the release of a worker-egg. The ovaries of 35% of these rosette workers contained mature, chorionated eggs. In a single worker ovary, always only one mature egg was found. Some of the eggs, dissected from the ovarioles, showed a reticulate chorion pattern. Worker-eggs which lacked this pattern were significantly bigger than patterned eggs. Scanning electron micrographs revealed that the patterned worker-eggs are similar in appearance to queen-eggs.
After a worker-egg had been removed experimentally from a broodcell, the same cell could be oviposited by a worker again. Light microscopic analysis revealed that all these worker-eggs lacked the reticulate chorion pattern and were very similar in their morphology. In a colony without a laying queen workers laid eggs which had a reticulate pattern on the chorion. Since these eggs developed into males, we assume that the pattern on the chorion is characteristic for reproductive eggs. We also assume that the queen prevents the release of reproductive eggs by the workers. However, she does not inhibit the development of this type of egg.