Nectar Concentration Research Articles

Effects of erectable glossal hairs on a honeybee's nectar-drinking strategy

With the use of a scanning electron microscope, we observe specific microstructures of the mouthpart of the Italian bee (Apis mellifera ligustica), especially the distribution and dimensions of hairs on its glossa. Considering the erection of glossal hairs for trapping nectar modifies the viscous dipping model in analyzing the drinking strategy of a honeybee. Theoretical estimations of volume intake rates with respect to sucrose solutions of different concentrations agree with experimental data, which indicates that erectable hairs can significantly increase the ability of a bee to acquire nectar efficiently. The comparison with experimental results also indicates that a honeybee may continuously augment its pumping power, rather than keep it constant, to drink nectar with sharply increasing viscosity. Under the modified assumption of increasing working power, we introduce the rate at which working power increases with viscosity and discuss the nature-preferred nectar concentration of 35% by theoretically calculating optimal concentration maximizing energetic intake rates under varying increasing rates. Finally, the ability of the mouthparts of the honeybee to transfer viscous nectar may inspire a concept for transporting microfluidics with a wide range of viscosities.

Stabilizing selection on nectar concentration in wild Petunia axillaris, as revealed by genetic analysis of pollen dispersal

Most animal-pollinated plants produce nectar as a pollinator reward. Despite the main role that nectar plays in plant-pollinator interactions, the impact of natural variation in nectar traits on realized male fitness is poorly known. Here, we assessed this relation for a wild Petunia axillaris population using paternity-based direct selection gradient analysis, which allowed us also to infer pollen dispersal patterns. Because male fecundity may depend on other traits which could be associated with nectar characteristics (i.e. volume and concentration), we also considered selection on other key reproductive traits. The analysis revealed that P. axillaris was a strict outcrosser, but that successful pollination occurred mainly among neighbours. Individual plants varied greatly in their male fecundity. Nectar concentration, a key feature of nectar that determines its profitability, was subjected to stabilizing selection. Selection through male function also affected corolla area (positive directional selection), corolla tube length (negative directional selection), and floral display size (stabilizing selection), but none of these traits were phenotypically correlated with nectar characteristics. Because nectar concentration affects the ability and foraging efficiency of different flower visitors to feed on nectar, stabilizing selection may reflect either the preference of the most effective pollinators, or antagonistic selection driven by pollinators and non-pollinating nectar consumers.

Floral divergence in closely related Leucospermum tottum (Proteaceae) varieties pollinated by birds and long-proboscid flies

The Proteaceae are renowned for their floral diversity but surprisingly the role of pollinators in driving evolutionary divergence in this family has been underexplored. Here we focus on recently diverged taxa to gain insight into the processes that generate diversity by testing whether two varieties of Leucospermum tottum might have originated by pollinator mediated adaptive divergence. L. tottum var. tottum has pale salmon-coloured horizontally-oriented flowers, long nectar tubes, and small volumes of concentrated nectar. L. tottum var. glabrum has red and yellow vertically oriented flowers, short nectar tubes, and large volumes of dilute nectar. Despite the morphological divergence, the varieties are indistinguishable using eight molecular markers, indicating a very early stage of differentiation. Consistent with their morphologies, L. tottum var. tottum is pollinated by long-proboscid flies (Philoliche rostrata and Philoliche gulosa), Cape sugarbirds (Promerops cafer), and, to a lesser extent, by Orange-breasted sunbirds (Anthobaphes violacea), whereas, L. tottum var. glabrum is pollinated only by Orange-breasted sunbirds. A. violacea visits both varieties, but makes more frequent contact with pollen presenters when foraging on L. tottum var. glabrum. The exclusion of birds caused a steeper reduction in seed production in L. tottum var. glabrum than in L. tottum var. tottum, consistent with specialization for bird-pollination in this variety. Additionally, L. tottum var. glabrum exhibits autogamy, whereas L. tottum var. tottum does not. Floral divergence between the two L. tottum varieties corresponds with divergence in pollinator use.

More is not always better: a hidden cost of the flight‐fecundity trade‐off in the hawk moth, Manduca sexta (1100.2)

Flight and reproduction are two energetically demanding life‐history traits, but empirical data for the existence of a trade‐off between them is equivocal. Trade‐offs are partly determined by the amount of resources available: trade‐offs are more pronounced when resources are scarce and can be undetectable when resources are abundant. Using Manduca sexta hawk moths (Sphingidae) we tested the effects of nectar concentration (0%, 6%, 12%, 24%) and flight duration (0.5 h and 2.0 h) on flight performance, fecundity and the trade‐off between these two traits. Flight performance was highest on 24% nectar with significant within‐subjects interaction effects for distance and duration with diet, flight, and days flown. Nectar concentration was positively correlated with flight metabolic rate when standardized for speed and postprandial metabolic rate increased with nectar concentration. As a consequence, moths that were fed 6% nectar produced significantly more eggs compared to unfed moths or moths fed higher concentration nectar. Muscle mass was negatively correlated with egg number suggesting a trade‐off between flight structure (but not flight performance) and fecundity. The number of eggs or muscle mass had no effect on flight performance. Most importantly, our results suggest that the high‐energy content of resources can be a hidden cost underlying the flight‐fecundity trade‐off.Grant Funding Source: Supported by NSF grant IOS‐1053318

밀원수종 쉬나무 수꽃과 암꽃의 화밀분비량, 당 함량 및 아미노산 분석

본 연구는 밀원수종으로 관심의 대상이 되고 있는 쉬나무를 대상으로 수꽃과 암꽃의 화밀 분비량, 당 함량 및 아미노산을 분석하고 수확할 수 있는 꿀의 양을 추정하기 위하여 실시하였다. 경기도 화성시의 2012년 쉬나무 수꽃의 개화 최성기는 7월 24일부터 26일이었으며, 평균 화밀분비량은 <TEX>$2.73{\pm}0.73{\mu}L$</TEX>, 화밀 당도는 17.4%를 나타냈다. 2012년 암꽃의 개화 최성기는 8월 7일부터 9일이었으며 평균 화밀분비량은 <TEX>$0.63{\pm}0.49{\mu}L$</TEX>, 화밀 당도는 25.7%를 나타냈다. 기상인자와 상관분석 결과, 화밀 분비량과 화밀 당도는 온도와 습도의 영향을 많이 받는다는 것을 알 수 있었다. 반면, 꽃 한 개당 당 함량을 산출한 결과, 수꽃은 <TEX>$48.0{\pm}5.2{\mu}g$</TEX>, 암꽃은 <TEX>$37.8{\pm}8.7{\mu}g$</TEX>으로 분석되었으나, 유의적인 차이는 없었다(Mann-Whitney's U-test, p=0.400). 이러한 당 함량을 가지고 수꽃 1개 화서에서는 최소 67.8 g, 암꽃 1개 화서에서는 최소 53.3 g의 꿀을 수확할 수 있을 것으로 추정하였다. 또한 아미노산 분석 결과, Serine, Glycine 및 Alanine은 수꽃에서 더 많은 함량이 검출된 반면, Asparatate, Glutamate, Asparagine 및 Glutamine은 암꽃에서 더 많은 함량을 나타내어 수꽃과 암꽃에서 7개의 아미노산 함량이 유의적으로 차이가 있음을 알 수 있었다. The purpose of study was to analyze secreted nectar volume, nectar sugar content and amino acid in addition to estimating honey quantities that can ultimately reap in male and female flowers of Evodia daniellii Hemsl.. The maximum blooming period of male flowers was on 24 to 26 July in 2012. On average, nectar volume secreted by nectary was <TEX>$2.73{\pm}0.73{\mu}L$</TEX> from one male flower and nectar concentration showed 17.4%. The maximum blooming period of female flowers was on 7 to 9 August in 2012. Nectar volume secreted by nectary was <TEX>$0.63{\pm}0.49{\mu}L$</TEX> from one female flower and nectar concentration showed 25.7%, averagely. As results of correlation analysis between the meteorological factors and nectar characteristics, we found that nectar quantities and concentration were influenced by temperature and relative humidity. Sugar content was calculated at <TEX>$48.0{\pm}5.2{\mu}g$</TEX> per a male flower and <TEX>$37.8{\pm}8.7{\mu}g$</TEX> per a female flower, which meant that both values were not significantly different (Mann-Whitney's U-test, p=0.400). The minimum estimates of honey harvest for a male and female inflorescence were 67.8 g and 53.5 g, respectively. Analysis of amino acid showed that Serine, Glycine and Alanine were more abundant in male flowers, however Asparatate, Glutamate, Asparagine and Glutamine were more abundant in female flowers.

Drinking problems on a ‘simple’ diet: physiological convergence in nectar-feeding birds

Regulation of energy and water are by necessity closely linked in avian nectarivores, because the easily available sugars in nectar are accompanied by an excess of water but few electrolytes. In general, there is convergence in morphology and physiology between three main lineages of avian nectarivores that have evolved on different continents - the hummingbirds, sunbirds and honeyeaters. These birds show similar dependence of sugar preferences on nectar concentration, high intestinal sucrase activity and rapid absorption of hexoses via mediated and paracellular routes. There are differences, however, in how these lineages deal with energy challenges, as well as processing the large volumes of preformed water ingested in nectar. While hummingbirds rely on varying renal water reabsorption, the passerine nectarivores modulate intestinal water absorption during water loading, thus reducing the impact on the kidneys. Hummingbirds do not generally cope with salt loading, and have renal morphology consistent with their ability to produce copious dilute urine; by contrast, as well as being able to deal with dilute diets, honeyeaters and sunbirds are more than capable of dealing with moderately high levels of added electrolytes. And finally, in response to energy challenge, hummingbirds readily resort to torpor, while the passerines show renal and digestive responses that allow them to deal with short-term fasts and rapidly restore energy balance without using torpor. In conclusion, sunbirds and honeyeaters demonstrate a degree of physiological plasticity in dealing with digestive and renal challenges of their nectar diet, while hummingbirds appear to be more constrained by this diet.

Divergent Rules for Pollen and Nectar Foraging Bumblebees – A Laboratory Study with Artificial Flowers Offering Diluted Nectar Substitute and Pollen Surrogate

Almost all bees collect nectar and pollen from flowers. Female bees collect pollen to provision their nest cells, whereas they use nectar for individual energy supply and nest cell provisioning. Bees fine-tune nectar foraging to the amount and to the concentration of nectar, but the individual bees' response to variability of amount and concentration of pollen reward has not yet been studied thoroughly in laboratory settings. We developed an experimental set-up in which bumblebees simultaneously collected sugar solution and pollen from artificial flowers; natural pollen was mixed with cellulose powder or glass powder as a pollen surrogate. Here we show that bumblebee (Bombus terrestris) workers do not specialise in nectar or pollen collection, but regularly collect both rewards on the same day. When offered a fixed pollen reward and varied amounts and concentrations of sugar solution, the bumblebees fine-tuned sugar solution foraging dependent on both the volume and concentration, with strong preferences for the highest concentration and the greatest volume. In the reciprocal tests, when offered a fixed sugar reward and varied amounts and concentrations of pollen mixed with a nutrient-free pollen surrogate, the bumblebees follow more an all-or-none rule for pollen, accepting all amounts and concentrations except pure surrogate. It is discussed how the bumblebees' ability to sense sugar, and their apparent inability to sense the pollen protein content, shaped their foraging behaviour. It is argued that the rarity of nectar mimicry and the frequency of pollen mimicry in natural flowers might be interpreted in the context of divergent abilities of nectar and pollen recognition in bees.

Nectar Feeding Habits of Loten’s Sunbird Cinnyris lotenius and Purple-rumped Sunbird Leptocoma zeylonica in the Royal Botanical Gardens, Peradeniya, Sri Lanka

Sunbirds (Nectariniidae) are small passerines that feed largely on nectar. The aim of thiswork was to observe the relationship of the purple-rumped sunbird Leptocoma zeylonica andLoten’s sunbird Cinnyris lotenius with their host flowers, and to examine their relationshipwith the glucose concentration of nectar, flower count and the length of corolla. The studywas carried out in the Royal Botanical Gardens, Peradeniya, Sri Lanka, between February2013 and September 2013. For each observation, plant species visited for nectar feeding,method of obtaining food, glucose concentration of nectar, length of corolla, and flower countwere recorded. Both species of sunbirds visited Hamelia patens, Sanchezia speciosa,Heliconia rostrata, Megaskepasma erythrochlamys, Strobilanthes flaccidifolius,Graptophyllum pictum and Pachystachys spicata. The male Loten’s sunbird’s occurrence ona given flower is biased by the presence of female (Pearson correlation coefficient: 0.874; PValue:&lt;0.001). The Purple-rumped female’s occurrence is biased by the presence of male(Pearson correlation coefficient: 0.819; P-Value: &lt;0.001). The results also indicated that therewas no significant correlation between the occurrence of the bird and the glucoseconcentration of the flower (Pearson correlation coefficients: -0.045; P-Value: 0.740;[Loten’s male]; -0.094; P-Value: 0.489; [Loten’s female]; -0.061; P-Value: 0.653; [Purplerumpedmale]; 0.001; P-Value: 0.997; [Purple-rumped female]). Similarly, there was nosignificant correlation between the flower count with the occurrence of the bird (Pearsoncorrelation coefficients: 0.160; P-Value: 0.239; [Loten’s male], 0.171; P-Value: 0.208;[Loten’s female]; 0.172; P-Value: 0.595; [Purple rumped male]; 0.211; P-Value: 0.118;[Purple-rumped female]). The Loten’s sunbird has no significant correlation with flowercorolla length (Pearson correlation coefficients: -0.240; P-Value: 0.075; [Loten’s male]; -0.142; P-Value: 0.297; [Loten’s female]). The Purple-rumped sunbird has a significantcorrelation with the flower corolla length. (Pearson correlation coefficient: -0.399; P-Value:0.020; [Purple rumped male]; -0.452; P-Value: &lt;0.001; [Purple-rumped female]). Dependingon the length of corolla, the nectar obtaining method varied as probing or piercing.

Spring foraging resources and the behaviour of pollinating insects in fixed dune ecosystems

In temperate climates, foraging resources for pollinating insects are especially important in early spring when animals emerge from hibernation and initiate annual life cycles. One habitat, protected under EU law, which provides resources for a range of pollinating insects, but has received little research attention, is fixed (grey) dunes. Fixed dunes often contain creeping willow (Salix repens, Salicaceae), which may be an important early season resource for obligate flower visitors. We examined the springtime activity of flower visitors in fixed dune ecosystems in relation to sugar concentration and composition in nectar, composition of essential amino acids in pollen, and floral abundance. We also investigated whether the presence or absence of S. repens influenced the abundance and species richness of three obligate flower visiting guilds (solitary bees, bumblebees and hoverflies) in eight sites along the eastern and southern coasts of Ireland. Higher insect visitation rates were observed to species whose nectar contained greater concentrations of glucose and fructose. Solitary bee visitation rates were related to % Essential Amino Acid (EAA) in pollen and floral species richness. Ulex europeaus, and S. repens were the most abundant flowering species, but visitation rates were not related to floral abundance. Higher abundances of bumblebees and hoverflies were discovered at sites where S. repens was present. This study raises further questions about the nutritional requirements and preferences of obligate flower visitors in fixed dune ecosystems in spring time.

Sunbirds increase foraging success by using color as a cue for nectar quality

Nectar concentration and composition vary widely between plant species. Nectarivorous birds that associate floral character istics with nectar quality may be able to avoid less rewarding flowers and therefore forage more efficiently. We assessed the abilities of amethyst sunbirds (Chalcomitra amethystina) to utilize color cues to discriminate between concentrated (1 M) and dilute (0.25 M) sucrose solutions. In an outdoor aviary, birds were presented with 3 rich feeders among 6 poor feeders on a feeding board. Following the assessment of baseline performance with optically identical feeders, color cues were added to the feeders for a 6-h training period. To assess the retention of learnt visual cues, birds were tested 1 and 7 days after the training. Observations lasted for 3 h, with feeders being rearranged every 30 min to minimize spatial learning. In the absence of color cues, birds selected feeders randomly, but when color cues were available, they visited more rich than poor feeders. This more rapid identification of rich feeders resulted in a decrease in feeding duration and feeding frequency compared with the baseline performance. Energy uptake from rich feeders and therefore the rate of energy gain increased when birds foraged with color cues. No differences were found between Days 1 and 7 after training. Total energy intake decreased with visual cues, which may indicate a reduction in foraging costs when cues allow for location of rewarding feeders. Our findings demonstrate that sunbirds forage more efficiently with cues, which may lead to increased fitness.

Landscape scale variation in nectar amino acid and sugar composition in a Lepidoptera pollinated orchid species and its relation with fruit set

SummaryUnderstanding landscape scale variation in reproductive and pollination success is a major aim of plant population biology. A potential determinant of reproductive success that has received surprisingly little attention so far is variation in nectar chemical composition across plant individuals and populations. Using theLepidoptera pollinated fragrant orchid (Gymnadenia conopsea) as a model species, we aimed at providing a first account of landscape scale variation in nectar amino acid and sugar composition, its environmental drivers, and how it may affect plant fruit set.Nectar was sampled from 986 flowers from 296 individuals across eleven discrete populations of theG. conopsea. The proportions of sugars and amino acids were determined using high‐performance anion‐exchange chromatography. Nectar composition was related to soil characteristics of the populations, and to fruit set, using linear mixed models.Approximately, 20% of the variance in nectar traits was situated between populations, whereas the highest proportion of variance (c. 45%) was found among flowers within individuals. Soil carbon and nitrogen content affected both nectar concentration and composition. Furthermore, fruit set ofG. conopseaindividuals was found to be significantly related to nectar amino acid and sugar composition.Synthesis. These results show that landscape scale variation in nectar amino acid and sugar composition should be taken into account in future studies of plant reproductive success. Furthermore, there is also high within‐plant variation in both nectar amino acid and sugar composition. This variation may reduce geitonogamous pollination, but it may also limit rapid pollinator‐mediated selection on nectar composition.

Does Oeceoclades maculata (Orchidaceae) reabsorb nectar?

Nectar is the most common resource offered by orchid flowers. In some cases, flowers reabsorb nectar as part of a resource-recovery strategy. Nectar is present only in the morning in the widespread orchid Oececoclades maculata (Lindl.) Lindl. To determine whether this is due to reabsorption or evaporation of water, the volume of nectar and its concentration in previously bagged flowers were determined throughout the day at two hourly intervals. In addition, the entrance to the nectary of flowers of cultivated plants was obstructed with petroleum jelly in the morning, to prevent the evaporation of water and, in the afternoon, the presence of nectar was recorded. Furthermore, manually self-pollinated flowers, also with the entrance to the nectary obstructed, had their nectary checked 24 hours after pollination to determine whether post-pollination reabsorption occurred. In addition, the period when the pollinators of O. maculata foraged for nectar was determined in order to establish whether it was associated with the period when nectar was available. The volume and concentration of nectar in O. maculata flowers vary from 0.82 μl (25.10%) between 10–12 h and 0.36 μl (33.73%) between 16–18 h and this difference is caused by evaporation of water. Post-pollination reabsorption does not occur in this species. Pollinators forage most actively between 10–12 h. Thus, O. maculata does not reabsorb nectar, but evaporative water loss is a significant factor determining the variation in the volume and concentration of this reward and this is positively correlated with butterfly visitation.

Comparative Sucrose Responsiveness in Apis mellifera and A. cerana Foragers

In the European honey bee, Apis mellifera, pollen foragers have a higher sucrose responsiveness than nectar foragers when tested using a proboscis extension response (PER) assay. In addition, Africanized honey bees have a higher sucrose responsiveness than European honey bees. Based on the biology of the Eastern honey bee, A. cerana, we hypothesized that A. cerana should also have a higher responsiveness to sucrose than A. mellifera. To test this hypothesis, we compared the sucrose thresholds of pollen foragers and nectar foragers in both A. cerana and A. mellifera in Fujian Province, China. Pollen foragers were more responsive to sucrose than nectar foragers in both species, consistent with previous studies. However, contrary to our hypothesis, A. mellifera was more responsive than A. cerana. We also demonstrated that this higher sucrose responsiveness in A. mellifera was not due to differences in the colony environment by co-fostering two species of bees in the same mixed-species colonies. Because A. mellifera foragers were more responsive to sucrose, we predicted that their nectar foragers should bring in less concentrated nectar compared to that of A. cerana. However, we found no differences between the two species. We conclude that A. cerana shows a different pattern in sucrose responsiveness from that of Africanized bees. There may be other mechanisms that enable A. cerana to perform well in areas with sparse nectar resources.

The systematic significance of floral morphology, nectaries, and nectar concentration in epiphytic cacti of tribes Hylocereeae and Rhipsalideae (Cactaceae)

A long-standing interest in cactus taxonomy has existed since the Linnaean generation, but an appreciation of the reproductive biology of cacti started early in the 1900s. Numerous studies indicate that plant reproductive traits provide valuable systematic information. Despite the extensive reproductive versatility and specializations in breeding systems coupled with the striking floral shapes, the reproductive biology of the Cactaceae has been investigated in approximately 10% of its species. Hence, the systematic value of architectural design and organization of internal floral parts has remained virtually unexplored in the family. This study represents the most extensive survey of flower and nectary morphology in the Cactaceae focusing on tribes Hylocereeae and Rhipsalideae (subfamily Cactoideae). Our objectives were (1) to conduct comparative morphological analyses of flowers and floral nectaries and (2) to compare nectar solute concentration in these two tribes consisting of holo- and semi-epiphytic species. Flower morphology, nectary types, and sugar concentration of nectar have strong taxonomic implications at the tribal, generic and specific levels. Foremost, three types of nectaries were found, namely chamber nectary (with the open and diffuse subtypes), furrow nectary (including the holder nectary subtype), and annular nectary. All Hylocereeae species possess chamber nectaries, in which the nectarial tissue has both trichomes and stomata. The Rhipsalideae are distinguished by two kinds of floral nectaries: furrow and annular, both nectary types with stomata only. The annular nectary type characterizes the genus Rhipsalis. Nectar concentration is another significant taxonomic indicator separating the Hylocereeae and Rhipsalideae and establishing trends linked to nectar sugar concentration and amount of nectar production in relation to flower size. There is an inverse relationship between flower size and amount of nectar production in the smaller Rhipsalideae flowers, in which nectar concentration is more than two-fold higher despite the smaller volume of nectar produced when compared to the large Hylocereeae flowers. Variability of nectary morphology and nectar concentration was also evaluated as potential synapomorphic characters in recent phylogenies of these tribes. In conclusion, our data provide strong evidence of the systematic value of floral nectaries and nectar sugar concentration in the Cactaceae, particularly at different taxonomic levels in the Hylocereeae and Rhipsalideae.

Dose‐dependent effects of nectar alkaloids in a montane plant–pollinator community

SummaryAlthough secondary metabolites are prevalent in floral nectar, the ecological consequences for pollinators and pollination remain relatively unexplored. While often deterrent to pollinators at high concentrations, secondary metabolite concentrations in nectar tend to be much lower than secondary metabolite concentrations in leaves and flowers; yet, they may still affect the maintenance of pollination mutualisms.Delphinium barbeyi, a common montane herb, contains norditerpene alkaloids in its nectar but at concentrations that are substantially lower than those found in its leaves or flowers. By manipulating nectar alkaloid concentrations in the field and laboratory, we assessed the degree to which varying concentrations of alkaloids in nectar influenced pollinator behaviour and activity and plant reproduction.In the field, nectar alkaloids significantly reduced both the number of flower visits and the time spent per flower by free‐flying bumblebee pollinators, but we only observed effects at alkaloid concentrations 50 times that of natural nectar. When we supplementedD. barbeyinectar with alkaloids at concentrations almost 15 times that of natural nectar, we found no evidence for direct or pollinator‐mediated indirect effects on female plant reproduction.In the laboratory, the direct consumptive effects of nectar alkaloids on bumblebee pollinators were also concentration dependent. Bumblebees exhibited reduced mobility and vigour but only at alkaloid concentrations more than 25 times higher than those found in natural nectar.Synthesis. We found that nectar alkaloids have dose‐dependent effects on pollinator behaviour and activity. While concentrations of nectar alkaloids rivalling those found in leaves would negatively affect pollinator behaviour and pollination services, the natural concentrations of nectar alkaloids inD. barbeyihave no negative direct or pollinator‐mediated indirect effects on plant reproduction. These results provide experimental insight into the dose‐dependent ecological consequences of nectar secondary metabolites for pollinators and pollination, suggesting that low nectar alkaloid concentrations incurred no ecological costs forD. barbeyi.

Preferences and tradeoffs in nectar temperature and nectar concentration in the Asian hive bee Apis cerana

Honey bee foragers need to asses and make trade-offs between a number of potentially conflicting floral attributes. Here, we investigate multi-attribute decision making in the eastern honey bee, Apis cerana, when foraging on food sources that varied in warmth and sucrose concentration. We show that foragers prefer warm (30 °C) sucrose solution over cool (10 °C) sucrose solution and concentrated (30 % w/w) sucrose solution over dilute (15 % w/w) sucrose solution. When we offered the preferred sucrose concentration (30 % w/w) at the less-preferred temperature (10 °C), and the less-preferred sucrose concentration (15 % w/w) at the preferred temperature (30 °C), foragers prioritized warmth by choosing the warmer, but lower concentration solution. When the temperature difference was less extreme, bees preferred more concentrated cooler syrup (30 % ww at 15 °C over 15 % 30 °C). However, the addition of a decoy item to the choice set had a significant effect on the bees' preferences. Our results highlight the critical importance of considering context effects when measuring the foraging preferences of animals.

Why do ants shift their foraging from extrafloral nectar to aphid honeydew?

AbstractWhen aphids parasitize plants with extrafloral nectaries (EFNs) and aphid colony size is small, ants frequently use EFNs but hardly tend aphids. However, as the aphid colony size increases, ants stop using EFNs and strengthen their associations with aphids. Although the shift in ant behavior is important for determining the dynamics of the ant–plant–aphid interaction, it is not known why this shift occurs. Here, we test two hypotheses to explain the mechanism responsible for this behavioral shift: (1) Extrafloral nectar secretion changes in response to aphid herbivory, or (2) plants do not change extrafloral nectar secretion, but the total reward to ants from aphids will exceed that from EFNs above a certain aphid colony size. To judge which mechanism is plausible, we investigated secretion patterns of extrafloral nectar produced by plants with and without aphids, compared the amount of sugar supplied by EFNs and aphids, and examined whether extrafloral nectar or honeydew was more attractive to ants. Our results show that there was no inducible extrafloral secretion in response to aphid herbivory, but the sugar concentration in extrafloral nectar was higher than in honeydew, and more ant workers were attracted to an artificial extrafloral nectar solution than to an artificial aphid honeydew solution. These results indicate that extrafloral nectar is a more attractive reward than aphid honeydew per unit volume. However, even an aphid colony containing only two individuals can supply a greater reward to ants than EFNs. This suggests that the ant behavioral shift may be explained by the second hypothesis.

Determination of exposure levels of honey bees foraging on flowers of mature citrus trees previously treated with imidacloprid

Field and tunnel cage studies were undertaken to determine the extent to which honey bees foraging on citrus blossoms were exposed to imidacloprid and its metabolites when citrus trees were treated with soil applications of the insecticide. Residues were measured by LC/MS/MS in nectar and pollen samples from trees treated up to 232 days prior to bloom. Imidacloprid, imidacloprid olefin and 5-hydroxy imidacloprid were detected in nectar and pollen sampled from the flowers of citrus trees treated with imidacloprid up to 232 days prior to bloom. In tunnel studies, where foraging was restricted exclusively to citrus, imidacloprid residues in nectar extracted from flowers and from bee crops were similar (<10 ng mL(-1) ) and below the established no-observed-effects limit; however, the residue levels were about threefold higher in nectar sampled from comb. Concentrations of imidacloprid in nectar were higher in trees treated with higher application rates. Imidacloprid and its metabolites were detected in the nectar and pollen of citrus trees treated up to 232 days prior to the onset of bloom. However, based on published bioassay data, the imidacloprid concentrations in the floral nectar did not surpass levels that would compromise foraging activity under normal use conditions for imidacloprid. Further research is needed to assess the impact of elevated levels of imidacloprid within stored nectar in the comb.

Morphology, nectar characteristics and avian pollinators in five Andean Puya species (Bromeliaceae)

Five Andean Puya species (Puya alpestris, Puya chilensis, Puya coerulea, Puya raimondii and Puya venusta) were studied to determine the relationship between their avian visitors, and plant morphology and nectar characteristics. Our results showed a significant relationship between nectar concentration, presence of sterile apex and avian pollinators's species. In contrast, nectar composition was not related to the frequency of avian visits. We found that Puya species were mainly visited by specialist nectarivorous birds such as hummingbirds (i.e., P. coerulea and P. venusta), lacked a sterile apex and produced high nectar concentration in low volumes. In contrast, species mainly visited by generalist passerines (i.e., P. chilensis and P. alpestris) were characterized by the presence of a sterile apex and production of highly diluted nectar in large volumes. In a mono-specific group we found that P. raimondii produces highly concentrated nectar in large volumes, and its flowers were visited by hummingbirds and passerine birds. We found no effect of nectar composition on bird's visits. Our study highlights the interplay between morphological traits, nectar characteristics and the ecological framework to explain specialized and generalized birds pollination systems.

The Bananaquit, a Neotropical passerine nectar feeding bird, has a high protein requirement relative to other nectarivorous birds

For nectar-feeding birds, the low amino acid and protein content of nectar is likely a major nutritional constraint. Nectar-feeding birds present morphological, behavioral, and physiological adaptations that allow them to exploit nectar efficiently. One of these adaptations might be a low nitrogen requirement compared to birds of taxa that rely on other resources. The Bananaquit (Coereba flaveola) is considered a specialized nectar-feeding passerine. It is widely distributed in the Neotropics and one of the most abundant flower-visiting passerine in northern Venezuela. We measured maintenance nitrogen requirement (MNR) and total endogenous nitrogen loss (TENL) in captive Bananaquits fed on four diets of varying concentrations of protein (0, 1.5, 3.0, and 7.0 %). We found that the Bananaquit had a MNR of 8.7 mg N day–1 (313.2 mg N W–0.75 day–1) and a TENL of 3.3 mg N day–1 (111 mg N W–0.75 day–1), values in the high range of what was previously reported for other nectar-feeding birds. However, when compared to other species with different feeding habits (i.e. granivores) the Bananaquit presents a low nitrogen requirement. These high values suggest different physiological and behavioral strategies from other nectar-feeding birds or methodological issues associated to an unbalanced diet based on a protein plant source.