Nectar of a flower

What Is Nectar: Why Do Plants Produce Nectar

The Greek gods supposedly ate ambrosia and drank nectar, and hummingbirds drink nectar, but what exactly is it? If you’ve ever wondered what nectar is, and if you can get some out of your garden, you’re not alone.

What is Nectar?

Nectar is a sweet liquid produced by plants. It is especially produced by flowers on flowering plants. Nectar is very sweet and this is why butterflies, hummingbirds, bats, and other animals slurp it up. It gives them a good source of energy and calories. Bees collect nectar to turn into honey.

Nectar is more than just sweet, though. It is also rich in vitamins, salts, oils, and other nutrients. This sweet, nutritious liquid is produced by glands in a plant called the nectaries. Depending on the plant species, the nectaries may be located on different parts of the flower, including the petals, pistils, and stamen.

Why Do Plants Produce Nectar, and What Does Nectar Do?

It’s exactly because this sweet liquid is so attractive to some insects, birds, and mammals that plants produce nectar at all. It may provide these animals with a food source, but what nectar rich plants are up to is tempting them to aid in pollination. For plants to reproduce, they need to get pollen from one flower to another, but plants don’t move.

The nectar attracts a pollinator, like a butterfly. While feeding, pollen sticks to the butterfly. At the next flower some of this pollen is transferred. The pollinator is just out for a meal, but is unwittingly helping the plant procreate.

Plants to Attract Pollinators

Growing plants for nectar is rewarding because you provide natural sources of food for pollinators like butterflies and bees. Some plants are better than others for nectar production:

Bees

To attract bees, try:

  • Citrus trees
  • American holly
  • Saw palmetto
  • Sea grape
  • Southern magnolia
  • Sweetbay magnolia

Butterflies

Butterflies love the following nectar rich plants:

  • Black-eyed Susan
  • Buttonbush
  • Salvia
  • Purple coneflower
  • Butterfly milkweed
  • Hibiscus
  • Firebush

Hummingbirds
For hummingbirds, try planting:

  • Butterfly milkweed
  • Coral honeysuckle
  • Morning glory
  • Trumpet vine
  • Wild azalea
  • Red basil

By growing plants for nectar, you can enjoy seeing more butterflies and hummingbirds in your garden, but you also support these vital pollinators.

Nectar: A sweet reward from plants to attract pollinators

This is the ovary and nectary of a Nicotiana flower. Credit: Danny Kessler, Max Planck Institute for Chemical Ecology

Evolution is based on diversity, and sexual reproduction is key to creating a diverse population that secures competitiveness in nature. Plants had to solve a problem: they needed to find ways to spread their genetic material. Flying pollinators—insects, birds, and bats—were nature’s solution. Charles Darwin’s “abominable mystery” highlighted the coincidence of flowering plant and insect diversification about 120 million years ago and ascribed it to the coordinated specialization of flowers and insects in the context of insects serving as pollen carriers. To make sure the flying pollinators would come to the flowers to pick up pollen, plants evolved special organs called nectaries to attract and reward the animals. These nectaries are secretory organs that produce perfumes and sugary rewards. Yet despite the obvious importance of nectar, the process by which plants manufacture and secrete it has largely remained a mystery.

New research from a team led by Carnegie’s Wolf Frommer, director of the Plant Biology Department, in collaboration with the Carter lab in Minnesota and the Baldwin lab in Jena, Germany, now identified key components of the sugar synthesis and secretion mechanisms. Their work also suggests that the components were recruited for this purpose early during the evolution of flowering plants. Their work is published March 16 by Nature.

The team used advanced techniques to search for transporters that could be involved in sugar transport and were present in nectaries. They identified the transport protein SWEET9 as a key player in three diverse flowering plant species and demonstrated that it is essential for nectar production.

In specially engineered plants lacking the SWEET9 transporter, the team found that nectar secretion did not occur, but rather sugars accumulated in the stems. Importantly, when they added a copy of the SWEET9 gene, the plants produced more nectar. In parallel, they also identified genes necessary for the production of sucrose, called sucrose phosphate synthase genes, which turned out to also be essential for nectar secretion.

Since sugars are apparently the drivers for secretion of nectary fluids, they uncovered a whole pathway for how sucrose is manufactured in the nectary and then transported into the extracellualar space of nectaries by SWEET9. In this interstitial area the sugar is converted into a mixture of sucrose and other sugars, namely glucose and fructose. In the plants tested, these three sugars comprise the majority of solutes in the nectar, a prerequisite for collection by bees for honey production.

These are flowers of wild tobacco Nicotiana attenuata. Credit: Danny Kessler, Max Planck Institute for Chemical Ecology

“SWEETs are key transporters for transporting essential nutrients from leaves to seeds. We believe that the nectarial SWEET9 sugar transporter evolved around the time of the formation of the first floral nectaries, and that this process may have been a major step necessary for attracting and rewarding pollinators and thus increasing the genetic diversity of plants,” Frommer said.

Explore further

Just what makes that little old ant… change a flower’s nectar content? More information: Nectar secretion requires sucrose phosphate synthases and the sugar transporter SWEET9, Nature, DOI: 10.1038/nature13082 Journal information: Nature Provided by Carnegie Institution for Science Citation: Nectar: A sweet reward from plants to attract pollinators (2014, March 16) retrieved 1 February 2020 from https://phys.org/news/2014-03-nectar-sweet-reward-pollinators.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.

Did you know

Which plants are bees attracted to?

Bees are attracted to plants that produce nectar and pollen. Nectar is a sweet substance that attracts bees, which in turn pollinate plants so they can develop seeds and propagate their species. Bees also need pollen in their diet.

In Slovenia, there are around 1000 species of plants that produce nectar and pollen for bees to collect. Some of these plants are important for the country’s economy, as they provide bees with a surplus of honey. Beekeepers can extract this surplus from beehives.

Why is it important to plant honey plants?

Due to modern farming practices and deforestation, and because flowering meadows are disappearing and monocultures are starting to prevail, there are fewer and fewer food sources for bees, especially in summer.

Honey plants ensure more food for bees, thus helping them survive the winter and start pollinating again in spring. Honey plants also help preserve biodiversity and protect the environment.

Which plants produce the most nectar?

Carniolan honey bee

For bees, the most important plants in nature are:

  • spring vegetation, such as hazel, snowdrops, primroses, saffron, willow, hellebore, heather, wild cherry, dandelion;
  • fruit trees;
  • acacia, linden, maple, chestnut;
  • woodland undergrowth and
  • meadow flowers.

Bee-friendly ornamental plants

Bees can also benefit from plants that we grow for decorative purposes. By planting native ornamental plants we can create a bee-friendly garden that will always provide some nectar flow and, at the same time, take pride in our green oasis.

Nectar plants that we can plant in the garden include:

Which honey plants can be used on larger cultivated plots?

There are many such plants and we usually plant them in summer, when most fields are empty. Apart from providing a feast for bees, they are also good for the soil, making it more fertile.

Out in the fields we can plant:

  • Lacy phacelia or purple tansy (Phacelia tanacetifolia), which we can plant any time of year due to its short growing season. After flowering, we plough it in and enrich the soil with humus;
  • All types of clovers: excellent nectar plants that we plough in after flowering and enrich the soil with nitrogen, or scythe them and use them as feed for animals;
  • Pumpkins: provide plenty of pollen in autumn when bees need it most;
  • Sunflowers: after flowering, they greatly enhance the structure of soil and enrich it with humus;
  • Rapeseed and poppy;
  • Buckwheat: a long-neglected plant with enormous potential. We plant it in summer and when it fades, we can harvest the seeds and ground them into flour.

View the embedded image gallery online at:
https://www.worldbeeday.org/en/did-you-know/86-best-honey-plants-to-help-save-bees.html#sigProId2b00a00b90

Fields should always be green. For every season there is a plant that is not only beneficial to bees but also beneficial to soil and farmers.

Author: Jure Justinek, Slovenian Beekeepers’ Association

flowers produce a sweet liquid called

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GIZMOSPollinationFlowerFruitSE (1).pdf – Student…

Student Exploration: Pollination: Flower to Fruit Vocabulary: anther, cross pollination, filament, fruit, nectar, ovary, ovule, pedicel, petal, pistil, pollen, pollen tube, pollination, receptacle, self pollination, sepal, stamen, stigma, style Prior Knowledge Question (Do this BEFORE using the Gizmo .) Plants use sunlight to produce sugar. Flowering plants make some of this sugar available to animals in the form of nectar (a sweet liquid found in flowers) and fruit . 1. Why do plants provide bees, butterflies, hummingbirds, and other animals with nectar? Plants provide bees, butterflies, hummingbirds, and other animals with nectar because it has nutrients. 2. Why do plants provide animals with fruits such as strawberries, apples, and mangoes? Plants provide animals with fruits such as strawberries, apples, and mangoes to spread seeds. Gizmo Warm-up Plants don’t produce nectar and delicious fruit just to be nice. As you will learn, bees and other pollinators play a critical role in helping plants to reproduce. Fruits play a role in allowing plants to spread to new locations. The Pollination: Flower to Fruit Gizmo™ will take you through the reproductive cycle of flowering plants. To familiarize yourself with some of the parts of a flower, begin on the IDENTIFICATION tab. 1. Look at the list of Flower Parts on the left. Which of these parts have you heard of before? Petal, pedicel, anther, pistil, ovary, ovule, pollen, pollen tube, sepal, stigma, stamen. 2. On the Closed view , drag the Petal , Pedicel , and Sepal terms into the correct spaces. (Use trial and error.) Turn on Show information about selected parts of the flower .

Which flowers are the best source of nectar?

There is growing evidence that both domestic honeybees and wild pollinators are in trouble, and the many wildflowers that depend on them for pollination are also declining. But are pollinator declines driving flower losses or vice versa? Or are other separate factors causing the declines?

Nectar and pollen are the main floral resources for pollinators and lack of food is believed to be one of the major causes of pollinator decline in Great Britain. However, we don’t really know the food value to pollinators of the different flower species. We have reasonable lists of plants that attract pollinators, but not much of the detail is truly evidence based.

We know that a total of 3842 plant species are found in the UK, according to The Countryside Survey (1). Of those 3842 plant species, only 450 cover 99% of UK landscape and more than half of those 450 plants are not rewarding to pollinators at all.

What we have been missing is good evidence on which flowers provide the most value to pollinators and, therefore, which habitats are the best….until now…

The AgriLand project (2), funded by the UK Insect Pollinators Initiative (3), has addressed these questions by surveying both pollinators and wildflowers across the country, and by examining the importance of land use and the structure of the British landscape using historical datasets and national data on some of the most likely causes of declines.

Part of the project, carried out by researchers at Bristol University, set about identifying the top 220 flowering plants in the UK – which ones produce the most pollen and nectar, and which species and habitats contribute the most at the national scale.

The top five most common plants in England, Scotland and Wales were:

  • Heather (Calluna vulgaris)
  • White clover (Trifolium repens)
  • Bilberry (Vaccinium myrtillus)
  • Bramble (Rubus fruticosus)
  • Creeping buttercup (Ranunculus repens)

The researchers looked for field sites where the targeted plant species grow, sampled 2 populations for each species in 2011 and 2012 and measured pollen and nectar production per flower. They bagged the plants for 24 hours then collected nectar using micro-capillary tubes and measured the volume and sugar concentration per flower. They also collected unopened stamens and extracted, counted and measured the pollen grains.

The top 10 plant species for nectar production in terms of µg of sugar/flower/day were:

  1. Himalayan balsam (Impatiens glandulifera)
  2. Yellow water iris (Iris pseudacerus)
  3. Gladioli (Gladiolus spp.)
  4. Common comfrey (Symphytum officinale)
  5. Blackberry (Rubus fruticosus agg.)
  6. Hedge bindweed (Calystegia sepium)
  7. Honeysuckle (Lonicera periclymenum)
  8. Sweet pea (Lathyrus latifolius)
  9. Foxglove (Digitalis purpurea)
  10. Rhododendron (Rhododendron panticum)

But that’s only part of the story. It was important to know and understand which plants would produce the most nectar over a given area or habitat in order to define which provide the most value. So the researchers multiplied the nectar per flower by the number of flowers per floral unit. They then related it to flower abundance and phenology (from existing evidence in literature) and came up with quite a different list:

The top 10 plant species for nectar per unit cover per year (kg of sugar/ha/year) were:

  1. Marsh thistle (Cirsium palustre)
  2. Grey willow (Salix cinerea.)
  3. Common knapweed (Centaurea nigra.)
  4. Bell heather (Erica cinerea)
  5. Common comfrey (Symphytum officinale.)
  6. Spear thistle (Cirsium vulgare)
  7. Ragwort (Senecio jacobea)
  8. Common hogweed (Heracleum sphondylium)
  9. Common bugloss (Anchusa officinalis)
  10. Chives (Allium schoenoprasum)

By then factoring in data on plant species composition and proportional cover in each national habitat from the UK Countryside Survey 2007, the researchers came up with a league table for the nectar productivity of UK habitats (kg of sugars/ha/year):

  1. Calcareous grassland
  2. Broadleaf woodland
  3. Neutral grassland
  4. Shrub Heath
  5. Improved grass
  6. Bracken
  7. Fen
  8. Acid grass
  9. Bog
  10. Conifer
  11. Arable

The plant species that contribute the most at a national scale were White clover, Marsh thistle and Heather, which together contribute almost 50% of the national nectar provision.

This research highlights the critical importance of the maintenance of our natural grassland habitats and woodlands, but it also confirms the need to improve our arable areas by creating and managing floristically enhanced habitats, like improved grass margins, in a way that Conservation Grade’s Fair to Nature farmers currently do.

It should be noted that non-native plants such as Himalayan balsam, while they may be good nectar sources, are very invasive and are a major problem in habitat conservation, shading out other plant species.

(1) The Countryside Survey (http://www.countrysidesurvey.org.uk/reports-2007) provides scientifically reliable evidence about the state or ‘health’ of the UK’s countryside.

(2) The Agriland Project (www.agriland.leeds.ac.uk/) is a partnership between The University of Leeds, University of Reading, University of Bristol, Defra’s Food and Environment Research Agency (FERA), and Natural Environment Research Council’s Centre for Ecology and Hydrology.

(3) The Insect Pollinator Initiative is a range of innovative research projects aimed at understanding and mitigating the biological and environmental factors that adversely affect insect pollinators. (http://www.bbsrc.ac.uk/funding/opportunities/2009/insect-pollinators-initiative.aspx )

PMC

  • Andersson L. 1993. Rubiaceae – introduction. In: Harling G, Andersson L, eds. Flora of Ecuador No 47. Nordic Journal of Botany, 3–11.
  • Andersson L, Rova JHE, Guarin FA. 2002. Relationships, circumscription, and biogeography of Arcytophyllum (Rubiaceae) based on evidence from cpDNA. Brittonia 54: 40–49.
  • Backlund M, Oxelman B, Bremer B. 2000. Phylogenetic relationships within the Gentianales based on ndhF and rbcL sequences, with particular reference to the Loganiaceae. American Journal of Botany 87: 1029–1043.
  • Baker HG. 1975. Sugar concentration in nectar from hummingbird flowers. Biotopica 7: 37–41.
  • Baker HG, Baker I. 1982. Chemical constituents in nectar in relation to pollination mechanisms and phylogeny. In: Nitecki MH, ed. Biochemical aspects of evolutionary biology. Chicago, IL: University of Chicago Press, 131–171.
  • Baker HG, Baker I. 1983. Floral nectar constituents in relation to pollinator type. In: Jones CE, Little RJ, eds. Handbook of experimental pollination biology. New York, NY: Van Nostrand Reinhold, 117−141.
  • Baker HG, Baker I. 1990. The predictive value of nectar chemistry to the recognition of pollinator types. Israel Journal of Botany 39: 157–166.
  • Baker HG, Baker I, Hodges SA. 1998. Sugar composition of nectar and fruits consumed by birds and bats in the tropics and subtropics. Biotropica 30: 559–586.
  • Barthlott W, Lauer W, Placke A. 1996. Global distribution of species diversity in vascular plants: towards a world map of phytodiversity. Erdkunde 50: 317–327.
  • Bateson M. 2002. Recent advances in our understanding of risk-sensitive foraging preferences. Proceedings of the Nutrition Society 61: 509–516.
  • Bernardello G, Galetto G, Jaramillo L, Grijalba E. 1994. Floral nectar chemical composition of some species from Reserva Río Guajalito, Ecuador. Biotropica 26: 113–116.
  • Boesch DF. 1977. Application of numerical classification in ecological investigations of water pollution. Special Scientific Report, Institute of Marine Science, Virginia.
  • Bolten AB, Feinsinger P. 1978. Why do hummingbird flowers secrete dilute nectar? Biotropica 10: 307–308.
  • Bussmann RW. 2001. The montane forests of Reserva Biológica San Francisco (Zamora-Chinchipe, Ecuador). Die Erde 132: 9–25.
  • Clarke KR. 1993. Non-parametric multivariate analyses of changes in community structure. Australian Journal of Ecology 18: 117–143.
  • Clarke KR, Gorley RN. 2001. PRIMER v5: user manual/tutorial. Plymouth: PRIMER-E, 1–91.
  • Cresswell JE. 1998. Stabilizing selection and the structural variability of flowers within species. Annals of Botany 81: 463–473.
  • Dorr LJ, Stergios B, Smith AR, Cuello ANL. 2000. Catalogue of the vascular plants of Guaramacal National Park, Portuguesa and Trujillo states, Venezuela. Contributions from the United States National Herbarium, Smithsonian Institution, Washington 40.
  • Dziedzioch C. 2001. Artenzusammensetzung und Ressourcenangebot kolibribesuchter Pflanzen im Bergwald Südecuadors. Doctoral Thesis, University of Ulm, Germany.
  • Elisens WJ, Freeman CE. 1988. Floral nectar sugar composition and pollinator type among New World genera in tribe Antirrhineae (Scrophulariaceae). American Journal of Botany 75: 971–978.
  • Faegri K, van der Pijl L. 1980. The principles of pollination ecology. Oxford: Pergamon Press.
  • Freeman CE, Reid WH, Becvar JE, Scogin R. 1984. Similarity and apparent convergence in the nectar-sugar composition of some hummingbird-pollinated flowers. Botanical Gazette 145: 132–135.
  • Galetto L, Bernardello G. 2003. Nectar sugar composition in angiosperms from Chaco and Patagonia (Argentina): do animal visitors matter? Plant Systematics and Evolution 238: 69–86.
  • Galetto L, Bernadello G, Sosa CA. 1998. The relationship between floral nectar composition and visitors in Lycium (Solanaceae) from Argentina and Chile: what does it reflect? Flora 193: 303–314.
  • Gentry AH. 1988. Tree species richness of upper Amazonian forests. Proceedings of the National Academy of Sciences of the USA 85: 156–159.
  • Goldblatt P, Manning JC, Bernhardt P. 1998. Adaptive radiation of bee-pollinated Gladiolus species (Iridaceae) in Southern Africa. Annals of the Missouri Botanical Garden 85: 492–517.
  • Gottsberger G, Schrauwen J, Linskens HF. 1984. Amino acids and sugars in nectar, and their putative evolutionary significance. Plant Systematics and Evolution 145: 55–77.
  • Grant JR, Struwe L. 2003. De Macrocarpaeae Grisebach (ex Gentianaceis) speciebus novis III: six new species of moon-gentians from Parque Nacional Podokarpus, Ecuador. Havard Papers in Botany 8: 61–81.
  • Grassle JF, Smith W. 1976. A similarity measure sensitive to the contribution of rare species and its use in investigation of variation in marine benthic communities. Oecologia 25: 13–22.
  • Haber WA, Frankie GW. 1989. A tropical hawkmoth community: Costa Rican dry forest Sphingidae. Biotropica 21: 155–172.
  • Helversen Ov. 1993. Adaptation of flowers to pollination by glossophagine bats. In: Barthlott W, Naumann CM, Schmidt-Loske K, Schumann KL, eds. Animal–plant interaction in tropical environments. Bonn: Zoologisches Forschungsinstitut und Museum Alexander König, 41–59.
  • Heyneman AJ. 1983. Optimal sugar concentration of floral costs. Oecologia 60: 198–213.
  • Homeier J. 2004. Baumdiversität, Waldstrucktur und Wachstumsdynamik zweier tropischer Bergregenwälder in Ecuador und Costa Rica. Doctoral Thesis, University of Bielefeld, Germany.
  • Jørgensen PM, León-Yánez S. 1999. Catalogue of the Vascular Plants of Ecuador. St Louis, MO: Missouri Botanical Garden Press.
  • Kacelnik A, Bateson M. 1996. Risky theories – the effects of variance on foraging decisions. American Zoologist 36: 402–434.
  • Kingslover JG, Daniel TL. 1983. Mechanical determination of nectar feeding strategy in hummingbirds: energetics, tongue morphology, and licking behavior. Oecologia 60: 214–226.
  • Kraemer M. 1998. Struktur und Dynamik der Pflanzen-Kolibri-Gemeinschaft von Bajo Calama, Kolumbien. Doctoral Thesis, University of Bonn, Germany.
  • Ladio AH, Aizen MA. 1999. Early reproductive failure increases nectar production and pollination success of late flowers in Alstroemeria aurea (Alstromeriaceae). Oecologia 120: 235–241.
  • Lasso E, Naranjo ME 2003. Effect of pollinators and nectar robbers on nectar production and pollen deposition in Hamelia patens (Rubiaceae). Biotropica 35: 57–66.
  • McDade LA, Weeks J. 2004a Nectar in hummingbird-pollinated Neotropical plants. I. Patterns of production and variability in 12 species. Biotropica 36: 196–215.
  • McDade LA, Weeks J. 2004b Nectar in hummingbird-pollinated Neotropical plants. II. Interactions with flower visitors. Biotropica 36: 216–230.
  • Machado IC, Loiola MI. 2000. Fly pollination and pollinator sharing in two synchronopatric species: Cordia multispicata (Boraginaceae) and Borreria alata (Rubiaceae). Revista Brasileira de Botânica 23: 305–311.
  • Machado IC, Sazima I, Sazima M. 1998. Bat pollination of the terrestrial herb Irlbachia alata (Gentianaceae) in northeastern Brazil. Plant Systematics and Evolution 209: 231–237.
  • Madsen JE, Øllgaard B. 1994. Floristic composition, structure, and dynamics of an upper montane forest in southern Ecuador. Nordic Journal of Botany 14: 403–423.
  • Manetas Y, Petropoulou Y. 2000. Nectar amount, pollinator visit duration and pollination success in the Mediterranean shrub Cistus creticus. Annals of Botany 86: 815–820.
  • Mantel N. 1967. The detection of disease clustering and generalized regression approach. Cancer Research 27: 209–220.
  • Martínez del Rio C, Baker HG, Baker I. 1992. Ecological and evolutionary implications of digestive processes: bird preferences and sugar constituents of floral nectar and fruit pulp. Experimentia 48: 544–551.
  • Matt F. 2001. Pflanzenbesuchende Fledermäuse im tropischen Bergregenwald: Diversität, Einnischung und Gildenstruktur. Doctoral Thesis, University of Erlangen-Nürnberg, Germany.
  • Morisita M. 1959. Measuring interspecific association and similarity between communities. Memoirs of the Faculty of Science, Kyushu University, Series E (Biology) 3: 65–80.
  • Nicolson SW, Fleming PA. 2003. Nectar as food for birds: the physiological consequences of drinking dilute sugar solutions. Plant Systematics and Evolution 238: 139–153.
  • Pacini E, Nepi M, Vesprini JL. 2003. Nectary biodiversity: a short review. Plant Systematics and Evolution 238: 7–21.
  • Paulsch A. 2002. Development and application of a classification system for undisturbed and disturbed tropical montane forests based on vegetation structure. Doctoral Thesis, University of Bayreuth, Germany.
  • Perret M, Chautems A, Spichiger R, Peixoto M, Savolainen V. 2001. Nectar sugar composition in relation to pollination syndromes in Sinningieae (Gesneriaceae). Annals of Botany 87: 267–273.
  • Petanidou T, Smets E. 1995. The potential of marginal lands for bees and apiculture – nectar secretion in Mediterranean shrublands. Apidologie 26: 39–52.
  • Pombal ECP, Morellato LPC. 1995. Polinização por moscas em Dendropanax cuneatum Decne. & Planch. (Araliaceae) em floresta semidecídua no sudeste do Brasil. Revista Brasileira de Botânica 18: 157–162.
  • Proctor M, Yeo P, Lack A. 1996. The natural history of pollination. Portland, OH: Timber Press.
  • Pyke GH, Waser NM. 1981. The production of dilute nectars by hummingbird and honeyeater flowers. Biotropica 13: 260–270.
  • Rathcke BJ. 1992. Nectar distributions, pollinator behavior, and plant reproductive success. In: Hunter MD, Ohgushi T, Price PW, eds. Effects of resource distribution on animal–plant interactions. San Diego, CA: Academic Press, 113–138.
  • Real LA, Caraco T. 1986. Risk and foraging in stochastic environments: theory and evidence. Annual Review of Ecology and Systematics 17: 371–390.
  • Roberts WM. 1996. Hummingbirds’ nectar concentration preferences at low volume: the importance of time scale. Animal Behaviour 52: 361–370.
  • Roces F, Winter Y, Helversen O v. 1993. Nectar concentration preference and water balance in Glossophaga soricina antillarum. In: Barthlott W, Naumann CM, Schmidt-Loske K, Schumann KL, eds. Animal–plant interaction in tropical environments. Bonn: Zoologisches Forschungsinstitut und Museum Alexander König, 159–165.
  • Sazima I, Buzato S, Sazima M. 1996. An assemblage of hummingbird-pollinated flowers in a montane forest in southeastern Brazil. Botanica Acta 109: 149–160.
  • Sazima M, Buzato S, Sazima I. 1999. Bat-pollinated flower assemblages and bat visitors at two Atlantic forest sites in Brazil. Annals of Botany 83: 705–712.
  • Schmitt U. 2000. Die Pflanzen-Kolibri-Gemeinschaft im Bergregenwald der Farallones de Cali, Reserva Natural Hato viejo, Kolumbien. Doctoral Thesis, University of Bonn, Germany.
  • Schwerdtfeger M. 1996. Die Nektarzusammensetzung der Asteridae und ihre Beziehung zu Blütenökologie und Systematik. Doctoral Thesis, University of Göttingen, Germany.
  • Shafir S, Bechar A, Weber EU. 2003. Cognition-mediated coevolution—context-dependent evaluations and sensitivity of pollinators to variability in nectar rewards. Plant Systematics and Evolution 238: 195–209.
  • Siegel S, Castellan NJ. 1988. Nonparametric statistics for the behavioural sciences. New York, NY: McGraw-Hill.
  • Simpson BB, Neff JL. 1983. Evolution and diversity of floral rewards. In: Jones CE, Little RJ, eds. Handbook of experimental pollination biology. New York, NY: Van Nostrand Reinhold, 142–159.
  • Stiles FG. 1976. Taste preferences, color preferences, and flower choice in hummingbirds. Condor 78: 10–26.
  • Stiles FG, Freeman CE. 1993. Patterns in floral nectar characteristics of some bird-visited plant species from Costa Rica. Biotropica 25: 191–205.
  • Struwe L, Kadereit J, Klackenberg J, Nilsson S, Thiv M, von Hagen KB. 2002. Systematics, character evolution, and biogeography of Gentianaceae, including a new tribal and subtribal classification. In: Struwe L, Albert VA, eds. Gentianaceae—systematics and natural history. Cambridge: Cambridge University Press, 21–309.
  • Tamm S, Gass CL. 1986. Energy intake rates and nectar concentration preferences by hummingbirds. Oecologia 70:20–23.
  • Torres C, Galetto L. 2002. Are nectar sugar composition and corolla tube length related to the diversity of insects that visit Asteraceae flowers? Plant Biology 4: 360–366.
  • Trueblood DD, Gallagher ED, Gould SM. 1994. Three stages of seasonal succession on the Savin Hill Cove mudflat, Boston Harbor. Limnology and Oceanography 39: 1440–1454.
  • Tschapka M. 2004. Energy density patterns of nectar resources permit coexistence within a guild of Neotropical flower-visiting bats. Journal of Zoology 263: 7–21.
  • Van Wyk BE. 1993. Nectar sugar composition in Southern African Papilionoideae (Fabaceae). Biochemical Systematics and Ecology 21: 271–277.
  • Vogel S. 1969. Chiropterophilie in der neotropischen Flora (Neue Mitteilungen II) Flora 158: 185–222.
  • Waser NM, Pyke, GH. 1981. The production of dilute nectars by hummingbird and honeyeater flowers. Biotropica 13: 260–270.
  • Weast RC. 1969. Handbook of chemistry and physics, 50th (1969–1970) edition. Cleveland, OH: The Chemical Rubber Co., D-207–208.
  • Webster GL, Rhode RM. 2001. Plant diversity of an Andean cloud forest. Checklist of vascular flora of Maquipucuna, Ecuador. University of California publications in Botany. Berkeley and Los Angeles, CA: University of California Press.
  • Witt T, Jürgens A, Geyer R, Gottsberger G. 1999. Nectar dynamics and sugar composition in flowers of Silene and Saponaria species (Caryophyllaceae). Plant Biology 1: 334–345.
  • Wolda H. 1981. Similarity indices, sampling size and diversity. Oecologia 50: 296–302.
  • Wolda H. 1983. Diversity, diversity indices and tropical cockroaches. Oecologia 58: 290–298.
  • Wolff D, Braun M, Liede S. 2003. Nocturnal versus diurnal pollination success in Isertia laevis (Rubiaceae): a sphingophilous plant visited by hummingbirds. Plant Biology 5: 71–78.
  • Wolff D, Witt T, Jürgens A, Gottsberger G. 2006. Nectar dynamics and reproductive success in Saponaria officinalis (Caryophyllaceae) in southern Germany. Flora (in press).
  • Wolff D, Liede-Schumann S. 2006. Evolution of flower morphology, pollen dimorphism, and nectar composition in Arcytophyllum, a distylous genus of Rubiaceae. Organisms, Diversity and Evolution (in press).
  • Zimmermann M. 1988. Nectar production, flowering phenology and strategies for pollination. In: Lovett Doust J, Lovett Doust L, eds. Plant reproductive ecology. New York: Oxford University Press, 157–178.

Nectar in Plant–Insect Mutualistic Relationships: From Food Reward to Partner Manipulation

CrossRef Full Text | Google Scholar

Gilbert, F. S., Haines, N., and Dickson, K. (1991). Empty flowers. Funct. Ecol. 5, 29–39. doi: 10.2307/2389553

CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

Heil, M. (2008). Indirect defence via tritrophic interactions. New Phytol. 178, 41–61. doi: 10.1111/j.1469-8137.2007.02330.x

PubMed Abstract | CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

Hölldobler, B., and Wilson, E. O. (1990). The Ants. Cambridge: Harvard University Press. doi: 10.1007/978-3-662-10306-7

CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

Google Scholar

CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

Maloof, J. E., and Inouye, D. W. (2000). Are nectar robbers cheaters or mutualists? Ecology 81, 2651–2661. doi: 10.2307/177331

CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

Ness, J. (2003). Catalpa bignonioides alters extrafloral nectar production after herbivory and attracts ant bodyguards. Oecologia 134, 210–218. doi: 10.1007/s00442-002-1110-6

PubMed Abstract | CrossRef Full Text | Google Scholar

Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

Google Scholar

CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

Google Scholar

Google Scholar

CrossRef Full Text | Google Scholar

Pyke, G. H. (1991). What does it cost a plant to produce floral nectar? Nature 350, 58–59. doi: 10.1038/350058a0

CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

Raguso, R. A. (2004). Why are some floral nectars scented? Ecology 85, 1486–1494. doi: 10.1890/03-0410

CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

Sachs, J. L. (2015). “The exploitation of mutualism,” in Mutualism, ed. J. L. Bronstein (Oxford: Oxford University Press), 93–106.

PubMed Abstract | CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

Schoonhoven, L. M., van Loon, J. J. A., and Dicke, M. (2005). Insect–Plant Biology. Oxford: Oxford University Press.

Google Scholar

CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

Smithson, A., and Gigord, L. D. (2003). The evolution of empty flowers revisited. Am. Nat. 161, 537–552. doi: 10.1086/368347

PubMed Abstract | CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

CrossRef Full Text | Google Scholar

PubMed Abstract | CrossRef Full Text | Google Scholar

Zimmermann, J. (1932). Über die extrafloralen nektarien der angiosperm. Beih. Bot. Cent. 49, 99–196.

Nectary

angiosperms

  • In angiosperm: Contribution to food chain

    …flowers provide food from floral nectaries that secrete sugars and amino acids. These flowers often produce fragrances that attract pollinators which feed on the nectar. Nectar-feeding animals include many insect groups (bees, butterflies, moths, flies, and even mosquitoes), many mammal groups (bats, small

  • In angiosperm: General features

    Small secretory structures called nectaries are often found at the base of the stamens and provide food rewards for pollinators. In some cases the nectaries coalesce into a nectary or staminal disc. In many cases the staminal disc forms when a whorl of stamens is reduced into a nectiferous…

  • In angiosperm: The corolla

    Petals often bear nectaries that secrete sugar-containing compounds, and petals also produce fragrances to attract pollinators; the fragrance of a rose (Rosa; Rosaceae) is derived from the petals. Petals often develop a nectar-containing extension of the tubular corolla, called a spur. This may involve one petal, as in…

  • Asparagales
    • In Asparagales: Flowers

      Septal nectaries, located within the walls of the ovary, are widespread in the order; they are, however, rare in Orchidaceae, where nectaries located on the tepals are frequent. Perigonal nectaries characterize some groups of Iridaceae.

  • orchids
    • In orchid: Characteristic morphological features

      There are several types of nectaries in the orchids, including extrafloral types that secrete nectar on the outside of the buds or inflorescence (flower cluster) while the flower is developing. Shallow cuplike nectaries at the base of the lip are common. Some nectaries are in long spurs that develop either…

An adult bee’s diet is primarily made up of three types of food. Honey, Nectar and Pollen. In this post, we will discover how each of these food groups provide essential nutrient to a bee.

Nectar

Where does nectar come from?

Nectar actually begins in the leaves of plants. The plant draws in carbon dioxide and water and produces sugar using the energy from the sun. This process is called photosynthesis. The sugar flows through the plant (think sap flow from a Sugar Maple tree). The nectar flows through the plant and feeds it. Roots, stems, leaves, flowers and fruit use this sugar supply to grow.

Excess sugar water is secreted in the base of flowers where bees and other pollinators like butterflies and hummingbirds can drink it.

How do Bees Use Nectar?

Worker-foraging bees collect nectar by sucking droplets with their proboscis (a straw like tongue, see figure below). The nectar on its own provides immediate energy in the form of carbohydrate sugars. Excess nectar is stored in the bee’s stomach until it gets back to the hive.

Once back at the hive, the nectar is passed from bee to bee. An enzyme in the bee’s stomach turn the sugar into a diluted honey. This passage also helps remove some of the excess water.

The un-ripe honey is then stored in comb cells where worker bees fan it with their wings to evaporate the rest of the excess water until it becomes honey.

For more information on how honey is produced check out my post The Canning Bee: Why Honey Doesn’t Spoil

Honey

Honey is used as a stored food. This is the bee’s winter stockpile for times of the year when flowers are not in bloom.

The bees keep honey in comb cells capped with wax for future use.

Just as gardeners might can or freeze excess vegetables from the summer harvest to enjoy throughout the winter, bees essentially do the same. They work all spring and summer so they have plenty of food to make it through the fall and winter.

Pollen

As you probably remember from 6th grade Biology class, in a flower blossom there are male and female parts. The male part is called the stamen and produces a sticky powder called pollen. The female part is called the pistil and has a sticky end (stigma) which is capable of collecting pollen. Think of the pollen as sperm in the reproductive process. The pollen leaves the male and is received by the female to produce fruit.

The problem is that plants don’t mate. That’s where bees come in.

Pollen provides healthy fats and proteins to bees. It rounds out their otherwise sugar/carbohydrate based diet. Worker-foraging bees collect pollen in pollen baskets, a type of collection device on their legs, to take back to the hive so that non foraging bees (young nurse bees, drones etc.) can benefit from the protein and fats as well.

In the collection process, bits of pollen stick to the bee and is distributed to the female parts of the blossom as the insect moves from stamen to pistol. This fertilized the flower and makes fruit production possible.

Once the pollen is brought back to the hive it is packed into brood cells usually around the perimeter of the frame. When needed, the pollen is then mixed with honey to produce Bee Bread. Nurse bees consume the most bee bread as it helps them to produce Royal Jelly to feed growing larvae.

As a new beekeeper, just starting out with a new hive of bees, it can be challenging to identify what you see in the cells of each comb in the hive. Soon after working in the hive several times you will soon learn the differences between capped and uncapped honey comb, capped worker brood and capped drone comb. You will also recognize heater bee cells, pollen and emerged bee cells and queen cells.

The Cathedral Hive Comb – several types of cells in this comb
In the Brood Nest area of the hive the bees will create a band of honeycomb above the brood cells. These honey stores are a source of food and that band also creates warmth during the winter months. Honeycomb and wax is a heat sink and insulator for the hive.
Top band on the comb: Capped honey cells – the band of white wax coverings
Middle and Bottom of Comb: Capped worker brood cells – Light yellow capped cells from middle to bottom of comb. The light yellow color indicates that are freshly laid by the queen.
Open Cells: Heater Bee empty cells:these empty cells scattered throughout the brood cells are cells for heater bees to crawl into and warm up the broodnest when needed. These ‘heater bees’ will crawl into a cell and vibrate their abdomen to create warmth for the brood cells around them. This is one technique of how the bees regulate the needed consistent temperature of 91-96 degrees F (32-35 C ) in the broodnest area of the hive.
The Golden Mean Hive Comb – again several types of cells in this comb
Just as the above Cathedral Hive comb we again see the band of capped honey above the brood nest cells
Top of comb: Capped honey cells – the band of white wax coverings
Middle of comb: Uncapped nectar – Open cells in middle (soon to be honey).
Bottom of Comb: Capped worker brood cells – Light yellow capped cells from middle to bottom of comb. The light yellow color indicates that are freshly laid by the queen.
A beautiful comb from the Cathedral Hive. The different color in the wax shows where the honey was stored and where the colony raised brood in the comb. The lighter yellow comb at the top is where the bees stored their honey. The darker comb shows where the brood is being raised in the hive. The bees coat each cell in the broodnest area with a ‘shellac’, a form of propolis providing an antimicrobial, anti-fungal and antiviral environment for the broodnest leading to a perfect spot for the queen to lay some eggs. And perfect for keeping the hive free of disease. Each time the bee emerges from a cell the bees recoat that cell with the shellac so the queen can again lay in a clean enviroment. When assessing a hive these differences in wax can give you clues to where the brood is being raised in the hive. Ideally in a top bar hive you want there to be honey stored above the broodnest for some very important reasons. One the large band of honey is very accessible to the bees when they are raising their young, mixing pollen and nectar to feed larvae. Secondly the large band of honey acts as an ‘insulator’ being a heat sink of warmth in the winter to help the bees keep a warm, regulated hive. And in the summer the honeycomb serves as a cooling insulator so that the bees can again keep the hives from overheating and helping them keep the delicate temperature of the broodnest constant. With the Cathedral Hive the larger comb gives the bees ample space for a large band of honey at the top of the comb and this honey equals nutrition, fuel to live and acts, as mentioned above, an insulator against heat and cold. Going into winter the bees will fill empty brood cells with honey and this is called ‘backfilling’ the comb which will add to the insulation factor of the honeycomb.

Newly Capped Honey Comb
With open cells that may be filled with nectar, called uncapped honeycomb

Newly Capped Honey Comb -CloseUp

Capped honey cells are often confused with newly capped worker brood cells (image below). Capped honey cells are slightly indented versus the capped worker brood cells that have a slight protrusion to them.

Newly Capped Honey Comb -CloseUp
Capped honey cells are often confused with newly capped worker brood cells (image below). Capped honey cells are slightly indented versus the capped worker brood cells that have a slight protrusion to them.

Capped Worker Brood Cells
Capped worker brood cells are often confused with capped honey comb cells (image above). Capped worker brood has a slight bump protruding from the cell.

Capped Worker Brood Cells -Darker
When the comb has had at least one cycle of brood laid in it and the bees emerged, the comb becomes a little darker than a first year comb (above image) where the capped worker brood is light in color. The comb becomes darker due to the bees coating the cells with their ‘shellac’ before the queen lays another egg in the cell. The combs become darker and darker. You will want to rotate out (harvest) brood comb after a few years as the comb can build up pesticides and the cells in the comb will also become smaller and smaller and will no longer be good combs for the queen to lay in.

Various Cells -Darker Comb

This can be a typical comb you may see in the brood nest area. There are many empty cells where worker bees have emerged. Brood combs normally have a band of honey at the top of the comb. This is honey that can be used to feed the young larvae. This comb also has some capped drone cells on the very left side of the comb.

Capped Drone Comb -Lighter Comb
Again this can be a typical comb you may see in the brood nest area, except this is capped drone comb which can be mistaken for capped worker brood (see images above). Capped drone comb protrudes out more than the worker brood. Drone comb looks more like an eraser at the end of a pencil. Again this comb had a band of capped honey at the top and the darker cells are capped honey.

Capped Drone Comb with Capped Honey Comb – CloseUp
This is a challenging identification but the slightly darker cells are capped honey and the remaining capped cells are capped drone comb.

Capped Drone Comb -Lighter Comb
This is the same comb at a side angle as the above 2 pictures. There are a few empty cells where the drones emerged.

Capped Worker Brood Comb with Heater Bee cells (open cells)
Another image of capped worker brood with some empty cells among the capped brood which are kept intentionally open by the laying queen so that heater bees can go into those empty cells and warm the adjacent larvae if necessary. The brood nest needs to be at a consistent temperature and the heater bees help regulate this temperature.

Capped Worker Brood Comb with Heater Bee cells -CloseUp
A closeup of the image above. Some of the empty cells have nectar in them. (the shiny looking cells). The there are some empty cells where heater bees can do their job of regulating the brood nest temperature.

Open Larvae Cells and Capped Worker Brood Comb

Open Larvae Cells and Capped Worker Brood Comb -CloseUp

Queen cells
Queen cells are normally found on the edge of the comb in top bar hives. They are described as looking look like a small peanut shape.

Emergency Queen Cells

Emergency queen cells are found in the middle of the comb, as the bees have taken a 1-3 days old worker bee egg (before it is a larvae) and built wax up around it to form a queen cell that they will then continue to feed royal jelly to make a queen.

Emergency Queen Cells

Emergency Queen Cells

Emergency Queen cells in the middle of the comb drawn out from a 1-3 day old worker
egg before it is a larvae

Capped Drone Cells

Capped Worker Brood Cells -Darker

Capped Worker Brood Cells in darker comb. At the top of the comb is capped honey cells

Capped Worker Brood Cells -Darker

Capped Worker Brood Cells -Darker

By Clarence Collison

Honey bees forage for two distinct nutrient sources in the form of nectar
(energy) and pollen (nitrogen).

Honey bees forage for two distinct nutrient sources in the form of nectar (energy) and pollen (nitrogen). Fewell and Winston (1996) investigated the effect of varying energy stores on nectar and pollen foraging. No significant changes in nectar foraging in response to changes in honey storage levels within colonies were found. Individual foragers did not vary activity rates or nectar load sizes in response to changes in honey stores, and colonies did not increase nectar intake rates when honey stores within the hive were decreased. This result contrasts with pollen foraging behavior, which is extremely sensitive to colony state. They were able to show that individual foraging decisions during nectar collection and colony regulation of nectar intake are distinctly different from pollen foraging.

A honey bee colony can skillfully choose among nectar sources. It will selectively exploit the most profitable source in an array and will rapidly shift its foraging efforts following changes in the array. How does this colony-level ability emerge from the behavior of individual bees? The answer lies in understanding how bees modulate their colony’s rates of recruitment and abandonment for nectar sources in accordance with the profitability of each source (Seeley et al. 1991). A forager modulates its behavior in relation to nectar source profitability: as profitability increases, the tempo of foraging increases, the intensity of dancing increases and the probability of abandoning the source decreases. How does a forager assess the profitability of its nectar source? Bees accomplish this without making comparisons among nectar sources. Neither do the foragers compare different nectar sources to determine the relative profitability of any one source, nor do the food storers compare different nectar loads and indicate the relative profitability of each load to the foragers. Instead, each forager knows only about its particular nectar source and independently calculates the absolute profitability of its source.

Artwork by Tom Seeley.

Even though each of a colony’s foragers operates with extremely limited information about the colony’s food sources, together they will generate a coherent colony level response to different food sources in which better ones are heavily exploited and poorer ones are abandoned. This is shown by a computer simulation of nectar-source selection by a colony in which foragers behave as described above. Nectar source selection by honey bee colonies is a process of natural selection among alternative nectar sources as foragers from more profitable sources “survive” (continued visiting their source) longer and “reproduce” (recruit other foragers) better than do foragers from less profitable sources. Hence this colonial decision-making is based on decentralized control. They suggest that honey bee colonies possess decentralized decision-making because it combines effectiveness with simplicity of communication and computation within a colony (Seeley et al. 1991).

Nectar is collected from flowering plants by adult worker bees. When nectar foragers return to their colonies from the field, they give their loads to nestmates near the colony entrance (i.e. receiver bees). She sometimes transfers her entire load to one bee, but other times she makes a series of unloadings to several bees (Huang and Seeley 2003). Receiver bees transfer the nectar to other nestmates who continue to pass it on until ultimately the nectar is placed in a cell on a comb somewhere in the hive (Seeley 1992). During the Spring and Summer, large quantities of nectar are collected and eventually converted into honey that is stored for later use when the plants are not blooming or weather is not suitable for foraging. Combs with just honey or nectar are found above or adjacent to the brood nest. Nectar also is placed in cells on combs where brood is reared. Placing nectar in cells of comb containing brood makes it readily available to nurse bees who feed these resources to the larvae.

Nixon and Ribbands (1952) first described the transfer of nectar from foragers to nestmates in a colony. Within 3.5 hours after releasing just six foragers that were fed 32P labeled sugar water into a colony, most of the other foragers (62%) and about a fifth of the worker population in the brood area received some of the labeled food. The rapid transfer of nectar from foragers to other nestmates indicates the numerous trophallactic contacts made among workers in a hive. The exchange of nectar among workers in some cases is for food processing and storage. However, the radioactive marker was also detected in nurse bees within four hours of releasing the labeled foragers. This suggests that some incoming nectar is disseminated to combs with brood. The transfer of incoming nectar to cells around the brood might help to coordinate the behaviors of nestmates involved in nectar collection, storage, and rearing brood.
The speed at which a successful forager transfers the honey stomach contents (unloading rate) from donor to recipient is related to the profitability offered by the recently visited food source.
Two of the main characteristics that define food source profitability are the flow of solution delivered by the feeder and the time invested by the forager feeding at the source (feeding time). Wainselboim et al. (2002) investigated which of these two variables is related to unloading rate. They individually trained donor foragers to a regulated-flow feeder that presented changes in the delivered flow of solution within a single foraging bout, while feeding time remained constant. With the range of flows used, bees attained maximum honey stomach loads in all experiments. During the subsequent trophallactic encounter with an unfed recipient hivemate, unloading rate was differentially affected by the changes in flow of solution presented during the previous foraging trip at the source, depending on whether there had been an increase or a decrease in flow rate, but did not increase the unloading rate when presented with an increase at the food source. Thus, forager honey bees seem to be able to detect variations in the delivered flow of solution, since they modulate unloading rate in relation to these changes, although decreases in food value seem to be perceptually weighted in relation to increases, independently of the time invested in the food-gathering process.

The food storer bees in a colony are the bees that collect nectar from returning foragers and store it in the honey combs. They are the age group (generally 12-18 day old bees) that is older than the nurse bees but younger than the foragers. Food storers make up approximately 20% of the colony members (Seeley 1989).

When a honey bee laden with nectar returns to the hive, she acquires information about the balance between her colony’s nectar collecting rate and its nectar processing capacity by noting the time spent searching to find a food-storer bee (who unloads and stores the forager’s nectar). By modeling this search process, and experimentally testing a basic prediction of the model, search time was found to be an accurate indicator of the ratio of the two variables, with reliability guaranteed by the rules of probability. For example, if the collecting rate increases while the process capacity remains constant, then the proportion of food storers in the unloading area decreases, hence there is an automatic increase in the expected number of bees that a forager must sample before finding a food-storer bee (Seeley and Tovey 1994).

The flow of incoming nectar into honey bee colonies was simulated by feeding a sucrose solution labeled with a novel protein (IgG) marker and then analyzing bee and colony samples using an enzyme-linked immunosorbant assay (ELISA) (DeGrandi-Hoffman and Hagler 2000). The labeled sucrose solution was quickly transported to food storage and brood combs. Within two hours, equal percentages of worker bees from food storage combs, nurse bees and nectar samples tested positive for the marker. Percentages of nurse bees and larvae testing positive also were equal within the first two hours of feeding it to a colony and these percentages increased over time. These results suggest that workers with nectar loads deposit them into cells on either food storage or brood comb with equal frequency. The labeled sucrose solution transported to the brood comb is subsequently used by nurse bees to feed larvae.

Nectar foragers upon returning to the hive, sometimes perform a mysterious behavior called the tremble dance. In performing this dance, a forager shakes her body back and forth, at the same time rotating her body axis by about 50° every second or so, all the while walking slowly across the comb. During the course of a dance, which on average lasts 30 minutes, the bee travels about the broodnest portion of the hive. It has been shown experimentally that a forager will reliably perform this dance if she visits a highly profitable nectar source but upon return to the hive experiences great difficulty finding a food-storer bee to take her nectar. This suggests that the message of the tremble dance is “I have visited a rich nectar source worthy of greater exploitation, but already we have more nectar coming into the hive than we can handle.” It also has been shown experimentally that the performance of tremble dances is followed quickly by a rise in a colony’s nectar processing capacity and by a drop in a colony’s recruitment of additional bees to nectar sources. These findings suggest that the tremble dance has multiple meanings. For bees working inside the hive, its meaning is apparently “I should switch to the task of processing nectar,” while for bees working outside the hive (gathering nectar), its meaning is apparently “I should refrain from recruiting additional foragers to my nectar source.” Hence it appears that the tremble dance functions as a mechanism for keeping a colony’s nectar processing rate matched with its nectar intake rate at times of greatly increased nectar influx. Evidently the tremble dance restores this match in part by stimulating a rise in the processing rate, and in part by inhibiting any further rise in the intake rate (Seeley 1992).

Nectar is converted into honey through a maturation process. The most prominent feature of this process is a considerable water loss (40 to 70% of nectar initial weight) that takes place in two stages: an initial evaporation carried out by the bee, which brings down water content to 40 to 50%, and the final evaporation that takes place in the honeycomb, which yields a product with 15 to 18% water (Ruiz-Argueso and Rodrigues-Navarro 1975).

Foragers add enzymes (invertase, glucose oxidase) to nectar during foraging, so some digestion is already occurring before nectar is brought back to the hive (Huang 2010). Invertase converts sucrose into two six-carbon sugars, glucose and fructose. A small amount of the glucose is attacked by the second enzyme, glucose oxidase, and gets converted into gluconic acid and hydrogen peroxide. Gluconic acid makes honey acidic, and hydrogen peroxide has germ-killing properties, both contributing to honey’s unfriendly disposition to bacteria, mold, and fungi.
Receiver bees upon receiving nectar from foragers begin to dry the nectar either on their mouthparts, by forming a large drop between the proboscis and the mandibles, or by depositing it into cells and fanning over the cells. The moisture has to be reduced to 17-18% before bees consider the honey “ripe” and then seal the cells.

While in the forager’s honey stomach, nectar does not become more concentrated (Park 1927, 1932); instead it is slightly diluted by the addition of digestive juices. The surplus water is evaporated in the hive, either during the manipulation by the mouthparts of the bee or when the nectar is in the cells. Oertel et al. (1951) initiated experiments to determine the rapidity of hydrolysis or inversion of cane sugar (sucrose) in the honey stomach of the bee and the effect of internal secretions on the concentration of the nectar or cane-sugar syrups in the honey stomach. Both rapid inversion of sucrose and dilution of honey stomach contents were observed.

Two main groups of bacteria, classified as Gluconobacter and Lactobacillus, are present in ripening honey. A third bacterial group, classified as Zymomonas, and several types of yeast are occasionally isolated. Both in natural honey and in synthetic syrup, the bacterial population decreases in the course of the ripening process. Lactobacillus and Gluconobacter disappear after minimum moisture (about 18%) is reached (Ruiz-Argueso and Rodrigues-Navarro 1975). It seems that Lactobacillus decreases more rapidly than Gluconobacter both in natural honey and in synthetic syrup. It is difficult to establish the contribution of these bacteria to the ripening process.

Clarence Collison is an Emeritus Professor of Entomology and Department Head Emeritus of Entomology and Plant Pathology at Mississippi State University, Mississippi State, MS.

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