FROM NECTAR TO HONEYFROM NECTAR TO HONEY

“ “ A plant perspective”A plant perspective”

ChestnutChestnut orchardorchard

• Pollinating a chestnut tree with a bucket truck

What is the nature of the relationship What is the nature of the relationship

between pollinators and plants? between pollinators and plants?

• Plants provide nectar (and pollen) as inducements/rewards for pollinators to visit flowers.

• Pollinators help ensure the reproductive success of the plants.

• Each evolves so as to maximize rewards obtained and minimize costs/effort.

PlantPlant--pollinator rpollinator relationships are importantelationships are important

• An estimated one-third of all crop plants need honey bees for pollination.

• Natural plant communities depend on • Natural plant communities depend on pollinators to maintain the community structure/composition.

• Lack of pollinators can cause plant species to become endangered or go extinct.

Why Why do plants do plants need pollinators for need pollinators for

““Reproductive SuccessReproductive Success” ? ” ?

• Some plants do not need pollinators

o They are wind pollinated or can mechanically self pollinate.

• About 80% of plants need cross-pollination to produce viable seed or healthy offspring.

o Separate male and female plants

o Plants with separate male and female flowers

o Self-incompatible plants

Winterberry (Winterberry (Ilex Ilex verticillataverticillata) ) female plantfemale plant

•

• Robert H. Mohlenbrock. USDA SCS. 1989. Midwest wetland flora: Field office illustrated guide to

plant species. Midwest National Technical Center, Lincoln. Courtesy of USDA NRCS Wetland Science Institute

Male and female chestnut flowersMale and female chestnut flowers

Plant Plant PhenologyPhenology

• Plant Phenology is the timing of major biological events such as bud-break, flower bud formation, flowering, or fruit maturation.

• This timing is controlled by a variety of environmental and internal factors.

• “Ecotypes” are plants genetically adapted to specific climates.

What determines if or when a plant What determines if or when a plant fflowers?lowers?

• Annuals vs. Perennials

• Plant age/developmental stage

• Vernalization (exposure to “winter” conditions) • Vernalization (exposure to “winter” conditions)

• Nutrients and water

• Light intensity and quality (photosynthesis)

• Day length (short day, long day or day neutral)

• Temperature (Growing degree days)

DayDay--length length ssensitive plants ensitive plants

GrowingGrowing--degreedegree daysdays

• Growing degree days (GDD), are a tool for predicting plant (and insect pest) development rates and phenology.

• Plant growth is usually strongly influenced by the ambient temperature. ambient temperature.

• GDD are calculated by taking the average of the dailyTmax and Tmin compared to a base temperature, Tbase, which is usually about 10 °C.

• The sum of days above the base temperature is the GDD

Growing Degree Day Chart Growing Degree Day Chart

Common name Latin nameNumber of growing degree days baseline

10 °C

Witch hazel Hamamelis spp. begins flowering at <1 GDD

Red maple Acer rubrum begins flowering at 1-27 GDD

Sugar maple Acer saccharum begin flowering at 1-27 GDD

Norway maple Acer platanoides begins flowering at 30-50 GDD

White ash Fraxinus americana begins flowering at 30-50 GDD

Crabapple Malus spp. begins flowering at 50-80 GDD

Common lilac Syringa vulgaris begin flowering at 80-110 GDD

Black locust Robinia pseudoacacia begins flowering at 140-160 GDD

Catalpa Catalpa speciosa begins flowering at 250-330 GDD

Elderberry Sambucus canadensis begins flowering at 330-400 GDD

Purple loosestrife Lythrum salicaria begins flowering at 400-450 GDD

Sumac Rhus typhina begins flowering at 450-500 GDD

Butterfly bush Buddleia davidii begins flowering at 550-650 GDD

The relationship of plants and pollinators The relationship of plants and pollinators is an example of coevolution is an example of coevolution

• Plants must “advertise” to attract specific pollinators.

• Plants must offer appropriate rewards to pollinators

Nectar and or pollen (or trick them).Nectar and or pollen (or trick them).

• Plants must regulate their nectar production, since it has energetic costs.

o Timing

o Amount

o Composition

How do honey bees know what flowers How do honey bees know what flowers

will be rewarding to visit?will be rewarding to visit?

• Flower shape, color and contrast, : blue, yellow, ultraviolet

• Bee guides on petals

• Size of inflorescences

• Smell (volatile organic compounds, VOCs)

o ex. benzyl acetone is an common attractant

• Memory

MimulusMimulus flowers flowers

Bee GuidesBee Guides-- IllustrationIllustration

NectariesNectaries

• Floral vs. ExtrafloralNectaries

• Floral Nectary structure varies widely structure varies widely between different plant species

• Mechanism of nectar secretion varies between species

How is nectar produced?How is nectar produced?

• Floral nectaries usually have direct connections to the plant vascular system (xylem and phloem)

• Sucrose transported in the phloem supplies sugars, • Sucrose transported in the phloem supplies sugars, water is transported in the xylem.

• Cells within the nectary may also break down stored starch to produce sugars that exported out of the cells

Many types of substances are found in nectarMany types of substances are found in nectar

• The unique tastes and colors of monofloralhoneys demonstrate that nectars from different plants are different.

oClover honey

o Tupelo honey

oChestnut honey

oClethra honey

The composition of nectar is usually The composition of nectar is usually

“tailored” to particular types of pollinators“tailored” to particular types of pollinators

• The ratios of different types of sugars varies in different species of plants.different species of plants.

• Specific pollinators prefer different types of nectar (sugar type and concentration)

What classes of substances are What classes of substances are commonly found in nectar?commonly found in nectar?

• Sugars (mono and disaccharides)

• Sucrose, glucose, fructose are most common

(total sugar concentrations of 5-80%)

• Amino acids (used to build proteins)• Amino acids (used to build proteins)

• Nectarins (nectar proteins) that protect against microbial contamination of the nectar

• Other substances – vitamin C, organic acids, VOCs

Many other substances also occur in nectarMany other substances also occur in nectar

• They include compounds naturally produced throughout the plant or transported in the vascular system.

• They help prevent certain types of yeast and bacteria from contaminating nectar.

• They encourage pollinators to visit different flowers and facilitate cross-pollination.

• Plant Secondary compounds may be present in nectar.

o Flavonoids (carotenoids)

o Vitamins (ex. vitamin C)

Alkaloids (ex. Caffeine and nicotine)

Other substances found Other substances found in in nectarnectar

o Alkaloids (ex. Caffeine and nicotine)

o Glycosides (these have repellent effects)

o “Toxins” in nectar can result in toxic honey

• Rhododendron sp., Oleander sp., Ragwort sp.

Bees chemically modify nectar Bees chemically modify nectar

to make honeyto make honey

o Storage of nectar in honey stomach

o Enzymatic modification (enzymes in the bees

hypopharyngeal glands) ex. Invertase, glucose hypopharyngeal glands) ex. Invertase, glucose oxidase

o Concentration of nectar by bees (evaporation)

o Action of bacteria (lactic acid bacteria)

found in honey stomach

Honey bee anatomy Honey bee anatomy

MMeasuring nectar production easuring nectar production

• Individual flowerso Collect nectar and measure amount and

concentration.

o Botanical research o Botanical research

• Plant community o Total nectar production in a specific area

o In an area harvested by a particular hive, weigh hive data is indicative of total nectar production

What influences how much nectar an What influences how much nectar an

individual plant produces? individual plant produces?

• Genetics

o Differences between species

o Differences between individual plants of the same o Differences between individual plants of the same species

• Developmental and environmental factors

o Differences between flowers on a plant

Total daily sugar production rates per flower can

vary 10 fold (0.6-5.5 mg /flower)

What influences how much nectar an What influences how much nectar an

individual flower produces? individual flower produces?

• Development stage of plant and flower

• Flower age (production peaks at anthesis)

• Time of day effects

• Bee forging activity

o Dynamic nectar replenishment

o Nectar resorption if unused

• How many flowers have been pollinated

Dynamic regulation of nectar productionDynamic regulation of nectar production

““Evolutionary considerations”Evolutionary considerations”

• Outcrossing may be optimized by not continually producing nectar or some plants not producing as much (modifying pollinator behavior)

• Whether plant has been pollinated and how many flowers have been pollinated

• Energy for seed and fruit production and need for re-directing resources

What influences how much nectar What influences how much nectar a a

plant community plant community produces? produces?

• This is a more complex problem.

• How can this be measured?

What factors influence What factors influence total nectar production, total nectar production, nectar nectar standing standing crop, and honey flow?crop, and honey flow?

• Total nectar availability at any particular time is the product of many factors

o How many different species are flowering

o When a species flowers

o What species are flowering and their NPR

o How long the plants flower

o Plant population sizes

o Location and climate

Nectar production and weigh hive Nectar production and weigh hive datadata

Local plant species that supply nectar and Local plant species that supply nectar and pollen to honey bees, and when they flowerpollen to honey bees, and when they flower

Plant Nectar/Pollen Bloom Dates

Alder

(Alnus incana) P Feb - Apr

Alfalfa

(Medicago sativa) (Good honey plant) N & P Jul - Aug

Apple

(Malus spp.) (Major) N & P Apr - May

(Malus spp.) (Major) N & P Apr - May

Aster

(Aster spp.) (Major) N & P Sep-Frost

Azalea (Rhododendron spp.)

(some types may produce poisonous nectar) N Jun - Aug

Basswood (SA)

(Tilia americana) (Good honey plant) (Major) N & P Jun - Jul

Birdsfoot trefoil

(Lotus corniculatus L.) N Jun - Aug

Black Locust (SA)

(Robinia pseudo-acacia) (short bloom period) N & P May - Jun

Blackberry

(Rubus spp.) (Major) N & P May - Jun

Blueberry

(Vaccinium corymbosum) N May - Jun

Boneset, Joe-Pye weed

(Eupatorium spp.)N & P Aug - Sep

Butterfly Weed

(Asclepias tuberosa) N Jul - Aug

Canola

(Brassica napus L.)N & P May - Jun

Cat-Tail

(Typha latifolia) P Jun - Jul

Catalpa

Catalpa speciosa) N & P Jun - Jul

Chestnut

(Castanea dentata) P May - Jun

Clethra Summersweet

(Clethra alnifolia) N Jul - Aug

Common Vetch

(Vicia cracca L.) N & P Jul - Aug

Crab Apple

(Malus spp.) N & P Mar - Jun

Dandelion

(Taraxicum officinale) (Major) N & P Apr - May

Environmental conditions affect nectar production

• Nectar is produced as a result of current photosynthesis.

• Nectar production may use from 2% to more than 37% • Nectar production may use from 2% to more than 37% of a plants available energy.

• This energy expenditure can affect future growth and reproduction.

Environmental conditions affect Environmental conditions affect nectar productionnectar production

• Factors influencing net photosynthesis will

influence nectar production rates.

o Sunlight

o Water (20% reduction with mild water stress)

o Temperature (day and night temperatures)

How How are are plantplant--pollinator interactions pollinator interactions being being

altered by climate altered by climate and land and land use use changes?changes?

• http://honeybeenet.gsfc.nasa.gov/

• http://honeybeenet.gsfc.nasa.gov/Sites/ScaleHiveSite.php?• http://honeybeenet.gsfc.nasa.gov/Sites/ScaleHiveSite.php?

SiteID=MA002

• https://www.usanpn.org/

ChangesChanges in land usein land use

• Loss of agricultural land

• Suburbanization

• Prevailing landscaping practices

• General lack of appreciation of importance of natural ecosystems and diversity

CClimate changelimate change

• Changes in seasonal average temperatures and associated changes in relative day and night temperatures are having large effects on plant growth and phenology.

• Flowering earlier is correlated with ending flowering earlier in the season.

• USA National Phenology Network is enlisting citizen scientists to document patterns.

Changes in plant phenology and Changes in plant phenology and

associated times of nectar flowassociated times of nectar flow

• Important considerations

Variation between locations• Variation between locations

o Natural year to year variability

o Consistent directional trends

(on av. flowering 1/2 day earlier every year since 1970s)

Bee communities, and the plants they Bee communities, and the plants they

depend on, are confronting many issues depend on, are confronting many issues

• I hope this presentation has provided useful information concerning:

• The complexity and dynamics of the evolutionary • The complexity and dynamics of the evolutionary relationship between honey bees and plants.

• The responsiveness of plants to their environment and their bee visitors.

• Constraints on flowering and nectar production.

Thank you!Thank you!