Bees, fruit pollination and
some current issues affecting bee health.
Common Ground Advice Note 25
Catherine Simmonds for Common Ground
Catherine is a bee keeper and a poet. Her latest book is We have heard Ravens – poems drawn from Dorothy Wordsworth’s Journals (Flagon Press, 2008)
At its height in late spring early summer a healthy western honeybee colony will be made up of:
1 Queen (female)
300 - 3000 Drones (male)
50’000 – 60’000 Workers (non reproductive females)
25’000 – 30’000 will be older workers & foragers
25’000 – 30’000 will be young workers or ‘nurse bees’ who stay in the hive and rear the brood:
6’000 eggs (from which larvae will hatch)
9’000 larvae requiring food
20’000 older larvae sealed in cells, which need no attention other than to be kept warm.
Older worker bees are available for foraging only if there are enough young workers to feed the brood and ‘cover’ it – keeping the brood-nest temperature steady at 34-35 °C. If for any reason the brood is left exposed it is at risk of chilling and can die.
As well as raw materials for honey, foragers must collect sufficient pollen to provide protein for the developing brood. The honey getting capacity of a colony depends not only on the total population of bees in the hive, but on the balance between older and younger worker bees.
All bees emerging from their cells: new queens, drones and workers carry on changing and maturing inside the hive until they are ready to perform their respective functions which are:
Queen - to leave the hive once she physically ready, mate with congregated drones and return to the hive with enough stored sperm to begin her lifelong egg laying.
Drones – to leave the hive and mate with virgin queens.
Workers – To remain in the hive for the first three weeks, cleaning vacated cells, feeding young larvae, making wax to build new comb, processing incoming stores of honey and pollen and then in most cases to go on to become flying / foraging bees - collecting pollen before moving on to nectar. Some bees will specialise in collecting propollis (resin for sealing and cleaning the hive) and or water.
The fuel consumption of a flying bee is about ½ mg honey per km or 3 million km to the litre. In providing one kilogram of surplus honey for market, the colony has had to consume something like a further 8kg to keep itself going, the foraging for which has probably covered a total flight path equal to six orbits round the earth – at a fuel consumption of about 25g of honey for each orbit. In British units, this means 7 million miles to the gallon; a pound of honey on the breakfast table necessitates a total flight path equivalent to three orbits round the earth, each orbit using up an ounce of honey as fuel.
from Eva Crane, A Book of Honey (1980 IBRA)
Pollination – some statistics
80 percent of flowering plants worldwide are pollinated by insects
Of those 85% are pollinated by bees
As many as 90% of fruit tree flowers are dependent on honey bees
The list of flowering plants pollinated by honeybees includes about 170’000 species
The number of flowering plant species that are dependant on honeybees and without which they would fare badly is estimated to be above 40’000
This worldwide sea of flowers is pollinated by just nine species of bee and in Europe and Africa by only one = Apis Mellifera (meaning ‘honey carrying’)
A single colony of honeybees may visit several million flowers on a single working day.
Because bees inform one another about newly discovered areas of flowers, visits to all nectar yielding flowers are rapidly achieved.
Honeybees are also generalists that can cope with just about all flower types.
Flowers that depend on bees can afford to produce less pollen than those that depend on wind, as bees are such efficient pollinators.
Because flowering plants and bees evolved together, the presence and activities of bees actually changed the way plants behave and the eventual form they took. Ferns, which pre-date plants with flowers, excrete large quantities of sweet ‘sieve tube juice’ as a waste by-product of photosynthesis. Flowering plants have retained this process and learnt to make nectar out of the original waste product purely for the consumption and attraction of bees – a trade off that allows them to produce less pollen (than relying on wind) or risk being pollinated by a more destructive insect (like a beetle) that would eat the flower parts themselves in the process of pollination.
A single cherry blossom can produce more than 30g of nectar per day and an entire cherry tree almost 2kg.
The amount a single foraging bee will bring home with each flight can reach 40mg – about the daily production of a single cherry blossom.
A foraging bee itself has a body weight of only 90mg and therefore accommodates almost half its own bodyweight again in nectar.
At 2mg per blossom per day for an apple blossom, a far larger number of apple blossoms need to be emptied.
A bee needs to visit two cherry blossoms or 20 apple blossoms to fill her crop. Each visit a bee makes only yields a small amount of nectar made available by the plant at that time and which replenishes when she leaves.
Estimated record for a bee is having visited 3’000 flowers in a single day.
Producing nectar is a strategy to lure bees and costs plants in form of raw materials and energy.
To save foragers visiting each flower to see if there is nectar present, foraging bees who have taken the last drop of nectar will mark the flower with a chemical ‘empty’ signal. This fades in about the same time the flower takes to replenish the nectar store. It is this kind of hive wide communication and co-operation that makes the honeybees such an efficient pollinator.
When out foraging, honeybees don’t just stop at any flower they happen to find. They exhibit loyalty to a particular nectar source thus individual bees learn and then remain loyal to particular flowers and will work those exclusively as long as they are available. This makes them extremely valuable to farmers and fruit growers who want a crop pollinated but can cause problems when a higher nectar yielding crop (e.g. oil seed rape, white clover) is right next to or in among a lower yielding one (e.g. an apple orchard.)
Bees usually fly 2- 4 km to forage but in extremis can fly up to 10km.
from Jurgen Tautz. The Buzz about Bees (2008 Springer)
Fruit Crops and Bees
Wikipedia article - Fruit Tree Pollination: en.wikipedia.org/wiki/Fruit_tree_pollination
Report on State of New South Wales Agriculture : www.dpi.nsw.gov.au/__data/assets/pdf_file/0019/117109/bee-cherry-plum-pollination.pdf
During the bloom each season, apple growers usually provide pollinators to carry the pollen.Symptoms of inadequate pollination are small and misshapen apples, and slowness to ripen. The seeds can be counted to evaluate pollination. Well-pollinated apples are the best quality, and will have seven to ten seeds. Apples with fewer than three seeds will usually not mature and will drop from the trees in the early summer. Inadequate pollination can result from either a lack of pollinators or from poor pollinating weather at bloom time. It generally requires multiple bee visits to deliver sufficient grains of pollen to accomplish complete pollination.
Pears are similar to apples, with the notable exception that pear blossoms are much less attractive to bees, due to lower sugar content than apple or contemporaneous wildflower nectar. Bees may abandon the pear blossoms to visit dandelions or a nearby apple orchard. There are two possible methods used to compensate. One is saturation pollination, that is to stock so many bees that all area blossoms are worked regardless of the attractiveness to the bees. The other is to delay the movement of the beehives into the orchards until there is about 30 per cent bloom. The bees are moved into the orchard during the night and will usually visit the pear blossoms for a few hours until they discover the richer nectar sources. The recommended number of hives per acre is 1.
Many citrus varieties are seedless and are produced parthenocarpically without pollination. Some varieties may be capable of producing fruit either way, having seeds in the segments, if pollinated, and no seeds if not.
Citrus that requires pollination may be self compatible, thus pollen must be moved only a short distance from the anther to the stigma by a pollinator. Some citrus, such as Meyer Lemons, are popular container plants. When these bloom indoors, they often suffer from blossom drop because no pollinators have access.
A study in Victoria (New Zealand) demonstrated the importance of bees as the primary agent for pollinating cherries. Trees caged from bees had a 2% fruit set, as compared to uncaged trees exposed to the activities of bees which had a 35.9% fruit set. The yields were 1.9 kg/tree for the caged trees and 35.2 kg/tree for the uncaged trees. It was also found that 97% of the insects that visited the cherry flowers were honeybees. Wind is not a factor in pollinating Prunus spp. (cherries and plums) and honeybees are by far the majority of the insect visitors to plum blossom. Honeybees collect nectar and pollen from blossoms and find this group of plants very attractive. Sugar concentrations as high as 55% in sweet cherry nectar have been recorded which makes the blossom very attractive to bees. For plums and cherries a stocking rate of 2–3 hives/ha is generally regarded as adequate to pollinate most crops.
Current Threats to Bee Health
from individual Wikipedia entries on Varroa, Nosema, Apis Cerana, Bees and Climate Change & CCD; also Oklahoma State University research Honey bees, Bumble Bees, Carpenter Bees & Sweat Bees: osuextra.okstate.edu/pdfs/F-7317web.pdf
Recent high level losses from the apiaries of beekeepers worldwide have drawn attention to the fact that domesticated honey bees are suffering a crisis in their health and ability to maintain colony strength and function. Similar declines in bumblebees and wild bees have been recorded although it is not clear if the same factors underlie the problems these other pollinators are facing.
The Varroa mite originated in eastern Asia crossing from its natural host Apis cerana* (Eastern or Indian honey bee) to Apis mellifera (Western or European honey bee) and spread into Europe, probably via Russia. Since the 1980’s Varroa has been carried into most other beekeeping regions of the world affecting thousands of colonies via an international trade in live bees & queen bees which are shipped world-wide, and are believed to be responsible for the spread of the mite to both North and South America, and Africa and New Zealand. Although Apis cerana is the natural host to both the miteVarroa destructor and the parasite Nosema ceranae, both are serious pests of the Western honeybee. The parasitic Varroa mite damages honeybee colonies by reducing vigour of individual bees. It is an external parasite which sucks body fluids from its host and wound sites may provide entry points for disease organisms. Bees parasitized during the larval stage may live as adults for shorter periods, die before emergence, weigh less, appear deformed or seldom leave the colony to forage. As more emerging bees are weakened by its activity, the colony as a whole experiences impaired immunity to other threats and viruses. If the colony collapses from infestation, bees that abandon the hive may carry mites to other hives which they will try to join. Apis cerana, having co-evolved with these parasites, exhibits much more careful grooming than Apis mellifera, and thus has an effective defence mechanism against Varroa, which Apis mellifera does not have – (although some current research shows it is learning to bite the mites). Also Apis cerana workers do not re-use old wax as often as in other bee species, they usually tear down old combs and build new wax constantly. Other than these key behaviours much of their behaviour and biology (at least in the wild) is very similar to that of Apis mellifera.
It arises mostly in the spring after bad weather when the bees have been confined to the hive. Most strongly the female workers are afflicted, less the drones. Since afflicted bees rarely participate in feeding the queen, she is likewise more rarely infected. Most important symptom is dysentery (“diarrhoea”), which shows itself through yellow spotting above the entrance of the hive. In addition flight inability (“crawler”) can occur due to disjointed wings. Further symptoms are increase of girth of the abdomen, missing sting reflex and earlier supersedure of the queen. The honey production and life expectancy of the bees sink due to the reduced utilization of pollen. Nosema is spread by spores from infected bees, which nurse bees ingest when cleaning the hive. It can be treated with antibiotics although there is current disagreement about whether colonies should be treated prophylacticically (to prevent infection) or only when they are proven to be infected.
Chinese researchers (Huang et al.) found Nosema ceranae in spring 2005 in Taiwan for the first time also in the western honeybee (Apis mellifera). Shortly afterwards Spanish bee researchers reported that the new pathogene was also discovered in 2005 in Spain and has displayed a notably higher virulence than the western version. The disease caused by Nosema ceranae in western honeybees exhibits heavier disease patterns deviating from the typical nosema findings, including unusually heavy intestine injuries in the bees, no diarrhoea, preferential affliction of older collecting bees, which die faraway from the hives, and conditioning collapse of the bee colonies. Furthermore it was observed within fewer years the strongly increased propagation of Nosema cerana and its occurrence at unusual seasons (all-year-season). Therefore a higher reinfection rate of the bee colonies is assumed, since the pathogene survives longer in the external environment. (W)
The term Colony Collapse Disorder was first applied to a drastic rise in the number of failing western honey bee colonies in North America in late 2006. It is not a disease in itself and therefore confusion frequently arises about when exactly to apply the term to a range of current disorders of bee health and colony behaviour where bees appear to abscond, or die in the field, when empty hives are uncovered (frequently after over wintering periods when the beekeeper doesn’t inspect the hive due to low temperatures which would chill brood and bees exposed by inspection). Many authorities attribute CCD to biotic factors such as: Varroa mites and insect diseases including Nosema apis / Nosema ceranae and Israel acute paralysis virus. Other proposed causes include environmental change-related stresses; malnutrition; pesticides (e.g. neonicotinoids, based on the nerve toxin nicotine); genetically modified (GM) crops with pest control characteristics such as transgenic maize and the stress induced by the practices of migratory beekeeping. Current research favours the weakening effects of the combination of persistent Varroa infestation with the increased threat from more virulent types of Nosema. Weakenss in bee colonies due to the above may then be exacerbated by the declining quality of available forage and increasingly erratic climatic & seasonal variations which put colonies under increased stress.
Biodiversity & Climate Change
It is under discussion how much honeybees and other pollinators are being adversely affected by climate change. Foraging is regulated by temperature. Western honeybees are cold blooded and will leave the colony (which they heat themselves using muscle activity) only when the air temperature reaches about 12 °C (Bumblebees will fly at about 7 °C, Apis Cerana can cope with lower temperatures still). The temperature at which the brood is reared also governs a bees’ lifespan. The lower numbers of brood which are reared at lower temperatures in autumn & wintertime live longer than the more numerous summer-reared bees. It is possible that warming winters may confuse this genetic trigger and result in young winter bees that don’t survive long enough to participate in caring for the new brood in late spring. Unchecked Varroa levels in the winter brood nest will also shorten the life of these vitally important winter reared bees. Temperatures affect the way plants can produce both nectar and pollen. Very hot drought conditions will cause the nectar flow to dry up. Very heavy rain washes the uncollected pollen from the flowers. An unusually dry and warm winter can alter the flowering cycle of many plants, and a sudden blast of hot temperatures as plant buds and pollen grains are beginning to form can create sterile pollen. Flowers are also blooming earlier than in the past, and catkin bearing plants such as willows and hazel – typically the first pollen sources for western honeybees have been blossoming some weeks before the bees are ready to fly again in the spring.
Changing Agricultural Practice / Pesticides
As honey bees co-evolved with flowering plants, their decline directly affects the pollination and success of a number of bee dependant wildflowers, which in turn creates a poverty of wild forage and leaves bees more dependant on agricultural land and crops, some of which e.g. wheat or silage grassland can be very barren for bees and some of which e.g. maize, cotton may have been genetically modified or treated with bee toxic pesticides. Worldwide changes in pasture and crop management is under consideration as a factor in CCD whereby bees suffer malnourishment as a result of poor or unsuitable forage.
Phone Mast Radiation
Bees use the vibration of their own movement and buzzing to communicate with each other and the acoustic properties of beeswax transmit these messages throughout the colony, telling other foragers where to go. When in flight the way they interpret UV radiation and polarised light from the sun governs their ability to leave the hive for forage and return safely. Some concern has been raised about the increasing concentration of electro magnetic waves upon which all wireless telecommunications including mobile phones, wireless internet and powerful military and emergency services systems rely. Some researchers have raised the possibility that some of these systems are broadcasting too close to the bees own range and causing navigation problems and therefore colony losses.
Researchers at the University of Virginia have discovered that air pollution from automobiles and power plants has been inhibiting the ability of pollinators such as bees and butterflies to find the fragrances of flowers. Pollutants such as ozone, hydroxyl, and nitrateradicals bond quickly with volatile scent molecules of flowers, which consequently travel shorter distances intact. There results a vicious cycle in which pollinators travel increasingly longer distances to find flowers providing them with nectar, and flowers receive inadequate pollination to reproduce and diversify.
The current thinking on solving the problems facing the Western Honey bee are to make use of the bee’s genome and sequence a bee which is more resistant to disease.
This seems to sidestep the more difficult issue of an inability to protect and preserve a biodiverse habitat in which bees and other pollinators can thrive.
There is interest in the reintroduction of black bees, once native to northern Europe but decimated by the bee disease Acarine in 1919. They are held to be better at foraging in less settled, cooler and wetter climates, less susceptible to Nosema and some say better at coping with Varroa than the yellow-coloured Italian honey bees which were introduced to apiaries all over Northern Europe after the Acarine disaster. The Western honeybee, Apis Mellifera, has in any case been exported well outside of its natural range. It was a foreign introduction into the USA and as such no native American flora is dependant on its activity. It is the agricultural crops that were introduced to the United States after colonisation that depend on its presence. In Europe the environmental situation is different because certain wildflowers depend on native bees for reproduction. Tighter regulations and more bee-aware development of pesticides would be welcomed by beekeepers but these routes remain dependant on scientists being able to prove conclusively that current build ups of toxic substances in both plant pollen and bees wax is adversely affecting the reproductive health of bees.
The British Beekeepers Association (BBKA) works to promote bees and beekeeping: www.britishbee.org.uk. Contact the General Secretary, BBKA, The National Beekeeping Centre, National Agricultural Centre, Stoneleigh Park, Warwickshire CV8 2LG. Tel: 02476 696679. Contact them for swarm help.
Guidelines for Beehives in Community Orchards
Other community orchard advice notes:
Produce: what to look for
Sources of funding