Zoology

Honey Bee Navigation



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Honey bees first originated in tropical Eurasia some eight to eleven million years ago. There are now at least ten distinct species and numerous sub-species, predominantly in Asia, such as the Asian giant or rock honey bee (Apis dorsata), the Asian dwarf honey bee (Apis florea) and the South-Asian cavity nesting bee (Apis cerena indica). The honey bee most familiar to people living in Europe and North America is a cavity nesting bee called the western honey bee (Apis mellifera), which reached Europe approximately 10,000 years ago and is the species most commonly kept in commercial hives.

Due to its economic value, not only in the production of honey but also in the pollination of flowering crop plants, most scientific research has focussed on the western honey bee. This research has discovered some amazing capabilities in this little animal, including the ability to utilise a range of senses and methods to navigate within its environment. These include the use of landmarks, sun position, polarisation of the sky and the Earth's magnetic field.

Experimentation indicates that the use of landmarks is their primary method of navigation. When adult honey bees first emerge from the pupa they initially remain in the hive, performing all the necessary duties there, such as building the comb structure, nursing larvae and tending to the Queen. Only when they are older do they start to venture out. Their initial flights are orientation flights, they do not forage during these, but memorise the landmarks in an expanding zone around their hive. Once sufficiently experienced they join the hive's squadrons of foragers, receiving directions to quality food sources from more experienced foragers that fulfill the role of scouts.

Scouts will usually find the resources the hive needs within a two mile radius of the hive, but have been known to travel as much as five miles if necessary. They search for nectar to make honey, pollen to be used as an immediate food supply, propolis (tree resin) to be used as a sealant to close openings against draughts or invaders, and water. Upon returning to the hive, they perform a "waggle dance" that tells their hivemates the direction and distance of the resource.

This symbolic dance language is a combination of position, duration and acoustics. The bee lands on a vertical side of the hive and angles its body in relation to the position of the sun and the location of the resource to give direction. The duration of the dance indicates the distance from the hive. It is not clear what meaning the sounds convey. It is interesting to note that the Asian dwarf honey bee, although capable of hearing, does not use an acoustic component in its dance language.

When the skies are overcast, polarisation in combination with the bees circadian rhythms and an innate knowledge of solar movement allows bees to still be amazingly accurate in their navigation. Research has been done that shows inexperienced bees still know the approximate place of the sun on overcast days and that bees kept in the dark increase oxygen consumption by 20 to 30 times at the appropriate time of day for them to be up and about foraging.

In theory all of the above methods of navigation could be used by a human without requiring the aid of technology, but the western honey bee has one more piece of equipment in its natural toolkit. In its dorsal anterior abdomen are specialised cells called trophocytes that accumulate granules of iron from their pollen diet. There is very little iron in pollen, so this may take some time which possibly explains why adult workers don't travel outside the hive until later in life.

Within the iron granules is a small percentage of superparamagnetic magnetite, that is influenced by minute changes in the Earth's magnetic field. Increases in field strength causes the iron granules to swell slightly which triggers a release of intracellular calcium ions causing a magnetosignal to travel via the cell's cytoskeleton and thus initiating a neural response. This is probably most used by scout bees in times of resource shortage when they might be forced to travel greater distances into less well-known areas. It is also used within the hive in the alignment of the honeycomb structure.

It is probable that all of these methods are used in conjunction with each other, with the current environmental situation determining which mode is in the primary role. Navigation is of critical importance to the hive's survival, so it is quite understandable that the honey bees would have and use several methodologies, although that does tend to make it more difficult for experimental researchers, who typically like to modify one thing and study its impact.

Currently there is considerable concern over honey bee die offs, known as Colony Collapse Disorder, and what impacts this might have on agriculture. A recent study on 23 farms in New Jersey and Pennsylvania with watermelon crops found that approximately 90 percent of them would have their polinisation needs met by native wild bee species, although this won't help in the commercial production of honey.

Possible causes being investigated include the effects of mobile phone towers, but the most likely cause is the increased use of pesticides on newly created pesticide resistant food crops. In New Zealand, where there are no commercial genetically modified crops and pesticide use is limited, the only problems the hives have are with the recently arrived varroa mite, Colony Collapse Disorder does not currently occur.



Sources:

Capaldi, E. & Dyer, F. (1999) The role of orientation flights on homing performance in honeybees. Journal of Experimental Biology 202(12): p1655.

Dreller, C. & Kirchner, W. (1994) Hearing in the Asian honeybees Apis dorsata and Apis florea. Insectes Sociaux 41(3): p291.

Dyer, F. (2002) The biology of the dance language. Annual Review of Entomology 47(1): p917.

Dyer, F. & Dickinson, J. (1995) Development of sun compensation by honeybees: how partially experienced bees estimate the sun's course. Proceedings of the National Academy of Sciences of the United States of America 91(10): p4471.

Hsu, C., Ko, F., Li, C., Fann, K. & Lue, J. (2007) Magnetoreception system in honeybees (Apis mellifera). Retrieved from
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1851986

Oldroyd, B. (2007) What's killing American honey bees? Retrieved from
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1892840

Randall, D., Burggren, W & French, K. (2002) Echart Animal Physiology Mechanisms and Adaptations 5th Edition. New York: W.H. Freeman and Company.

Sen Sarma, M., Whitfield, C. & Robinson, G. (2007) Species differences in brain gene expression profiles associated with adult behavioural maturation in honey bees. BMC Genomics 8: p202.

Winfree, R., Williams, N., Dushoff, J. & Kremen, C. (2007) Native bees provide insurance against ongoing honey bee losses. Ecology Letters 10(11): p1105.

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