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Honey Bees: The Columbus of the Insect WorldBy

Laura MyhillSupervisor: Dr Alan Waterfall

©Wei Feng Xue, Image Bank

Introduction

Honey bees (Apis mellifera) are known for theirimportant role in the environment as the chiefpollinators for agricultural crops and plants. Theirrecent decline in numbers is of great concern andhas stimulated research efforts to furtherunderstand the behaviour and ecology of thisfascinating animal.

For centuries humans have maintained a specialrelationship with the honey bee through thepractice of bee keeping. This has helped scientiststo study the honey bee and its unique behaviours.

The honey bee is of interest to the fields of animalbehaviour, neuroscience and robotics. Bees displaya range of complex behaviours despite a brainvolume of only 1 mm³, which containsapproximately 950, 000 neurons (Menzel et al.,2006). Thus, when compared to other researchspecies such as the rat and pigeon, the honey beebrain can be considered as a relatively simplestructure.

It is difficult to imagine the use of a tiny insectbrain to the complex field of neuroscience whenwe only think of honey bees as little insects thatbuzz around. What we do not consider is how dothey know where they are going? Do they simplyfly around and land on any flower that takes theirfancy? When thought of in this light the smallworld of the honey bee becomes very interesting.

The main objectives of my investigation were toestablish how the honey bee is able to navigatesuccessfully in its environment, and whether theirability to learn would make a good model of spatiallearning.

Spatial Learning

Spatial learning is a form of associative learningthat is essential for navigation. In the case of thehoney bee it allows foragers to recogniselandmarks in the environment and deduce fromthese what actions are needed to move towardstheir goal.

If foragers navigate with the help of visuallandmarks they must learn the outcomes offollowing those landmarks. For example, picture aforager flying from the hive to a meadow full offlowers. In the meadow there is a prominent tree;just to the left of the tree is a particularly goodpatch of high-yielding flowers. From experiencethe forager will have learnt which direction thefield is with regards to the position of the hiveentrance. Once she is out in the open meadow theprominent landmark tree is visible to her. Alsofrom prior foraging trips she will have learnt andcommitted to memory that if she flies towards thetree and then bears left she will reach the patch offlowers.

In most cases the product of spatial learning is theformation of spatial memories that can be calledupon to remember the location of food sources or

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other locations. In the example above, the foragerlearnt that flying left of the landmark tree took hercloser rather than further away from herdestination. She has also made an associationbetween the prominent, landmark tree and thepatch of flowers – this is associative learning.

Tests of Spatial Learning Displacing honey beeswithin their normal foraging range is a usefulmethod of testing their capabilities for spatiallearning and memory. Generally, these testsinvolve displacing bees as they depart from theirhive or feeding station and releasing them at adifferent site within their range. An experimentbased on this method, conducted by James Gouldand colleagues, released bees one at a time afterdisplacement and involved the monitoring of flightdirection after release. In this test the foragerswere released within site of a large tree thatserved as a prominent, visual landmark (Figure 1).Foragers were found to fly directly to the foodsource along an unfamiliar route. It is thought thatthe bees were able to recognise the landmark andwork out their location with respect to thelandmark and destination (food source) (Gouldand Gould, 1994).

In addition to these visual cues, odours are alsoimportant for the final approach to the flower.Research has shown that odours are a useful cueto direct foraging animals to a particular foodsource. In the case of the honey bee, the flowers

in which it seeks to obtain its meal of pollen andnectar, give off a unique odour that signals theirposition within the environment. The closer thehoney bee is to its goal the stronger theconcentration of the odour particles in the air. Thisgradient concentration is able to guide the honey

bee to the exact flower which is producing theodour.

Navigation

Honey bees are able to navigate familiar and novelroutes with an accuracy that is comparable withthat of higher vertebrates. In addition, this isachieved with remarkably fewer neurons and apoor visual system. As a result of these limitations,honey bees have a well-developed range ofnavigational strategies, with positional anddirectional information supplied from the sun,physical environmental landmarks, polarized lightand odours.

Studies by James and Carol Gould have confirmedthat the primary navigational tool used by honeybees is the sun. From a young age honey bees willlearn the position of the sun with regard to localvisual landmarks. These memories will serve asimportant ‘maps’ for when the bees mature andbegin to forage in the environment.

Figure 1: Illustration of the

foraging range and flight pathsof displaced foragers. Singledotted line shows the novelroute taken by the displacedforagers. Paired arcs show thefamiliar route taken byforagers from hive to foodsource (Gould and Gould,1994)

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The use of visual landmarks is an important cuethat allows the displaced forager to locate itsdesired destination. It is known that as a honeybee approaches and departs from a food source, itwill learn and commit to memory any landmarksand their spatial coordinates in relation to the foodsource (Lehrer and Collett, 1994). This form ofspatial learning may also be a component of thetheory of cognitive maps, which as hypothesisedby Gould (1986), is not restricted to vertebratespecies, and is the explanation for the accuracy inwhich honey bees navigate.

The theory of ‘mental’ or ‘cognitive’ maps hasbeen proposed for various species, including thehoney bee, and involves the formation of a‘mental’ map of the animal’s surroundings. Thistheory is used as an explanation for the ability ofdisplaced individuals to accurately find their wayback to their nest site or original destination, via anovel route.

Displacement experiments performed by Gould(1986) tested this theory of cognitive maps inhoney bees. James Gould trained several groupsof bees (Apis mellifera ligustica) to differentfeeding stations within a normal foraging distance.Trained bees were then captured as they weresetting off from the hive, and were displaced todifferent sites in the area. Gould then monitoredthe direction of flight and flight times to theexpected goal. The theory that invertebrates canonly navigate via route-specific landmarks, wouldhave resulted in foragers returning via a knownroute to the hive and then picking up the path that

they were originally flying towards (Figure 3).Instead, by recording the flight times of displacedforagers, Gould concluded that foragers werenavigating to their original goal via a novel route,aided by an awareness of their position in relationto local visual cues. For example, bees that weretrained to forage at site A were displaced to site Bas they were leaving the hive. If the bees had amental map of the local area they would be able tofly directly to site A on a novel route (their originaldestination before being displaced), without having to fly via the hive. This experiment disputesthe theory that honey bees are only able tonavigate via memories of route-specific landmarks,preventing them from travelling new routesbetween two familiar sites.

An alternative to the cognitive map theory is theidea that honey bees store a sequence of visualimages as they fly along a familiar route (Gould,1986), this is known as a ‘route-based system’

(Gould and Gould, 1994). If this was the case, inthe above experiment the displaced foragerswould have had to fly back to the hive beforesetting out to the food source. However, asalready explained this did not happen, whichpermits the assumption that the foragerssuccessfully navigated along a novel route to thefood source with the help of a cognitive map oftheir range (Gould and Gould, 1994).

Neurobiology

It is clear from the honey bees amazing ability tolearn and navigate successfully, that there is

Figure 3: Displacement experiments

conducted by Gould (1986). Honey bees(Apis mellifera ligustica) were able totravel along a novel route between twofamiliar sites, aided by a cognitive mapof the local area.

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something special occurring in its brain that isallowing it to perform these behaviours. The factthat the honey bee can learn and navigate is notspecial in itself as this has been studied in manyother species. However what is special is that thehoney bee achieves all of this in its short lifespanwith only 950, ooo neurons.

This may not mean much unless compared toother species – for example the estimated totalnumber of neurons in the central nervous systemfor:

- common octopus and small mammals –30 to 100 million neurons

- whales and elephants – exceeding 200billion neurons

- humans – 10 billion to 1 trillionneurons (Williams and Herrup, 1988)

The reason for all the interest in the honey beebrain is that due to its small size it is possible thatthe essential neural components for spatiallearning and/or navigation are present in thelimited neurons of the honey bee brain. This hasfuelled numerous studies on the structure andfunction of specific areas in the brain.

Previous research has highlighted prominent brainstructures that are involved in sensory processingand integration. These structures have beentermed the mushroom bodies, which are thoughtto be analogous to the mammalian hippocampus.The mammalian hippocampus is the centre ofhigher-order processing, spatial learning andmemory formation (Kolb and Whishaw, 2006).

The mushroom bodies have been found to receivea variety of neuronal inputs from the sensoryorgans, such as the compound eyes and theproboscis. Paired with the role of formingmemories it has been proposed that themushroom bodies are a likely site for spatial-related learning. This is a fair proposal that fitswith the requirements of spatial learning. Asmentioned the foraging honey bee will use itssenses to locate its food source, whether itreaches its destination by using its eyes or its senseof smell. The honey bee will then remember thelocation of the food source and the journey taken;therefore strengthening the idea that themushroom bodies are involved with spatiallearning.

The neurobiology of spatial learning in the honeybee is a key part of understanding how such tinyforagers are able to navigate and memorise their

environments. However it seems that the onlyway to study this type of learning is to monitor themovements of free-flying bees. This has beendone successfully in behavioural studies, howeverto understand the neural processes occurringduring this behaviour recordings must be takenfrom the neurons themselves. At the presentthere is no such technique for spatial learning, butthis is not the case for olfactory learning. Bothspatial and olfactory learning are considered to beforms of associative learning, and with olfactorylearning being one of the most studied forms oflearning in invertebrates, information gatheredfrom these studies may be applied to spatiallearning.

Conclusion

Despite the potential of the honey bee brain toprovide fascinating information on the neuralprocesses of navigation and spatial learning, it isproving very tricky to obtain. The maindisadvantage of using the honey bee as a model isthe lack of experimental techniques available tomanipulate and record from such a tiny nervoussystem.

However this is what research is all about. Thedevelopment of techniques and methods runshand-in-hand with the successes of obtainingground-breaking information. The honey bee hasalready proved its worth in confirming the use ofcognitive mapping and polarized light fornavigation, and undoubtedly has more secrets tobe uncovered.

Further reading

Gould, J.L. and Gould, C.G. (1995) The Honey Bee,3rd Edition, Scientific American Library, New York.

Capaldi, E.A., Robinson, G.E. and Fahrbach, S.E.(1999) Neuroethology of spatial learning: The birdsand the bees. Annual Review of Psychology, 50: 651– 682

References

Gould, J.L. (1986) The locale map of honey bees:Do insects have a cognitive maps? Science, 232: 861– 863

Gould, J.L. and Gould, C.G. (1994) The Animal Mind,2nd Edition, Scientific American Library, New York.

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Gould, J.L. and Gould, C.G. (1995) The Honey Bee,3rd Edition, Scientific American Library, New York.

Kolb, B. and Whishaw, I.Q. (2006) An Introductionto Brain and Behaviour, 2nd Edition, WorthPublishers, New York.

Lehrer, M. and Collett, T.S. (1994) Approaching anddeparting bees learn different cues to the distanceof a landmark. Journal of Comparative Physiology A,175: (2) 1432 – 1351

Menzel, R., Leboulle, G. and Eisenhardt, D. (2006)Small brains, bright minds. Cell, 124: 237 – 239

Williams, R.W. and Herrup, K. (1988) The Control ofthe Neuron Number. Annual Review ofNeuroscience, 11: 423 – 453

Honey bee image contributor Wei Feng Xue, imagecourtesy Centre for Bioscience, the HigherEducation Academy, Image bankhttp://www.bioscience.heacademy.ac.uk/imagebank/

Student Profile“Laura is 21 years old and decided to pursueher interest in biology by studying AnimalScience. Throughout her degree she hasdeveloped an interest in research andanimal health, and is due to begin her MResin Parasitology at the School of Biology.Laura ultimately hopes to complete a PhDand continue to pursue a career inresearch”