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A bumble bee belongs to the bee genus Bombus, and are known as social insects. This means that they live in a colony which is headed by a queen. Unlike honey bees which live in colonies often exceeding 50,000 bees, bumble bees live in colonies of just 50 or so.
A Bumble bee colony
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Focusing on bumble bees
Bumble bees, and the pleasure and profit they afford, were the subject of
Why are bumble bees special in relation to other bees
Though bumble bees are highly social their colonies are not perennial. The young, mated queens have to survive over winter alone and initiate new nests in the spring making them vulnerable to attack by parasites and pathogens. Their physiology and morphology makes bumble bees ideally suited to living at high latitudes and altitudes because they can forage in cool, unfavourable weather. Bumble bees can thus make the most of nectar and pollen available in the early spring and early in the day before honey bees can forage.
Sarah Corbet also discussed how bumble bees were 'special' in their utilization of floral resources. They are large insects, requiring large quantites of fuel nectar to fly and to build up the colony. Bumble bee species differ in the length of their tongues so they profit from different flower types. They can determine what type and volume of nectar is available, and they may modify their visiting behaviour accordingly, for example timing their return visits to flowers to coincide with replenishment of the nectar.
In our paper on bumble bees as pollinators (Juliet Osborne & Ingrid Williams, IACR-Rothamsted, UK) we emphasized that they are an important component of semi-natural ecosystems and the integrity of certain vegetation types depends upon them. Many wild flower species depend on bumble bees for pollination and consequently for reproductive success and survival, whilst animals such as birds and small mammals rely on seed and fruits produced as a direct result of bee pollination. (Also see reprint below).
Bumble bees are in decline in the UK and if this continues, then the survival of many wild flower populations may be threatened as their pollinator service is withdrawn. This in turn may lead to a further drop in the number of wild bees due to the consequent drop in available forage. We gave examples of how such a spiral might be triggered by a dramatic event, such as spraying of insecticide toxic to bees or it might be exacerbated by the progressive fragmentation of semi-natural vegetation or a general reduction in nest site and wild flower availability caused by intensive farming. The outcome is similar drab vegetation with fewer animal species.
Bumble bees for pleasure
Bumble bees are large and attractive insects, and their association with attractive flowers makes them enticing subjects of study, not just to scientists but also to amateur naturalists and children. Dr Manja Kwak (Groningen, The Netherlands) described an excellent scheme which she set up in The Netherlands to encourage children to observe nature closely and critically by watching bumble bees in the wild or in their own gardens if appropriate flowers are grown (though one must be careful to choose seed mixtures that really do contain species useful to bumble bees). The colour markings of different bumble bee species make them relatively easy to identify and simple observations of bee foraging behaviour require only inexpensive equipment. For example children can easily look at flower choice, identify the pollen loads (using easily obtained colour charts) and examine flower constancy by following individually marked bees. Results from observations by children involved in Manja Kwak's scheme are to be published in the Autumn.
As commercial pollinators Bumble bees provide an essential pollination service for some of our crops. By looking closely at the effectiveness of different bees at removing pollen from flowers, transporting it and delivering it to stigmas, we can assess which bee species might be most suitable as a managed pollinator for a particular crop (Osborne & Williams, IACR-Rothamsted, UK). Though honey bees are most often imported to field crops, bumble bees and honey bees are not necessarily interchangeable as pollinators of a particular plant species. This was illustrated by Dr Don Griffiths (CIBA Bunting, UK) and Melanie Hughes (Luddington, UK) who described the use of bumble bees for the pollination of tomatoes in glasshouses.
Don Griffiths described how tomatoes are grown and the history of the pollination problems, while Melanie Hughes provided an insight into how bumble bees are reared commercially and the problems faced by commercial breeders. Tomato growers are willing to pay high prices for bumble bee colonies because, in terms of quality and quantity of fruit, bumble bees are more effective pollinators of tomato flowers than honey bees or vibrating 'electric bees'. Bumble bees, unlike honey bees, vibrate their wings at very high frequency to trigger the release of pollen from the tomato flowers and this results in effective pollination.
Melanie Hughes described how commercial bumble bees are expensive because of the difficulties of rearing colonies for pollination all year round and the importance of providing colonies of standard quality. Year round breeding has been achieved by artifically overwintering mated queens by exposing them to carbon dioxide. This, together with the use of young worker honey bees as helpers, stimulates the queens to oviposit.
Three bumble bee rearing companies were represented at the meeting with demonstration colonies to illustrate the refinement of the rearing boxes which must provide food, space, ventilation and protection during transport and in the glasshouse. Melanie Hughes emphasized that bumble bee colonies have no 'shelf-life' and tomato growers cannot easily predict exactly when they will need colonies, so the companies have developed methods of retarding colonies and overwintering queens to make colony production more flexible to cope with fluctuating demand.
Growers of other high value glasshouse crops, such as aubergines, sweet peppers and strawberries, are also buying bumble bees for pollination (Griffiths, CIBA Bunting, UK). As yet, there is little use of these colonies for field crops. Sarah Corbet pointed out that it is risky to transport commercial bumble bee colonies from one country to another because of the dangers of introducing parasites or pathogens or altering the bumble bee gene pool in the country receiving the bees. The pollination service provided by wild bumble bees needs to be further recognized and we should thus seriously consider management strategies for maintaining and increasing existing wild populations of bumble bees.
As indicators of the success of landscape management Dr Gary Fry (NINA, Norway) discussed the relationship between wild bumble bees and land use in the countryside. He demonstrated strong correlations between the number of bumble bees and the number of flowers, carabids, hoverflies, butterflies and even small mammals, suggesting that on farms, the abundance and diversity of bumble bees could be used as an indicator of biodiversity and the quality of habitats.
Bumble bees are easy to count and identify, and monitoring could be used to assess the success of land management strategies applied by farmers. Butterflies have previously been used for this purpose, and Fry suggested that bumble bees could be monitored at the same time, giving farmers the added benefit of information on the wild pollinators available to pollinate crops. If land is managed to encourage bumble bees, then not only will the number of pollinators increase, but the landscape will also support larger populations of insect predators and parasitoids, which may reduce crop pest populations.
The symposium described the many ways in which bumble bees can be useful and provided an insight into the different methods of studying bumble bees for both pleasure and profit. At one end of the scale are the intricate studies of pollen movement to examine the effectiveness of bees as pollinators of crops and wild flowers (described by Osborne & Williams). At a larger scale are the observations of bees on patches of flowers for pleasure (illustrated by Corbet and Kwak) and the study of colony dynamics and breeding for profit (described by Griffiths and Hughes). Gary Fry emphasized the need for very large-scale studies to examine the relationships between nest sites and forage resources if we are to manage the landscape appropriately to augment wild bumble bee populations and halt the decline already seen in the UK.
The symposium gave pleasure to the people attending and contributing. I hope that bumble bee populations will profit from the publicity. The papers from the symposium are published by IBRA as a book Bumble bees for pleasure and profit edited by Andrew Matheson, which is available from IBRA Publications Sales.
This report was written by Juliet L. Osborne of IACR - Rothamsted, Harpenden, Herts, UK, and was originally published in Bee World.