The book introduces techniques and approaches to original work so that anyone with an interest can usefully contribute to furthering our understanding and appreciation of these wonderful and important insects.
The book introduces techniques and approaches to original work so that anyone with an interest can usefully contribute to furthering our understanding and appreciation of these wonderful and important insects.
Bumblebees
130
Bumblebees
130Paperback(Third Edition)
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Overview
The book introduces techniques and approaches to original work so that anyone with an interest can usefully contribute to furthering our understanding and appreciation of these wonderful and important insects.
Product Details
| ISBN-13: | 9781907807060 |
|---|---|
| Publisher: | Pelagic Publishing |
| Publication date: | 01/01/2011 |
| Series: | Naturalists' Handbooks , #6 |
| Edition description: | Third Edition |
| Pages: | 130 |
| Product dimensions: | 5.80(w) x 8.20(h) x 0.40(d) |
| Age Range: | 13 - 18 Years |
Read an Excerpt
CHAPTER 1
Introduction
Bumblebees are likeable creatures, and are among the most attractive of British insects and the most amenable to study. Friendlier than honeybees, they do not sting unless severely molested. Furrier, more rotund and colourful, and often larger than honeybees, and conspicuous by their deep buzz and their habit of working in gardens, they are a familiar sight in summer in town and country.
In spring a bumblebee colony is founded by a queen, who has overwintered. Initially she lays eggs that give rise to workers. These look after the nest, defend it and collect food for it. Usually many workers are produced before eggs are laid which develop into males and young queens, who leave the nest and mate (see section 3.2).
The appeal of bumblebees as subjects for study is partly due to their predictable behaviour. Most animals are forever compromising between multiple objectives such as feeding, seeking a mate, laying eggs, and defending a territory. In contrast many of the bumblebees we see are foraging workers, whose main task is the collection of nectar and pollen to supply themselves and their colony. Because we can follow just what these foragers are doing we can begin to ask how well they are doing it, and this quantitative approach is facilitated by the ease with which the energy and water content of a flower's nectar can be measured (see sections 6.1 and 9.4). (Pollen collection is at least equally important, but more challenging to study.)
Bumblebees are interesting too for their social behaviour. Their colonies, rather small and lasting less than a year in temperate regions, are simpler to work with than those of honeybees and can be managed quite easily in nest-boxes.
Perhaps the most important practical element of interest is the role of bumblebees as pollinators, often underestimated and still poorly understood. Much more needs to be known about them as pollinators of crops and our native flora, and about their nesting requirements and biology. The need is urgent, as pressures on land use are intensifying, population sizes and the number of bumblebee species are declining markedly, and valuable bee-pollinated crops are put at risk of reduced yields.
CHAPTER 2
Distribution and recognition
2.1 Distribution and decline
The world fauna of bumblebees, about 250 species (Williams, 1998), is centred on the North Temperate Zone, extending through Europe, Asia and North America. Apart from some species in South America the only bumblebees native to the southern hemisphere are in the East Indian archipelago. British species (B. ruderatus, B. hortorum, B. terrestris and B. subterraneus) were established in New Zealand in the nineteenth century for clover pollination (Hopkins, 1914); and recently Bombus ruderatus has become established in South America, having been introduced to Chile from New Zealand for the same purpose (Arretz & Macfarlane, 1986). In addition, there has been an increasing number of accidental or intentional introductions, including B. lucorum, B hypnorum and B. pascuorum to Iceland (Pr?s-Jones & others, 1981; Olafsson and Kristjánsson, personal communication) and B. terrestris to Tasmania (Semmens & others, 1993, Buttermore, 1997), Israel and Japan (Dafni, 1998), among others; while non-native species and subspecies continue to be incidentally introduced on a large scale as a result of escapes from commercial bumblebee colonies used for glasshouse pollination (see Chapter 7). Out of their own environment such species have unforeseen and usually bad effects, outcompeting or interbreeding with local species (Kondo & others, 2009) and subspecies (Ings & others, 2010), thereby reducing biodiversity (Goka, 1998), and introducing diseases (Goka & others, 2001; Colla & others, 2006). There are very few sensible arguments in favour of the intentional introduction of a species to an area where it has not previously existed. The true scope of adverse effects of an introduction on the native flora and fauna is almost always unforeseeable. For pollination purposes local species should always be used in preference to imported non-native ones. A few countries, such as Norway and Israel, have taken a lead in banning the import of bumblebees. International legislation to further this aim is urgently needed, with particular controls on the commercial use of non-native species and subspecies.
The British bumblebee fauna of, currently, 24 species includes 18 'true' bumblebees (Bombus) and 6 parasitic 'cuckoo' bumblebees (previously in the genus Psithyrus, which is now regarded as a subgenus within the genus Bombus, Williams, 1998). It contains representatives of a wide range of subgeneric groups, which have recently been revised into a simpler scheme (Cameron & others, 2007; Williams & others, 2008), and we are fortunate in having a correspondingly wide diversity of ecology and behaviour to study. Since the last edition of this book we have gained B. hypnorum (Goulson & Williams, 2001), almost certainly through human agency; lost B. subterraneus to extinction; and also 'gained' B. cryptarum (Bertsch & others, 2004, 2005; Bertsch, 2009; Macdonald, 2006; Murray & others, 2008), a cryptic species that we already had but, embarrassingly, had not recognised!
When we compare the present distribution of true bumblebees in mainland Britain with records made before 1960, it is apparent that there have been marked changes over recent decades (fig. 1; Williams, 1982). Six species are widespread over much of Britain, and you can probably see most of them in any year: B. pascuorum, B. lucorum, B. hortorum, B. pratorum, B. terrestris and B. lapidarius. The newly arrived B. hypnorum is spreading, rapidly (see map p. 127), and may soon join this group. For convenience these widespread species are illustrated on the cover. Four species are very local and restricted to southern Britain, and their distributions have contracted: B. ruderatus, B. sylvarum, B. humilis, and B. ruderarius. Four others are widespread but very patchy, and have disappeared from many localities: B. muscorum, B. monticola, B. soroeensis and B. jonellus. B. magnus is one of the B. lucorum complex, along with B. cryptarum, and is associated with heath and moorland areas in the north and west. B. distinguendus is now rare and mainly restricted to coastal sites; although it was once widespread. Apart from B. subterraneus, last recorded in 1988 (but now being re-introduced at Dungeness in southern England), two other species, which were always uncommon, are presumed to be extinct: B. cullumanus and B. pomorum. Neither has been seen for many years.
The map (fig. 1) shows where the three main biogeographic elements occur in Britain, and will give you some idea of how many bumblebee species to expect around your home. Over much of the country there are only six or seven species. Although this impoverishment of the fauna makes identification easier, it must be regarded as a conservation problem (Chapter 7). Direct information on the impact of declines in bumblebee populations for the pollination of wild flowers and crops is hard to come by. Work in New Zealand (Macfarlane & others, 1983) has shown that supplementing bumblebee populations dramatically increases seed yields (fig. 2): the implication is that declining bumblebee populations will have the opposite effect.
As more members of the public become interested and submit records, our knowledge of the changing distribution of British bumblebees is improving, but it deserves further study (pp. 77 and 119–130).
2.2 Recognising bumblebees
There should be no difficulty in recognising a bumblebee by sight and by sound. Plates 1–4 show you what they look like. Bumblebees are all members of the genus Bombus (meaning 'booming'), and they are divided into a number of distinct subgenera, which differ slightly in their biology and characteristics. The most distinct of these, the cuckoo bumblebees (genus Bombus, subgenus Psithyrus, meaning 'murmuring'), resemble the other, more conventional Bombus species, the 'true' bumblebees, but have a softer buzz, a sparser coat of hair showing the shiny black cuticle through it, and no pollen-collecting apparatus on their legs. Cuckoo bumblebees are inquilines in the nests of true bumblebees (section 5.1).
With a little experience it soon becomes possible to recognise most of the common species of true bumblebees in the field, without disturbing them, on the basis of colour pattern. This is a valuable asset in ecological studies. The Quick-Check Key (p. 78) and the colour plates should help to make this possible. Initially, though, it will be necessary to catch and examine a few bees of each type in order to name them (technique, p. 94–95).
There are several distinct colour patterns among British bumblebees. Surprisingly, each is adopted not by one species only, but by a group of species that may not be closely related to each other at all (e.g. B. lapidarius, B. ruderarius, B. pomorum, B. cullumanus and B. (Ps.) rupestris). These are apparently examples of Müllerian mimicry (see Williams, 2007 & 2008, for a fuller consideration). A predator that gets stung whenever it tries to eat a bee with a particular colour pattern will eventually learn to associate the colour pattern with a painful sting and therefore to avoid it. The commoner the colour pattern that a bee wears, the sooner predators will learn to avoid it. A bee can therefore reduce the risk of getting eaten by sharing a common uniform with many other bees of the same or different species. These Müllerian mimicry groups involve cuckoo bumblebees as well as true bumblebees, and can confuse ecologists as well as predators.
2.3 Reading about bumblebees
Since the start of the new millennium a range of excellent new books on bumblebees has been published. Goulson's Bumblebees - behaviour, ecology, conservation (2010) and Benton's Bumblebees (2006) provide up-to-date coverage of the expanding literature on bumblebee biology and natural history, and Benton also includes keys to species. A useful Field guide to the bumblebees of Great Britain & Ireland has been produced by Edwards & Jenner (2009). Books with a more regional emphasis include Benton's The bumblebees of Essex (2000), Macdonald's Bumblebees – naturally Scottish (2003) and Macdonald & Nesbit's Highland bumblebees (2006).
Some earlier classics remain well worth reading. The first major book on British bumblebees was F.W.L. Sladen's The humble-bee, its life history and how to domesticate it, first published in 1912. With superb coloured illustrations and delightful anecdotal accounts of the species, reflecting acute biological observation, this excellent book was republished in 1989. Free & Butler's Bumblebees, published in 1959, and also now available again, was a worthy successor, and included a field key by Yarrow which, for the first time, made it possible for beginners to name their bees. Alford's Bumblebees (1975) covers the biology of bumblebees and their associates and parasites, and includes a key, more critical but harder to use than Free & Butler's. That key was the basis for the Bumblebee Distribution Maps Scheme that gave so much valuable information on bumblebee distribution before it ended in 1976. A brief popular account of bumblebee biology appears in Alford's The Life of the bumblebee (1978). Bumble bees for pleasure and profit edited by Matheson (1996) outlines the beginnings of the commercial use of bumblebees.
North American bumblebees are considered in Plath's Bumblebees and their ways (1934), which has long been out of print; while Heinrich's Bumblebee economics (1979) describes some fascinating aspects of bumblebee ecology and physiology. Kearns & Thomson The natural history of bumblebees – a sourcebook for investigations (2001) is a practical guide to North American bumblebees and outlines their biology, and useful topics and techniques for further research.
British bumblebees' names have changed from time to time, and some of the names in use now are different from those in earlier books. In this book we use the names given in the checklist by Fitton & others (1978), but we retain B. magnus (Alford, 1975), add B. hypnorum (Goulson & Williams, 2001) and split B. lucorum into B. lucorum and B. cryptarum (Bertsch & others, 2004). Names and synonyms are listed on p. 115.
There is a rapidly expanding range of websites containing up-to-date information on bumblebee biology and distribution. Some links to this are given on p. 107.
CHAPTER 3
The natural history of true bumblebees
3.1 Natural history
The different species of true bumblebee are alike in some aspects of their biology, for example in the main features of their life cycle (section 3.2), but very different in others. Some of the idiosyncrasies of British species begin to emerge from intensive studies of their ecology (table 1). To illustrate this point we shall introduce four of the commonest species.
Bombus terrestris (of the earth; from the Latin terra) In spring the gigantic queens of B. terrestris are among the first to emerge from hibernation (fig. 3). In the past, if cold weather was followed by a warm spell, some queens would occasionally emerge in midwinter, and attempt to nest if flowers were available (Prys-Jones, 1982). Since the 1990s B. terrestris has more regularly been starting a winter generation, on a limited scale, in some parts of southern Britain. Lack of males observed in winter may mean these colonies are not, at least as yet, successfully producing sexuals; and up to now winter nesting activity has depended entirely on introduced plants, flowering in urban situations in gardens and parks (Stelzer & others, 2010).
In most species the queen and worker have the same coloured tail, but British B. terrestris queens have brownish tails and workers usually have white or buff ones (pl. 1.3 and 1.4). Towards the end of the nesting period some workers have queen-like coloration. The reason for this is not clear, but it may be that declining vigour of the queen eventually allows the expression of at least some queen-like characteristics in all the female offspring (see p. 19, 'complex' species).
Most workers of B. terrestris look quite similar to those of B. lucorum, and small individuals can be difficult to separate. Both species have a short broad face and a relatively short tongue, features associated with their habit of collecting nectar from rather short open flowers. They also have the ability to bite a hole in the corolla tube of deeper flowers (fig. 4), such as honeysuckle Lonicera periclymenum, comfrey Symphytum officinale and field bean Vicia faba. This enables them to extract nectar which they would be unable to reach from the front of the flower. In Britain only queens and workers of B. terrestris and B. lucorum have been observed to rob flowers regularly in this way, but other bumblebees (and even honeybees) often re-use the holes, acting as secondary robbers.
Sometimes almost every flower in a field bean crop may be robbed. It is hard to evaluate the impact this has on crop pollination. On the one hand one might expect that bees removing nectar in this way, without contacting the anthers and stigma, would impair pollination. On the other hand it has been suggested that robbery may sometimes cause long-tongued bumblebees, which do not rob, to visit more flowers for each load of nectar, so enhancing pollen transfer. Hole-biting may attract more honeybees to a clover crop, but if most of these are gathering nectar via rob-holes they may fail to effect cross-pollination.
Probably the most important consideration is that pollen-collecting bees are unaffected by hole-biting and remain successful pollinators. This may account for the fact that robbery of red clover does not appear to decrease seed set (Hawkins, 1961). Certainly in New Zealand, where introduced bumblebees are very important pollinators of red clover, robbery by B. terrestris is common, yet in areas where this species is the main visitor to the crop it is still a useful pollinator (Gurr, 1975).
(Continues…)
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