Table of Contents
Preface ix
Acknowledgement xi
Chapter 1 Introduction 1
1.1 Evolution and phylogeny 2
1.2 The life cycle 5
Chapter 2 Thermoregulation 13
2.1 Warming up 13
2.2 Controlling heat loss 16
2.3 Thermoregulation of the nest 18
Chapter 3 Social Organization and Conflict 21
3.1 Caste determination 22
3.2 Division of labour 25
3.3 Sex determination 34
3.4 Control of reproduction and queen-worker conflicts 34
3.4.1 Timing of reproduction 37
3.4.2 Matricide 39
3.5 Sex ratios in 'true' bumblebees 40
3.6 Sex ratios in Psithyrus 43
Chapter 4 Finding a Mate 45
4.1 Territoriality 45
4.2 Nest surveillance 46
4.3 Hilltopping 46
4.4 Scent-marking and patrolling 47
4.5 Inbreeding avoidance 50
4.6 Evolution of male mate-location behaviour 51
4.7 Queen-produced sex attractants 51
4.8 Monogamy versus polyandry 52
Chapter 5 Natural Enemies 57
5.1 True predators 57
5.2 Parasitoids 62
5.2.1 Conopidae (Diptera) 62
5.2.2 Sarcophagidae (Diptera) 64
5.2.3 Braconidae (Hymenoptera) 65
5.2.4 Mutilidae (Hymenoptera) 65
5.3 Parasites and commensals 66
5.3.1 Viruses 66
5.3.2 Prokaryotes (Bacteria and others) 66
5.3.3 Fungi 67
5.3.4 Protozoa 67
5.3.5 Nematodes 70
5.3.6 Mites (Acarina) 71
5.3.7 Other commensals 73
5.4 The immune system of bumblebees 73
5.5 Social parasitism 75
5.5.1 Nest usurpation 75
5.5.2 Social parasitism by drifting workers 76
5.5.3 Cuckoo bees (Psithyrus) 77
Chapter 6 Foraging Economics 81
6.1 Foraging range 84
6.1.1 Measuring foraging range 86
6.1.1.1 Marking experiments and direct observation 86
6.1.1.2 Modelling foraging range 87
6.1.1.3 Homing experiments 88
6.1.1.4 Radar tracking 91
6.1.1.5 Mass-marking and pollen analysis 92
6.1.2 Do bumblebees forage close to their nests? 94
6.1.3 Differences between bumblebee species 95
6.1.4 Management implications 97
Chapter 7 Exploitation of Patchy Resources 101
7.1 The ideal free distribution 102
7.1.1 Search patterns within patches 102
7.1.2 Non-random choice of patches 106
7.2 The marginal value theorem 107
Chapter 8 Choice of Flower Species 113
8.1 Learning and flower constancy 114
8.1.1 Explanations for flower constancy 115
8.1.2 Can flowers be cryptic? 120
8.2 Infidelity in flower choice 123
8.3 Variation in learning ability 124
8.4 Coping with deceptive unrewarding flowers 125
8.5 The influence of pollen quality on flower choice 126
Chapter 9 Intraspecific Floral Choices 131
9.1 Direct detection of rewards 131
9.2 Flower size 132
9.3 Flower age 132
9.4 Flower sex 133
9.5 Flower symmetry 134
9.6 Flower scent 135
9.7 Thermal rewards 135
9.8 Motivation and choosiness 136
Chapter 10 Foraging Cues Gained from Other Bees 137
10.1 Communication in the nest 137
10.2 Visual responses to other bees on flowers 140
10.3 Scent marking of flowers 140
10.3.1 Repellent versus attractant marks 146
10.3.2 The evolution of scent marking 147
Chapter 11 Competition and Niche differentiation in Bumblebee communities 151
Chapter 12 Bumblebbes as pollinators 161
12.1 Pollination of cops 162
12.1.1 Honeybees versus bumblebees 163
12.1.2 Approaches to enhancing bumblebee pollination 165
12.2 Pollination of wild flowers 171
12.2.1 Nectar robbing 172
Chapter 13 Conservation 177
13.1 Causes of declining bumblebee numbers 181
13.1.1 Loss of habitat 181
13.1.2 Pesticides 186
13.1.3 Impacts of non-native bees and commercial beekeeping 188
13.1.4 Population structure and habitat fragmentation 191
13.1.5 Do bumblebees Suffer from inbreeding depression? 198
13.2 Why are some bumblebee species still abundant? 199
13.3 Consequences of declining bumblebee numbers 204
13.4 Conservation strategies 206
13.4.1 Enhancing bumblebee diversity in farmland 206
13.4.1.1 Field margin management and wildflower strips 206
13.4.1.2 Restoring and maintaining species-rich grasslands 210
13.4.1.3 Providing nest sites 211
13.4.1.4 Organic farming 212
13.4.2 The importance of urban areas 213
13.4.3 Translocations and reintroductions 215
13.5 Summary 216
Chapter 14 Bumblebees Abroad: Effects of Introduced Bees 219
14.1 Competition with native organisms for floral resources 221
14.1.1 Effects on foraging of native organisms 222
14.1.2 Evidence for population-level changes in native organisms 225
14.2 Competition for nest sites 227
14.3 Introgression with native bees 228
14.4 Transmission of parasites or pathogens to native organisms 228
14.5 Effects on pollination of native flora 231
14.6 Pollination of exotic weeds 233
14.7 Summary and conclusions 235
References 239
Index 311
