Books:
1. Plant reproductive ecology: patterns and strategies - Jon Lovett Doust, Lesley Lovett Doust
2. Crop pollination by bees - Keith S. Delaplane, D. F. Mayer
Journals:
1. Pyke GH (1979) Optimal foraging in bumblebees - rule of movement between flowers within inflorescences. Animal Behaviour 27: 1167–1181.
2. Heinrich B (1983) Do bumblebees forage optimally, and does it matter? american zoologist 23: 273–281.
3. Pyke GH (1980) Optimal foraging in bumblebees - calculation of net rate of energyintake and optimal patch choice. Theoretical Population Biology 17: 232–246.