1. Maynard Smith J, Harper DD. Animal Signals. Oxford: Oxford University Press, 2003.
2. Bradbury JW, Vehrencamp SL. Principles of Animal Communication. Sunderland, MA: Sinauer Associates, 2011.
3. Floral rewards: alternatives to pollen and nectar;Simpson;Ann Mo Bot Gard,1981
4. What does it cost a plant to produce floral nectar?;Pyke;Nature,1991
5. Renner SS. Rewardless flowers in the angiosperms and the role of insect cognition in their evolution. In: Waser NM, Ollerton J, eds. Plant-pollinator interactions: from specialization to generalization. Chicago, IL: University of Chicago Press, 2006:123–144.