Bees use signals from plants to identify worthwhile visits. In some species the flowers remain open, intact and turgid until they are pollinated, after which they are no longer attractive to pollinators. The negative cues involved in this include cessation of nectar and scent production, change in colour, wilting, permanent flower closure, and petal drop. Even receptive inflorescences can vary in their attraction to bees. In general, inflorescences with a larger number of open flowers have higher nectar rewards, and bees preferentially land on those inflorescences. Once landed on an inflorescence, bees prefer wide, relatively shallow flowers, presumably because the nectar is more accessible to evaporation which concentrates it and increases the energetic profit of the visit.
These observations from ecological studies form the basis of a practical crop pollination recommendation. It is advisable for growers to delay the introduction of bee hives in an orchard until the crop has already begun a modest amount of flowering. This practice will provide bees with an abundance of floral signals that will encourage them to concentrate on the crop instead of non-target plants in the area. It is customary in apple to delay hive introduction until the crop is at about 5% bloom.
Directionality of bee foraging
Bees, having encountered a patch of profitable flowers, tend to forage in a more-or-less straight line. This behaviour limits the chance of a bee revisiting a flower recently emptied of its nectar. The most straightforward implication for crop pollination involves those crops in which a main variety is inter-planted with one or more pollenizer varieties to ensure cross-pollination. Optimal foraging theory would suggest that the main varieties and pollenizers should be planted in the same orchard row to increase chances of bees cross-pollinating them.
