5.4. A cautionary note about recommendations
Delaplane and Mayer (2000) list recommended colony densities and their average for many crops based on information collected from standard pollination references and historical extension bulletins. Recommendations about the optimal number of colonies per hectare ultimately often come from experiences of growers and beekeepers who have adjusted bee densities based on trial and error over time. A commonly recommended starting density is 2.5 colonies of standard strength (often cited as having ≥8 combs, two-thirds covered with adult bees or ≥6 combs well covered with brood) per hectare. This may be adjusted knowing the relationship of crop yield with factors that affect foraging activity or pollination. Examples of such factors among include:
- Plant reproductive biology, including cultivars that are more difficult to pollinate effectively, e.g. ‘Delicious’ apples (Malus domestica), because of a high frequency of sideworking honey bees; more bees are needed for such plants.
- Field size: larger fields usually need more supplemental pollinators than small fields because small fields often have greater densities of native pollinators.
- Prevailing weather: a region or season with historically poor weather for bee flight may warrant a higher stocking density.
- Competition: the extent to which the target crop is competing with weeds or neighbouring crops for a limited pool of pollinators
- Ambient densities of native
A case study of how these particular factors have been used to adjust pollination management involves lowbush blueberry (Vaccinium angustifolium Aiton and V. myrtilloides Michx.) in the northeastern USA. The crop is difficult because it requires much pollen movement, honey bees do not “buzz pollinate” (sonicate) the ericaceous flowers, many commercial fields are large and have insufficient densities of native pollinators, weather during bloom is often poor, and bees seek pollen from sources other than blueberries. Large-scale commercial growers have tested the value of increased stocking densities. Through this experience the largest growers now prefer to rent colonies that are more populous than average and stock them typically at 10-12/hectare and up to 20-25/hectare in historically high-yielding areas (Danka: unpub. obs.).