How many bee hives per acre do I need to pollinate a crop?

Average bee hive densities (hives per acre) recommended for crops grown in the USA range from 1-7. Most crops that benefit from honey bees require 2-3. Recommended numbers have inched upwards in recent years because of a drop in wild honey bee densities. More managed bees are required to make up the difference.
– Keith Delaplane, University of Georgia