Commercial pollination services are mostly provided by honeybees through a long-standing and well-organized market. Recently, honeybee pests and other problems have reduced available supplies, while expansion of almond acreage has increased peak-season demand. The resulting leap in pollination fees follows from these market fundamentals.
See PDF paper here: Bee-conomics and the Leap in Pollination Fees. Daniel A. Sumner and Hayley Boriss.