Before he retired Prof Calderone put out an epic document which has gotten almost no attention, despite being industry funded. In it he states:

The number of colonies declined from 3.53 million in 1989 to 2.30 million in 2008. The long-term downward trend was underway well before the arrival of parasitic mites or CCD. This suggests that the downward trend may be independent of recent, large losses being reported. 

Regardless of the cause, the decline in colony numbers does not yet appear to have reduced the production or yield of insect pollinated crops.

The beekeeping industry has proven remarkably resilient, replacing colonies that die throughout the year in time for the next season. This resiliency may be based on economic factors, especially the price of honey and  opportunities for pollination contracts. 

Economic opportunities may play a greater role in explaining the long-term trend than other factors.

To maintain its competitive position, the beekeeping industry will need to develop a sustainable, market-based system of bee breeding and colony management that can continue to provide an adequate and reliable supply of high quality, healthy pollinators at competitive prices.

Calderone NW (2012) Insect Pollinated Crops, Insect Pollinators and US Agriculture: Trend Analysis of Aggregate Data for the Period 1992–2009. PLoS ONE

Funding: This project was funded in part by a grant from the National Honey Board. The funders had no role in study design, data collection and analysis, decision where to publish or preparation of the manuscript.

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