The following very interesting study was done in 2007-08. CCD is a world wide problem that pretty much everybody has heard of by now.
You can draw your own conclusions as to its' cause, but the science here makes it pretty clear to me that while there are multiple possible causes, chemical contaminants play a large part. This is interesting to me as I have had the company of two feral hives living in the walls of both my barn and my farmhouse for many years. They have always been healthy colonies and I suspect it is because they have always had plenty of wildflowers for nectar and pollen, and haven't been near any agricultural chemicals. I now have a hive I can inspect, housed in a Langstroth box. We'll see if they do as well as the other two feral hives. It will be nice to finally be able to harvest some of our own honey.
Recent declines in honey bees for crop pollination threaten fruit, nut, vegetable and seed production in the United States. A broad survey of pesticide residues was conducted on samples from migratory and other beekeepers across 23 states, one Canadian province and several agricultural cropping systems during the 2007–08 growing seasons.
We have used LC/MS-MS and GC/MS to analyze bees and hive matrices for pesticide residues utilizing a modified QuEChERS method. We have found 121 different pesticides and metabolites within 887 wax, pollen, bee and associated hive samples. Almost 60% of the 259 wax and 350 pollen samples contained at least one systemic pesticide, and over 47% had both in-hive acaricides fluvalinate and coumaphos, and chlorothalonil, a widely-used fungicide. In bee pollen were found chlorothalonil at levels up to 99 ppm and the insecticides aldicarb, carbaryl, chlorpyrifos and imidacloprid, fungicides boscalid, captan and myclobutanil, and herbicide pendimethalin at 1 ppm levels. Almost all comb and foundation wax samples (98%) were contaminated with up to 204 and 94 ppm, respectively, of fluvalinate and coumaphos, and lower amounts of amitraz degradates and chlorothalonil, with an average of 6 pesticide detections per sample and a high of 39. There were fewer pesticides found in adults and brood except for those linked with bee kills by permethrin (20 ppm) and fipronil (3.1 ppm).
The 98 pesticides and metabolites detected in mixtures up to 214 ppm in bee pollen alone represents a remarkably high level for toxicants in the brood and adult food of this primary pollinator. This represents over half of the maximum individual pesticide incidences ever reported for apiaries. While exposure to many of these neurotoxicants elicits acute and sublethal reductions in honey bee fitness, the effects of these materials in combinations and their direct association with CCD or declining bee health remains to be determined.
Below is a healthy swarm from the hive in my barn's wall. This occurs yearly. I will capture the next swarm.