This post is pretty long and thorough (I looked into this topic thoroughly for a class I took), but it provides a useful background for talking about bee health--bear with me! An upcoming post will address how YOU can do your part to help local bee populations!
Colony collapse disorder
Bees are important
What is killing the bees?
Culprit 1: Habitat Loss
Culprit 2 : Agriculture Practices
Neonics are usually applied to plant seeds, and then are present in all parts of the plant, including the pollen and nectar, as the plant grows. It can also persist in the soil. One symptom of colony collapse disorder is that the bees "disappear" from the hives, as if they can't remember where their hive is. Bees that are around treated fields also exhibit tremors and convulsions, signs of insecticide poisoning. A 2013 study also showed that neonics affect the immune systems of bees making them more susceptible to diseases.
Culprit 3 : Migratory Beekeeping
Migratory beekeeping is stressful for bees, making them more susceptible to diseases. Migratory beekeeping also concentrates bees from around the country to one crop, which facilitates the spread of diseases to other hives. Migratory beekeeping is a symptom of out poor agriculture practices, which makes this type of pollination necessary for farmers to make a living.