I keep bees.
I think it's probably the GM plants. The 'bt' varieties of them produce their own insecticide. Pests that try to eat the plants are poisoned before they do much damage. But the plant produces the insecticide throughout its body -- its nectar is poison, its pollen is poison. There is a theory, and evidence, that this is also responsible for the frightening decline in the population of Monarch butterflies.
My bees are fine, though there has been plenty of cell-phone use and cell-phone towers out here for years. As I understand it the areas that first reported this 'dissapearing bees' thing are heavily agricultural regions -- areas where bees are bound to be encountering GM crops.