Consider Bt corn. The insecticide is a protein that binds to receptors in the guts of certain chewing insects and messes up the gut, killing the insect. Organic growers have used the stuff as a "natural insecticide" for years.

In one test, they fed honey bees feed with 10x the concentration of this protein that is found in the Bt corn pollen. There was no effect on healthy bees.

However, quite by accident, the bees in the study were infected by a parasite. The bees fed the Bt toxin did much worse than the control groups. So something there suggests that the combination of the Bt toxin and the parasite is bad.

However, the die off in bees is happening in Britain, where they've been pretty resistant to gengineered crops.

ETA:

http://conspiracyfactory.blogspot.co...abel/BT%20corn