The population of feral honeybees in the US has been steadily decreasing for the past half-century, and is now almost nonexistent. In the same timescale, commercial honeybees experienced a shallower decline in population. However, since 2006, they have started rapidly disappearing in North America and Europe. Many scientists agree that the confluence of factors that drove population decline before 2006 is still in effect, but that something probably changed in light of the new rash of colony collapses.
Identifying the causes of CCD is a complex proposition, but the disorder's symptoms and effects are quite simple. It usually occurs when worker bees first depart their hives to forage, in winter or early spring. Then they don't return. Their hives typically have an active queen, ample food, and a developing brood – not exactly the home a bee would abandon under normal circumstances. Many scientists have since suggested that pesticides may disorient bees or affect their memory, making them unable to navigate home.
Chensheng Lu, an environmental scientist at Harvard and the lead author on the Bulletin of Insectology paper, was curious as to how the insecticide may be introduced into the colony, and decided to investigate high-fructose corn syrup, which for the past decade has been used by beekeepers to supplement hives that have been decanted of honey. Much of the US corn crop is treated with neonicotinoids, and so trace amounts of the insecticides can often be found in the sugary syrup.
Lu and colleagues designed an experiment that would expose hives to concentrations ranging from 20 to 400 parts per billion. Within 4 months, 15 of the 16 experimental hives had been emptied by what appeared to be CCD, according to the researchers.