The cause of mass bee deaths may be even more complicated than we thought. A new study released Wednesday by United States Department of Agriculture (USDA) and University of Maryland researchers has revealed that tiny amounts of fungicides can greatly increase a bee's risk of dying from a Nosema infection.
And that's bad news, because Nosema is the gut parasite recently reclassified as a fungus that is considered the most common disease of adult honey bees.
The complete bee death study was published in open access journal PLOS One.
The research was sparked at least in part to find out if there was a single cause of Colony Collapse Disorder, a widespread and imperfectly understood disease that can wipe out entire bee hives.
What they found instead was that working bees set loose to pollinate agricultural crops are exposed to a witches' brew of chemicals that includes 35 different pesticides and multiple fungicides.
Most disturbing: This study disproved the belief that the fungicides were harmless.
In a USDA statement, study author Jeff Pettis explained: "Honey bees that were fed pollen that contained the fungicide chlorothalonil...were almost three times more likely to become infected when exposed to the parasite Nosema, compared with control bees."
In the same statement, UM co-author Dennis vanEngelsdorp emphasized that their work "highlights the need to closely look at fungicides and bee safety, as fungicides currently are considered safe and can be sprayed during the bloom on many crops."
Two chemicals used to treat for mites, previously considered safe and even healthy for bees, also affected the bees' ability to resist Nosema infection.
Neonicotinoid insecticides like the one involved in a recent mass bumblebee die-off in Oregon are already under suspicion. They are known to kill bees and should only be used in situations where bees won't be put at risk.
But the new study means that scientists studying Colony Collapse Disorder and mass bee death need to look at other chemicals too.